Nanotechnologie Argovia (Poggio)Head of Research Unit Prof. Dr.Martino PoggioOverviewMembersPublicationsProjects & CollaborationsProjects & Collaborations OverviewMembersPublicationsProjects & Collaborations Projects & Collaborations 16 foundShow per page10 10 20 50 Revealing 2D magnetism via nanoscale magnetometry Research Project | 4 Project MembersTwo-dimensional (2D) magnets have emerged as a new frontier in magnetism, both in terms of fundamental questions - including why such magnetism is stable at all - as well as from the device engineering point of view. In general, the stacking, twisting, and combining of van der Waals (vdW) materials with control down to individual atomic layers has started a revolution in heterostructure engineering. Layer-by-layer control offers a multitude of possible material combinations, without constraints imposed by lattice mismatch, along with the prospect of making compact devices, in which large electric fields can easily be applied. These new tools give researchers unprecedented control of interactions and band structure, as exemplified by the 2018 realization of superconducting twisted bilayer graphene. In the realm of magnetism, these methods can be used to tune the magnetic properties of a material or even to make materials, which are non-magnetic in the bulk, magnetic in 2D. Most importantly, both in view of understanding the physics of 2D magnetism and exploiting it for applications, vdW engineering may allow us to realize new and useful magnetic phases, which are only possible in 2D. In order to fully take advantage of these new developments, we must understand the role of anisotropy, disorder, inhomogeneity, and characteristic length-scales in 2D magnets and their heterostructures. Such investigations require sensitive local probes and techniques for measuring magnetism in small volumes. Our group, which has long worked at the forefront of sensitive magnetic imaging and torque magnetometry, is ideally positioned for such measurements. Here, we propose to apply our unique and highly sensitive tools to three types of measurements in 2D magnets: The characterization of static magnetism : determining the magnetic state and its dependence on the number of layers, anisotropy, as well as the presence of spatially modulated states, domains, defects, and inhomogeneities. The study of phase transitions and magnetic reversal : measuring the stability of magnetic phases, the nature of phase transitions, the process of magnetic reversal, and the role of domains and inhomogeneity therein. Understanding how to engineer 2D magnets : observing the effects of stacking, twisting, and applying electric fields to controllably induce phase transitions, magnetic reversal, magnetic texture, or new magnetic phases. The work of unravelling the mechanisms behind 2D magnetism is in its infancy. Given the inadequacy of conventional magnetic probes, we are convinced that our unique nanometer-scale magnetic field imaging and ultrasensitive torque magnetometry tools have much to contribute towards this effort. The results can be expected to have implications for 2D spintronic devices, 2D antiferromagnets, and the design of quantum materials via 2D vdW engineering in general. Scanning Nanowire Quantum Dot Research Project | 2 Project MembersIn this project we aim to combine the exceptional sensitivity of nanowire quantum dots as detectors of charge with scanning probe capabilities of customized cantilevers. The resulting scanning nanowire quantum dot will enable imaging of localized charges and electron densities with high sensitivity, high resolution, and under a large variety of environmental circumstances. FIBsuperProbes / Focused Ion Beam fabrication of superconducting scanning Probes Research Project | 3 Project MembersOur vision is to enable a new era in scanning probe microscopy (SPM), in which nanometer-scale sensing devices - specifically superconducting devices - can be directly patterned on-tip and used to reveal new types of contrast. To realize this vision, we will use focused ion beam (FIB) techniques to produce sensors with unprecedented size, functionality, and sensitivity directly on the tips of custom-designed cantilevers. The key to this undertaking will be the unique capability of FIB to mill, grow, or structurally modify materials - especially superconductors - at the nanometer-scale and on non-planar surfaces. Our FIB-fabricated probes will include on-tip nanometer-scale Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) for mapping magnetic fields, magnetic susceptibility, electric currents, and dissipation. Crucially, the custom-built cantilevers, on which the sensors will be patterned, will enable nanometer-scale distance control, endowing our probes with exquisite spatial resolution and simultaneous topographic contrast. The resulting imaging techniques will significantly surpass state-of-the-art SPM and help us to unravel poorly understood phenomena in physics, chemistry, and material science, which are impossible to address with today's technology. New Scanning Probes for Nanomagnetic Imaging Research Project | 1 Project MembersRecent years have seen rapid progress in nanometer-scale magnetic imaging technology, with scanning probe microscopy driving remarkable improvements in both sensitivity and resolution. Among the most successful tools are magnetic force microscopy (MFM), spin-polarized scanning tunneling microscopy, as well as scanning magnetometers based on nitrogen-vacancy centers in diamond, Hall-bars, and superconducting quantum interference devices (SQUIDs). Here, we propose the development and application of two particularly promising scanning probe techniques. The first is scanning SQUID microscopy, which - in its most advanced form - achieves record sensitivity to both stray magnetic flux and local thermal dissipation. Recently, it has been used to study the dynamics of superconducting vortices and to map nanometer-scale transport. In order to extend its applicability and optimize its functionality, we aim to realize a nanometer-scale SQUID integrated on an atomic force microscopy (AFM) tip, producing a hybrid AFM-SQUID sensitive to surface forces, stray magnetic flux, and local temperature. The second is based on newly developed nanowire (NW) force sensors, which have recently enabled a form of AFM capable of mapping both the size and direction of tip-sample forces. Using NWs functionalized with magnetic tips, we intend to realize a form of vectorial MFM capable of mapping stray magnetic fields with enhanced sensitivity and resolution compared to the state of the art. The unique capabilities of these two scanning probes will provide new types of imaging contrast for nanometer-scale magnetic structures such as domain walls , magnetic vortices , and magnetic skyrmions , whose equilibrium configurations and dynamical properties are crucial for both fundamental understanding and spintronic applications. In addition to studying magnetic nanostructures and spin-dependent phenomena, we will apply our newly developed techniques to the study of mesoscopic current flow in topological insulators and two-dimensional materials . Further target systems include superconducting films and nanostructures , in which our sensitive probes could help clarify the microscopic mechanisms of superconductivity. Ultrasensitive Force Microscopy and Cavity Optomechanics using Nanowire Cantilevers Research Project | 2 Project Membersp «Discovery and Nanoengineering of Novel Skyrmion-hosting Materials» Research Project | 2 Project MembersMagnetic Skyrmions are particle-like spin textures. They exhibit nanoscale dimensions and can be persistent due to topological protection. These nanoobjects have been first discovered at low temperatures in a small number of bulk single crystals of high purity and quality. Such chiral magnets are now of substantial interest for both fundamental condensed matter physics due to topological effects and applied sciences such as spintronics. The physics and manipulation of Skyrmions stabilized by Dzyaloshinskii-Moriya interaction (DMI) are relatively well established in bulk materials at low temperatures. The results promise novel device concepts in magnetic storage and information technology offering low power consumption. Technologically relevant structures will necessarily involve nanostructures operated at room temperature. The research on nanosystems is however mostly at the theoretical and numerical level because the relevant materials pose key challenges in the synthesis and fabrication of strain-free thin films that support the Skyrmion phase. Despite strong efforts, Skyrmions at room temperature have been observed only very recently in metallic ultrathin films and the bulk metallic alloy CoZnMn. Corresponding semiconductors and insulators that will decisively enhance the technological impact remain to be discovered.In this proposal we aim to go beyond the state-of-the-art of existing Skyrmionic schemes in that we intend to:-Systematically search for novel metallic, semiconducting, and insulating materials hosting Skyrmions at high temperatures-Achieve strain-free thin films and free-standing nanostructures with volume-DMI for Skyrmion-based devices -Image and manipulate Skyrmions up to the microwave frequency regime and down to the single Skyrmion level to set the base for Nanoskyrmionics.These ambitious goals can be achieved only by intimately combining different disciplines at their highest level and from diverse areas of research. In our proposal, we combine: computational materials discovery in condensed matter physics, chemical synthesis and molecular beam epitaxy, state-of-the-art neutron diffraction, nanotechnology and GHz spectroscopy. We propose to implement chemical precipitation from a solution as well as van der Waals epitaxy for strain-free thin film deposition. Direct correlation between the materials nature (structure, chemical composition, disorder configuration) and physical properties (magnetization, Skyrmion structure, dynamics) will be achieved by applying new computational and nanosensing techniques. The interdisciplinary efforts and results will lead to a paradigm-shift by providing a clear microscopic picture of the role and potential of Skyrmions in engineering, setting the stage for Skyrmionic science and technology at room temperature. Quantum sensing and imaging of spin textures in skyrmion materials Research Project | 1 Project Membersa Investigating Individual Multiferroic and Oxidic Nanoparticles Research Project | 2 Project Membersa Quantum sensing and imaging of core-shell magnetic nanotubes Research Project | 2 Project MembersNanoscale magnetic structures with non-trivial spin-textures are of great practical interest for applications in compact classical data storage or in quantum-technologies such as spin-qubits or quantum sensors. Recent cantilever and nanoSQUID magnetometry experiments on ferromagnetic nanotubes (NTs) carried out by the Poggio group suggest the existence of non-trivial magnetic vortex states. Despite their potential usefulness, these magnetic configurations remain underexplored due to limitations in conventional sensing and imaging approaches. Here, we propose to gain further insight into these nanometer-scale magnetic structures using scanning quantum sensors based on nitrogen vacancy (NV) centers in diamond recently developed in the Maletinsky lab 4 . On the one hand, our study will benchmark these quantum sensing tools against state-of-the-art, classical imaging approaches. On the other hand, the experiments will shed new light on magnetic configurations and reversal in nanometer-scale magnets. These insights may, in turn, have an impact on quantum-technologies, either in the application of strong nanomagnets for spin-manipulation and magnetic resonance force microscopy, or in the resonant enhancement of weak magnetic fields for quantum sensing. Ultrasensitive detection of quantum phenomena in nanowire hybrids Research Project | 1 Project MembersThe fabrication of artifical nanostructures has matured over the last decades to its current state in which it is straightforward, though not always trivial, to create objects with well-defined geometry and crystal structure. This leads to a large degree of control over electronic, vibrational, and photonic properties of nanoscale structures such as nanobeams, photonic and phononic crystals, membranes, nanotubes, and nanowires. In my research proposal for an SNF Ambizione grant I plan to use such well-designed nanoscale objects, in particular self-assembled nanowires. This I plan to do in two projects that aim to study with ultrahigh precision the internal structure of nanowires, and use the nanowires in hybrid systems in which multiple degrees of freedom are coupled. Both projects build upon existing knowledge and expertise, and do not require complicated measurement apparatus. The coupling of different physical quantities forms the very foundation of fundamental experiments investigating quantum measurement. Through such coupling, it becomes possible to implement quantum non-demolition (QND) and weak measurements, and investigate decoherence mechanisms, quantum entanglement, and ultimately the transition from quantum to classical physics. An object which combines the coupled quantities in one, monolithic, unit forms a very powerful platform for the study of such effects. Nanowires are such objects, as they are excellent nanomechanical resonators, can host optically active quantum dots and additionally are prototypical systems expected to exhibit intruiging mesoscopic physics, such as that of emergent Majorana fermions and Luttinger liquids. In the lab in Basel, with which I am currently affiliated as a Postdoctoral researcher, we have demonstrated two types of coupling in nanowires which I intend to exploit in this context. First, nonlinear coupling has been shown to exist between transverse motional modes of nanowires, which could be used to implement QND measurements and bidimensional sensing protocols. The second kind of coupling is a strain-induced interaction between a quantum dot two-level system and mechanical dynamics in nanowire heterostructures. Also this type of coupling can be used to implement QND measurements, and furthermore can be used to study the unexplored physical regime of complex nonlinear dynamics coupled to quantum two-level systems. Read-out of both the mechanical motion of the nanowires and of the photons emitted by embedded quantum dots can be much improved by placing the nanowire in an optical cavity. Moreover, such a cavity allows to strongly couple the nanowire motion as well as the quantum dots to the light field. In particular, in the case of nanowires with embedded quantum dots this provides a straightforward path to the experimental realization of a tripartite hybrid system. I aim to use cavities formed by the ends of fiber pairs, specifically modified for this purpose. Such fiber cavities have recently attracted a lot of interest, and are particularly useful for the study of nanowires due to their small dimensions and ease of integration in scanning probe setups. A second, related, project has as a goal to study the internal electronic structure of nanowires using capacitive sensing. Through capacitive coupling of a nanowire to a microwave resonant circuit, the nanowire's quantum capacitance can be determined. By placing the nanowire and resonant circuit in a standard scanning probe setup, spatial information on the electronic density of states can be obtained through the measured quantum capacitance. This kind of imaging finds potential application in localization of charge defects on nanoscale objects with ultrahigh spatial resolution, quantum dot physics, and possibly even in detecting signatures of strongly interacting electrons and Majorana fermions. 12 12 OverviewMembersPublicationsProjects & Collaborations
Projects & Collaborations 16 foundShow per page10 10 20 50 Revealing 2D magnetism via nanoscale magnetometry Research Project | 4 Project MembersTwo-dimensional (2D) magnets have emerged as a new frontier in magnetism, both in terms of fundamental questions - including why such magnetism is stable at all - as well as from the device engineering point of view. In general, the stacking, twisting, and combining of van der Waals (vdW) materials with control down to individual atomic layers has started a revolution in heterostructure engineering. Layer-by-layer control offers a multitude of possible material combinations, without constraints imposed by lattice mismatch, along with the prospect of making compact devices, in which large electric fields can easily be applied. These new tools give researchers unprecedented control of interactions and band structure, as exemplified by the 2018 realization of superconducting twisted bilayer graphene. In the realm of magnetism, these methods can be used to tune the magnetic properties of a material or even to make materials, which are non-magnetic in the bulk, magnetic in 2D. Most importantly, both in view of understanding the physics of 2D magnetism and exploiting it for applications, vdW engineering may allow us to realize new and useful magnetic phases, which are only possible in 2D. In order to fully take advantage of these new developments, we must understand the role of anisotropy, disorder, inhomogeneity, and characteristic length-scales in 2D magnets and their heterostructures. Such investigations require sensitive local probes and techniques for measuring magnetism in small volumes. Our group, which has long worked at the forefront of sensitive magnetic imaging and torque magnetometry, is ideally positioned for such measurements. Here, we propose to apply our unique and highly sensitive tools to three types of measurements in 2D magnets: The characterization of static magnetism : determining the magnetic state and its dependence on the number of layers, anisotropy, as well as the presence of spatially modulated states, domains, defects, and inhomogeneities. The study of phase transitions and magnetic reversal : measuring the stability of magnetic phases, the nature of phase transitions, the process of magnetic reversal, and the role of domains and inhomogeneity therein. Understanding how to engineer 2D magnets : observing the effects of stacking, twisting, and applying electric fields to controllably induce phase transitions, magnetic reversal, magnetic texture, or new magnetic phases. The work of unravelling the mechanisms behind 2D magnetism is in its infancy. Given the inadequacy of conventional magnetic probes, we are convinced that our unique nanometer-scale magnetic field imaging and ultrasensitive torque magnetometry tools have much to contribute towards this effort. The results can be expected to have implications for 2D spintronic devices, 2D antiferromagnets, and the design of quantum materials via 2D vdW engineering in general. Scanning Nanowire Quantum Dot Research Project | 2 Project MembersIn this project we aim to combine the exceptional sensitivity of nanowire quantum dots as detectors of charge with scanning probe capabilities of customized cantilevers. The resulting scanning nanowire quantum dot will enable imaging of localized charges and electron densities with high sensitivity, high resolution, and under a large variety of environmental circumstances. FIBsuperProbes / Focused Ion Beam fabrication of superconducting scanning Probes Research Project | 3 Project MembersOur vision is to enable a new era in scanning probe microscopy (SPM), in which nanometer-scale sensing devices - specifically superconducting devices - can be directly patterned on-tip and used to reveal new types of contrast. To realize this vision, we will use focused ion beam (FIB) techniques to produce sensors with unprecedented size, functionality, and sensitivity directly on the tips of custom-designed cantilevers. The key to this undertaking will be the unique capability of FIB to mill, grow, or structurally modify materials - especially superconductors - at the nanometer-scale and on non-planar surfaces. Our FIB-fabricated probes will include on-tip nanometer-scale Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) for mapping magnetic fields, magnetic susceptibility, electric currents, and dissipation. Crucially, the custom-built cantilevers, on which the sensors will be patterned, will enable nanometer-scale distance control, endowing our probes with exquisite spatial resolution and simultaneous topographic contrast. The resulting imaging techniques will significantly surpass state-of-the-art SPM and help us to unravel poorly understood phenomena in physics, chemistry, and material science, which are impossible to address with today's technology. New Scanning Probes for Nanomagnetic Imaging Research Project | 1 Project MembersRecent years have seen rapid progress in nanometer-scale magnetic imaging technology, with scanning probe microscopy driving remarkable improvements in both sensitivity and resolution. Among the most successful tools are magnetic force microscopy (MFM), spin-polarized scanning tunneling microscopy, as well as scanning magnetometers based on nitrogen-vacancy centers in diamond, Hall-bars, and superconducting quantum interference devices (SQUIDs). Here, we propose the development and application of two particularly promising scanning probe techniques. The first is scanning SQUID microscopy, which - in its most advanced form - achieves record sensitivity to both stray magnetic flux and local thermal dissipation. Recently, it has been used to study the dynamics of superconducting vortices and to map nanometer-scale transport. In order to extend its applicability and optimize its functionality, we aim to realize a nanometer-scale SQUID integrated on an atomic force microscopy (AFM) tip, producing a hybrid AFM-SQUID sensitive to surface forces, stray magnetic flux, and local temperature. The second is based on newly developed nanowire (NW) force sensors, which have recently enabled a form of AFM capable of mapping both the size and direction of tip-sample forces. Using NWs functionalized with magnetic tips, we intend to realize a form of vectorial MFM capable of mapping stray magnetic fields with enhanced sensitivity and resolution compared to the state of the art. The unique capabilities of these two scanning probes will provide new types of imaging contrast for nanometer-scale magnetic structures such as domain walls , magnetic vortices , and magnetic skyrmions , whose equilibrium configurations and dynamical properties are crucial for both fundamental understanding and spintronic applications. In addition to studying magnetic nanostructures and spin-dependent phenomena, we will apply our newly developed techniques to the study of mesoscopic current flow in topological insulators and two-dimensional materials . Further target systems include superconducting films and nanostructures , in which our sensitive probes could help clarify the microscopic mechanisms of superconductivity. Ultrasensitive Force Microscopy and Cavity Optomechanics using Nanowire Cantilevers Research Project | 2 Project Membersp «Discovery and Nanoengineering of Novel Skyrmion-hosting Materials» Research Project | 2 Project MembersMagnetic Skyrmions are particle-like spin textures. They exhibit nanoscale dimensions and can be persistent due to topological protection. These nanoobjects have been first discovered at low temperatures in a small number of bulk single crystals of high purity and quality. Such chiral magnets are now of substantial interest for both fundamental condensed matter physics due to topological effects and applied sciences such as spintronics. The physics and manipulation of Skyrmions stabilized by Dzyaloshinskii-Moriya interaction (DMI) are relatively well established in bulk materials at low temperatures. The results promise novel device concepts in magnetic storage and information technology offering low power consumption. Technologically relevant structures will necessarily involve nanostructures operated at room temperature. The research on nanosystems is however mostly at the theoretical and numerical level because the relevant materials pose key challenges in the synthesis and fabrication of strain-free thin films that support the Skyrmion phase. Despite strong efforts, Skyrmions at room temperature have been observed only very recently in metallic ultrathin films and the bulk metallic alloy CoZnMn. Corresponding semiconductors and insulators that will decisively enhance the technological impact remain to be discovered.In this proposal we aim to go beyond the state-of-the-art of existing Skyrmionic schemes in that we intend to:-Systematically search for novel metallic, semiconducting, and insulating materials hosting Skyrmions at high temperatures-Achieve strain-free thin films and free-standing nanostructures with volume-DMI for Skyrmion-based devices -Image and manipulate Skyrmions up to the microwave frequency regime and down to the single Skyrmion level to set the base for Nanoskyrmionics.These ambitious goals can be achieved only by intimately combining different disciplines at their highest level and from diverse areas of research. In our proposal, we combine: computational materials discovery in condensed matter physics, chemical synthesis and molecular beam epitaxy, state-of-the-art neutron diffraction, nanotechnology and GHz spectroscopy. We propose to implement chemical precipitation from a solution as well as van der Waals epitaxy for strain-free thin film deposition. Direct correlation between the materials nature (structure, chemical composition, disorder configuration) and physical properties (magnetization, Skyrmion structure, dynamics) will be achieved by applying new computational and nanosensing techniques. The interdisciplinary efforts and results will lead to a paradigm-shift by providing a clear microscopic picture of the role and potential of Skyrmions in engineering, setting the stage for Skyrmionic science and technology at room temperature. Quantum sensing and imaging of spin textures in skyrmion materials Research Project | 1 Project Membersa Investigating Individual Multiferroic and Oxidic Nanoparticles Research Project | 2 Project Membersa Quantum sensing and imaging of core-shell magnetic nanotubes Research Project | 2 Project MembersNanoscale magnetic structures with non-trivial spin-textures are of great practical interest for applications in compact classical data storage or in quantum-technologies such as spin-qubits or quantum sensors. Recent cantilever and nanoSQUID magnetometry experiments on ferromagnetic nanotubes (NTs) carried out by the Poggio group suggest the existence of non-trivial magnetic vortex states. Despite their potential usefulness, these magnetic configurations remain underexplored due to limitations in conventional sensing and imaging approaches. Here, we propose to gain further insight into these nanometer-scale magnetic structures using scanning quantum sensors based on nitrogen vacancy (NV) centers in diamond recently developed in the Maletinsky lab 4 . On the one hand, our study will benchmark these quantum sensing tools against state-of-the-art, classical imaging approaches. On the other hand, the experiments will shed new light on magnetic configurations and reversal in nanometer-scale magnets. These insights may, in turn, have an impact on quantum-technologies, either in the application of strong nanomagnets for spin-manipulation and magnetic resonance force microscopy, or in the resonant enhancement of weak magnetic fields for quantum sensing. Ultrasensitive detection of quantum phenomena in nanowire hybrids Research Project | 1 Project MembersThe fabrication of artifical nanostructures has matured over the last decades to its current state in which it is straightforward, though not always trivial, to create objects with well-defined geometry and crystal structure. This leads to a large degree of control over electronic, vibrational, and photonic properties of nanoscale structures such as nanobeams, photonic and phononic crystals, membranes, nanotubes, and nanowires. In my research proposal for an SNF Ambizione grant I plan to use such well-designed nanoscale objects, in particular self-assembled nanowires. This I plan to do in two projects that aim to study with ultrahigh precision the internal structure of nanowires, and use the nanowires in hybrid systems in which multiple degrees of freedom are coupled. Both projects build upon existing knowledge and expertise, and do not require complicated measurement apparatus. The coupling of different physical quantities forms the very foundation of fundamental experiments investigating quantum measurement. Through such coupling, it becomes possible to implement quantum non-demolition (QND) and weak measurements, and investigate decoherence mechanisms, quantum entanglement, and ultimately the transition from quantum to classical physics. An object which combines the coupled quantities in one, monolithic, unit forms a very powerful platform for the study of such effects. Nanowires are such objects, as they are excellent nanomechanical resonators, can host optically active quantum dots and additionally are prototypical systems expected to exhibit intruiging mesoscopic physics, such as that of emergent Majorana fermions and Luttinger liquids. In the lab in Basel, with which I am currently affiliated as a Postdoctoral researcher, we have demonstrated two types of coupling in nanowires which I intend to exploit in this context. First, nonlinear coupling has been shown to exist between transverse motional modes of nanowires, which could be used to implement QND measurements and bidimensional sensing protocols. The second kind of coupling is a strain-induced interaction between a quantum dot two-level system and mechanical dynamics in nanowire heterostructures. Also this type of coupling can be used to implement QND measurements, and furthermore can be used to study the unexplored physical regime of complex nonlinear dynamics coupled to quantum two-level systems. Read-out of both the mechanical motion of the nanowires and of the photons emitted by embedded quantum dots can be much improved by placing the nanowire in an optical cavity. Moreover, such a cavity allows to strongly couple the nanowire motion as well as the quantum dots to the light field. In particular, in the case of nanowires with embedded quantum dots this provides a straightforward path to the experimental realization of a tripartite hybrid system. I aim to use cavities formed by the ends of fiber pairs, specifically modified for this purpose. Such fiber cavities have recently attracted a lot of interest, and are particularly useful for the study of nanowires due to their small dimensions and ease of integration in scanning probe setups. A second, related, project has as a goal to study the internal electronic structure of nanowires using capacitive sensing. Through capacitive coupling of a nanowire to a microwave resonant circuit, the nanowire's quantum capacitance can be determined. By placing the nanowire and resonant circuit in a standard scanning probe setup, spatial information on the electronic density of states can be obtained through the measured quantum capacitance. This kind of imaging finds potential application in localization of charge defects on nanoscale objects with ultrahigh spatial resolution, quantum dot physics, and possibly even in detecting signatures of strongly interacting electrons and Majorana fermions. 12 12
Revealing 2D magnetism via nanoscale magnetometry Research Project | 4 Project MembersTwo-dimensional (2D) magnets have emerged as a new frontier in magnetism, both in terms of fundamental questions - including why such magnetism is stable at all - as well as from the device engineering point of view. In general, the stacking, twisting, and combining of van der Waals (vdW) materials with control down to individual atomic layers has started a revolution in heterostructure engineering. Layer-by-layer control offers a multitude of possible material combinations, without constraints imposed by lattice mismatch, along with the prospect of making compact devices, in which large electric fields can easily be applied. These new tools give researchers unprecedented control of interactions and band structure, as exemplified by the 2018 realization of superconducting twisted bilayer graphene. In the realm of magnetism, these methods can be used to tune the magnetic properties of a material or even to make materials, which are non-magnetic in the bulk, magnetic in 2D. Most importantly, both in view of understanding the physics of 2D magnetism and exploiting it for applications, vdW engineering may allow us to realize new and useful magnetic phases, which are only possible in 2D. In order to fully take advantage of these new developments, we must understand the role of anisotropy, disorder, inhomogeneity, and characteristic length-scales in 2D magnets and their heterostructures. Such investigations require sensitive local probes and techniques for measuring magnetism in small volumes. Our group, which has long worked at the forefront of sensitive magnetic imaging and torque magnetometry, is ideally positioned for such measurements. Here, we propose to apply our unique and highly sensitive tools to three types of measurements in 2D magnets: The characterization of static magnetism : determining the magnetic state and its dependence on the number of layers, anisotropy, as well as the presence of spatially modulated states, domains, defects, and inhomogeneities. The study of phase transitions and magnetic reversal : measuring the stability of magnetic phases, the nature of phase transitions, the process of magnetic reversal, and the role of domains and inhomogeneity therein. Understanding how to engineer 2D magnets : observing the effects of stacking, twisting, and applying electric fields to controllably induce phase transitions, magnetic reversal, magnetic texture, or new magnetic phases. The work of unravelling the mechanisms behind 2D magnetism is in its infancy. Given the inadequacy of conventional magnetic probes, we are convinced that our unique nanometer-scale magnetic field imaging and ultrasensitive torque magnetometry tools have much to contribute towards this effort. The results can be expected to have implications for 2D spintronic devices, 2D antiferromagnets, and the design of quantum materials via 2D vdW engineering in general.
Scanning Nanowire Quantum Dot Research Project | 2 Project MembersIn this project we aim to combine the exceptional sensitivity of nanowire quantum dots as detectors of charge with scanning probe capabilities of customized cantilevers. The resulting scanning nanowire quantum dot will enable imaging of localized charges and electron densities with high sensitivity, high resolution, and under a large variety of environmental circumstances.
FIBsuperProbes / Focused Ion Beam fabrication of superconducting scanning Probes Research Project | 3 Project MembersOur vision is to enable a new era in scanning probe microscopy (SPM), in which nanometer-scale sensing devices - specifically superconducting devices - can be directly patterned on-tip and used to reveal new types of contrast. To realize this vision, we will use focused ion beam (FIB) techniques to produce sensors with unprecedented size, functionality, and sensitivity directly on the tips of custom-designed cantilevers. The key to this undertaking will be the unique capability of FIB to mill, grow, or structurally modify materials - especially superconductors - at the nanometer-scale and on non-planar surfaces. Our FIB-fabricated probes will include on-tip nanometer-scale Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) for mapping magnetic fields, magnetic susceptibility, electric currents, and dissipation. Crucially, the custom-built cantilevers, on which the sensors will be patterned, will enable nanometer-scale distance control, endowing our probes with exquisite spatial resolution and simultaneous topographic contrast. The resulting imaging techniques will significantly surpass state-of-the-art SPM and help us to unravel poorly understood phenomena in physics, chemistry, and material science, which are impossible to address with today's technology.
New Scanning Probes for Nanomagnetic Imaging Research Project | 1 Project MembersRecent years have seen rapid progress in nanometer-scale magnetic imaging technology, with scanning probe microscopy driving remarkable improvements in both sensitivity and resolution. Among the most successful tools are magnetic force microscopy (MFM), spin-polarized scanning tunneling microscopy, as well as scanning magnetometers based on nitrogen-vacancy centers in diamond, Hall-bars, and superconducting quantum interference devices (SQUIDs). Here, we propose the development and application of two particularly promising scanning probe techniques. The first is scanning SQUID microscopy, which - in its most advanced form - achieves record sensitivity to both stray magnetic flux and local thermal dissipation. Recently, it has been used to study the dynamics of superconducting vortices and to map nanometer-scale transport. In order to extend its applicability and optimize its functionality, we aim to realize a nanometer-scale SQUID integrated on an atomic force microscopy (AFM) tip, producing a hybrid AFM-SQUID sensitive to surface forces, stray magnetic flux, and local temperature. The second is based on newly developed nanowire (NW) force sensors, which have recently enabled a form of AFM capable of mapping both the size and direction of tip-sample forces. Using NWs functionalized with magnetic tips, we intend to realize a form of vectorial MFM capable of mapping stray magnetic fields with enhanced sensitivity and resolution compared to the state of the art. The unique capabilities of these two scanning probes will provide new types of imaging contrast for nanometer-scale magnetic structures such as domain walls , magnetic vortices , and magnetic skyrmions , whose equilibrium configurations and dynamical properties are crucial for both fundamental understanding and spintronic applications. In addition to studying magnetic nanostructures and spin-dependent phenomena, we will apply our newly developed techniques to the study of mesoscopic current flow in topological insulators and two-dimensional materials . Further target systems include superconducting films and nanostructures , in which our sensitive probes could help clarify the microscopic mechanisms of superconductivity.
Ultrasensitive Force Microscopy and Cavity Optomechanics using Nanowire Cantilevers Research Project | 2 Project Membersp
«Discovery and Nanoengineering of Novel Skyrmion-hosting Materials» Research Project | 2 Project MembersMagnetic Skyrmions are particle-like spin textures. They exhibit nanoscale dimensions and can be persistent due to topological protection. These nanoobjects have been first discovered at low temperatures in a small number of bulk single crystals of high purity and quality. Such chiral magnets are now of substantial interest for both fundamental condensed matter physics due to topological effects and applied sciences such as spintronics. The physics and manipulation of Skyrmions stabilized by Dzyaloshinskii-Moriya interaction (DMI) are relatively well established in bulk materials at low temperatures. The results promise novel device concepts in magnetic storage and information technology offering low power consumption. Technologically relevant structures will necessarily involve nanostructures operated at room temperature. The research on nanosystems is however mostly at the theoretical and numerical level because the relevant materials pose key challenges in the synthesis and fabrication of strain-free thin films that support the Skyrmion phase. Despite strong efforts, Skyrmions at room temperature have been observed only very recently in metallic ultrathin films and the bulk metallic alloy CoZnMn. Corresponding semiconductors and insulators that will decisively enhance the technological impact remain to be discovered.In this proposal we aim to go beyond the state-of-the-art of existing Skyrmionic schemes in that we intend to:-Systematically search for novel metallic, semiconducting, and insulating materials hosting Skyrmions at high temperatures-Achieve strain-free thin films and free-standing nanostructures with volume-DMI for Skyrmion-based devices -Image and manipulate Skyrmions up to the microwave frequency regime and down to the single Skyrmion level to set the base for Nanoskyrmionics.These ambitious goals can be achieved only by intimately combining different disciplines at their highest level and from diverse areas of research. In our proposal, we combine: computational materials discovery in condensed matter physics, chemical synthesis and molecular beam epitaxy, state-of-the-art neutron diffraction, nanotechnology and GHz spectroscopy. We propose to implement chemical precipitation from a solution as well as van der Waals epitaxy for strain-free thin film deposition. Direct correlation between the materials nature (structure, chemical composition, disorder configuration) and physical properties (magnetization, Skyrmion structure, dynamics) will be achieved by applying new computational and nanosensing techniques. The interdisciplinary efforts and results will lead to a paradigm-shift by providing a clear microscopic picture of the role and potential of Skyrmions in engineering, setting the stage for Skyrmionic science and technology at room temperature.
Quantum sensing and imaging of spin textures in skyrmion materials Research Project | 1 Project Membersa
Quantum sensing and imaging of core-shell magnetic nanotubes Research Project | 2 Project MembersNanoscale magnetic structures with non-trivial spin-textures are of great practical interest for applications in compact classical data storage or in quantum-technologies such as spin-qubits or quantum sensors. Recent cantilever and nanoSQUID magnetometry experiments on ferromagnetic nanotubes (NTs) carried out by the Poggio group suggest the existence of non-trivial magnetic vortex states. Despite their potential usefulness, these magnetic configurations remain underexplored due to limitations in conventional sensing and imaging approaches. Here, we propose to gain further insight into these nanometer-scale magnetic structures using scanning quantum sensors based on nitrogen vacancy (NV) centers in diamond recently developed in the Maletinsky lab 4 . On the one hand, our study will benchmark these quantum sensing tools against state-of-the-art, classical imaging approaches. On the other hand, the experiments will shed new light on magnetic configurations and reversal in nanometer-scale magnets. These insights may, in turn, have an impact on quantum-technologies, either in the application of strong nanomagnets for spin-manipulation and magnetic resonance force microscopy, or in the resonant enhancement of weak magnetic fields for quantum sensing.
Ultrasensitive detection of quantum phenomena in nanowire hybrids Research Project | 1 Project MembersThe fabrication of artifical nanostructures has matured over the last decades to its current state in which it is straightforward, though not always trivial, to create objects with well-defined geometry and crystal structure. This leads to a large degree of control over electronic, vibrational, and photonic properties of nanoscale structures such as nanobeams, photonic and phononic crystals, membranes, nanotubes, and nanowires. In my research proposal for an SNF Ambizione grant I plan to use such well-designed nanoscale objects, in particular self-assembled nanowires. This I plan to do in two projects that aim to study with ultrahigh precision the internal structure of nanowires, and use the nanowires in hybrid systems in which multiple degrees of freedom are coupled. Both projects build upon existing knowledge and expertise, and do not require complicated measurement apparatus. The coupling of different physical quantities forms the very foundation of fundamental experiments investigating quantum measurement. Through such coupling, it becomes possible to implement quantum non-demolition (QND) and weak measurements, and investigate decoherence mechanisms, quantum entanglement, and ultimately the transition from quantum to classical physics. An object which combines the coupled quantities in one, monolithic, unit forms a very powerful platform for the study of such effects. Nanowires are such objects, as they are excellent nanomechanical resonators, can host optically active quantum dots and additionally are prototypical systems expected to exhibit intruiging mesoscopic physics, such as that of emergent Majorana fermions and Luttinger liquids. In the lab in Basel, with which I am currently affiliated as a Postdoctoral researcher, we have demonstrated two types of coupling in nanowires which I intend to exploit in this context. First, nonlinear coupling has been shown to exist between transverse motional modes of nanowires, which could be used to implement QND measurements and bidimensional sensing protocols. The second kind of coupling is a strain-induced interaction between a quantum dot two-level system and mechanical dynamics in nanowire heterostructures. Also this type of coupling can be used to implement QND measurements, and furthermore can be used to study the unexplored physical regime of complex nonlinear dynamics coupled to quantum two-level systems. Read-out of both the mechanical motion of the nanowires and of the photons emitted by embedded quantum dots can be much improved by placing the nanowire in an optical cavity. Moreover, such a cavity allows to strongly couple the nanowire motion as well as the quantum dots to the light field. In particular, in the case of nanowires with embedded quantum dots this provides a straightforward path to the experimental realization of a tripartite hybrid system. I aim to use cavities formed by the ends of fiber pairs, specifically modified for this purpose. Such fiber cavities have recently attracted a lot of interest, and are particularly useful for the study of nanowires due to their small dimensions and ease of integration in scanning probe setups. A second, related, project has as a goal to study the internal electronic structure of nanowires using capacitive sensing. Through capacitive coupling of a nanowire to a microwave resonant circuit, the nanowire's quantum capacitance can be determined. By placing the nanowire and resonant circuit in a standard scanning probe setup, spatial information on the electronic density of states can be obtained through the measured quantum capacitance. This kind of imaging finds potential application in localization of charge defects on nanoscale objects with ultrahigh spatial resolution, quantum dot physics, and possibly even in detecting signatures of strongly interacting electrons and Majorana fermions.
