We have detected and manipulated the naturally occurring ͱ N statistical polarization in nuclear ... more We have detected and manipulated the naturally occurring ͱ N statistical polarization in nuclear spin ensembles using magnetic resonance force microscopy. Using protocols previously developed for detecting single electron spins, we have measured signals from ensembles of nuclear spins in a volume of roughly ͑150 nm͒ 3 with a sensitivity of roughly 2000 net spins in a 2.5 h averaging window. Three systems have been studied, 19 F nuclei in CaF 2 , and 1 H nuclei ͑protons͒ in both polymethylmethacrylate and collagen, a naturally occurring protein. By detecting the statistical polarization, we not only can work with relatively small ensembles, but we eliminate any need to wait a longitudinal relaxation time T 1 to polarize the spins. We have also made use of the fact that the statistical polarization, which can be considered a form of spin noise, has a finite correlation time. A method similar to one previously proposed by Carlson et al. ͓Bull. Am. Phys. Soc. 44, 541 ͑1999͔͒ has been used to suppress the effect of the statistical uncertainty and extract meaningful information from time-averaged measurements. By implementing this method, we have successfully made nutation and transverse spin relaxation time measurements in CaF 2 at low temperatures.
At high amplitudes of excitation surface waves on water distribute their energy according to a Ko... more At high amplitudes of excitation surface waves on water distribute their energy according to a Kolmogorov type of turbulent power spectrum. We have used diffusing light photography to measure the power spectrum and to quantify the presence of large structures in the turbulent state.
Bulletin of the American Physical Society, Mar 19, 2009
The ruthenate superconductor Sr 2 RuO 4 may have a chiral order parameter of the form p x ±ip y, ... more The ruthenate superconductor Sr 2 RuO 4 may have a chiral order parameter of the form p x ±ip y, , making it a candidate for nucleation of excitations with non-Abelian statistics that could enable topologically-protected quantum computing. To test this scenario, we have measured the magnetic response of Sr 2 RuO 4 nanocrystals to search for spontaneous chiral currents and half-integer vortices. Each nanocrystal (2µm x 2µm x 0.5µm) was extracted from a large single crystal with bulk transition temperature in the range 1.2K-1.4K. It was then glued into the pickup loop of a flux transformer or a gradiometer that is inductively-coupled to a dc-SQUID magnetometer. We monitor the diamagnetic screening of the crystal and the entry of discrete vortices in perpendicular and parallel applied magnetic fields and as a function of temperature to search for the existence of half-quantum vortices in this system. We are also developing other techniques such as nanoscale Scanning SQUID Microscopy for probing the vortex dynamics in Sr 2 RuO 4 .
We report a method for Fourier-transform magnetic resonance imaging of statistically polarized na... more We report a method for Fourier-transform magnetic resonance imaging of statistically polarized nanoscale samples. Periodic magnetic field gradient pulses, which are generated by ultrahigh current densities in a nanoscale metal constriction, spatially encode the spin density in the sample and create temporal correlations in the spin noise. We demonstrate this technique using a silicon nanowire mechanical oscillator as a force sensor to image 1H spins in polystyrene. We obtain a two-dimensional projection of the sample proton density with approximately 10-nm resolution. Fourier encoding offers better sensitivity than point-by-point techniques for high resolution imaging of statistically polarized samples.
Pressure-and magnetic-field-dependent inelastic light (Raman) scattering studies of the magnetica... more Pressure-and magnetic-field-dependent inelastic light (Raman) scattering studies of the magnetically frustrated, magnetodielectric spinel Mn3O4 were performed as a function of temperature. Pressure-dependent Raman measurements show that the magnetic easy axis direction in Mn3O4 can be controlled-and the ferrimagnetic transition temperature increased-with applied pressure. Further, combined pressure-and magnetic-field-tuned Raman measurements reveal a rich magnetostructural phase diagram-including a pressure-and field-induced magnetically frustrated tetragonal phase in the PH phase diagram-that can be generated in Mn3O4 with applied pressure and magnetic field.
Bulletin of the American Physical Society, Mar 15, 2017
Submitted for the MAR17 Meeting of The American Physical Society Probing and controlling fluxoid ... more Submitted for the MAR17 Meeting of The American Physical Society Probing and controlling fluxoid states in multiply-connected mesoscopic superconducting structures HRYHORIY POLSHYN, TYLER NAIBERT, RAFFI BUDAKIAN, University of Illinois at Urbana-Champaign-New ways to investigate and manipulate fluxoid and vortex states of mesoscopic superconducting structures are of great interest. The states with multiple vortices or winding numbers could be useful for the study of vortex interactions and interference effects, the braiding of Majorana bound states by winding vortices, and the development of novel superconducting devices. We demonstrate a methodology based on magnetic force microscopy that allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. By using micromagnet as a source of inhomogeneous magnetic field, we can efficiently explore the configuration space of fluxoid states. Scanning over the structure reveals the energy crossing points of the lowest laying fluxoid states. This is due the strong interaction of cantilever with thermally activated fluxoid transitions at points of degeneracy. We show that measured patterns of fluxoid transitions allow to identify the states, investigate their energetics, and manipulate them. Further, we show that the dynamics of driven fluxoid transitions can be described by stochastic resonance model, which provides a unique way of measuring fluxoid transition rate and related energy barrier for chosen transitions even in complicated structures.
Bulletin of the American Physical Society, Mar 15, 2016
Submitted for the MAR16 Meeting of The American Physical Society Study of vortex states and dynam... more Submitted for the MAR16 Meeting of The American Physical Society Study of vortex states and dynamics in mesoscopic superconducting samples with MFM GREGORY POLSHYN, TYLER NAIBERT, VICTOR CHUA, RAFFI BUDAKIAN, University of Illinois at Urbana-Champaign-Vortex states in superconducting (SC) structures, their dynamics and ways to manipulate them are topics of great interest. We report a new method of magnetic force microscopy (MFM) that allows the study of vortex states in mesoscopic SC samples. For the case of a SC ring, which is biased to a half-integer flux quantum, the flux modulation through the ring caused by the motion of the magnetic tip drives the ring between two consecutive fluxoid states. The corresponding current switching in the ring produces strong position-dependent forces on the cantilever. In the regime where the frequency of the thermally activated jumps between fluxoid states is close to the frequency of the cantilever, large changes in the cantilever frequency and dissipation are observed. This effect may be understood as a stochastic resonance (SR) process. These changes in the cantilevers mechanical properties are used to image the barrier energies between fluxoid states. Additionally, SR imaging of the barrier energies are used to study the effect of the locally applied magnetic field from the MFM tip on the barrier heights. We report the results of measurements for Al rings. Further, the same imaging technique can be applied to more sophisticated SC structures such as arrays of Josephson junctions.
Controlling multiferroic behavior in materials will enable the development of a wide variety of t... more Controlling multiferroic behavior in materials will enable the development of a wide variety of technological applications. However, the exact mechanisms driving multiferroic behavior are not well understood in most materials. Two such materials are the spinels MnV 2O4 and Mn3O4, where mechanical strain is thought to play a role in determining magnetic behavior. Bulk studies of MnV2O4 have yielded conflicting and inconclusive results, due in part to the presence of mesoscale magnetic inhomogeneity, which complicates the interpretation of bulk measurements. To study the sub-micron-scale magnetic properties of Mn-based spinel materials, we performed magnetic force microscopy (MFM) on MnV 2O4 samples subject to different levels of mechanical strain. We also used a crystal grain mapping technique to perform spatially registered MFM on Mn 3O4. These local investigations revealed 100-nm-scale "stripe" modulations in the magnetic structure of both materials. In MnV2O4, the magnetization of these stripes is estimated to be M z ~ 10 5 A/m, which is on the order of the saturation magnetization reported previously. Cooling in a strong magnetic field eliminated the stripe patterning only in the low-strain sample of MnV 2O4. The discovery of nanoscale magnetostructural inhomogeneity that is highly susceptible to magnetic field control in these materials necessitates both a revision of theoretical proposals and a reinterpretation of experimental data regarding the low-temperature phases and magnetic-field-tunable properties of these Mn-based spinels.
Recently Jang et al. 1 reported the observation of half-height magnetization steps ("half-steps")... more Recently Jang et al. 1 reported the observation of half-height magnetization steps ("half-steps") in cantilever magnetometry measurements of mesoscopic annular Sr 2 RuO 4 particles. Such magnetization features were interpreted as the presence of half-quantum vortices (HQVs) 2. In an attempt to examine our findings, very recently Cai at el. 3 have performed magnetotransport measurements of micron-size rings fabricated from small Sr 2 RuO 4 crystals. While fabrication of such samples and subsequent verification of our findings is highly desirable, we would like to point out that, at the current state of affairs, the direct comparison is incomplete partly due to the fact that the measurements of Ref. 3 were lacking an important ingredient-the in-plane magnetic field. We would also like to offer clarification on few questionable statements made in Ref. 3. Cai et al. raised a concern that the field periodic-*
In this paper, we focus on ultrasensitive cantilevers for the detection of nuclear magnetic reson... more In this paper, we focus on ultrasensitive cantilevers for the detection of nuclear magnetic resonance (NMR) at frequencies that coincide with the nuclear spin precession (Larmor) frequency, around 1 MHz. The small size of these cantilevers precludes the usual practice of locating the reflective paddle near the tip, so a torsional configuration has to be used to allow the paddle to be situated at the distal end, providing improved optical access. These torsional oscillators, fabricated in part with electron-beam lithography, have ribs 200 nm wide and 1.5 m tall attached to arms 200 nm thick and 12 m long. Fabrication details and characterization results are presented.
We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of sing... more We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of single crystal Mn3O4, combined with temperature-and field-dependent x-ray diffraction studies, revealing the novel magnetostructural phases in Mn3O4. Our temperature-dependent studies showed that the commensurate magnetic transition at T2=33K in the binary spinel Mn3O4 is associated with a structural transition from tetragonal to orthorhombic structures. Field-dependent studies showed that the onset and nature of this structural transition can be controlled with an applied magnetic field, and revealed evidence for a field-tuned quantum phase transition to a tetragonal spin-disordered phase for H [110]. Pressure-dependent Raman measurements showed that the magnetic easy axis direction in Mn3O4 can be controlled-and the ferrimagnetic transition temperature increased-with applied pressure. Finally, combined pressure-and magnetic-field-tuned Raman measurements revealed a rich magnetostructural phase diagram-including a pressure-and fieldinduced magnetically frustrated tetragonal phase in the PH phase diagram-that can be generated in Mn3O4 with applied pressure and magnetic field.
by the same author) that it ought to be possible to detect a single-proton by inductively couplin... more by the same author) that it ought to be possible to detect a single-proton by inductively coupling the nuclear spin to the motion of a mechanical oscillator. A first experiment, published by Rugar, Yannoni and Sidles (Nature 360, 563 (1992)), demonstrated, what they called, the mechanical detection of magnetic resonance. In the present paper, published in Nature, a 10 7 times improvement has been realized and the authors argue convincingly that indeed the signal is due to a single spin.
We propose a highly efficient dynamic nuclear polarization technique that is robust against field... more We propose a highly efficient dynamic nuclear polarization technique that is robust against field inhomogeneity. This technique is designed to enhance the detection sensitivity in nano-MRI, where large Rabi field gradients are required. The proposed technique consists of an adiabatic half passage pulse followed by an adiabatic linear sweep of the electron Rabi frequency and can be considered as an adiabatic version of nuclear orientation via electron spin locking (adiabatic-NOVEL). We analyze the spin dynamics of an electron-nuclear system that is under microwave irradiation at high static magnetic field and at cryogenic temperature. The result shows that an amplitude modulation of the microwave field makes adiabatic-NOVEL highly efficient and robust against both the static and microwave field in-homogeneity.
In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sens... more In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sensitive cantilevers in a number of unique scanning probe microscopy (SPM) settings. We describe the fabrication of ultra-low dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning probe applications. Our fabrication process produces, with high yield, ultra-high aspect ratio vertical SiNWs that exhibit exceptional force sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited force sensitivity of 9.7 ± 0.4 aN/ √ Hz at room temperature and 500 ± 20 zN/ √ Hz at 4 K. To facilitate their use in SPM, the SiNWs are patterned within 7 µm from the edge of the substrate, allowing convenient optical access for displacement detection.
Harnessing the properties of vortices in superconductors is crucial for fundamental science as we... more Harnessing the properties of vortices in superconductors is crucial for fundamental science as well as technological applications; thus, it has been an ongoing goal to develop experimental techniques that can locally probe and control vortices. Here, we present a scanning probe technique that enables studies of vortex dynamics in superconducting systems by leveraging the resonant behavior of a raster-scanned, magnetic-tipped cantilever. Key features of this experimental platform are the high degree of tunability and the local nature of the probe. Applying this technique to lattices of superconductor island arrays on a metal, we obtain a variety of striking spatial patterns that encode information about the energy landscape for vortices in the system. We interpret these patterns in terms of local vortex dynamics, and extract the relative strengths of the characteristic energy scales in the system, such as the vortex-magnetic field and vortex-vortex interaction strengths, as well as t...
We have detected and manipulated the naturally occurring ͱ N statistical polarization in nuclear ... more We have detected and manipulated the naturally occurring ͱ N statistical polarization in nuclear spin ensembles using magnetic resonance force microscopy. Using protocols previously developed for detecting single electron spins, we have measured signals from ensembles of nuclear spins in a volume of roughly ͑150 nm͒ 3 with a sensitivity of roughly 2000 net spins in a 2.5 h averaging window. Three systems have been studied, 19 F nuclei in CaF 2 , and 1 H nuclei ͑protons͒ in both polymethylmethacrylate and collagen, a naturally occurring protein. By detecting the statistical polarization, we not only can work with relatively small ensembles, but we eliminate any need to wait a longitudinal relaxation time T 1 to polarize the spins. We have also made use of the fact that the statistical polarization, which can be considered a form of spin noise, has a finite correlation time. A method similar to one previously proposed by Carlson et al. ͓Bull. Am. Phys. Soc. 44, 541 ͑1999͔͒ has been used to suppress the effect of the statistical uncertainty and extract meaningful information from time-averaged measurements. By implementing this method, we have successfully made nutation and transverse spin relaxation time measurements in CaF 2 at low temperatures.
At high amplitudes of excitation surface waves on water distribute their energy according to a Ko... more At high amplitudes of excitation surface waves on water distribute their energy according to a Kolmogorov type of turbulent power spectrum. We have used diffusing light photography to measure the power spectrum and to quantify the presence of large structures in the turbulent state.
Bulletin of the American Physical Society, Mar 19, 2009
The ruthenate superconductor Sr 2 RuO 4 may have a chiral order parameter of the form p x ±ip y, ... more The ruthenate superconductor Sr 2 RuO 4 may have a chiral order parameter of the form p x ±ip y, , making it a candidate for nucleation of excitations with non-Abelian statistics that could enable topologically-protected quantum computing. To test this scenario, we have measured the magnetic response of Sr 2 RuO 4 nanocrystals to search for spontaneous chiral currents and half-integer vortices. Each nanocrystal (2µm x 2µm x 0.5µm) was extracted from a large single crystal with bulk transition temperature in the range 1.2K-1.4K. It was then glued into the pickup loop of a flux transformer or a gradiometer that is inductively-coupled to a dc-SQUID magnetometer. We monitor the diamagnetic screening of the crystal and the entry of discrete vortices in perpendicular and parallel applied magnetic fields and as a function of temperature to search for the existence of half-quantum vortices in this system. We are also developing other techniques such as nanoscale Scanning SQUID Microscopy for probing the vortex dynamics in Sr 2 RuO 4 .
We report a method for Fourier-transform magnetic resonance imaging of statistically polarized na... more We report a method for Fourier-transform magnetic resonance imaging of statistically polarized nanoscale samples. Periodic magnetic field gradient pulses, which are generated by ultrahigh current densities in a nanoscale metal constriction, spatially encode the spin density in the sample and create temporal correlations in the spin noise. We demonstrate this technique using a silicon nanowire mechanical oscillator as a force sensor to image 1H spins in polystyrene. We obtain a two-dimensional projection of the sample proton density with approximately 10-nm resolution. Fourier encoding offers better sensitivity than point-by-point techniques for high resolution imaging of statistically polarized samples.
Pressure-and magnetic-field-dependent inelastic light (Raman) scattering studies of the magnetica... more Pressure-and magnetic-field-dependent inelastic light (Raman) scattering studies of the magnetically frustrated, magnetodielectric spinel Mn3O4 were performed as a function of temperature. Pressure-dependent Raman measurements show that the magnetic easy axis direction in Mn3O4 can be controlled-and the ferrimagnetic transition temperature increased-with applied pressure. Further, combined pressure-and magnetic-field-tuned Raman measurements reveal a rich magnetostructural phase diagram-including a pressure-and field-induced magnetically frustrated tetragonal phase in the PH phase diagram-that can be generated in Mn3O4 with applied pressure and magnetic field.
Bulletin of the American Physical Society, Mar 15, 2017
Submitted for the MAR17 Meeting of The American Physical Society Probing and controlling fluxoid ... more Submitted for the MAR17 Meeting of The American Physical Society Probing and controlling fluxoid states in multiply-connected mesoscopic superconducting structures HRYHORIY POLSHYN, TYLER NAIBERT, RAFFI BUDAKIAN, University of Illinois at Urbana-Champaign-New ways to investigate and manipulate fluxoid and vortex states of mesoscopic superconducting structures are of great interest. The states with multiple vortices or winding numbers could be useful for the study of vortex interactions and interference effects, the braiding of Majorana bound states by winding vortices, and the development of novel superconducting devices. We demonstrate a methodology based on magnetic force microscopy that allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. By using micromagnet as a source of inhomogeneous magnetic field, we can efficiently explore the configuration space of fluxoid states. Scanning over the structure reveals the energy crossing points of the lowest laying fluxoid states. This is due the strong interaction of cantilever with thermally activated fluxoid transitions at points of degeneracy. We show that measured patterns of fluxoid transitions allow to identify the states, investigate their energetics, and manipulate them. Further, we show that the dynamics of driven fluxoid transitions can be described by stochastic resonance model, which provides a unique way of measuring fluxoid transition rate and related energy barrier for chosen transitions even in complicated structures.
Bulletin of the American Physical Society, Mar 15, 2016
Submitted for the MAR16 Meeting of The American Physical Society Study of vortex states and dynam... more Submitted for the MAR16 Meeting of The American Physical Society Study of vortex states and dynamics in mesoscopic superconducting samples with MFM GREGORY POLSHYN, TYLER NAIBERT, VICTOR CHUA, RAFFI BUDAKIAN, University of Illinois at Urbana-Champaign-Vortex states in superconducting (SC) structures, their dynamics and ways to manipulate them are topics of great interest. We report a new method of magnetic force microscopy (MFM) that allows the study of vortex states in mesoscopic SC samples. For the case of a SC ring, which is biased to a half-integer flux quantum, the flux modulation through the ring caused by the motion of the magnetic tip drives the ring between two consecutive fluxoid states. The corresponding current switching in the ring produces strong position-dependent forces on the cantilever. In the regime where the frequency of the thermally activated jumps between fluxoid states is close to the frequency of the cantilever, large changes in the cantilever frequency and dissipation are observed. This effect may be understood as a stochastic resonance (SR) process. These changes in the cantilevers mechanical properties are used to image the barrier energies between fluxoid states. Additionally, SR imaging of the barrier energies are used to study the effect of the locally applied magnetic field from the MFM tip on the barrier heights. We report the results of measurements for Al rings. Further, the same imaging technique can be applied to more sophisticated SC structures such as arrays of Josephson junctions.
Controlling multiferroic behavior in materials will enable the development of a wide variety of t... more Controlling multiferroic behavior in materials will enable the development of a wide variety of technological applications. However, the exact mechanisms driving multiferroic behavior are not well understood in most materials. Two such materials are the spinels MnV 2O4 and Mn3O4, where mechanical strain is thought to play a role in determining magnetic behavior. Bulk studies of MnV2O4 have yielded conflicting and inconclusive results, due in part to the presence of mesoscale magnetic inhomogeneity, which complicates the interpretation of bulk measurements. To study the sub-micron-scale magnetic properties of Mn-based spinel materials, we performed magnetic force microscopy (MFM) on MnV 2O4 samples subject to different levels of mechanical strain. We also used a crystal grain mapping technique to perform spatially registered MFM on Mn 3O4. These local investigations revealed 100-nm-scale "stripe" modulations in the magnetic structure of both materials. In MnV2O4, the magnetization of these stripes is estimated to be M z ~ 10 5 A/m, which is on the order of the saturation magnetization reported previously. Cooling in a strong magnetic field eliminated the stripe patterning only in the low-strain sample of MnV 2O4. The discovery of nanoscale magnetostructural inhomogeneity that is highly susceptible to magnetic field control in these materials necessitates both a revision of theoretical proposals and a reinterpretation of experimental data regarding the low-temperature phases and magnetic-field-tunable properties of these Mn-based spinels.
Recently Jang et al. 1 reported the observation of half-height magnetization steps ("half-steps")... more Recently Jang et al. 1 reported the observation of half-height magnetization steps ("half-steps") in cantilever magnetometry measurements of mesoscopic annular Sr 2 RuO 4 particles. Such magnetization features were interpreted as the presence of half-quantum vortices (HQVs) 2. In an attempt to examine our findings, very recently Cai at el. 3 have performed magnetotransport measurements of micron-size rings fabricated from small Sr 2 RuO 4 crystals. While fabrication of such samples and subsequent verification of our findings is highly desirable, we would like to point out that, at the current state of affairs, the direct comparison is incomplete partly due to the fact that the measurements of Ref. 3 were lacking an important ingredient-the in-plane magnetic field. We would also like to offer clarification on few questionable statements made in Ref. 3. Cai et al. raised a concern that the field periodic-*
In this paper, we focus on ultrasensitive cantilevers for the detection of nuclear magnetic reson... more In this paper, we focus on ultrasensitive cantilevers for the detection of nuclear magnetic resonance (NMR) at frequencies that coincide with the nuclear spin precession (Larmor) frequency, around 1 MHz. The small size of these cantilevers precludes the usual practice of locating the reflective paddle near the tip, so a torsional configuration has to be used to allow the paddle to be situated at the distal end, providing improved optical access. These torsional oscillators, fabricated in part with electron-beam lithography, have ribs 200 nm wide and 1.5 m tall attached to arms 200 nm thick and 12 m long. Fabrication details and characterization results are presented.
We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of sing... more We present temperature-, magnetic-field-, and pressure-dependent Raman scattering studies of single crystal Mn3O4, combined with temperature-and field-dependent x-ray diffraction studies, revealing the novel magnetostructural phases in Mn3O4. Our temperature-dependent studies showed that the commensurate magnetic transition at T2=33K in the binary spinel Mn3O4 is associated with a structural transition from tetragonal to orthorhombic structures. Field-dependent studies showed that the onset and nature of this structural transition can be controlled with an applied magnetic field, and revealed evidence for a field-tuned quantum phase transition to a tetragonal spin-disordered phase for H [110]. Pressure-dependent Raman measurements showed that the magnetic easy axis direction in Mn3O4 can be controlled-and the ferrimagnetic transition temperature increased-with applied pressure. Finally, combined pressure-and magnetic-field-tuned Raman measurements revealed a rich magnetostructural phase diagram-including a pressure-and fieldinduced magnetically frustrated tetragonal phase in the PH phase diagram-that can be generated in Mn3O4 with applied pressure and magnetic field.
by the same author) that it ought to be possible to detect a single-proton by inductively couplin... more by the same author) that it ought to be possible to detect a single-proton by inductively coupling the nuclear spin to the motion of a mechanical oscillator. A first experiment, published by Rugar, Yannoni and Sidles (Nature 360, 563 (1992)), demonstrated, what they called, the mechanical detection of magnetic resonance. In the present paper, published in Nature, a 10 7 times improvement has been realized and the authors argue convincingly that indeed the signal is due to a single spin.
We propose a highly efficient dynamic nuclear polarization technique that is robust against field... more We propose a highly efficient dynamic nuclear polarization technique that is robust against field inhomogeneity. This technique is designed to enhance the detection sensitivity in nano-MRI, where large Rabi field gradients are required. The proposed technique consists of an adiabatic half passage pulse followed by an adiabatic linear sweep of the electron Rabi frequency and can be considered as an adiabatic version of nuclear orientation via electron spin locking (adiabatic-NOVEL). We analyze the spin dynamics of an electron-nuclear system that is under microwave irradiation at high static magnetic field and at cryogenic temperature. The result shows that an amplitude modulation of the microwave field makes adiabatic-NOVEL highly efficient and robust against both the static and microwave field in-homogeneity.
In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sens... more In recent years, self-assembled semiconductor nanowires have been successfully used as ultra-sensitive cantilevers in a number of unique scanning probe microscopy (SPM) settings. We describe the fabrication of ultra-low dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning probe applications. Our fabrication process produces, with high yield, ultra-high aspect ratio vertical SiNWs that exhibit exceptional force sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited force sensitivity of 9.7 ± 0.4 aN/ √ Hz at room temperature and 500 ± 20 zN/ √ Hz at 4 K. To facilitate their use in SPM, the SiNWs are patterned within 7 µm from the edge of the substrate, allowing convenient optical access for displacement detection.
Harnessing the properties of vortices in superconductors is crucial for fundamental science as we... more Harnessing the properties of vortices in superconductors is crucial for fundamental science as well as technological applications; thus, it has been an ongoing goal to develop experimental techniques that can locally probe and control vortices. Here, we present a scanning probe technique that enables studies of vortex dynamics in superconducting systems by leveraging the resonant behavior of a raster-scanned, magnetic-tipped cantilever. Key features of this experimental platform are the high degree of tunability and the local nature of the probe. Applying this technique to lattices of superconductor island arrays on a metal, we obtain a variety of striking spatial patterns that encode information about the energy landscape for vortices in the system. We interpret these patterns in terms of local vortex dynamics, and extract the relative strengths of the characteristic energy scales in the system, such as the vortex-magnetic field and vortex-vortex interaction strengths, as well as t...
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