Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M52: Spin DefectsFocus Recordings Available
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Sponsoring Units: GMAG DMP FIAP Chair: Noah Mendelson, University of Technology Sydney Room: McCormick Place W-475A |
Wednesday, March 16, 2022 8:00AM - 8:36AM |
M52.00001: Coherent Coupling of Mechanics to a Single Nuclear Spin Invited Speaker: Marko Loncar
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Wednesday, March 16, 2022 8:36AM - 8:48AM |
M52.00002: Radio-frequency control of optically-induced dynamic nuclear polarization in diamond Roberta Pigliapochi, Daniela Pagliero, Artur Lozovoi, Pablo R Zangara Optical spin pumping of nitrogen-vacancy (NV)-hosting diamonds has attracted increasing attention as a means for a more broadly accessible DNP implementation, primarily for the ability to operate under convenient experimental conditions of room temperature and low magnetic fields. However, the mechanisms describing the generation and transport of polarization within the crystal host are still only partly understood. In this work, we combine field-cycling experiments with selective radio-frequency (RF) excitation to probe transitions between hybrid nuclear and electronic spin states near energy-matching conditions between the NV and surrounding paramagnetic impurities. We analyze and model the dependence of the nuclear polarization on the applied magnetic field, the RF frequency, and the RF power. Our results indicate that the observed nuclear polarization can be understood as originating from a reduced, specific set of strongly-hyperfine-coupled nuclear spins. This kind of hyperfine spectroscopy sheds light on intriguing pathways to generate nuclear polarization without the use of optical or microwave excitation. |
Wednesday, March 16, 2022 8:48AM - 9:24AM |
M52.00003: Image of Dynamic Local Exchange Interactions in the dc Magnetoresistance of Spin-Polarized Current through a Dopant Invited Speaker: Stephen R McMillan Components for quantum information processing and quantum sensing require localized spin-coherent states. These states can be realized in isolated magnetic dopants embedded in a non-magnetic semiconducting host. A critical requirement for utilizing a dopant-based system is an understanding of how the complex host environment influences the coherent spin dynamics at an individual site. In this work, we consider the dc magnetoresistance through a spin-1/2 dopant that is addressed by a spin-polarized scanning tunneling microscope (SP-STM) and exchange-coupled to an inert spin-1/2 center [1]. The stochastic Liouville formalism is employed to calculate the current through the individual dopant. We predict a substantial increase in resistance at finite magnetic fields due to the formation of a non-trivial bottleneck in the spin-correlated transport. The resonance between the Zeeman and exchange coupling leads to a cancelation in the coherent evolution of the dopant spin resulting in an on-site polarization opposing that of the SP-STM. This feature provides a precise method for measuring the dopant exchange coupling to a nearby electronic spin and by direct analog hyperfine coupling in the presence of nuclear spins. This technique does not require the use of ac electric or magnetic fields and is sensitive to exchange or hyperfine energies well below the thermal energy of the system. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M52.00004: Dissipationless Circulating Currents and Fringe Magnetic Fields Near a Single Spin Embedded in a Two-Dimensional Electron Gas Adonai Rodrigues da Cruz, Michael E Flatté The combination of spin-orbit coupling with broken spatial inversion symmetry in semiconductors (e.g. zinc-blende quantum-wells and surfaces) and localized spin states originated from a single magnetic defect is a promising system to realize future semiconductor spintronics devices [1]. We present a theory of dissipationless circulating current induced by a magnetic defect in a two-dimensional electron gas with both Bychkov-Rashba and Dresselhaus spin-orbit coupling [2]. The shape and spatial extent of these dissipationless circulating currents depend dramatically on the relative strengths of spin-orbit fields with differing spatial symmetry, offering the potential to use an electric gate to manipulate nanoscale magnetic fields and couple magnetic defects. The spatial structure of the fringing magnetic field emerging from the current is calculated and provides a direct way to measure the spin-orbit fields of the host, as well as the defect spin orientation, through scanning nanoscale magnetometry [3]. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M52.00005: Spin Polarized STM Studies of Fe Dopants and Dimers on the GaAs (110) Surface Rebekah Smith, Cuneyt Sahin, Michael E Flatté, Jay A Gupta The characterization and control of single impurity states in semiconductors is of fundamental interest, and underlies a variety of approaches for next-generation classical and quantum computing. Here we report a joint experimental / theoretical study of individual Fe atoms, substituted for Ga in the GaAs(110) surface. Spin-resolved scanning tunneling microscopy reveals a variety of charge / spin states of the Fe dopants through distinct contrast in topographic imaging and distinct electronic states in tunneling spectroscopy. To study magnetic interactions, dimers of Fe are formed by STM atomic manipulation with controlled separation, and also exhibit distinct contrast and electronic states. The experimental results are consistent with our density functional theory calculations, which show a variety of spin-polarized states in the energy range studied. Comparison with bulk- and surface-slab calculations provides insight into how the surface influences the properties of individual and coupled Fe dopants. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M52.00006: Exchange Interaction in Iron Dimers on GaAs (110) Surface Cuneyt Sahin, Michael E Flatté Substitutional dopants in semiconductors such as transition metal Fe, Mn, and Co in III-V compounds offer excellent platforms to study magnetic phenomena for future applications in spintronics, optoelectronics, and quantum information processing. The main subjects of this study are single Fe and Fe-dimers on (110) GaAs surfaces. Based on the density functional theory we first calculate the electronic structure and orbital projected density of states for the single iron on the surface and in the bulk of the GaAs. We compare these results with previous studies in the literature, find an excellent agreement in the bulk calculations, and discuss agreements and dissimilarities for the surface calculations especially in the electronic states appearing in the bandgap. Next, we calculate the density of states, orbital projected densities, and electronic band structures of the Fe dimers on the surface. We also calculate the strength of the Fe-Fe exchange interactions in dimers as a function of the distance and direction. Finally, we include a variable Hubbard U term to show how the ground state alters between ferromagnetic and antiferromagnetic configurations with changing U. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M52.00007: High contrast shallow spin defects in hexagonal boron nitride enhanced by surface plasmon for quantum sensing Xingyu Gao, Boyang Jiang, Andres E Llacsahuanga Allcca, Kunhong Shen, Mohammad A Sadi, Abhishek B Solanki, Peng Ju, Zhujing Xu, Pramey Upadhyaya, Yong Chen, Sunil A Bhave, Tongcang Li The recently discovered spin defects in hexagonal boron nitride (hBN) are emerging candidates for quantum sensing. However, the sensitivity of negatively charged boron vacancy (VB-) defects is limited by its weak photoluminescence and relatively low contrast of the optically detected magnetic resonance (ODMR). Here, we report a simultaneous enhancement of the photoluminescence of hBN spin defects by up to 17-fold by the surface plasmon of a gold-film microwave waveguide. We observed a record-high ODMR contrast of 46% at room temperature. We also explore the effects of microwave and laser powers on the ODMR, and improve the sensitivity of hBN spin defects for magnetic field detection. Our samples were created by low-energy He+ ion implantation which generates shallow spin defects close to the hBN surface. We show that T1 and T2 relaxation times are independent of the ion energy, indicating that the spin properties of VB- defects are nearly independent of the depth. |
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