Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R63: Defects: Structure and Strain 2 |
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Sponsoring Units: DMP DCMP FIAP Chair: Rachel Goldman, Univ of Michigan - Ann Arbor Room: Mile High Ballroom 4D |
Thursday, March 5, 2020 8:00AM - 8:36AM |
R63.00001: Dynamic Dark-Field X-ray Microscopy to Probe Mesoscale Defects and their Dynamics Invited Speaker: Leora Dresselhaus-Cooper Many problems in semiconductor physics require a detailed understanding of material defects at the mesoscale (e.g. dislocations, stacking faults, twins, etc.). While techniques exist to probe material defects, they are mainly limited to surface measurements or rastered scans that cannot measure the dynamics of irreversible processes. Dark-field X-ray microscopy (DFXM) can now directly image defects in single- and poly-crystals, spatially resolving the lattice strain and inclination with high sensitivity (ε~10-5) and resolution across hundreds of micrometers. I extend DFXM to study structural dynamics, resolving how material defects show how crystals respond disturbances in their surroundings. I will show real-time movies that visualize how long-range dislocation patterns evolve in both temperature and time and will extend this to high-intensity X-ray radiation damage to demonstrate dynamic DFXM’s capabilities. These results present important opportunities for semiconductor physics, as they can now address important problems at the mesoscale. Results from these findings can directly connect to dislocation models that have previously relied on multi-scale modeling and indirect measurements for refinement. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R63.00002: High-throughput identification of point defects in SiC Joel Davidsson, Viktor Ivady, Rickard Armiento, Igor Abrikosov Qubits and single photon emitters are examples of point defects applications. Before a point defect can be utilized in these applications, an important step is to identify and understand both the defect type and different configurations. A promising way to identify a defect is to combine experimental data with ab initio calculations which include zero-phonon lines and hyperfine coupling parameters. In earlier work, we made a convergence study for divacancies in 4H-SiC. Due to the size of the supercell and the number of calculations needed, we restrict us to the PBE exchange functional. Based on our understanding of the convergence of these calculations, we made an automatic workflow that can calculate zero-phonon lines for many different defects. Each defect is calculated for a range of different configurations, charges, spins, and possible excitations. Currently, we are running these calculations in a high-throughput manner and producing a database for an array of different defects. We present the results from the workflow for various vacancy configurations in 4H-SiC. Our preliminary results suggest that with this choice of methodology, useful data are obtained at a feasible computational cost for a large number of defect types and configurations available in SiC. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R63.00003: Theoretical Investigations of the Hyperfine Coupling in Group IV-Vacancy Centers in Diamond Using Hybrid Density Functional Theory Rodrick Kuate Defo, Efthimios Kaxiras, Steven Richardson Recently, single-photon emitters comprised of Group IV (Si, Ge, Sn, and Pb)-vacancy centers in diamond have attracted considerable interest in the literature because of their potential applications in quantum information processing and quantum metrology. Because some of these Group IV-vacancy color centers are paramagnetic, their electronic properties can be experimentally characterized using electron paramagnetic resonance (EPR) which is a direct measure of the hyperfine interaction at a microscopic level. It has been demonstrated that an understanding of the core spin polarization is essential to providing accurate hyperfine tensors in a number of point defects in diamond, including the NV(_) center.1,2 In this work we use density-functional theory (DFT) with the HSE06 exchange functional to compute the hyperfine tensors of several paramagnetic Group IV-vacancy centers in diamond and we compare our results with other experimental and theoretical results where available. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R63.00004: Theory on spectral diffusion and electrically driven interferometry of qubits Péter Udvarhelyi, Gergo Thiering, Viktor Ivady, Adam Gali Scalable spin-to-photon interfaces require quantum emitters with strong optical-transition dipole moment and low coupling to phonons and stray electric fields. Here, we show that inversion symmetry is not a prerequisite criterion for a spectrally stable quantum emitter. We find that identical electron density in ground and excited states can eliminate the coupling to the stray electric fields. We demonstrate this effect on silicon-vacancy qubit in silicon carbide by first principles methods (SiC) [1,2]. Our study opens an additional rationale in seeking promising materials towards the realization of robust spin-to-photon interfaces. Furthermore, we show by density functional theory that low-symmetry of defects can provide coherent optical and spin subsystems that can be harnessed to achieve electrically driven interferometry of SiC divacancy qubits [3]. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R63.00005: Progress for high photon collection of color centers in quantum materials Tony Zhou, Preston Zhou, Gabriel Silverman, Kelechi Ukah, Ling Xie, Amir Yacoby Color centers in materials have attracted enormous amount of attention due to their interesting quantum properties for quantum computation, quantum optics[1], and quantum sensing applications[2]. The most notable research has been focused on NV centers, SiV centers in diamond, divacancy in silicon carbide, and etc. There is also an increasing focus on defects, exciton physics in 2D materials. These collections of point-like entities share common optical technique in studies. Thus, efficient collection of each associated photons serves as the ultimate bottle neck in all applications. In this work, we present an effective approach to tackle this fundamental limit and use NV center as an example for its application[3,4]. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R63.00006: Modeling the Electronic Structure of Phosphorus Donor Clusters in Quantum Devices Quinn Campbell, Peter A Schultz, Mitchell I Brickson, Noah T Jacobson, Leon N Maurer, Ezra Bussmann, Shashank Misra, Andrew Baczewski Modeling the electronic structure of phosphorus donor clusters is essential for understanding and predicting the behavior of quantum devices fabricated using atomic precision advanced manufacturing (APAM) techniques. Scanning Tunneling Microscope (STM) lithography is one such technique for creating nanoelectronic devices by placing activated shallow dopants in silicon with atomic precision. To model these devices, we first use kinetic Monte Carlo parameterized from first principles calculations to predict the geometry of phosphorus donor clusters. From these geometries, we predict device performance by applying multivalley effective mass theory, developing a formalism for using a basis of anisotropic atomic orbitals for the envelope functions. We then compare the predicted electronic structure of these donor clusters to experimentally realized devices, reporting on observables such as charging energy and tunnel coupling. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R63.00007: Electron paramagnetic resonance study of sodium guests in silicon clathrates, a cage-like crystalline silicon allotrope William Schenken, Yinan Liu, Lakshmi Krishna, Ahmad Afif Abdul Majid, Carolyn Koh, P Craig Taylor, Reuben T Collins Si clathrates are cage-like crystalline Si allotropes with potentially exciting properties. They are synthesized in the presence of alkali guest atoms, e.g. Na, which occupy interstitial sites in the cages. However, Na guests degenerately dope the crystal. Realizing the potential of these materials requires fundamental understanding of guest properties in the host crystal structure. We present an EPR study of Na guests in Type II Si clathrate powders with ≤1 at. % Na. At low temperature, the spectrum shows four lines from the hyperfine interaction of the Na valence electron with the 23Na nucleus (I=3/2). We attribute a line to Si dangling bonds in a highly disordered phase surrounding each grain, and identify doublets around the four hyperfine lines as arising from interactions with a 29Si nucleus (I=1/2) in the surrounding cage. We estimate about half of the electronic wavefunction on the Si sub-lattice extends past the confining cage. Additional structure is observed halfway between the strong hyperfine lines, which we attribute to interactions of two 23Na nuclei (I=3) in adjacent cages. A relatively broad line is attributed to clustered sodium. The relative intensities show the Na distribution is inhomogeneous. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R63.00008: Quadrupolar interactions between acceptor pairs in p-doped semiconductors Adam Durst, Genesis Yang-Mejia, Ravindra Nautam Bhatt We consider the interaction between acceptor pairs in doped semiconductors in the limit of large inter-acceptor separation relevant for low doping densities. Modeling individual acceptors via the spherical model of Baldereschi and Lipari, we calculate matrix elements of the quadrupole tensor between the four degenerate ground states and show that the acceptor has a nonzero quadrupole moment. As a result, the dominant contribution to the large-separation acceptor-acceptor interaction comes from direct (charge-density) terms rather than exchange terms. The quadrupole is the leading nonzero moment, so the electric quadrupole-quadrupole interaction dominates for large separation. We calculate the matrix elements of the quadrupole-quadrupole interaction Hamiltonian in a product-state basis and diagonalize, obtaining a closed-form expression for the energy spectrum. All dependence on material parameters enters via an overall prefactor, resulting in surprisingly simple and universal results. This simplicity can be traced to the nontrivial vanishing of a particular Wigner 6-j symbol. Results are relevant to the control of two-qubit interactions in quantum computing implementations based on acceptor spins, as well as the thermodynamic properties of insulating p-type semiconductors. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R63.00009: Nanoscale NV-detected Electron Spin Resonance at 115 GHz and 4.2 Tesla Benjamin Fortman, Junior Pena, Susumu Takahashi The nitrogen-vacancy (NV) center is a promising candidate for single-spin electron spin resonance (ESR). NV-detected ESR enables ESR analysis for paramagnetic spins with sensitivity of a single spin. We have recently shown that the spectral resolution of NV-detected ESR is improved by carefully adjusting microwave (MW) pulse duration and intensity [1]. Pulsed ESR spectroscopy at high magnetic fields offers higher spectral resolution and greater spin polarization than measurements at lower magnetic fields. However, the shift to high fields requires a high frequency MW source whose output power is often much lower than that of a low frequency MW source. This results in incomplete population inversion due to limited excitation bandwidths and spin relaxation. Within this talk we present our development and application of adiabatic pulses at 115 GHz to overcome this challenge. We utilize these pulses to control the spin states of single NV centers and to perform ESR using a single NV center at a field of 4.2 Tesla [2]. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R63.00010: Defects in 4H-SiC Studied by Electrically Detected Magnetic Resonance and Electrically Detected Electron Nuclear Resonance Ryan Waskiewicz, Brian Manning, Duane McCrory, Patrick Lenahan We utilize electrically detected magnetic resonance (EDMR) and electrically detected electron nuclear double resonance (EDENDOR) to observe defects responsible for recombination in fully processed 4H-SiC bipolar junction transistors (BJTs). The EDMR response in these devices is detected via spin dependent recombination (SDR) within the space charge region of the forward biased emitter-base junction with the collector grounded. (We link the observed response to silicon vacancies in the 4H-SiC.) We demonstrate the application of EDENDOR on these devices. To the best of our knowledge, this is the first demonstration of EDENDOR on a fully processed device. The EDENDOR measurements combines the power of EDMR with a nuclear magnetic resonance (NMR) excitation, allowing for the identification of magnetic nuclei near the observed defects. Our EDENDOR measurements indicate the presence of 14N nuclei near the silicon vacancies that are measured with EDMR. This work brings the unparalleled analytical power of ENDOR to applications with functional nanoscale devices. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R63.00011: Hybrid spintronics as a novel platform for quantum sensing. Artur Lozovoi, Harishankar Jayakumar, Damon Daw, Carlos Meriles Defects in semiconductors are emerging as a robust solid-state platform for quantum sensing and quantum information processing. These applications demand efficient readout of the defect spin state with high fidelity. We propose a novel spin readout technique1 based on a non-local hybrid spin-to-charge conversion that takes advantage of drift and diffusion of the charge carriers in semiconductors in the presence of electric field. In this approach, spin-dependent generation of charge carriers from the target defects with superior spin properties is coupled to emitters with high quantum efficiency, optical cycling frequency and favorable photoionization properties . We implement this technique in type IIa diamonds and demonstrate that it provides higher sensitivity compared to the conventional spin readout techniques. We note that the proposed approach is universal in its nature and can be applied to spin-active impurities in other semiconductor materials. In addition to that, we use this technique to characterize charge dynamics and capture cross-sections of optically active and dark defects in diamond. |
Thursday, March 5, 2020 10:36AM - 10:48AM |
R63.00012: High-density defect ensembles in SiC for superradiance and magnetometry Peter Brereton, Seth Rittenhouse, Joseph Wiedemann, Jeffrey R Vanhoy, John Abraham The silicon vacancy in SiC has recently become of great interest as a platform for quantum sensing and quantum information processing. In particular, recent theoretical work has shown that the spin 3/2 multiplet of a single silicon vacancy in 4H-SiC can achieve magnetic field sensitivities sufficient to detect single nuclear spins [1]. However, there has been less work done in the high-density, radiatively coupled regime in SiC. Superradiant coupling between atoms [2] and nitrogen vacancies in diamond [3] has been demonstrated experimentally and has been proposed as a route toward ultra-sensitive quantum sensing in the solid state. We explore the details of the superradiant transition in the 4H-SiC silicon vacancy and show possible routes toward engineering suitable defect ensembles. |
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