Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F53: Defects in SiC and hBNFocus Live
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Sponsoring Units: DMP DCOMP FIAP Chair: Lee Bassett, University of Pennsylvania |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F53.00001: High-throughput identification of point defects in SiC Joel Davidsson, Viktor Ivady, Rickard Armiento, Igor Abrikosov Point defects in wide-band-gap semiconductors are used in many applications such as single photon emitters. 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. This is difficult due to the vast number of possible defects present in one material. 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. Based on our understanding of the convergence of these calculations, we made a collection of automatic workflows called ADAQ [arXiv:2008.12539]. Here, each defect is calculated for a range of different configurations, charges, spins, and possible excitations. Currently, we are running these calculations and producing a database for an array of different defects. So far, we have screened about 8000 native defects 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. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F53.00002: First Principle Characterization of Optical Charge State Conversion of the Carbon Antisite-Vacancy in 4H-SiC Oscar Bulancea Lindvall, Viktor Ivády, Rickard Armiento, Igor Abrikosov Wide band-gap semiconductors such as Silicone Carbide (SiC) can host color centers with potential for near-infrared optical emissions and spin properties suitable for quantum technologies. Charge state control of such defects is vital, as any change in the charge state can lead to the loss of favorable properties. Charge state transitions can occur due to the optical pumping used to excite the defect and modeling of such events is therefore an important part of color center characterization. In this work, we study the carbon antisite-vacancy pair (CSiVC) in 4H-SiC which shows promise for optical transitions at telecom wavelength1 and is thought to be involved in ultrabright transitions at room temperature2. We theoretically characterize this defect, focusing on the optical excitations with charge-state altering capabilities and show that our results can predict thresholds for optical charge transitions. In addition, we calculate relevant hyperfine coupling tensors for all paramagnetic charge states and discuss our results in the light of recent EPR measurements3 demonstrating evidence of optically driven charge state transitions. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F53.00003: The mystery of the missing neutral Si vacancy in 3C-SiC solved Peter Schultz, Renee M. Van Ginhoven, Arthur Edwards The simple silicon vacancy is an iconic defect in 3C-SiC whose full characterization has thus far proven an inscrutable challenge. The negatively charged v(1-) is well-understood, experiment and theory converging to a high-spin quartet with Td structure. For v(0), however, standard DFT predicted a high-spin triplet (Torpo, 1999) that, despite a Jahn-Teller degeneracy, remained an undistorted Td. This conflicted with experiments (e.g., Itoh, 1997; Son 1997) which found no such Td triplet, nor other unambiguous signature of a v(0). This absence prompted use of more exotic electronic structure approaches (Deak, 1999; Zywietz, 2000), which found a lower energy singlet-spin v(0), in principle invisible to spin-sensitive experiments such as EPR. We find a lower energy yet for a high-spin triplet v(0) distorted from Td, confirmed in extrapolations from supercells up to large 1000-sites using DFT/GGA. A new manifestation of finite cell error is diagnosed which, when remedied, yields an energy lowering dominated more by an electronic than a structural distortion, prompted by the Jahn-Teller-like degeneracy. This gives a description of the v(0) more consistent with observations (or lack thereof). --- SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F53.00004: Spin Structure and Resonant Driving of Spin-1/2 Defects in SiC Benedikt Tissot, Guido Burkard Transition metal (TM) defects in silicon carbide (SiC) have favorable spin coherence propertiesand are suitable as spin-photon interfaces for quantum communication. We model defects that have one active electron with spin 1/2 in a d-orbital subspace. The spin structure, as well as the magnetic and optical (electric) resonance properties of the active electron due to the interplay of the crystal potential and spin-orbit coupling are described by a general model derived using group theory. We employ a Schrieffer-Wolff transformation to identify the selection rules within the first and second order in the spin-orbit coupling. The resulting effective Hamiltonian links the g-tensor to the spin-orbit coupling and describes the dependence of the Rabi frequency on the direction of the static and driving field. This theoretical description can be instrumental to perform and optimize spin control in TM defects. |
Tuesday, March 16, 2021 12:18PM - 12:54PM Live |
F53.00005: The light years: Atomic-scale quantum photonics with combined optical and electron microscopy Invited Speaker: Jennifer Dionne Pearl Jam’s hit, “The Light Years,” declares “We were but stones, light made us stars.” Bringing light to the transmission electron microscope promises to transform our understanding of quantum materials, enabling both observation of light-mediated processes and control of optical emission. This presentation will describe our efforts to probe and control color centers in two promising materials: 1) hexagonal boron nitride (hBN) and 2) diamond nanoparticles. First, we investigate color centers in hBN, a wide bandgap semiconductor with bright, room temperature quantum emission. Through high resolution transmission electron imaging, we find that multiple emitters are located within a diffraction-limited spot, each contributing to the observed quantum emission. We also find four unique classes of quantum emitters with distinct spectral signatures, each of which is strain-tunable. Next, we investigate quantum emission from individual nanodiamonds. Within larger nanoparticles (>100nm), we observe heterogeneity of emission, including a red-shifting of the 738nm SiV emission across the nanoparticle, and increased intensity of the phonon sideband; the strongest emission is observed along grain boundaries. Within smaller nanoparticles (down to 1.7nm), we observe robust, single-defect emission. By combining atomic-scale imaging with AI, we help elucidate the atomic structure of individual quantum optical defects within sub-5nm nanodiamonds. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F53.00006: Probing the Optical Dynamics of Quantum Emitters in Hexagonal Boron Nitride Raj Patel, David Hopper, Tzu-Yung Huang, Jordan A Gusdorff, Benjamin Porat, Lee Bassett Hexagonal boron nitride (h-BN) is a van der Waals material that hosts defect-based quantum emitters (QEs) at room temperature. Recent observations suggest existence of multiple distinct defect structures hosting QEs. Theoretical proposals suggest vacancies, their complexes and substitutional atoms as likely defect candidates. However, experimental identification of the QEs’ electronic structure is lacking, and key details of the QEs’ charge and spin properties remain unknown. Here, we probe the optical dynamics of QEs in h-BN using photon emission (PE) statistics and photoluminescence (PL) spectroscopy for various excitation powers and wavelengths. The PL spectra exhibit emission lineshapes consistent with individual phonon-assisted optical transitions. However, the PE statistics reveal complicated optical dynamics and suggest there are multiple non-radiative transitions consistent with electronic and charge states. Remarkably, the QEs’ antibunching and bunching rates scale nonlinearly with the optical pumping rate, suggesting the existence of short-lived states and multiple charge or spin manifolds as key elements in the QEs’ optical dynamics. We compare these observations to theoretical models of the QEs’ electronic structure. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F53.00007: Excitation Energies of Defects in Hexagonal Boron Nitride via an Embedding Method using Auxilliary-Field Quantum Monte Carlo Brian Busemeyer, Shiwei Zhang Defects in 2-d hexagonal boron nitride (h-BN) have shown promise for applications as color centers as well as possible qubit realizations. Producing these applications in a 2-d system is especially tantalizing because of the additional control available in manufacturing 2-d systems. However, the types and properties of defects in BN are varied, difficult to characterize experimentally, and different approximate first-principles treatments yield qualitatively different predictions for a given defect. We applied high-accuracy first-principles auxiliary-field quantum Monte Carlo (AFQMC) calculations to predict vertical excitations and intersystem crossings for the CBVN defect in h-BN. We were able to reach sufficiently large supercell sizes by applying an embedding method. Correlations within a given radius around the defect are treated with AFQMC, and this calculation is embedded in a bulk treated with independent-electron theory. The favorable scaling of AFQMC allowed us to expand the radius defining the correlated orbitals until all quantities were well-converged. This approach opens new possibilities for accurate many-body treatment of defect systems using embedding in combination with AFQMC. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F53.00008: Formation energies of charged defects in 2D materials - a new perspective Andrew O'Hara, Blair Tuttle, Xiaoguang Zhang, Sokrates T Pantelides Formation energies of defects in semiconductors play a major role in a wide range of properties. Supercell schemes have been widely used for calculations. In the conventional formulation, a divergence arises from periodic Coulomb interactions and, in the “jellium” scheme, is removed by setting the average electrostatic potential to zero. A posteriori corrections are used to determine the infinite-supercell limit. For 2D materials, where unscreened Coulomb tails are present in the vacuum regions, additional complications arise. In this work, we present an alternative formulation, derived from statistical mechanics, which dictates that supercells are naturally neutral: “charged defects” are merely ionized, by trading carriers with the energy bands (charge neutrality of the crystal is an essential ingredient of the statistical mechanics of electrons in semiconductors). We show that the jellium approach can be derived from the statistical-mechanics-backed theory by invoking ad hoc approximations. We report density-functional-theory calculations showing that the differences between the two methods are especially large in 2D materials, e.g., h-BN, where they can be of order 1 eV. Convergence rates are excellent. |
Tuesday, March 16, 2021 1:30PM - 2:06PM Live |
F53.00009: Scaling quantum systems with silicon carbide and molecules Invited Speaker: David Awschalom Scaling spin-based quantum technologies requires new platforms for creating and controlling quantum states. We begin with the divacancy defect (VV0) in silicon carbide (SiC), which combines long lived spin states with a tunable optical interface. First, we leverage the semiconducting host material by integrating single spin qubits into wafer-scale, commercial optoelectronic devices, enabling near terahertz-scale tuning and a mitigation of spectral diffusion in the defect’s optical structure [1]. |
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