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 P18: First-Principles Approaches for Quantum DefectsInvited Session Live
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Sponsoring Units: DCOMP Chair: Chris Van de Walle, University of California, Santa Barbara |
Wednesday, March 17, 2021 3:00PM - 3:36PM Live |
P18.00001: Optical properties of quantum defects from first-principles calculations Invited Speaker: Audrius Alkauskas Optical spectroscopy of point defects provides a wealth of information and, along with magnetic resonance spectroscopy, is one of the most powerful tools for defect identification and analysis. While the general theory of optical properties of defects has been formulated several decades ago, practical calculations of various properties has been far behind similar calculations for molecules and pristine solids for very good reasons. In this talk I will review several recent advances regarding the study of optical properties of defects with a special focus on quantum defects [1]: (i) the calculation of luminescence and absorption lineshapes [2], including the recently developed practical methodology to treat the multi-mode dynamical Jahn-Teller effect; (ii) radiative capture rates [3]; (iii) absolute photoionization cross-sections. The talk will be illustrated with recent examples of successful defect identification [4]. The outstanding challenges and unsolved problems will be also outlined. |
Wednesday, March 17, 2021 3:36PM - 4:12PM Live |
P18.00002: Quantum Defects and Recombination in Two Dimensions Invited Speaker: Yuan Ping When applying first-principles computational techniques to quantum defects in two-dimensional (2D) systems, care needs to be taken in handling the Coulomb interactions with the reduced dimensionality and stronger many-body interaction. We will show our recent progress on developing first-principles methods for charged defects in two-dimensional materials. We will show how to correctly handle reduced dimensionality on the defect formation energies and ionization energies from hybrid functionals and GW approximations, using quantum defects in hexagonal boron nitride as a test-bed system [1-2]. |
Wednesday, March 17, 2021 4:12PM - 4:48PM Live |
P18.00003: Boron Dangling Bonds as Single Photon Emitters in Hexagonal Boron Nitride Invited Speaker: Mark Turiansky First-principles calculations have proven invaluable in the identification of novel quantum defects in a variety of semiconductor hosts. Hexagonal boron nitride (h-BN) is one such host that exhibits promising properties: h-BN has an ultra-wide band gap, two-dimensional crystal structure, and excellent stability. Single-photon emission has been observed in h-BN, and the emitters around 2 eV possess a wealth of interesting features that are promising for quantum applications. However, a conclusive identification of the microscopic origin has proven elusive. In this work, we employ hybrid density functional theory to demonstrate that the properties of boron dangling bonds are consistent with the experimental reports. Specifically, doubly occupied boron dangling bonds give rise to optical emission at 2.06 eV with a Huang-Rhys factor of 2.3. The emission is linearly polarized, with indirect excitation into the conduction band explaining the lack of dipole alignment seen in experiment. The boron dangling bond possesses a metastable triplet state, which can explain the observed spin dependence. We will discuss recent developments to the model, including the behavior of the boron dangling bond in a monolayer of h-BN. Our work demonstrates that dangling bonds may also be efficient quantum defects in other materials. |
Wednesday, March 17, 2021 4:48PM - 5:24PM Live |
P18.00004: Spin Dynamics of Single Quantum Defects Invited Speaker: Michael Flatté Realizing spin qubits for quantum computing and sensing applications relies on the ability to predict the response of a spinful quantum defect to both intentional and unintentioanl external perturbations from first principles. Intentional perturbations include spin interactions with various bosons, including photons, phonons and magnons, whereas unintentional ones include the role of fluctuating charges or spins in the environment. Simulating these perturbations requires a rigorous dynamical theory that maintains coherences throughout the relevant timescales. Recently we predicted[1] the potential to measure very small exchange interactions between spins through the formation of a bottleneck state, formed from a coherent singlet-triplet superposition, in spin-polarized transport oblique to a magnetic field. Spin-polarized scanning tunneling probes could reveal therefore the micro-eV exchange energies we have predicted between spin centers separated by up to 2 nm[2]. Similar sensitivities to the dipole electric field generated from a chromophore could be similarly detected by a single NV center, proving a new avenue for single-photon detection.[3] When quantum coherence can be maintained in the field excitation, such as for highly coherent magnons in small magnetic regions, the spin-magnon coupling could entangle NV centers separated by several microns[4]. |
Wednesday, March 17, 2021 5:24PM - 6:00PM Live |
P18.00005: Electronic structure and coherence properties of spin defects in two-and three-dimensional semiconductors from first principles Invited Speaker: Giulia Galli We report on recent progress in investigating the electronic structure [1] and coherence properties [2] of spin defects in three- and two-dimensional materials using first principles electronic structure calculations (DFT and many body perturbation theory), and spin Hamiltonians [3]. In particular we present results for defects in SiC, and MoS2. |
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