arXiv subjects

Joseph Sink

Publications and source records attributed to Joseph Sink.

7 recordsLinked to original sources

arXiv2026

Nuclear-Electron Hyperfine Coupling of the Shallow States Associated with Vacancies in Gallium Nitride

We use multiband real space Green's functions computed using open-boundary conditions for clean GaN to exactly solve the potential-scattering Dyson equation to obtain the electronic structure of single nitrogen and gallium vacancies. From these vacancy solutions, we compute the local density of states as well as the Fermi contact and anisotropic contributions to the hyperfine field in the vicinity of the defect. These quantities directly affect electrically-detected magnetic resonance signals, which can be used to identify these defects when present in GaN devices.

cond-mat.mtrl-sci↗

arXiv2025

Microscopic Scattering Approach to In-Gap States: Cr Adatoms on Superconducting \beta-Bi2Pd

We develop a microscopic scattering formalism to describe Yu-Shiba-Rusinov (YSR) states due to a single Cr adatom on the Bi-terminated surface of $\beta-Bi_2Pd$, by combining ab initio Wannier functions with a real-space Green's function approach in the Bogoliubov-de Gennes formalism. Our framework reproduces key scanning tunneling spectroscopy features, including a single particle-hole asymmetric YSR peak and isotropic dIdV maps around the impurity. Decomposing the YSR states reveals contributions from four nearly degenerate C4v representations, with energy broadening masking their individual signatures. Spin-orbit coupling induces partial spin polarization, while the spatial asymmetry between particle and hole components arises from Cr d-Bi p hybridization. These results highlight the importance of realistic band structures and microscopic modeling for interpreting STM data and provide a foundation for studying impurity chains hosting topological excitations.

cond-mat.supr-con↗

arXiv2025

Imaging the Acceptor Wave Function Anisotropy in Silicon

We present the first scanning tunneling microscopy (STM) images of hydrogenic acceptor wave functions in silicon. These acceptor states appear as square ring-like features in STM images and originate from near-surface defects introduced by high-energy bismuth implantation into a silicon (001) wafer. Scanning tunneling spectroscopy confirms the formation of a p-type surface. Effective-mass and tight-binding calculations provide an excellent description of the observed square ring-like features, confirming their acceptor character and attributing their symmetry to the light- and heavy-hole band degeneracy in silicon. Detailed understanding of the energetic and spatial properties of acceptor wave functions in silicon is essential for engineering large-scale acceptor-based quantum devices.

cond-mat.mes-hall↗

arXiv2025

Ab initio calculations of erbium crystal field splittings in oxide hosts

We present an effective ab initio method to calculate the crystal field coefficients of an erbium (Er3+) ion experiencing different local site symmetries in several wide-band-gap oxides, and then evaluate crystal field splittings of these Er3+ ions for their ground and excited states. The optical transitions between the ground state (Z) and excited state (Y) manifolds of the environmentally shielded 4f states of these Er3+ ions have wavelengths ~1.5 microns and thus have potential applications to quantum communications and quantum memories. These results are in excellent agreement with recent low-temperature measurements, provided the inadequate calculation of the 4f shell screening is adjusted by reducing the radial extent of the 4f wavefunctions by approximately a factor of 2.

cond-mat.mtrl-sci↗

arXiv2025

Ab initio calculations of erbium crystal field splittings in oxide hosts: role of the 4f radial wave function

We expand here our description of a newly developed simple and effective ab initio method of calculating crystal field coefficients (CFCs) of rare-earth atoms in insulating hosts, focusing on Er in wide band gap oxide hosts MgO, ZnO, TiO$_2$, CaWO$_4$, and PbWO$_4$, which exemplify different local site symmetries. These hybrid functional calculations, which incorporate a portion of exact exchange from Hartree-Fock theory, reproduce the experimentally identified insulating band gaps of these oxides. The negative values of cohesive and formation energies confirm the structural and chemical stability of these oxides, whereas the defect formation energies indicate that Er doped ZnO, CaWO$_4$, and PbWO$_4$ are easier to form compared to Er doped MgO and TiO$_2$. Er doped in these oxide hosts exhibits a spin magnetic moment of $\sim$ 3 $\mu_B$ confirming the $3+$ valence state. The CFCs of these hosted Er are determined from charge densities and potentials obtained from non-spin-polarized calculations, involving a 4\textit{f} core approximation. These CFCs are subsequently used to solve an effective Hamiltonian and generate the crystal field splitting of Er 4f. These calculated Er 4f energy levels are in good agreement with available experiments.

cond-mat.mtrl-sci↗

arXiv2023

Wurtzite/Zincblende Crystal Phase GaAs Heterostructures in the Tight Binding Approximation

Crystal phase semiconductor heterostructures allow for electron confinement without uncertainties caused by chemical intermixing found in material heterostructures and are candidates for next generation optoelectronics devices ranging from single-photon emitters to high efficiency LEDs. While there has been a great deal of experimental work developing fabrication processes for these structures, theoretical calculations have been limited due to a lack of atomistic models that are able to incorporate the zincblende and wurtzite within the same structure. Here, we present calculations of the electronic energies in GaAs nanowires containing various thicknesses of zincblende and wurtzite layers using a recently developed tight-binding model for wurtzite III-V semiconductors that is compatible with a zincblende model. By comparing results in the flat-band and the unscreened limits, we explain the sensitivity of experimentally observed band gaps on zincblende and wurtzite well widths. Our calculations suggest that experiments on devices are likely near the flat-band limit under typical operating conditions.

cond-mat.mtrl-sci↗

arXiv2022

Empirical Tight-Binding Parameters for Wurtzite group III-V(non-Nitride) and IV Materials

Many commonly used nearest neighbor tight binding models for cubic semiconductors often result in inaccurate band structures when transferred to hexagonal polytypes. The resulting bandgaps are systematically too small, and in some cases calculations may erroneously predict a metal for the wurtzite polytype. We have calculated a set of $\rm spds^*$ tight binding parameters for the hexagonal phases of non-nitride III-V and group V semiconductors fit to experimental data and empirical pseudopotential calculations. Our fitting procedure constrains the parameters to be as close as possible to those for the cubic polytype so as to make the the parameters maximally transferable. Our parameters, when combined with the existing cubic parameters, provide a model suitable for modeling the electronic structure of polytypic heterostructures containing both the wurtzite and zincblende crystal phases.

cond-mat.mtrl-sci↗