David Facemyer - Academia.edu (original) (raw)
Papers by David Facemyer
Physical Review B
High-spin systems, like those that incorporate rare-earth 4 f elements, are increasingly relevant... more High-spin systems, like those that incorporate rare-earth 4 f elements, are increasingly relevant in many fields. Although research on such systems is sparse, the large Hilbert spaces they occupy are promising for many applications. In this work, we examine a one-dimensional linear array of europium atoms on a Au(111) surface and study their electronic and magnetic excitations. Ab initio calculations using VASP with the Perdew-Burke-Ernzerhof (PBE) functional + U are employed to study the structure. We find Eu atoms have a net charge when on gold, consistent with a net magnetic moment of 3.5μ B. Examining various spin-projection configurations, we can evaluate first-and second-neighbor exchange energies in an isotropic Heisenberg model between spin-7 2 moments to obtain J 1 ≈ −1.2 K and J 2 ≈ 0.2 K for a relaxed-chain atomic separation of a ≈ 5 Å. These parameters are used to obtain the full spin excitation spectrum of a physically realizable four-atom chain. The large |J 1 |/J 2 ratio results in a highly degenerate ferromagnetic ground state that is split by a significant easy plane single-ion anisotropy of 0.6 K. Spin-flip excitations are calculated to extract differential conductance profiles such as those obtained by scanning tunneling microscopy techniques. We uncover interesting behavior of local spin excitations, especially as we track their dispersion with applied magnetic fields.
Cornell University - arXiv, Dec 16, 2022
High spin systems, like those that incorporate rare earth 4f elements (REEs), are increasingly re... more High spin systems, like those that incorporate rare earth 4f elements (REEs), are increasingly relevant in many fields. Although research in such systems is sparse, the large Hilbert spaces they occupy are promising for many applications. In this work, we examine a one-dimensional linear array of europium (Eu) atoms on a Au(111) surface and study their electronic and magnetic excitations. Ab initio calculations using VASP with PBE+U, spin-orbit coupling, and the HSE hybrid functional are employed to study the structure. We find Eu atoms to have a net charge when on gold, consistent with a net magnetic momemt of 3.5µB. Examining various spin-projection configurations, we can evaluate first and second neighbor exchange energies in an isotropic Heisenberg model between spin-7 2 moments to obtain J1 ≈ −0.9 K and J2 ≈ 4.3 K for the relaxed-chain atomic separation of a ≈ 5 A. These parameters are used to obtain the full spin excitation spectrum of a physically realizable four-atom chain. The large J2/|J1| 4.8 ratio results in a singlet ground state with dimer-like antiferromagnetic correlations between second neighbors. The seemingly small J1 values significantly affect the spectra, underscoring the important role that nearest-neighbor coupling plays in this system, including possible Dzyaloshinskii-Moriya interactions. Spin-flip excitations are calculated to extract differential conductance profiles as those obtained by scanning tunneling microscopy techniques. We uncover interesting behavior for local higher spin excitations, especially as we track their dispersion with applied magnetic fields.
APS March Meeting Abstracts, 2019
It has been suggested theoretically and realized experimentally that combining organic material a... more It has been suggested theoretically and realized experimentally that combining organic material and inorganic semiconductors in one heterostructure would result in resonant interactions between the Frenkel excitons in the organic material and the Wannier-Mott excitons in the semiconductors, leading to the formation of an exciton hybridization state. The new materials, possessing the complimentary characteristics of both exciton types, such as large exciton radius, enormous oscillator strength and room-temperature operation properties, would enhance optical nonlinearities and promise to have useful applications in both the field of Bose-Einstein condensation of polaritons and polariton lasers. In this work, we consider a strong coupling of the hybrid excitons and photons near excitonic resonance analytically with the purpose of determining the electronic structure, energy, and dispersion relation of the hybrid exciton-polariton. We study different confinement parameters for various n...
arXiv: Mesoscale and Nanoscale Physics, 2019
In this work electronic structures and optical properties of organic-inorganic exciton and polari... more In this work electronic structures and optical properties of organic-inorganic exciton and polaritons in two-dimensional heterostructures combining both organic and semiconductor materials are studied. In those systems, Wannier-Frenkel hybrid exciton has unique and interesting properties that can improve the efficiency of optical materials. When an organic-semiconductor combined heterostructure is illuminated by high-intensity electromagnetic radiation with the frequency of the photons at or near the resonance frequency of the Wannier-Frenkel exciton, we obtain a macroscopically occupied system of hybrid polaritons. We will theoretically determine electronic structure, energy and dispersion relation of the hybrid excitons and polaritons. By analyzing the parameters of the systems and the interactions between the Wannier and Frenkel excitons and the photons, we then discuss the conditions for hybridization.
Physical Review B
High-spin systems, like those that incorporate rare-earth 4 f elements, are increasingly relevant... more High-spin systems, like those that incorporate rare-earth 4 f elements, are increasingly relevant in many fields. Although research on such systems is sparse, the large Hilbert spaces they occupy are promising for many applications. In this work, we examine a one-dimensional linear array of europium atoms on a Au(111) surface and study their electronic and magnetic excitations. Ab initio calculations using VASP with the Perdew-Burke-Ernzerhof (PBE) functional + U are employed to study the structure. We find Eu atoms have a net charge when on gold, consistent with a net magnetic moment of 3.5μ B. Examining various spin-projection configurations, we can evaluate first-and second-neighbor exchange energies in an isotropic Heisenberg model between spin-7 2 moments to obtain J 1 ≈ −1.2 K and J 2 ≈ 0.2 K for a relaxed-chain atomic separation of a ≈ 5 Å. These parameters are used to obtain the full spin excitation spectrum of a physically realizable four-atom chain. The large |J 1 |/J 2 ratio results in a highly degenerate ferromagnetic ground state that is split by a significant easy plane single-ion anisotropy of 0.6 K. Spin-flip excitations are calculated to extract differential conductance profiles such as those obtained by scanning tunneling microscopy techniques. We uncover interesting behavior of local spin excitations, especially as we track their dispersion with applied magnetic fields.
Cornell University - arXiv, Dec 16, 2022
High spin systems, like those that incorporate rare earth 4f elements (REEs), are increasingly re... more High spin systems, like those that incorporate rare earth 4f elements (REEs), are increasingly relevant in many fields. Although research in such systems is sparse, the large Hilbert spaces they occupy are promising for many applications. In this work, we examine a one-dimensional linear array of europium (Eu) atoms on a Au(111) surface and study their electronic and magnetic excitations. Ab initio calculations using VASP with PBE+U, spin-orbit coupling, and the HSE hybrid functional are employed to study the structure. We find Eu atoms to have a net charge when on gold, consistent with a net magnetic momemt of 3.5µB. Examining various spin-projection configurations, we can evaluate first and second neighbor exchange energies in an isotropic Heisenberg model between spin-7 2 moments to obtain J1 ≈ −0.9 K and J2 ≈ 4.3 K for the relaxed-chain atomic separation of a ≈ 5 A. These parameters are used to obtain the full spin excitation spectrum of a physically realizable four-atom chain. The large J2/|J1| 4.8 ratio results in a singlet ground state with dimer-like antiferromagnetic correlations between second neighbors. The seemingly small J1 values significantly affect the spectra, underscoring the important role that nearest-neighbor coupling plays in this system, including possible Dzyaloshinskii-Moriya interactions. Spin-flip excitations are calculated to extract differential conductance profiles as those obtained by scanning tunneling microscopy techniques. We uncover interesting behavior for local higher spin excitations, especially as we track their dispersion with applied magnetic fields.
APS March Meeting Abstracts, 2019
It has been suggested theoretically and realized experimentally that combining organic material a... more It has been suggested theoretically and realized experimentally that combining organic material and inorganic semiconductors in one heterostructure would result in resonant interactions between the Frenkel excitons in the organic material and the Wannier-Mott excitons in the semiconductors, leading to the formation of an exciton hybridization state. The new materials, possessing the complimentary characteristics of both exciton types, such as large exciton radius, enormous oscillator strength and room-temperature operation properties, would enhance optical nonlinearities and promise to have useful applications in both the field of Bose-Einstein condensation of polaritons and polariton lasers. In this work, we consider a strong coupling of the hybrid excitons and photons near excitonic resonance analytically with the purpose of determining the electronic structure, energy, and dispersion relation of the hybrid exciton-polariton. We study different confinement parameters for various n...
arXiv: Mesoscale and Nanoscale Physics, 2019
In this work electronic structures and optical properties of organic-inorganic exciton and polari... more In this work electronic structures and optical properties of organic-inorganic exciton and polaritons in two-dimensional heterostructures combining both organic and semiconductor materials are studied. In those systems, Wannier-Frenkel hybrid exciton has unique and interesting properties that can improve the efficiency of optical materials. When an organic-semiconductor combined heterostructure is illuminated by high-intensity electromagnetic radiation with the frequency of the photons at or near the resonance frequency of the Wannier-Frenkel exciton, we obtain a macroscopically occupied system of hybrid polaritons. We will theoretically determine electronic structure, energy and dispersion relation of the hybrid excitons and polaritons. By analyzing the parameters of the systems and the interactions between the Wannier and Frenkel excitons and the photons, we then discuss the conditions for hybridization.