arXiv subjects

Neil Drummond

Publications and source records attributed to Neil Drummond.

6 recordsLinked to original sources

arXiv2024

Off-shell selfenergy for 1-D Fermi liquids

The selfenergy in Born approximation including exchange of interacting one-dimensional systems is expressed in terms of a single integral about the potential which allows a fast and precise calculation for any potential analytically. The imaginary part of the self energy as damping of single-particle excitations shows a rich structure of different areas limited by single-particle and collective excitation lines. The corresponding spectral function reveals a pseudogap, a splitting of excitation into holons and antiholons as well as bound states.

cond-mat.str-el↗

arXiv2024

Electronic quantum wires in extended quasiparticle picture

A one-dimensional quantum wire of Fermions is considered and ground state properties are calculated in the high density regime within the extended quasiparticle picture and Born approximation. Expanding the two-particle Green functions determines the selfenergy and the polarization as well as the response function on the same footing. While the on-shell selfenergies are strictly zero due to Pauli-blocking of elastic scattering, the off-shell behaviour shows a rich structure of a gap in the damping of excitation which is closed when the momentum approaches the Fermi one. The consistent spectral function is presented completing the first two energy-weighted sum rules. The excitation spectrum shows a splitting due to holons and antiholons as non-Fermi liquid behaviour. A renormalization procedure is proposed by subtracting an energy constant to render the Fock exchange energy finite. The effective mass derived from meanfield shows a dip as onset of Peierls instability. The correlation energy is calculated with the help of the extended quasiparticle picture which accounts for off-shell effects. The corresponding response function leads to the same correlation energy as the selfenergy in agreement with perturbation theory. The reduced density matrix or momentum distribution is calculated with the help of a Padé regularization repairing deficiencies of the perturbation theory. A seemingly finite step at the Fermi energy indicating Fermi-liquid behaviour is repaired in this way.

cond-mat.str-el↗

arXiv2023

Quantum Monte Carlo study of Doppler broadening of positron annihilation radiation in semiconductors and insulators

Positron annihilation in solid state matter can be utilized to detect and identify open-volume defects. The momentum distribution of the annihilation radiation is an important observable in positron-based measurements, and can reveal information on the chemical surroundings of the defect sites. In this work we present a variational quantum Monte Carlo method for simulation of the momentum densities of annihilating electron-positron pairs in semiconductors and insulators. We study finite-size effects, effects of lattice vibrations, and different levels of trial wave functions. Small simulation cells and simple wave function forms are found to be sufficient for accurate calculations in simulation of pristine lattices, enabling cheap accumulation of results. We compare calculated predictions of the Doppler broadening of the 511-keV 2γ annihilation line of the in aluminium nitride and silicon against experimental data measured from reference samples. Our results achieve better agreement with experiments in the these materials than conventional state-of-the-art methods, and proves that direct modeling of the electron-positron correlations is important for a supporting theory of positron annihilation sprectroscopies

cond-mat.mtrl-sci↗

arXiv2022

Polaron spectroscopy of a bilayer excitonic insulator

Recent advances in fabrication of two dimensional materials and their moiré heterostructures have opened up new avenues for realization of ground-state excitonic insulators, where the structure spontaneously develops a finite interlayer electronic polarization. We propose and analyze a scheme where an optically generated intralayer exciton is screened by excitations out of the excitonic insulator to form interlayer polarons. Using Quantum Monte-Carlo calculations we first determine the binding energy of the biexciton state composed of inter- and intralayer excitons, which plays a central role in understanding polaron formation. We describe the excitations out of the ground-state condensate using BCS theory and use a single interacting-quasiparticle-pair excitation Ansatz to describe dynamical screening of optical excitations. Our predictions carry the hallmarks of the excitonic insulator excitation spectrum and show how changing the interlayer exciton binding energy by increasing the layer separation modifies the optical spectra.

cond-mat.mes-hall↗

arXiv2019

Binding energies of excitonic complexes in type-II quantum rings from diffusion quantum Monte Carlo calculations

Excitonic complexes in type-II quantum-ring heterostructures may be considered as artificial atoms due to the confinement of only one charge-carrier type in an artificial nucleus. Binding energies of excitons, trions, and biexcitons in these nanostructures are then effectively ionization energies of these artificial atoms. The binding energies reported here are calculated within the effective-mass approximation using the diffusion quantum Monte Carlo method and realistic geometries for gallium antimonide rings in gallium arsenide. The electrons form a halo outside the ring, with very little charge density inside the central cavity of the ring. The de-excitonization and binding energies of the complexes are relatively independent of the precise shape of the ring.

cond-mat.mes-hall↗

arXiv2015

Three-particle Complexes in Two-Dimensional Semiconductors

We map the three-body problem in two dimensions onto one particle in a three dimensional potential treatable by a purposely-developed boundary-matching-matrix method. We evaluate binding energies of trions $X^{\pm}$, excitons bound by a donor/acceptor charge $X^{D/A}$, and overcharged acceptors/donors in two-dimensional atomic crystals of transition metal dichalcogenides, where interaction between charges features logarithmic behavior at intermediate distances. We find that dissociation energy of $X^{\pm}$ is, typically, much larger than that of localised exciton complexes, so that trions are more resilient to heating, despite that their recombination line in optics is much less red-shifted from the exciton line, as compared to $X^{D/A}$

cond-mat.mes-hall↗