Non-equilibrium Green's function study of magneto-conductance features and oscillations in clean and disordered nanowires

TL;DR

This study uses non-equilibrium Green's function models to analyze magneto-conductance oscillations in semiconductor nanowires, revealing how disorder, geometry, and dephasing influence the dominance of Aharonov-Bohm and Al'tshuler-Aronov-Spivak oscillations.

Contribution

It introduces a comprehensive quantum transport model that captures the transition between AB and AAS oscillations in disordered nanowires, including effects of surface roughness and dephasing.

Findings

AB oscillations dominate in clean nanowires with surface confinement.

AAS oscillations become dominant with increased disorder and length.

Dephasing suppresses higher harmonics, allowing AB oscillations to re-emerge.

Abstract

We explore various aspects of magneto-conductance oscillations in semiconductor nanowires, developing quantum transport models based on the non-equilibrium Green's function formalism. In the clean case, Aharonov-Bohm (AB - h/e) oscillations are found to be dominant, contingent upon the surface confinement of electrons in the nanowire. We also numerically study disordered nanowires of finite length, bridging a gap in the existing literature. By varying the nanowire length and disorder strength, we identify the transition where Al'tshuler-Aronov-Spivak (AAS - h/2e) oscillations start dominating, noting the effects of considering an open system. Moreover, we demonstrate how the relative magnitudes of the scattering length and the device dimensions govern the relative dominance of these harmonics with energy, revealing that the AAS oscillations emerge and start dominating from the center of the band, much higher in energy than the conduction band-edge. We also show the ways of suppressing the oscillatory components (AB and AAS) to observe the non-oscillatory weak localization corrections, noting the interplay of scattering, incoherence/dephasing, the geometry of electronic distribution, and orientation of magnetic field. This is followed by a study of surface roughness which shows contrasting effects depending on its strength and type, ranging from magnetic depopulation to strong AAS oscillations. Subsequently, we show that dephasing causes a progressive degradation of the higher harmonics, explaining the re-emergence of the AB component even in long and disordered nanowires. Lastly, we show that our model qualitatively reproduces the experimental magneto-conductance spectrum in [Holloway et al, PRB 91, 045422 (2015)] reasonably well while demonstrating the necessity of spatial-correlations in the disorder potential, and dephasing.