Nonequilibrium Green's function study of magnetoconductance features and oscillations in clean and disordered nanowires

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.

Robust all-electrical topological valley filtering using monolayer 2D-Xenes

“…We must remark at this stage that only static impurities inside the channel are considered within the above approach. An unexplored frontier in terms of understanding the stability of topological edge/interface states is the inclusion of momentum relaxing dephasing [52][53][54][55][56] phase breaking processes [57][58][59] and ultimately inelastic scattering processes [60,61], that can be well facilitated by using the Keldysh non-equilibrium Green's function approach [62].…”

Role of dephasing on the conductance signatures of Majorana zero modes

“…All this has led to a side-by-side strong theoretical push [17][18][19][20][21][22][23][24][25] , where a lot of focus has been on resolving the issue about the origins of the observed ZBCP. In parallel, there is also a strong need to push for theoretical works that go beyond minimal 1D models in order to include multi-mode effects 12,26,27 , realistic potentials [28][29][30][31][32][33] , the inclusion of disorder [22][23][24][25] and also scattering and relaxation effects 34 . While the importance of ascertaining the topological origin of the observed experimental conductance signatures is of great importance, in this paper, we take the route of analyzing the nature of a topological MZM in a typical three terminal N-TS-N configuration and the corresponding ZBCP, first in the coherent transport regime, and then in the non-coherent regime where dephasing effects due to relaxation mechanisms are present.…”

“…Non-coherent transport: In the case of non-coherent transport, intra-channel interactions such as electronelectron interactions, dephasing and inelastic scattering can be included via the scattering self energy Σ r s . In this paper, we include intra-channel interactions in the form of channel fluctuating impurities with localized potentials U (r i ) at the sites, such that their correlator D(i, j) = U (r i )U * (r i ) can be used to find the scattering self energies within the self consistent Born approximation 26,27,43,44,55,56…”

Momentum relaxation effects in 2D-Xene field effect device structures

“…The object of this paper is to delve into the topological field effect transition in 2D-Xene materials with quantum transport models in the coherent ballistic regime and the non-coherent regime with dephasing effects [45][46][47] resulting from momentum relaxation processes [44,[48][49][50][51][52][53][54]. The transition between the QSH and the QVH states is analyzed in detail using the NEGF technique [45,55].…”