arXiv subjects

Vincent Sacksteder

Publications and source records attributed to Vincent Sacksteder.

3 recordsLinked to original sources

arXiv2022

Magnetoresistance when Spin Effects on Conduction are Weak

This paper considers certain materials, including topological insulators, where spin rotation symmetry is broken much more strongly than time reversal symmetry. When these materials are in the diffusive regime, i.e. when they have disorder that is strong enough to cause an electron to scatter many times while crossing a sample, electrons and holes move in pairs that have zero spin and are insensitive to spin physics. Working within this spinless scenario, we show that Fourier transforming the magnetoconductance with respect to external magnetic field obtains a curve describing the area distribution of loops traced by electrons and holes within the sample. We present loop area distributions of Landau levels, weak (anti)localization, conduction governed by Levy flights, and linear-in-field resistance. Of these four the last two are new results. Comparing these distributions, we argue that the linear-in-field resistance seen in some topological insulators is caused by the same diffusive scattering that causes weak antilocalization. The difference is that linear-in-field resistance materials retain a level of quantum coherence that is usually seen only on the surface of 2-D wires or in ring geometries. In an appendix we include some speculative material about linear-in-temperature resistance.

cond-mat.mes-hall↗

arXiv2018

Many-body renormalisation of forces in f-electron materials

We present the implementation of Dynamical Mean-Field Theory (DMFT) in the CASTEP \emph{ab-initio} code. We explain in detail the theoretical framework for DFT+DMFT and we demonstrate our implementation for three strongly-correlated systems with $f$-shell electrons: $γ$-cerium, cerium sesquioxide Ce$_{2}$O$_{3}$ and samarium telluride SmTe by using a Hubbard I solver. We find very good agreement with previous benchmark DFT+DMFT calculations of cerium compounds, while for SmTe, which was never studied within DFT+DMFT before to the best of our knowledge, we show the improved agreement with the experimental structural parameters as compared with LDA. Our implementation works equally well for both norm-conserving and ultra-soft pseudopotentials, and we apply it to the calculation of total energy, bulk modulus, equilibrium volumes and internal forces in the two cerium compounds. In Ce$_{2}$O$_{3}$ we report a dramatic reduction of the internal forces acting on coordinates not constrained by unit cell symmetries. This reduction is induced by the many-body effects, which can only be captured at the DMFT level. In addition, we derive an alternative form for treating the high-frequency tails of the Green function in Matsubara frequency summations. Our treatment allows a reduction in the bias when calculating the correlation energies and occupation matrices to high precision.

cond-mat.str-el↗

arXiv2015

Modification and Control of Topological Insulator Surface States Using Surface Disorder

We numerically demonstrate a practical means of systematically controlling topological transport on the surface of a three dimensional topological insulator, by introducing strong disorder in a layer of depth $d$ extending inward from the surface of the topological insulator. The dependence on $d$ of the density of states, conductance, scattering time, scattering length, diffusion constant, and mean Fermi velocity are investigated. The proposed control via disorder depth $d$ requires that the disorder strength be near the large value which is necessary to drive the TI into the non-topological phase. If $d$ is patterned using masks, gates, ion implantation, etc., then integrated circuits may be fabricated. This technique will be useful for experiments and for device engineering.

cond-mat.mes-hall↗