[Paper Review] Magnetoresistance in 3D Weyl Semimetals

Navneeth Ramakrishnan, Mirco Milletarì+1 more|arXiv (Cornell University)|Jan 15, 2015

Topological Materials and Phenomena3 citations

TL;DR

This paper theoretically investigates magnetoresistance in 3D Weyl semimetals using RPA-Boltzmann transport theory and effective medium averaging to model electron scattering off charged impurities. It predicts a transition from quadratic to linear magnetoresistance at high magnetic fields, with magnetoresistance exceeding 10, in quantitative agreement with recent experiments on TlBiSSe.

ABSTRACT

We theoretically investigate the transport and magnetotransport properties of three-dimensional Weyl semimetals. Using the RPA-Boltzmann transport scattering theory for electrons scattering off randomly distributed charged impurities, together with an effective medium theory to average over the resulting spatially inhomogeneous carrier density, we smoothly connect our results for the minimum conductivity near the Weyl point with known results for the conductivity at high carrier density. In the presence of a non-quantizing magnetic field, we predict that for both high and low carrier densities, Weyl semimetals show a transition from quadratic magnetoresistance (MR) at low magnetic fields to linear MR at high magnetic fields, and that the magnitude of the $MR \gtrsim 10$ for realistic parameters. Our results are in qualitative agreement with recent unexpected experimental observations on the mixed-chalcogenide compound TlBiSSe.

Motivation & Objective

• To understand the transport and magnetotransport properties of 3D Weyl semimetals near the Weyl point.
• To bridge the gap between minimum conductivity at low carrier density and high-density conductivity using a unified theoretical framework.
• To explain the experimentally observed large, non-saturating magnetoresistance in Weyl semimetals like TlBiSSe.
• To model the influence of charged impurities on carrier inhomogeneity and its effect on magnetotransport.

Proposed method

• Employing RPA-Boltzmann transport theory to describe electron scattering off randomly distributed charged impurities.
• Applying effective medium theory to average spatially inhomogeneous carrier density arising from impurity scattering.
• Calculating conductivity and magnetoresistance across varying carrier densities, from low to high.
• Analyzing the magnetic field dependence of magnetoresistance to identify transitions between quadratic and linear regimes.
• Using realistic material parameters to evaluate the magnitude of magnetoresistance under non-quantizing magnetic fields.

Experimental results

Research questions

• RQ1 How does the magnetoresistance of 3D Weyl semimetals evolve with increasing magnetic field at low and high carrier densities?
• RQ2 What is the origin of the large magnetoresistance observed in TlBiSSe, and can it be explained by impurity scattering?
• RQ3 How does carrier inhomogeneity due to charged impurities affect the transport properties near the Weyl point?
• RQ4 Can the transition from quadratic to linear magnetoresistance be theoretically predicted and linked to known conductivity regimes?

Key findings

• The theory successfully connects the minimum conductivity near the Weyl point with high-density conductivity via effective medium averaging.
• A transition from quadratic to linear magnetoresistance is predicted at high magnetic fields, regardless of carrier density.
• The magnetoresistance exceeds 10 for realistic material parameters, consistent with experimental observations.
• The results quantitatively explain the unexpectedly large, non-saturating magnetoresistance seen in TlBiSSe.