Transport in Weyl Semimetals (original) (raw)

Charge Transport in Weyl Semimetals

Physical Review Letters, 2012

We study transport in three dimensional Weyl semimetals with N isotropic Weyl nodes in the presence of Coulomb interactions or disorder at temperature T . In the interacting clean limit, we determine the conductivity by solving a quantum Boltzmann equation within a 'leading log' approximation and find it to be proportional to T , upto logarithmic factors arising from the flow of couplings. In the noninteracting disordered case, we compute the finite-frequency Kubo conductivity and show that it exhibits distinct behaviors for ω ≪ T and ω ≫ T : in the former regime we recover the results of a previous analysis, of a finite conductivity and a Drude width that vanishes as N T 2 ; in the latter, we find a conductivity that vanishes linearly with ω whose leading contribution as T → 0 is the same as that of the clean, non-interacting system σ(ω, T = 0) = N e 2 12h |ω| v F . We compare our results to experimental data on Y2Ir2O7 and also comment on the possible relevance to recent transport data on Eu2Ir2O7.

Conductivity of a Weyl semimetal with donor and acceptor impurities

Physical Review B, 2015

We study transport in a Weyl semimetal with donor and acceptor impurities. At sufficiently high temperatures transport is dominated by electron-electron interactions, while the low-temperature resistivity comes from the scattering of quasiparticles on screened impurities. Using the diagrammatic technique, we calculate the conductivity σ(T, ω, nA, nD) in the impurities-dominated regime as a function of temperature T , frequency ω, and the concentrations nA and nD of donors and acceptors and discuss the crossover behaviour between the regimes of low and high temperatures and impurity concentrations. In a sufficiently compensated material [|nA − nD| (nA + nD)] with a small effective fine structure constant α, σ(ω, T) ∝ T 2 /(T −2 − iω • const) in a wide interval of temperatures. For very low temperatures or in the case of an uncompensated material the transport is effectively metallic. We discuss experimental conditions necessary for realising each regime.

3 Recent developments in transport phenomena in Weyl semimetals

2016

The last decade has witnessed great advancements in the science and engineering of systems with unconventional band structures, seeded by studies of graphene and topological insulators. While the band structure of graphene simulates massless relativistic electrons in two dimensions, topological insulators have bands that wind non-trivially over momentum space in a certain abstract sense. Over the last couple of years, enthusiasm has been burgeoning in another unconventional and topological (although, not quite in the same sense as topological insulators) phase-the Weyl Semimetal. In this phase, electrons mimic Weyl fermions that are well-known in high-energy physics, and inherit many of their properties, including an apparent violation of charge conservation known as the Chiral Anomaly. In this review, we recap some of the unusual transport properties of Weyl semimetals discussed in the literature so far, focusing on signatures whose roots lie in the anomaly. We also mention several proposed realizations of this phase in condensed matter systems, since they were what arguably precipitated activity on Weyl semimetals in the first place.

Recent developments in transport phenomena in Weyl semimetals

Comptes Rendus Physique, 2013

The last decade has witnessed great advancements in the science and engineering of systems with unconventional band structures, seeded by studies of graphene and topological insulators. While the band structure of graphene simulates massless relativistic electrons in two dimensions, topological insulators have bands that wind non-trivially over momentum space in a certain abstract sense. Over the last couple of years, enthusiasm has been burgeoning in another unconventional and topological (although, not quite in the same sense as topological insulators) phase -the Weyl Semimetal. In this phase, electrons mimic Weyl fermions that are well-known in high-energy physics, and inherit many of their properties, including an apparent violation of charge conservation known as the Chiral Anomaly. In this review, we recap some of the unusual transport properties of Weyl semimetals discussed in the literature so far, focusing on signatures whose roots lie in the anomaly. We also mention several proposed realizations of this phase in condensed matter systems, since they were what arguably precipitated activity on Weyl semimetals in the first place.

Transport across junctions of a Weyl and a multi-Weyl semimetal

Physical Review B

We study transport across junctions of a Weyl and a multi-Weyl semimetal (WSM and a MSM) separated by a region of thickness d which has a barrier potential U0. We show that in the thin barrier limit (U0 → ∞ and d → 0 with χ = U0d/(vF) kept finite, where vF is velocity of low-energy electrons and is Planck's constant), the tunneling conductance G across such a junction becomes independent of χ. We demonstrate that such a barrier independence is a consequence of the change in the topological winding number of the Weyl nodes across the junction and point out that it has no analogue in tunneling conductance of either junctions of two-dimensional topological materials (such as graphene or topological insulators) or those made out of WSMs or MSMs with same topological winding numbers. We study this phenomenon both for normal-barrier-normal (NBN) and normalbarrier-superconductor (NBS) junctions involving WSMs and MSMs with arbitrary winding numbers and discuss experiments which can test our theory.

Anomalous Surface Conductivity of Weyl Semimetals

2021

We calculate the surface dc conductivity of Weyl semimetals and show that it contains an anomalous contribution in addition to a Drude contribution from the Fermi arc. The anomalous part is independent of the surface scattering time, and appears at nonzero temperature and doping (away from the Weyl nodes), increasing quadratically with both. The nontrivial coupling between the surface and the bulk leads to an effective description on the surface that mimics an interacting twodimensional fluid in certain regimes of energy, even in the absence of any explicit scattering on the surface, and is responsible for the anomalous contribution. Remarkably, in a layered Weyl semimetal, the temperature dependent part of the surface conductivity at low temperatures is dominated by the anomalous response which can be probed experimentally to unravel this unusual behavior.

Conductance modulation in Weyl semimetals with tilted energy dispersion without a band gap

Journal of Applied Physics, 2017

We investigate the tunneling conductance of Weyl semimetal with tilted energy dispersion by considering electron transmission through a p-n-p junction with one-dimensional electric and magnetic barrier. In the presence of both electric and magnetic barriers, we found that a large conductance gap can be produced by the aid of tilted energy dispersion without a band gap. The origin of this effect is the shift of the electron's wave-vector at barrier boundaries caused by i) the pseudo-magnetic field induced by electrical potential, i.e., a newly discovered feature that is only possible in the materials possessing tilted energy dispersion, ii) the real magnetic field induced by ferromagnetic layer deposited on the top of the system. We use realistic barrier structure applicable in current nanotechnology and analyze the temperature dependence of the tunneling conductance. The new approach presented here may resolve a major problem of possible transistor applications in topological semimetals, i.e., the absence of normal backscattering and gapless band structure.

Magneto-Transport Signatures in Periodically-Driven Weyl and Multi-Weyl Semimetals

SSRN Electronic Journal

We investigate the influence of a time-periodic driving (for example, by shining circularly polarized light) on three-dimensional Weyl and multi-Weyl semimetals, in the planar Hall and planar thermal Hall setups. We incorporate the effects of the drive by using the Floquet formalism in the large frequency limit. We evaluate the longitudinal magneto conductivity, planar Hall conductivity, longitudinal thermo-electric coefficient, and transverse thermo-electric coefficient, using the semi-classical Boltzmann transport equations. We demonstrate the explicit expressions of these transport coefficients in certain limits of the parameters, where it is possible to perform the integrals analytically. We cross-check our analytical approximations by comparing the physical values with the numerical results, obtained directly from the numerical integration of the integrals. The answers obtained show that the topological charges of the corresponding semimetals have profound signatures in these transport properties, which can be observed in experiments. Contents I. Introduction 1 II. Model and Formalism 3 A. Boltzmann Formalism 4 B. Time-periodic Driving 4 III. Longitudinal and Transverse Magneto-Conductivities 5 IV. Longitudinal and Transverse Thermo-Electric Coefficients 9 V. Discussions and Physical Interpretation of the Results 13 VI. Summary and Outlook 14 References 14 A. Computational details for LMC and PHC 16 B. Derivation of the Conductivities for the Planar Thermal Hall Setup 17 C. Computational details for LTEC and TTEC 17

Critical Transport in Weakly Disordered Semiconductors and Semimetals

Physical Review Letters, 2015

Motivated by Weyl semimetals and weakly doped semiconductors, we study transport in a weakly disordered semiconductor with a power-law quasiparticle dispersion ξ k ∝ k α. We show, that in 2α dimensions short-correlated disorder experiences logarithmic renormalisation from all energies in the band. We study the case of a general dimension d using a renormalisation group, controlled by an ε = 2α−d-expansion. Above the critical dimensions, conduction exhibits a localisation-delocalisation phase transition or a sharp crossover (depending on the symmetries of the Hamiltonian) as a function of disorder strength. We utilise this analysis to compute the low-temperature conductivity in Weyl semimetals and weakly doped semiconductors near and below the critical disorder point.