Charge Transport in Weyl Semimetals (original) (raw)
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Nernst and magnetothermal conductivity in a lattice model of Weyl fermions
Physical Review B, 2016
Weyl semimetals (WSM) are topologically protected three dimensional materials whose low energy excitations are linearly dispersing massless Dirac fermions, possessing a non-trivial Berry curvature. Using semiclassical Boltzmann dynamics in the relaxation time approximation for a lattice model of time reversal (TR) symmetry broken WSM, we compute both magnetic field dependent and anomalous contributions to the Nernst coefficient. In addition to the magnetic field dependent Nernst response, which is present in both Dirac and Weyl semimetals, we show that, contrary to previous reports, the TR-broken WSM also has an anomalous Nernst response due to a non-vanishing Berry curvature. We also compute the thermal conductivities of a WSM in the Nernst (∇T ⊥ B) and the longitudinal (∇T B) setup and confirm from our lattice model that in the parallel setup , the Wiedemann-Franz law is violated between the longitudinal thermal and electrical conductivities due to chiral anomaly.
Arxiv preprint arXiv: …, 2011
We study transport in three dimensional Weyl semimetals in the presence of Coulomb interactions or disorder. We consider N Weyl nodes with isotropic dispersion at temperature T. In the clean limit, including Coulomb interactions, we determine the conductivity by solving a quantum Boltzmann equation within a 'leading log' approximation. The conductivity is found to be proportional to T , upto logarithmic factors arising from the flow of couplings. In the disordered case, we use the Kubo formula to compute conductivity of non-interacting electrons in the presence of impurities. Here, the finite-frequency conductivity exhibits distinct behaviors, depending on whether ω ≪ T or 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 ; however, in the latter case, 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. A comparison is made with existing dc transport data in a pyrochlore iridate, which is predicted to have N = 24 Weyl nodes.
Generalized triple-component fermions: Lattice model, Fermi arcs, and anomalous transport
Physical Review B, 2019
We generalize the construction of time-reversal symmetry-breaking triple-component semimetals, transforming under the pseudospin-1 representation, to arbitrary (anti-)monopole charge 2n, with n = 1, 2, 3 in the crystalline environment. The quasiparticle spectra of such systems are composed of two dispersing bands with pseudospin projections ms = ±1 and energy dispersions E k = ± α 2 n k 2n ⊥ + v 2 z k 2 z , where k ⊥ = k 2 x + k 2 y , and one completely flat band at zero energy with ms = 0. We construct simple tight-binding models for such spin-1 excitations on a cubic lattice and address the symmetries of the generalized triple-component Hamiltonian. In accordance to the bulkboundary correspondence, triple-component semimetals support 2n branches of topological Fermi arc surface states and also accommodate a large anomalous Hall conductivity (in the xy plane), given by σ 3D xy ∝ 2n× the separation of the triple-component nodes (in units of e 2 /h). Furthermore, we compute the longitudinal magnetoconductivity, planar Hall conductivity, and magneto thermal conductivity in these systems, which increase as B 2 for sufficiently weak magnetic fields (B) due to the nontrivial Berry curvature in the medium. A generalization of our construction to arbitrary integer spin systems is also highlighted. 1 system in two dimensions, see D. Green, L. Santos, and C. Chamon, Phys. Rev. B 82, 075104 (2010), for example. 2 We here neglect the particle-hole asymmetry of the form S 0 (a + b k 2), where S 0 is a (2s+1) dimensional idenity matrix, which is always present in any real materials, since it does not affect the
Physical Review B
Weyl semimetals are known to host massless surface states called Fermi arcs. These Fermi arcs are the manifestation of the bulk-boundary correspondence in topological matter and thus are analogous to the topological chiral surface states of topological insulators. It has been shown that the latter, depending on the smoothness of the surface, host massive Volkov-Pankratov states that coexist with the chiral ones. Here, we investigate these VP states in the framework of Weyl semimetals, namely their density of states and magneto-optical response. We find the selection rules corresponding to optical transitions which lead to anisotropic responses to external fields. In the presence of a magnetic field parallel to the interface, the selection rules and hence the poles of the response functions are mixed.
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.
Exceptional transport properties of topological semimetals and metals
2018
Topological materials (TMs) represent a family of new quantum materials, and the quantum Hall effect is the first realized topological phenomenon in condensed-matter physics. Band inversion occurs in topological insulators, and symmetry allows the bulk gap to fully reopen. At the surface of the three dimensional topological insulator, bands cross linearly (Dirac cone) and the crossing point is protected by time reversal symmetry. In contrast to Weyl and Dirac semimetals, the Dirac cone forms in the bulk, wherein the nodal points are twoand four-fold degenerate, respectively. Quasiparticles residing at these nodal points are equivalent of Dirac and Weyl fermions in particle physics. Recently, many other topological materials like nodal line semimetals, double Weyl semimetals, triple point Fermion metals, etc. have also been discovered. Topology in the band structure makes these materials interesting by imparting many exotic physical characteristics. Our group is involved in crystal g...
From graphene and topological insulators to Weyl semimetals
Symmetry, Spin Dynamics and the Properties of Nanostructures, 2015
Here we present a short introduction into physics of Dirac materials. In particular we review main physical properties of various two-dimensional crystals such as graphene, sil-icene, germanene and others. We comment on the origin of their buckled two-dimensional shape, and address the issues created by Mermin-Wagner theorem prohibiting the existence of strictly two-dimensional, flat crystals. Then we describe main ideas which were leading to the discovery of two and three-dimensional topological insulators and Weyl fermions. We describe some of their outstanding electronic properties which have been originating due to the existence of the Dirac gapless spectrum. We also compare simplest devices made of Dirac materials. Analogies and differences between Dirac materials and optics are also discussed.
Interacting Weyl semimetals on a lattice
Journal of Physics A: Mathematical and Theoretical, 2014
Electron-electron interactions in a Weyl semimetal are rigorously investigated in a lattice model by non perturbative methods. The absence of quantum phase transitions is proved for interactions not too large and short ranged. The anisotropic Dirac cones persist with angles (Fermi velocities) renormalized by the interaction, and with generically shifted Fermi points. As in graphene, the optical conductivity shows universality properties: it is equal to the massless Dirac fermions one with renormalized velocities, up to corrections which are subdominant in modulus.