Dynamical density and spin response of Fermi arcs and their consequences for Weyl semimetals

Abstract

Weyl semimetals exhibit exotic Fermi-arc surface states, which strongly affect their electromagnetic properties. We derive analytical expressions for all components of the composite density-spin response tensor for the surfaces states of a Weyl-semimetal model obtained by closing the band gap in a topological insulating state and introducing a time-reversal-symmetry-breaking term. Based on the results, we discuss the electromagnetic susceptibilities, the current response, and other physical effects arising from the density-spin response. We find a magnetoelectric effect caused solely by the Fermi arcs. We also discuss the effect of electron-electron interactions within the random phase approximation and investigate the dispersion of surface plasmons formed by Fermi-arc states. Our work is useful for understanding the electromagnetic and optical properties of the Fermi arcs. arXiv:2001.00438v2 [cond-mat.mes-hall] 4 Apr 2020

Surface plasmonics of Weyl semimetals

“…2(a), (b). The first one is the linearly dispersing FA plasmon with a gap at q y = 0, in agreement with theoretical approaches using classical electrodynamics [17], hydrodynamic description [22], or quantum-mechanical calculations [18,20,21,23]. From the zeros of the real part of the equation RPA (q y , ω) = 0, we find the FA-plasmon disersion…”

“…Here, we show within a simple single-boundary model how the FA and the VP states conspire to give rise to new plasmon modes on a smooth surface of a WSM applying random phase approximations (RPA). We confirm that the FA plasmon is chiral and exhibits strong anisotropy and a singularity at zero momentum [17,18,[20][21][22][23] because the two-dimensional (2D) dispersion of the FA band evolves into an effectively one-dimensional (1D) one: the energy disperses linearly perpendicular to the z-direction connecting two Weyl nodes and remains almost constant along z. A spectacular consequence of this anisotropy is the finite gap which the FA plasmon acquires at q z = 0 and that vanishes when the longitudinal wavevector q z = 0.…”

“…In WSMs, topologically protected Fermi-arc (FA) states connecting two Weyl cones emerge on the surface due to the bulk-edge correspondence: the presence of topologically protected edge states is dictated by the topological invariant of the twisted bulk band structure. The FA states have been shown to induce a chiral linear FA surface plasmon with total nonreciprocity [17][18][19][20][21][22][23], i.e. it propagates only in one direction determined by the the chirality of the FA dispersion.…”

Plasmon in Nonsymmorphic Dirac semimetals

“…Plasmons are one of such collective modes that results from collective charge oscillations of the system [14,15]. The polarization function and plasmon modes have been studied extensively in 2D semimetals with Dirac like dispersion in the context of Graphene [16][17][18][19], surface of three-dimensional (3D) Weyl and Dirac semimetals [20][21][22][23][24][25][26][27][28][29][30], tilted Dirac semimetal [31,32], and the surface of 3D topological insulators [33][34][35][36]. Recently theory of anisotropic plasmon has also been investigated in Ref.…”

Anomalous Surface Conductivity of Weyl Semimetals

“…In contrast, WSMs have gapless states both in the bulk and on the surface, so an energy cut off is not available to disentangle the surface from the bulk. While the surface-bulk inseparability promises rich physics such as thickness-dependent quantum oscillations [54][55][56][57][65][66][67][68], unusual collective modes [69][70][71][72][73][74][75][76][77] and dissipative chiral transport [58], it invalidates a strictly surface Hamiltonian, thereby hindering a controlled theoretical description of the surface and leaving its electromagnetic response poorly understood.…”