Condensed matter realization of the axial magnetic effect

Abstract

The axial magneticeffect, i.e., the generation of an energy current parallel to an axial magnetic field coupling with opposite signs to left-and right-handed fermions, is a nondissipative transport phenomenon intimately related to the gravitational contribution to the axial anomaly. An axial magnetic field emerges naturally in condensed matter in so-called Weyl semimetals. We present a measurable implementation of the axial magnetic effect. We show that the edge states of a Weyl semimetal at finite temperature possess a temperature dependent angular momentum in the direction of the vector potential intrinsic to the system. Such a realization provides a plausible context for the experimental confirmation of the elusive gravitational anomaly. Anomalies have played an important role in the construction of consistent quantum field theory (QFT) and string theory models. Among them, the most intensively investigated case is that of the axial anomaly, which is responsible for the decay of a neutral pion into two photons [1]. Similarly, in a curved space, gravitational anomalies [2] can occur and mixed axialgravitational anomalies give rise to very interesting predictions as to the decay of the pion into two gravitons. While the former phenomenon is by now well established, experimental settings providing evidence of the gravitational anomaly are lacking. More recently anomalies are starting to play an interesting role as being responsible for exotic transport phenomena in QFT in extreme conditions. In the context of the quark-gluon plasma [3] it has become clear in recent years that, at finite temperature and density, quantum anomalies give rise to new nondissipative transport phenomena.The recognition of the role of topology in the classification of condensed matter systems started a long time ago with the prototypical example set by liquid helium [4]. The low energy excitations of He 3 are described by Dirac fermions, which made the system an interesting analog to study high energy phenomena. In this century, the advent of new materials (graphene, topological insulators and superconductors [5,6], and Weyl semimetals) whose low energy electronic properties are described by Dirac fermions in one, two, or three spatial dimensions has enlarged and widened the analogy between high energy and condensed matter. Simultaneously, new experiments on the quark-gluon plasma and recent developments in holography have opened an unexpected scenario where high energy and condensed matter physics merge. In this Rapid Communication we propose a condensed matter scenario for the experimental realization of the gravitational anomaly.The most commonly cited example of the new nondissipative transport phenomena occurring in the quark-gluon plasma is the chiral magnetic effect [7], which refers to the generation of an electric current parallel to a magnetic field whenever an imbalance between the number of right-and left-handed fermions is present. Another interesting example is the axial magnetic effect (AME), which is associated with the ...

Chern-Simons terms from thermal circles and anomalies

“…This implies the exciting prospect that mixed anomalies may be measured in Nature. (See [30] for a recent explicit proposal.) In the literature there are various notions of anomalies.…”

Chirality-Dependent Hall Effect in Weyl Semimetals

“…As a consequence, each nontrivial slice contributes an e 2 /h to the Hall conductivity [9-11] producing σ xy = be 2 /πh in the bulk, and also contributes one edge state to the surface forming a surface Fermi arc connecting the two projected Weyl points. Recently, the Weyl points and surface arcs appear to be observed in optical experiments [23][24][25].This progress may herald a flurry of exciting experiments on the appealing transport effects [26][27][28] predicted in WSM, e.g., the chiral magnetic effect [29][30][31][32][33][34][35][36] when b 0 becomes nontrivial in the absence of P symmetry, and the axial magnetic effect [37,38] when τ b, viewed as a gauge field coupling oppositely to the left-and right-handed Weyl fermions, varies spatially.Here we discover a universal effect in lightly-doped WSMs, by examining the semiclassical dynamics of Weyl quasiparticles in the ballistic regime. The presence of Weyl points leads to substantial Berry curvatures.…”

One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

“…(2.11), we simplify the thermalized matrix propagator for the quarks, 14) where n 1 and n 2 are denoted by n 1 = n F (k 0 ) and n 2 = 1 − n F (k 0 ), respectively. Thus the 11-component of the propagator matrix for quarks in the thermal medium can be read off, 15) which is found to be modified by the magnetic field.…”

“…Moreover the magnetic field may be assumed uniform because even though the spatial distribution of the magnetic field is globally inhomogeneous, but in the central region of the overlapping nuclei, the magnetic field in the transverse plane varies very smoothly, which is noticed in the hadron-string simulations [9] for Au-Au collisions at √ s N N = 200 GeV with an impact parameter, b = 10 fm. Therefore, a large number of QCD related phenomena are investigated in the strong and homogeneous magnetic field, such as the chiral magnetic effect related to the generation of electric current parallel to the magnetic field due to the difference in number of right and left-handed quarks [10][11][12], the axial magnetic effect due to the flow of energy by the axial magnetic field [13,14], the chiral vortical effect due to an effective magnetic field in the rotating QGP [15,16], the magnetic catalysis and the inverse magnetic catalysis at finite temperature arising due to the breaking and the restoration of the chiral symmetry [17][18][19][20][21], the thermodynamic properties [22][23][24], the refractive indices and decay constant [25,26] of mesons in a hot magnetized medium, the conformal anomaly and the production of soft photons [27,28] at RHIC and LHC, the dispersion relation in a magnetized thermal QED [29], the synchrotron radiation [30], the dilepton production from both the weakly [31][32][33][34] and the strongly [35] coupled plasma etc.…”