Anomalous magnetoconductivity and relaxation times in holography

Abstract

Abstract:We study the magnetoconductivity induced by the axial anomaly via the chiral magnetic effect in strongly coupled holographic models. An important ingredient in our models is that the axial charge is non-conserved beyond the axial anomaly. We achieve this either by explicit symmetry breaking via a non-vanishing non-normalisable mode of an axially charged scalar or using a Stückelberg field to make the AdS-bulk gauge field massive. The DC magnetoconductivites can be calculated analytically. They take a universal form in terms of gauge field mass at the horizon and quadratic dependence on the magnetic field. The axial charge relaxation time grows linearly with magnetic field in the large B regime. Most strikingly positive magnetoconductivity is still present even when the relaxation times are short τ 5 ≈ 1/(πT ) and the axial charge can not be thought of as an approximate symmetry. In the U(1) A explicit breaking model, we also observe that the chiral separation conductivity and the axial magnetic conductivity for the consistent axial current vanish in the limit of strong symmetry breaking.

Chiral magnetic conductivity in an interacting lattice model of parity-breaking Weyl semimetal

“…An experimental signature of the Chiral Magnetic effect is the quadratic enhancement of the electric conductivity in the direction of the applied constant magnetic field, which was originally predicted in [3] and has recently been observed in the Dirac semimetals Bi 1−x Sb x [4], ZrTe 5 [5] and Na 3 Bi [6]. Very similar behavior of the electric conductivity in the direction of the magnetic field has also been found in holographic models [7,8] and numerically in lattice QCD [9].…”

Holographic topological semimetals

“…The factor of 3 in the axial anomaly reflects the symmetry factor that arises in the corresponding triangle diagram in quantum field theory. We will introduce the mass deformation via a boundary value of the scalar field Φ [37]. Since the dual axial symmetry is explicitly broken, in the bulk this scalar field is introduced to be only axially charged.…”

Gradient resummation for nonlinear chiral transport: an insight from holography

“…During the last decade, macroscopic effects induced by the chiral anomaly were found to be of relevance in relativistic heavy ion collisions [19][20][21], and have been searched intensively at RHIC and LHC [22][23][24][25][26]. Finally, (pseudo-)relativistic systems in condensed matter physics, such as Dirac and Weyl semimetals, display anomaly-induced phenomena, which were recently observed experimentally [27][28][29][30][31][32][33] and can be studied via similar theoretical methods [34][35][36][37].…”