Effective holographic theory of charge density waves

Abstract

We use Gauge/Gravity duality to write down an effective low energy holographic theory of charge density waves. We consider a simple gravity model which breaks translations spontaneously in the dual field theory in a homogeneous manner, capturing the low energy dynamics of phonons coupled to conserved currents. We first focus on the leading two-derivative action, which leads to excited states with non-zero strain. We show that including subleading quartic derivative terms leads to dynamical instabilities of AdS$_2$ translation invariant states and to stable phases breaking translations spontaneously. We compute analytically the real part of the electric conductivity. The model allows to construct Lifshitz-like hyperscaling violating quantum critical ground states breaking translations spontaneously. At these critical points, the real part of the dc conductivity can be metallic or insulating.

v1: 20 pages + appendices, 3 figures. v2: various edits, references added, re-written as the long version of 1712.07994. v3: rewritten to include discussion of thermodynamically stable phases, typos corrected