Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality

TL;DR

This paper investigates how lattice effects influence strongly coupled fermionic systems with holographic duals, revealing unique band structure behaviors and local quantum criticality signatures that could help identify AdS2-like pseudogap metals experimentally.

Contribution

It introduces a weak potential limit analysis of lattice effects in holographic fermion systems, uncovering how local quantum criticality interacts with band structures and momentum-dependent exponents.

Findings

Lattice induces band gaps in holographic fermion models.

Deep IR AdS2 geometry exhibits momentum-dependent energy scaling.

Predicted crossovers between high energy and low energy regimes with distinct exponents.

Abstract

We study lattice effects in strongly coupled systems of fermions at a finite density described by a holographic dual consisting of fermions in Anti-de-Sitter space in the presence of a Reissner-Nordstrom black hole. The lattice effect is encoded by a periodic modulation of the chemical potential with a wavelength of order of the intrinsic length scales of the system. This corresponds with a highly complicated "band structure" problem in AdS, which we only manage to solve in the weak potential limit. The "domain wall" fermions in AdS encoding for the Fermi surfaces in the boundary field theory diffract as usually against the periodic lattice, giving rise to band gaps. However, the deep infrared of the field theory as encoded by the near horizon AdS2 geometry in the bulk reacts in a surprising way to the weak potential. The hybridization of the fermions bulk dualizes into a linear combination of CFT1 "local quantum critical" propagators in the bulk, characterized by momentum dependent exponents displaced by lattice Umklapp vectors. This has the consequence that the metals showing quasi-Fermi surfaces cannot be localized in band insulators. In the AdS2 metal regime, where the conformal dimension of the fermionic operator is large and no Fermi surfaces are present at low T/\mu, the lattice gives rise to a characteristic dependence of the energy scaling as a function of momentum. We predict crossovers from a high energy standard momentum AdS2 scaling to a low energy regime where exponents found associated with momenta "backscattered" to a lower Brillioun zone in the extended zone scheme. We comment on how these findings can be used as a unique fingerprint for the detection of AdS2 like "pseudogap metals" in the laboratory.