Fermi arcs and isotope effect of the magnetic penetration depth in underdoped cuprates

TL;DR

This paper investigates how the isotope effect on magnetic penetration depth relates to Fermi arcs in underdoped cuprates, finding that large isotope effects are incompatible with Fermi arcs and are explained by a nodal metal model.

Contribution

It demonstrates that the large isotope effect in the pseudogap region can be explained by a nodal metal model without Fermi arcs, challenging models that include Fermi arcs.

Findings

Large isotope effect incompatible with Fermi arcs in pseudogap state.

Nodal metal model explains the isotope effect with small electron-phonon coupling.

Fermi surface topology influences isotope effect behavior in underdoped cuprates.

Abstract

The isotope coefficient $\beta$ of the magnetic penetration depth in the superconducting state is studied at T=0 for a $d$-CDW and a nodal metal model. Disregarding superconductivity the Fermi surface of the first model possesses arcs whereas the second model has no arcs. We show that a large increase of $\beta$ in the pseudogap region is generically incompatible with Fermi arcs in the pseudogap state. Thus only the second model shows a large increase of $\beta$ with decreasing doping. The required electron-phonon coupling is small and compatible with first-principles calculations based on the local density approximation (LDA).