Striped superconductors: How the cuprates intertwine spin, charge and superconducting orders

TL;DR

This paper introduces the concept of striped superconductors in cuprates, a state with spatially modulated order parameter that explains various experimental phenomena and differs fundamentally from uniform superconductors.

Contribution

It proposes a new theoretical framework for striped superconductivity, supported by DMRG calculations and analysis of experimental data across different cuprate materials.

Findings

Identification of a new striped superconducting state.

Theoretical modeling of spatially modulated order parameter.

Correlation of the state with experimental observations in cuprates.

Abstract

Recent transport experiments in the original cuprate high temperature superconductor, {La$_{2-x}$Ba$_x$CuO$_4$}, have revealed a remarkable sequence of transitions and crossovers which give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the "striped superconductor," in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to outlining the salient experimental findings, we sketch the order parameter theory of the state, stressing some of the ways in which a striped superconductor differs fundamentally from an ordinary (uniform) superconductor, especially concerning its response to quenched randomness. We also present the results of DMRG calculations on a model of interacting electrons in which sign oscillations of the superconducting order are established. Finally, we speculate concerning the relevance of this state to experiments in other cuprates, including recent optical studies of {La$_{2-x}$Sr$_x$CuO$_4$} in a magnetic field, neutron scattering experiments in underdoped {YBa$_2$Cu$_3$O$_{6+x}$}, and a host of anomalies seen in STM and ARPES studies of {Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta} $}.