Topological Doping and Superconductivity in Cuprates: An Experimental Perspective

John M Tranquada

doi:10.3390/sym13122365

Abstract

Hole doping into a correlated antiferromagnet leads to topological stripe correlations, involving charge stripes that separate antiferromagnetic spin stripes of opposite phases. The topological spin stripe order causes the spin degrees of freedom within the charge stripes to feel a geometric frustration with their environment. In the case of cuprates, where the charge stripes have the character of a hole-doped two-leg spin ladder, with corresponding pairing correlations, anti-phase Josephson coupling across the spin stripes can lead to a pair-density-wave order in which the broken translation symmetry of the superconducting wave function is accommodated by pairs with finite momentum. This scenario is now experimentally verified by recently reported measurements on La2−xBaxCuO4 with x=1/8. While pair-density-wave order is not common as a cuprate ground state, it provides a basis for understanding the uniform d-wave order that is more typical in superconducting cuprates.

Highlights

Charge order has been observed in virtually all hole-doped cuprate superconductor families [1,2,3]
In 214 cuprates, such as La2− x Srx CuO4 (LSCO) and La2− x Bax CuO4 (LBCO), the charge-stripe order is generally accompanied by spin-stripe order [4,5,6,7,8], as originally observed in Nd-doped La2− x Srx CuO4 [9,10]; each of these orders breaks the translation symmetry of the square-lattice CuO2 planes
Emery [11] pointed out the topological character of the combined spin and charge stripe orders

Summary

Introduction

Charge order has been observed in virtually all hole-doped cuprate superconductor families [1,2,3]. In the case of cuprates with bond-parallel stripes, the charge stripes may be viewed as hole-doped, two-leg, spin S = 1/2 ladders, which are established to have strong superconducting correlations [23,24] This is a variation on the original proposal of superconducting charge stripes by Emery, Kivelson, and Zachar [25], who pointed out that a spin gap in a one-dimensional (1D) electron gas acts as a pairing amplitude; the difference is that they assumed that the spin gap would be transferred from the neighboring spin stripes, in which case one would never achieve superconductivity when the spin-stripe order is present. I fill in details that provide support for the story laid out above

Stripe Order and Decoupling of Spin Excitations

PDW Order

PDW Around Defects

Findings

Relations to Other Superconductors