Absence of spin gap in the superconducting ladder compound Sr_2Ca_{12}Cu_{24}O_{41}

TL;DR

This study investigates the spin excitation gap in the superconducting ladder compound Sr_2Ca_{12}Cu_{24}O_{41} and finds it collapses under pressure, indicating a transition to a gapless state.

Contribution

The paper provides experimental evidence of the collapse of the spin gap in Sr_2Ca_{12}Cu_{24}O_{41} under pressure, supporting theoretical predictions of a transition to a gapless phase.

Findings

Collapse of the spin gap under pressure

Transition to a gapless Tomonaga-Luttinger regime

Support for theoretical predictions in two-leg ladders

Abstract

Transport and 63^Cu-NMR, Knight shift and T_1, measurements performed on the two-leg spin ladders of Sr_2Ca_{12}Cu_{24}O_{41} single crystals show a collapse of the gap in ladder spin excitations when superconductivity is stabilised under a pressure of 29 kbar. These results support the prediction made with exact diagonalisation techniques in two-leg isotropic t-J ladders of a transition between a low-doping spin gap phase and a gapless 1-D Tomonaga-Luttinger regime.