Field-induced soft-mode quantum phase transition in La$_{1.855}$Sr$_{0.145}$CuO$_{4}$

TL;DR

This study demonstrates a magnetic field-induced quantum phase transition in La$_{1.855}$Sr$_{0.145}$CuO$_{4}$, where the magnetic excitation gap closes at a critical field, indicating a soft-mode driven transition.

Contribution

First direct evidence of a soft-mode quantum phase transition driven by magnetic field in a high-temperature superconductor.

Findings

Magnetic excitation gap decreases with increasing magnetic field.

Gap vanishes at critical magnetic field, inducing antiferromagnetic order.

Provides evidence for a soft-mode quantum phase transition.

Abstract

Inelastic neutron-scattering experiments on the high-temperature superconductor La$_{1.855}$Sr$_{0.145}$CuO$_{4}$ reveal a magnetic excitation gap $\Delta$ that decreases continuously upon application of a magnetic field perpendicular to the CuO$_2$ planes. The gap vanishes at the critical field required to induce long-range incommensurate antiferromagnetic order, providing compelling evidence for a field-induced soft-mode driven quantum phase transition.