Field-induced electronic phase separation in the high-temperature superconductor La$_{1.94}$Sr$_{0.06}$CuO$_{4+y}$

TL;DR

This study combines neutron diffraction and muon spin rotation to show that in La$_{1.94}$Sr$_{0.06}$CuO$_{4+y}$, magnetic stripe regions grow with an applied magnetic field without increasing the magnetic moment, revealing field-induced phase separation.

Contribution

It provides direct evidence that magnetic stripe regions expand under magnetic fields in a high-temperature superconductor, clarifying the nature of field-induced effects.

Findings

Magnetic volume fraction increases linearly with field.

Stripe-ordered regions grow with applied magnetic field.

Magnetic moment remains field-independent.

Abstract

We present a combined neutron diffraction and high field muon spin rotation ($\mu$SR) study of the magnetically ordered and superconducting phases of the high-temperature superconductor La$_{1.94}$Sr$_{0.06}$CuO$_{4+y}$ ($T_{\rm c} = 37.5(2)$~K) in a magnetic field applied perpendicular to the CuO$_2$ planes. We observe a linear field-dependence of the intensity of the neutron diffraction peak that reflects the modulated antiferromagnetic stripe order. The magnetic volume fraction extracted from $\mu$SR data likewise increases linearly with applied magnetic field. The combination of these two observations allows us to unambiguously conclude that stripe-ordered regions grow in an applied field, whereas the stripe-ordered magnetic moment itself is field-independent. This contrasts with earlier suggestions that the field-induced neutron diffraction intensity in La-based cuprates is due to an increase in the ordered moment. We discuss a microscopic picture that is capable of reconciling these conflicting viewpoints.