Persistence of characteristics of an ordered flux line lattice above the second peak in $Bi_2Sr_2CaCu_2O_{8+ \delta}$

TL;DR

This study uses Small Angle Neutron Scattering to investigate the flux line lattice in Bi-2212, revealing persistent lattice order above the second peak despite low scattered intensity, suggesting coexistence of different flux line states.

Contribution

First direct observation of flux line lattice characteristics above the second peak in Bi-2212 using neutron scattering, indicating persistent lattice order without symmetry breaking.

Findings

Flux line lattice persists above the second peak.

No evidence of symmetry-breaking structural features.

Possible coexistence of two flux line lattice states.

Abstract

We report Small Angle Neutron Scattering measurements of the flux lines lattice (FLL) in $Bi_2Sr_2CaCu_2O_{8+ \delta}$. As previously reported, the scattered intensity decreases strongly when the magnetic field is increased, but it remains measurable far above the second peak. The direct observation of Bragg peaks proves that the characteristics of a lattice are still present. No structural features related to a symmetry breaking, such as a liquid like or an amorphous state, can be observed. However, the associated scattered intensity is very low and is difficult to explain. We discuss the coexistence between two FLL states as a possible interpretation.