Bulk Superconductivity Induced by In-plane Chemical Pressure Effect in Eu0.5La0.5FBiS2-xSex

TL;DR

This study demonstrates that Se substitution in Eu0.5La0.5FBiS2 enhances in-plane chemical pressure, inducing bulk superconductivity with a maximum Tc of 3.8 K, and reveals a link between metallicity and superconductivity.

Contribution

It provides the first detailed phase diagram of Eu0.5La0.5FBiS2-xSex showing how Se substitution induces bulk superconductivity through enhanced metallicity and in-plane chemical pressure.

Findings

Maximum Tc of 3.8 K at x=0.8

Superconductivity correlates with increased metallicity

Observation of anomalous two-step transition under high magnetic fields

Abstract

We have investigated Se substitution effect to superconductivity of an optimally-doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex samples with x = 0-1 were synthesized. With increasing x, in-plane chemical pressure is enhanced. For x = 0.6, 0.8, and 1, superconducting transitions with a large shielding volume fraction are observed in magnetic susceptibility measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature electrical resistivity measurements, a zero-resistivity state is observed for all the samples, and the highest Tc is observed for x = 0.8. With increasing Se concentration, characteristics of electrical resistivity changes from semiconducting-like to metallic, suggesting that the emergence of bulk superconductivity is linked with the enhanced metallicity. A superconductivity phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established. Temperature dependences of electrical resistivity show an anomalous two-step transition under high magnetic fields. Hence, the resistivity data are analyzed with assuming in-plane anisotropy of upper critical field.