(Li0.84Fe0.16)OHFe0.98Se superconductor: Ion-exchange synthesis of large single crystal and highly two-dimensional electron properties

TL;DR

This study reports the successful synthesis of a large, high-quality (Li0.84Fe0.16)OHFe0.98Se single crystal with a Tc of 42 K, revealing highly two-dimensional electron properties and anomalous normal state behavior that offer new insights into high-temperature superconductivity.

Contribution

The paper introduces a hydrothermal ion-exchange method to synthesize large single crystals of (Li0.84Fe0.16)OHFe0.98Se and characterizes its unique two-dimensional electron transport properties.

Findings

Superconducting transition temperature (Tc) is 42 K.

High anisotropy with an out-of-plane to in-plane resistivity ratio of 2500 at 50 K.

Normal state exhibits highly two-dimensional and anomalous behavior.

Abstract

A large and high-quality single crystal (Li0.84Fe0.16)OHFe0.98Se, the optimal superconductor of newly reported (Li1-xFex)OHFe1-ySe system, has been successfully synthesized via a hydrothermal ion-exchange technique. The superconducting transition temperature (Tc) of 42 K is determined by magnetic susceptibility and electric resistivity measurements, and the zero-temperature upper critical magnetic fields are evaluated as 79 and 313 Tesla for the field along the c-axis and the ab-plane, respectively. The ratio of out-of-plane to in-plane electric resistivity,\r{ho}c/\r{ho}ab, is found to increases with decreasing temperature and to reach a high value of 2500 at 50 K, with an evident kink occurring at a characteristic temperature T*=120 K. The negative in-plane Hall coefficient indicates that electron carriers dominate in the charge transport, and the hole contribution is significantly reduced as the temperature is lowered to approach T*. From T* down to Tc, we observe the linear temperature dependences of the in-plane electric resistivity and the magnetic susceptibility for the FeSe layers. Our findings thus reveal that the normal state of (Li0.84Fe0.16)OHFe0.98Se becomes highly two-dimensional and anomalous prior to the superconducting transition, providing a new insight into the mechanism of high-Tc superconductivity.