Probing the anisotropy of (Li0.84Fe0.16)OHFe0.98Se by angular-dependent torque measurements

Abstract

A strongly correlated superconductor with reduced dimension attracts much interest since its critical temperature (${T}_{c}$) is often enhanced. Superconducting anisotropy is the key parameter to characterize the dimensional reduction of a superconductor. $({\mathrm{Li}}_{0.84}{\mathrm{Fe}}_{0.16}){\mathrm{OHFe}}_{0.98}\mathrm{Se}$ (FeSe11111) is a newly found iron-based superconductor by intercalating (Li/Fe)OH layers into FeSe. The large distance between the FeSe layers leads to a highly two-dimensional character of the electronic structure compared to bulk FeSe. By performing out-of-plane angular-dependent torque measurements on FeSe11111 single-crystal samples with ${T}_{c}=40$ K, we directly obtain the superconducting anisotropy parameter $\ensuremath{\gamma}$. It is found that $\ensuremath{\gamma}$ reaches about 20 at a reduced temperature $t(=T/{T}_{c})=0.8$, suggesting that FeSe11111 is more anisotropic than other families of iron-based superconductors. Further, $\ensuremath{\gamma}$ shows a temperature-dependent behavior, which points towards a multiband scenario. Our result provides thermodynamic evidence for the two-dimensional nature of the superconductivity in FeSe11111.