Possible superconducting fluctuation and pseudogap state above $T_c$ in CsFe${}_2$As${}_2$

Abstract

Resistive, magnetization, torque, specific heat and scanning tunneling microscopy measurements are carried out on the hole heavily doped CsFe${}_2$As${}_2$ single crystals. A characteristic temperature $T^{\ast }\sim 13$ K, which is several times higher than the superconducting transition temperature $T_c=2.15$ K, is observed and possibly related to the superconducting fluctuation or the pseudogap state. A diamagnetic signal detected by torque measurements starts from the superconducting state, keeps finite and vanishes gradually until a temperature near $T^{\ast }$. Temperature dependent resistivity and specific heat also show kinks near $T^{\ast }$. An asymmetric gap-like feature with the energy of 8.4 meV and a symmetric superconducting related gap of 2.2 meV on the scanning tunneling spectra are detected, and these pseudogap-related features disappear at temperatures up to at least 9 K. These observations by different experimental tools suggest the possible existence of superconducting fluctuation or pseudogap state in the temperature range up to 4 - 6 times of $T_c$ in CsFe${}_2$As${}_2$.

arXiv comment6 pages, 4 figures

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