Possible superconducting fluctuation and pseudogap state above Tc in CsFe2As2

Resistive, magnetization, torque, specific heat, and scanning tunneling microscopy measurements are carried out on heavily-hole-doped CsFe2As2 single crystals. A characteristic temperature T∗∼13 K, which is several times higher than the superconducting transition temperature Tc=2.11 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, remains finite, and vanishes gradually until a temperature near T∗. Temperature-dependent resistivity and specific heat also show kinks near T∗. An asymmetric gap-like feature with the energy of 8.4 meV and a symmetric superconductivity-related gap of 2.4 meV on the scanning tunneling spectra are detected, and the pseudogap-related features disappear at temperatures up to at least 9 K. These observations by different experimental tools suggest the possible existence of superconducting fluctuations or a pseudogap state in the temperature range up to four to six times Tc in CsFe2As2.