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Reemergence of superconductivity at 48K
in compressed iron selenide based superconductors

Superconductivity in some materials can be induced or tuned by chemical substitution, external pressure and magnetic field. Among these control parameters, pressure is a “clean” way to produce or manipulate superconductivity of matters without changing their chemistry.

Recently, a new finding from Prof. Zhongxian Zhao ‘s group at Institute of Physics, Chinese Academy of Science, demonstrated an unexpected superconducting phenomenon in a newly discovered iron selenide based superconductors under pressure condition. In this investigation, Prof. Liling Sun, a member of this group, and her colleagues in collaboration with Prof. Ho-Kwang Mao and Dr. Xiaojia Chen at Carnegie Institute found that the superconducting transition temperature (Tc) in this kind of superconductor decreases with increasing pressure from the maximum of 31 K to vanishing at around 10 GPa, then reappears at pressure above 11.5 GPa, which was identified by in-situ resistance and magnetic measurements in a self-integrated system developed by Zhao’s group. The Tc of the re-emerging superconducting phase reaches 48 K which is considerably higher than the first maximum (31 K), setting a new Tc record in iron selenide based superconductors. High-pressure x-ray diffraction measurements performed at Shanghai Synchrotron Source, in collaboration with Dr. Ke Yang and Aiguo Li, found that the basic structure of these compounds was not changed when the superconductivity reemerged. They believe that further studies can help to determine what is happening on a closer structural level in the pressure-induced superconducting state and shed insight on the underlying mechanism of high-Tc superconductors.

The work is the first observation on the pressure-induced reemergence of superconductivity among the high-Tc superconductors. It is also demonstrated that high pressure is an effective tool in manipulating quantum state of matters. This work is published by Nature on March 1, 2012 [Nature 483,67 (2012) ] and highlighted by Nature’s news online.

The samples studied were provided by Prof. Xiaolong Chen and Prof. Genfu Chen from Institute of Physics, Prof. Minghu Fang from Zhejiang University.

Pressure dependence of theTc for Tl0.6Rb0.4Fe1.67Se2, K0.8Fe1.7Se2 and K0.8Fe1.78Se2. The symbols represent the pressure–temperature conditions for which Tc values were observed from the resistive and alternating current susceptibility measurements; symbols with downward arrows represent the absence of superconductivity to the lowest temperature (4 K). All samples show two superconducting regions (SC-I and SC-II) separated by a critical pressure at around 10 GPa. NSC, the non-superconducting region above 13.2 GPa. The maximum Tc is found to be 48.7 K in K0.8Fe1.7Se2 at a pressure of 12.5 GPa. At higher pressures above 13.2 GPa, the samples are non-superconducting. Error bars are one standard deviation.

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