New Research


2012/02/01

“Research Front of Superconductivity Towards the Discovery of Room-temperature Superconductor”


Prof. Yoshio Kitaoka, Associate Prof. Hidekazu Mukuda, Assistant Prof. Mitsuharu Yashima

  “Superconductivity” - zero electrical resistance - was first discovered in 1911. Over the hundred years since then, many substances exhibiting superconductivity (SC) have been discovered. The upper right figure is a history of the discovery of superconducting materials and displays the increase in transition temperature (Tc) over that period. An unexpected breakthrough was the discovery of high-Tc SC in copper oxides in 1986. Soon after, Tc rose to 164 K in Hg-based compounds under pressure, which is still the record of Tc at present. Meanwhile, in 2008, a second high-Tc SC family was discovered in Fe-based compounds, which have brought about the second breakthrough. However, the reason for the high-Tc SC in these materials and the method for enhancing Tc values remain mysteries. The mechanism of high-Tc SC has not yet been identified despite more than 25 years of intensive research. Though NMR measurements on disorder-free CuO2 planes, we have experimentally uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and high-Tc SC, indicating that the AFM interaction plays a central role for the mechanism of high Tc copper oxides. In Fe-based superconductors, AFM appears near the SC as well, as shown in the lower right figure, but we have revealed experimentally that the AFM interaction is not always a unique factor leading to its high-Tc values. The multiband nature in Fe-based compounds is a key-feature crucially different from the single-band picture for the copper oxides. Moreover, the structural transition followed by the AFM order may cause orbital fluctuations in addition to spin fluctuations, which prevent us from a simple understanding of the mechanism in these new high-Tc compounds. This opens a new path to the next SC era in which we hope to discover a “room-temperature superconductor”.


Kitaoka Lab.
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