Gate-controlled BCS-BEC crossover in a two-dimensional superconductor

Yuji Nakagawa, Yuichi Kasahara, Takuya Nomoto, Ryotaro Arita, Tsutomu Nojima, Yoshihiro Iwasa

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Bardeen-Cooper-Schrieffer (BCS) superfluidity and Bose-Einstein condensation (BEC) are the two extreme limits of the ground state of the paired fermion systems. We report crossover behavior from the BCS limit to the BEC limit realized by varying carrier density in a two-dimensional superconductor, electron-doped zirconium nitride chloride. The phase diagram, established by simultaneous measurements of resistivity and tunneling spectra under ionic gating, demonstrates a pseudogap phase in the low-doping regime. The ratio of the superconducting transition temperature and Fermi temperature in the low-carrier density limit is consistent with the theoretical upper bound expected in the BCS-BEC crossover regime. These results indicate that the gate-doped semiconductor provides an ideal platform for the two-dimensional BCS-BEC crossover without added complexities present in other solid-state systems.

Original languageEnglish
Pages (from-to)190-195
Number of pages6
Issue number6538
Publication statusPublished - 2021 Apr 9

ASJC Scopus subject areas

  • General


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