Gate-controlled low carrier density superconductors: Toward the two-dimensional BCS-BEC crossover

Article

关键词: UNCONVENTIONAL SUPERCONDUCTIVITY;    FLUCTUATION CONDUCTIVITY;    TUNNELING SPECTROSCOPY;    NITRIDE HALIDES;    TEMPERATURE;    MAGNETOCONDUCTIVITY;    TRANSITION;    PHASE;    FIELD;    HF;   

DOI  :  10.1103/PhysRevB.98.064512

来源: SCIE

【 摘 要 】

Superconductivity mostly appears in high carrier density systems and sometimes exhibits common phase diagrams in which the critical temperature T-c continuously develops with carrier density. Superconductivity enhanced in the lightly doped regime has seldom been reported, although it is an ideal direction towards the crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensate (BEC) limits, where the behavior of Cooper pairs changes dramatically. Here we report transport properties and superconducting gaps in single-crystalline lithium-intercalated layered nitrides (LixHfNCl and LixZrNCl) down to the low-doping regime, enabled by a combination of ionic gating device and tunneling spectroscopy. Upon the reduction of doping, both systems display the increase of T-c, up to 24.9 K especially in LixHfNCl, with the concomitant enhancement of two-dimensionality leading to a pseudogap state below 35.5 K as well as the increase of superconducting coupling strengths 2 Delta/kB T-c reaching 5.9. Such behavior in the carrier density region as low as 10(20) cm(-3) indicates that lightly doped two-dimensional superconductors exhibit the unprecedented nature that is distinct from that in conventional superconductors, and offer a new route to access BCS-BEC crossover.

【 授权许可】

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