近日，上海交通大学的李听昕&刘晓雪及其研究小组与武汉大学的吴冯成等人合作并取得一项新进展。经过不懈努力，他们揭示电子和空穴掺杂Bernal双层石墨烯的可调谐超导性。相关研究成果已于2024年6月19日在国际权威学术期刊《自然》上发表。

本文报道了通过静电掺杂在电子和空穴掺杂的BBG/WSe₂器件中观察到的超导性和一系列味对称性破缺相。观察到的超导性的强度可以通过施加垂直电场来调节。电子掺杂和空穴掺杂超导的最大Berezinskii–KosterlitzThouless转变温度分别约为210mK和400mK。只有当外加电场驱动BBG电子或空穴波函数向WSe₂层移动时，超导性才会出现，这凸显了WSe₂层在观察到的超导性中的重要性。空穴掺杂的超导违反了泡利顺磁极限，符合伊辛类超导体。

相比之下，电子掺杂的超导性服从泡利极限，尽管在导带中邻近诱导的伊辛自旋轨道耦合也很显著。这一研究发现突出了与BBG中导带相关的丰富物理特性，为进一步研究晶体石墨烯的超导机制和基于BBG的超导体器件的开发铺平了道路。

据悉，基于石墨烯的高质量二维电子系统已经成为研究超导性的高度可调平台。具体而言，人们在电子和空穴掺杂的扭曲石墨烯涡流体系中都观察到了超导性，而在晶体石墨烯体系中，迄今为止只在空穴掺杂的菱形三层石墨烯(RTG)和空穴掺杂的Bernal双层石墨烯(BBG)中观察到超导性。最近，由于接近单层WSe₂, BBG中的超导性得到了增强。

附：英文原文

Title: Tunable superconductivity in electron- and hole-doped Bernal bilayer graphene

Author: Li, Chushan, Xu, Fan, Li, Bohao, Li, Jiayi, Li, Guoan, Watanabe, Kenji, Taniguchi, Takashi, Tong, Bingbing, Shen, Jie, Lu, Li, Jia, Jinfeng, Wu, Fengcheng, Liu, Xiaoxue, Li, Tingxin

Issue&Volume: 2024-06-19

Abstract: Graphene-based, high-quality, two-dimensional electronic systems have emerged as a highly tunable platform for studying superconductivity. Specifically, superconductivity has been observed in both electron- and hole-doped twisted graphene moiré systems whereas in crystalline graphene systems, superconductivity has so far been observed only in hole-doped rhombohedral trilayer graphene (RTG) and hole-doped Bernal bilayer graphene (BBG). Recently, enhanced superconductivity has been demonstrated in BBG because of the proximity to a monolayer WSe₂. Here we report the observation of superconductivity and a series of flavour-symmetry-breaking phases in electron- and hole-doped BBG/WSe₂ devices by electrostatic doping. The strength of the observed superconductivity is tunable by applied vertical electric fields. The maximum Berezinskii–KosterlitzThouless transition temperature for the electron- and hole-doped superconductivity is about 210mK and 400mK, respectively. Superconductivities emerge only when the applied electric fields drive the BBG electron or hole wavefunctions towards the WSe₂ layer, underscoring the importance of the WSe₂ layer in the observed superconductivity. The hole-doped superconductivity violates the Pauli paramagnetic limit, consistent with an Ising-like superconductor. By contrast, the electron-doped superconductivity obeys the Pauli limit, although the proximity-induced Ising spin–orbit coupling is also notable in the conduction band. Our findings highlight the rich physics associated with the conduction band in BBG, paving the way for further studies into the superconducting mechanisms of crystalline graphene and the development of superconductor devices based on BBG.

DOI: 10.1038/s41586-024-07584-w

Source: https://www.nature.com/articles/s41586-024-07584-w