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自旋轨道近邻双层石墨烯中的增强超导电性。

Enhanced superconductivity in spin-orbit proximitized bilayer graphene.

机构信息

T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA, USA.

Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA, USA.

出版信息

Nature. 2023 Jan;613(7943):268-273. doi: 10.1038/s41586-022-05446-x. Epub 2023 Jan 11.

Abstract

In the presence of a large perpendicular electric field, Bernal-stacked bilayer graphene (BLG) features several broken-symmetry metallic phases as well as magnetic-field-induced superconductivity. The superconducting state is quite fragile, however, appearing only in a narrow window of density and with a maximum critical temperature T≈ 30 mK. Here we show that placing monolayer tungsten diselenide (WSe) on BLG promotes Cooper pairing to an extraordinary degree: superconductivity appears at zero magnetic field, exhibits an order of magnitude enhancement in T and occurs over a density range that is wider by a factor of eight. By mapping quantum oscillations in BLG-WSe as a function of electric field and doping, we establish that superconductivity emerges throughout a region for which the normal state is polarized, with two out of four spin-valley flavours predominantly populated. In-plane magnetic field measurements further reveal that superconductivity in BLG-WSe can exhibit striking dependence of the critical field on doping, with the Chandrasekhar-Clogston (Pauli) limit roughly obeyed on one end of the superconducting dome, yet sharply violated on the other. Moreover, the superconductivity arises only for perpendicular electric fields that push BLG hole wavefunctions towards WSe, indicating that proximity-induced (Ising) spin-orbit coupling plays a key role in stabilizing the pairing. Our results pave the way for engineering robust, highly tunable and ultra-clean graphene-based superconductors.

摘要

在存在大垂直电场的情况下,伯纳尔堆叠双层石墨烯 (BLG) 具有几种对称性破缺的金属相以及磁场诱导的超导性。然而,超导态相当脆弱,仅出现在密度的狭窄窗口内,最大临界温度 T≈30mK。在这里,我们表明在 BLG 上放置单层二硒化钨 (WSe) 可以极大地促进库珀配对:超导性在零磁场下出现,T 增加了一个数量级,并且在密度范围内出现的范围要宽 8 倍。通过绘制 BLG-WSe 中量子振荡作为电场和掺杂的函数,我们确定超导性出现在正常态极化的整个区域,其中四个自旋谷中的两个主要被占据。面内磁场测量进一步表明,BLG-WSe 中的超导性在掺杂上表现出对临界场的显著依赖性,在超导圆顶的一端大致遵守钱德拉塞卡-克洛格斯顿(泡利)极限,但在另一端则明显违反。此外,超导性仅在将 BLG 空穴波函数推向 WSe 的垂直电场下出现,表明近邻诱导的(伊辛)自旋轨道耦合在稳定配对中起着关键作用。我们的结果为工程化稳健、高度可调且超清洁的基于石墨烯的超导材料铺平了道路。

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