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arXiv 2106.07640cond-mat.mes-hallcond-mat.str-el
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菱形三层石墨烯的超导电性

Superconductivity in rhombohedral trilayer graphene

Haoxin Zhou, Tian Xie, Takashi Taniguchi, Kenji Watanabe, Andrea F. Young

摘要:

我们报道了在静电掺杂空穴的菱形三层石墨烯中观察到的超导电性。超导性发生在两个不同的区域内的空间内的栅极调谐的电荷载流子密度和施加的电位移场,我们表示为SC 1和SC 2。高质量的样品允许通过量子振荡详细映射正常状态费米表面,这表明在这两种情况下,超导性产生于由环形费米海描述的正常状态,该环形费米海接近于费米表面简并度变化的同位旋对称性破缺过渡。SC 1的上离面临界场$B_{C\perp}\approx 10 \mathrm{mT}$和SC 2的上离面临界场$1\mathrm{mT}$,分别意味着相干长度$ξ$为200 nm和600 nm。横向磁电子聚焦的同时观测意味着平均自由程$\ell\gtrsim3.5\mathrm{μm}$。因此,超导性处于清洁极限的深处,具有无序参数$d=ξ/\ell<0.1$。SC 1出现从顺磁正常状态,并与泡利顺磁极限一致的面内磁场抑制。相比之下,SC2从自旋极化、谷非极化的半金属中出现。面内临界场的测量表明,这种超导体超过泡利极限至少一个数量级。我们讨论了我们的结果,在几个机制,包括传统的声子介导的配对,配对由于近端的同位旋顺序的波动,和固有的不稳定性的环形费米液体。我们在一个干净的和结构简单的二维金属托管各种门调谐磁状态的超导性的观察可能使一类新的场效应控制介观电子器件相结合的相关电子现象。

英文摘要:

We report the observation of superconductivity in rhombohedral trilayer graphene electrostatically doped with holes. Superconductivity occurs in two distinct regions within the space of gate-tuned charge carrier density and applied electric displacement field, which we denote SC1 and SC2. The high sample quality allows for detailed mapping of the normal state Fermi surfaces by quantum oscillations, which reveal that in both cases superconductivity arises from a normal state described by an annular Fermi sea that is proximal to an isospin symmetry breaking transition where the Fermi surface degeneracy changes. The upper out-of-plane critical field $B_{C\perp}\approx 10 \mathrm{mT}$ for SC1 and $1\mathrm{mT}$ for SC2, implying coherence lengths $ξ$ of 200nm and 600nm, respectively. The simultaneous observation of transverse magnetic electron focusing implies a mean free path $\ell\gtrsim3.5\mathrm{μm}$. Superconductivity is thus deep in the clean limit, with the disorder parameter $d=ξ/\ell<0.1$. SC1 emerge from a paramagnetic normal state and is suppressed with in-plane magnetic fields in agreement with the Pauli paramagnetic limit. In contrast, SC2 emerges from a spin-polarized, valley-unpolarized half-metal. Measurements of the in-plane critical field show that this superconductor exceeds the Pauli limit by at least one order of magnitude. We discuss our results in light of several mechanisms including conventional phonon-mediated pairing, pairing due to fluctuations of the proximal isospin order, and intrinsic instabilities of the annular Fermi liquid. Our observation of superconductivity in a clean and structurally simple two-dimensional metal hosting a variety of gate tuned magnetic states may enable a new class of field-effect controlled mesoscopic electronic devices combining correlated electron phenomena.

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