Superconductivity in the twisted bilayer graphene: emergent mystery in the magic angle, the topological bosons and the Bardeen Cooper Schrieffer - Bose Einstein unconventional crossover

被引：1

作者：

Davydov, V. N. ^{[1
]}

机构：

[1] Moscow MV Lomonosov State Univ, Leninsky Pr 71,App 121, Moscow 117296, Russia

来源：

PHILOSOPHICAL MAGAZINE | 2021年 / 101卷 / 22期

关键词：

Unconventional superconductivity; moire crystal; twisted bilayer graphene; magic angles; moire flat bands; Lifshitz topological transition; BCS-BEUC unconventional crossover; BCS-BEC CROSSOVER; LONG-RANGE ORDER; TRANSITIONS; SUPERFLUIDITY; MONOLAYER; LIQUIDS; STATES; BANDS; MODEL; SOUND;

D O I：

10.1080/14786435.2021.1970268

中图分类号：

T [工业技术];

学科分类号：

08 ;

摘要：

Theory of superconductivity in twisted bilayer graphene (tBLG) is presented, based on the fact that Dirac fermions are pairing creating the topological bosons as consequence of topologically protected Lifshitz topological transition (TPLTT). We have shown that multiple TPLTTs are realised at low twisting angles in tBLG. At TPLTT the Berry phase changes from 2 pi in bilayer graphene to pi in tBLG. It is favourable to form the Bardeen Cooper Schrieffer - Bose Einstein unconventional crossover (BCS-BEUC) when the attractive interaction for pairing dominates the repulsive screened Coulomb interaction. The theory yields a second-order phase transition for BCS-BEUC, and values of specific heat and the Ginzburg-Landau coherence length are calculated. The problem has been solved of emergent mystery in the magic angles at which there exists possibility for observation of BCS-BEUC. The solution is connected with the Umklapp processes when the quasiwave vector of the superconducting carriers is shifted from the Brillouin zone to other cell of the reciprocal space. The table is given of the allowed magic angles which include the corresponding effective masses of the pairing Dirac fermions.

引用

页码：2377 / 2411

页数：35

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