Interaction-driven giant thermopower in magic-angle twisted bilayer graphene

Abstract

Magic-angle twisted bilayer graphene has proved to be a fascinating platform to realize and study emergent quantum phases arising from the strong correlations in its flat bands. Thermal transport phenomena, such as thermopower, are sensitive to the particle-hole asymmetry, making them a crucial tool to probe the underlying electronic structure of this material. Here we have carried out thermopower measurements of magic-angle twisted bilayer graphene as a function of carrier density, temperature and magnetic field. We report the observation of an unusually large thermopower reaching a value of the order of 100 μV K −1 at a low temperature of 1 K. The thermopower exhibits peak-like features that violate the Mott formula in close correspondence to the resistance peaks appearing around the integer filling of the moiré bands, including the Dirac point. We show that the large thermopower peaks and their associated behaviour arise from the emergent highly particle-hole-asymmetric electronic structure, due to the sequential filling of the moiré flat bands and the associated recovery of Dirac-like physics. Furthermore, the thermopower shows an anomalous peak around the superconducting transition, which points towards the possible role of superconducting fluctuations in magic-angle twisted bilayer graphene.

Challenging breaking thermoelectric performance limits by twistronics

“…When there was no twist, the upper layer was also a non-planar structure, which has been experimentally and theoretically reported. [33][34][35] Moiré pattern was formed in the TBB structure, with electrons and holes concentrated on the moiré pattern (Fig. 1g).…”

“…Twisted superlattice of 2 dimensional (2D) materials may significantly improve their physical properties and has great potential in nano-devices. 22–36…”

“…TBG, as a typical twodimensional system, exhibits a strong Seebeck coefficient. 35 Meanwhile, the interlayer twisting reduces the lattice thermal conductivity to some extent, but the intrinsic high thermal conductivity of graphene makes it unsuitable for thermoelectric applications. 36 The experimentally studied two-dimensional structure of boron, i.e., borophene, has received considerable attention.…”

“…Twisted superlattice of 2 dimensional (2D) materials may signicantly improve their physical properties and has great potential in nano-devices. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] In this study, we theoretically examined the thermoelectric properties of twisted bilayer borophene (TBB) with a twist angle of 21.79°synthesized on a Ag(111) lm, and our results revealed that the a-phase TBB on synthesized Ag(111) lm possess great superior thermoelectric properties subject to twist angle modulation. TBB can be potentially used in thermoelectronic devices.…”

Moiré Superlattice MXene Nanosheets Constructed from Twisted Hexagon-Ti3AlC2 by Microwave-Assisted Lewis Molten Salt Etching: Implications for Structural Stability in Electrochemical Energy Storage

“…This special angle is the ″magic angle″ . When two or more layers of graphene are stacked together at this angle, it is called ″magic angle graphene″ . Similar layered materials such as hexagonal boron nitride (h-BN) and double layer transition metal choriocarbides have been found to have moiré superlattices.…”