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Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

Ghawri, B and Mahapatra, PS and Garg, M and Mandal, S and Bhowmik, S and Jayaraman, A and Soni, R and Watanabe, K and Taniguchi, T and Krishnamurthy, HR and Jain, M and Banerjee, S and Chandni, U and Ghosh, A (2022) Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene. In: Nature Communications, 13 (1).

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Official URL: https://doi.org/10.1038/s41467-022-29198-4


The planar assembly of twisted bilayer graphene (tBLG) hosts multitude of interaction-driven phases when the relative rotation is close to the magic angle (θm = 1.1∘). This includes correlation-induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as possibility of non-Fermi liquid (NFL) excitations. However, experimentally, manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity (ρ) and thermoelectric power (S) in tBLG for several twist angles between θ ~ 1.0 − 1.7∘. We observe an emergent violation of the semiclassical Mott relation in the form of excess S close to half-filling for θ ~ 1.6∘ that vanishes for θ ≳ 2∘. The excess S (≈2 μV/K at low temperatures T ~ 10 K at θ ≈ 1.6∘) persists upto ≈40 K, and is accompanied by metallic T-linear ρ with transport scattering rate (τ−1) of near-Planckian magnitude τ−1 ~ kBT/ℏ. Closer to θm, the excess S was also observed for fractional band filling (ν ≈ 0.5). The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.

Item Type: Journal Article
Publication: Nature Communications
Publisher: Nature Research
Additional Information: The copyright for this article belongs to the Nature Research.
Keywords: graphene, chemical compound; electrical resistivity; measurement method; observational method; scattering; sound scattering; symmetry, Article; bandwidth; bilayer membrane; electricity; energy transfer; entropy; low temperature; measurement accuracy; physics; superconductivity; temperature dependence; thermodynamics
Department/Centre: Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Division of Physical & Mathematical Sciences > Instrumentation Appiled Physics
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 15 Jun 2022 05:55
Last Modified: 15 Jun 2022 05:55
URI: https://eprints.iisc.ac.in/id/eprint/73563

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