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

Bhaskar Ghawri (), Phanibhusan S. Mahapatra (), Manjari Garg (), Shinjan Mandal, Saisab Bhowmik, Aditya Jayaraman, Radhika Soni, Kenji Watanabe, Takashi Taniguchi, H. R. Krishnamurthy, Manish Jain, Sumilan Banerjee, U. Chandni and Arindam Ghosh ()
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Bhaskar Ghawri: Indian Institute of Science
Phanibhusan S. Mahapatra: Indian Institute of Science
Manjari Garg: Indian Institute of Science
Shinjan Mandal: Indian Institute of Science
Saisab Bhowmik: Indian Institute of Science
Aditya Jayaraman: Indian Institute of Science
Radhika Soni: Indian Institute of Science
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
H. R. Krishnamurthy: Indian Institute of Science
Manish Jain: Indian Institute of Science
Sumilan Banerjee: Indian Institute of Science
U. Chandni: Indian Institute of Science
Arindam Ghosh: Indian Institute of Science

Nature Communications, 2022, vol. 13, issue 1, 1-7

Abstract: Abstract 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.

Date: 2022
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DOI: 10.1038/s41467-022-29198-4

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