Ghawri Bhaskar, Mahapatra Phanibhusan S, Garg Manjari, Mandal Shinjan, Bhowmik Saisab, Jayaraman Aditya, Soni Radhika, Watanabe Kenji, Taniguchi Takashi, Krishnamurthy H R, Jain Manish, Banerjee Sumilan, Chandni U, Ghosh Arindam
Department of Physics, Indian Institute of Science, Bangalore, 560012, India.
Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore, 560012, India.
Nat Commun. 2022 Mar 21;13(1):1522. doi: 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 (θ = 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) of near-Planckian magnitude τ ~ kT/ℏ. Closer to θ, 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.
当相对旋转接近魔角（θ = 1.1）时，扭曲双层石墨烯（tBLG）的平面组装体呈现出多种相互作用驱动的相。这包括在低温下揭示自发对称性破缺的关联诱导基态，以及非费米液体（NFL）激发的可能性。然而，在实验中，NFL效应在扭曲双层石墨烯输运性质中的表现仍然不明确。在这里，我们报告了对θ约为1.0 - 1.7之间几个扭曲角的tBLG中的电阻率（ρ）和热电功率（S）的同时测量。我们观察到，对于θ约为1.6，在接近半填充时出现了以过量S形式出现的对半经典莫特关系的明显违反，而对于θ≳2则消失。过量S（在θ≈1.6时，低温T≈10 K下约为2 μV/K）持续到≈40 K，并伴随着金属性的T线性ρ，其输运散射率（τ）接近普朗克量级τ≈kT/ℏ。更接近θ时，在分数带填充（ν≈0.5）时也观察到了过量S。非平凡的电输运和对莫特关系的违反相结合，为tBLG固有的NFL物理提供了令人信服的证据。
