接近半填充的扭曲双层石墨烯中热电性半经典描述的过剩熵和击穿
Excess entropy and breakdown of semiclassical description of thermoelectricity in twisted bilayer graphene close to half filling
摘要：
在具有扭曲双层石墨烯（tBLG）的莫尔系统中，库仑相关效应在低扭曲角（$θ$）下的放大是范霍夫奇点（vHS）处的几乎平坦的低能电子带和发散态密度（DOS）的结果。这不仅导致超导性、莫特绝缘态和量子反常霍尔效应接近临界（或魔）角$θ= θ_{c} \approx 1.1^\circ$，而且还导致非常规的金属态，据称表现出非费米液体（NFL）激发。然而，与超导电性和相关诱导的间隙在DOS，明确的签名NFL效应在金属状态下仍然实验难以捉摸。在这里，我们报告的电阻率（$ρ$）和热电功率（$S$）在tBLG在$θ\approx 1.6^\circ$的同时测量。我们观察到一个紧急违反的半经典莫特关系的形式超过$S$接近半填充。过量的$S$（$\approx 2$ $μ$ V/K在低温$T \sim 10$ K）持续到$\approx 40$ K，并伴随着金属$T$ -线性$ρ$，其传输散射率（$τ^{-1}$）接近普朗克量级$τ^{-1} \sim k_{B}T/\hbar$。非平凡的电输运和违反莫特关系的组合提供了令人信服的证据NFL物理固有的tBLG，在小扭转角和半填充。
英文摘要：
In moiré systems with twisted bilayer graphene (tBLG), the amplification of Coulomb correlation effects at low twist angles ($θ$) is a result of nearly flat low-energy electronic bands and divergent density of states (DOS) at van Hove singularities (vHS). This not only causes superconductivity, Mott insulating states, and quantum anomalous Hall effect close to the critical (or magic) angle $θ= θ_{c} \approx 1.1^\circ$, but also unconventional metallic states that are claimed to exhibit non-Fermi liquid (NFL) excitations. However, unlike superconductivity and the correlation-induced gap in the DOS, unambiguous signatures of NFL effects in the metallic state remain experimentally elusive. Here we report simultaneous measurement of electrical resistivity ($ρ$) and thermoelectric power ($S$) in tBLG at $θ\approx 1.6^\circ$. We observe an emergent violation of the semiclassical Mott relation in the form of excess $S$ close to half-filling. The excess $S$ ($\approx 2$ $μ$V/K at low temperature $T \sim 10$ K) persists up to $\approx 40$ K, and is accompanied by metallic $T$-linear $ρ$ with transport scattering rate ($τ^{-1}$) of near-Planckian magnitude $τ^{-1} \sim k_{B}T/\hbar$. The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG, at small twist angle and half-filling.
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