近日，印度科学研究所Arindam Ghosh团队研究了超净石墨烯中电荷和热流量子临界流的普遍性。相关论文于2025年8月13日发表在《自然—物理学》杂志上。

在狄拉克点附近，石墨烯预计存在于量子临界狄拉克流体状态，其中电荷和热量的流动可以用特征直流电导率和热力学变量（如熵和焓密度）来描述。虽然人们在最先进的石墨烯器件中已经报道了流体状粘质电荷流动，但电导率的值，预测是量子化的，并且仅由临界点的普适类决定，到目前为止还没有实验建立。

研究组通过结合接近狄拉克点的高质量器件的电导率和热传导率，发现了石墨烯输运中的量子临界普遍性。并发现它们是负相关的，正如相对论流体力学所期望的那样，并且特征电导率收敛于量子化值。研究组还观察到对Wiedemann-Franz定律的严重违反，在低温下接近狄拉克点的地方，洛伦兹数超过了半经典值200多倍。在高温下，在最干净的设备中，接近狄拉克点的有效动态粘度与熵密度比接近于最低粘度量子流体的系数。

附：英文原文

Title: Universality in quantum critical flow of charge and heat in ultraclean graphene

Author: Majumdar, Aniket, Chadha, Nisarg, Pal, Pritam, Gugnani, Akash, Ghawri, Bhaskar, Watanabe, Kenji, Taniguchi, Takashi, Mukerjee, Subroto, Ghosh, Arindam

Issue&Volume: 2025-08-13

Abstract: Close to the Dirac point, graphene is expected to exist in a quantum critical Dirac fluid state, where the flow of both charge and heat can be described with a characteristic d.c. electrical conductivity and thermodynamic variables such as entropy and enthalpy densities. Although the fluid-like viscous flow of charge has been reported in state-of-the-art graphene devices, the value of conductivity, predicted to be quantized and determined only by the universality class of the critical point, has not been established experimentally so far. Here we have discerned the quantum critical universality in graphene transport by combining the electrical and thermal conductivities in very high-quality devices close to the Dirac point. We find that they are inversely related, as expected from relativistic hydrodynamics, and the characteristic conductivity converges to a quantized value. We also observe a giant violation of the Wiedemann–Franz law, where the Lorentz number exceeds the semiclassical value by more than 200 times close to the Dirac point at low temperatures. At high temperatures, the effective dynamic viscosity to entropy density ratio close to the Dirac point in the cleanest devices approaches that of a minimally viscous quantum fluid within a factor of four.

DOI: 10.1038/s41567-025-02972-z

Source: https://www.nature.com/articles/s41567-025-02972-z