Observation of the Dirac Fluid and the Breakdown of the Wiedemann-Franz Law in Graphene

February 11, 2016

Fig. 1: Temperature and density dependent electrical and thermal conductivity* 
[Reprinted with permission from AAAS]

Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point, which can form a strongly coupled Dirac fluid. This charge neutral plasma of quasi-relativistic fermions is expected to exhibit a substantial enhancement of the thermal conductivity, thanks to decoupling of charge and heat currents within hydrodynamics. A Report in Science by a team of researchers from Philip Kim and Subir Sachdev groups, National Institute for Materials Science (Japan), and Raytheon BBN Technologies, describes employing high sensitivity Johnson noise thermometry to achieve an order of magnitude increase in the thermal conductivity and the breakdown of the Wiedemann-Franz law in the thermally populated charge neutral plasma in graphene. This result is a signature of the Dirac fluid, and constitutes direct evidence of collective motion in a quantum electronic fluid.

For more information, read the Press Release by Leah Burrows (SEAS), "A Metal that Behaves Like Water" (11 Feb 2016) and watch a SEAS movie, How to Make Graphene:

Prof. Sachdev
Also read an Interview with Prof. Sachdev in Quanta Magazine: Kevin Hartnett, "Taming Superconductors With String Theory" (21 Jan 2016).

Photo of Prof. Sachdev by Katherine Taylor for Quanta Magazine
Prof. Sachdev

*Jesse Crossno, Jing K. Shi, Ke Wang, Xiaomeng Liu, Achim Harzheim, Andrew Lucas, Subir Sachdev, Philip Kim, Takashi Taniguchi, Kenji Watanabe, Thomas A. Ohki, Kin Chung Fong, "Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in graphene," Science (11 Feb 2016) DOI: 10.1126/science.aad0343.