The Wiedemann-Franz law in doped Mott insulators without quasiparticles

• Published in: Science (American Association for the Advancement of Science) Vol. 382; no. 6674; pp. 1070 - 1073
• Main Authors: Wang, Wen O., Ding, Jixun K., Schattner, Yoni, Huang, Edwin W., Moritz, Brian, Devereaux, Thomas P.
• Format: Journal Article
• Language: English
• Published: Washington The American Association for the Advancement of Science 01.12.2023; AAAS
• Subjects: Absolute zero; Charge materials; Charge transport; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Elementary excitations; Insulators; Lorenz number; Mathematical models; Numerical methods
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.ade3232

Many metallic quantum materials display anomalous transport phenomena that defy a Fermi liquid description. Here, we use numerical methods to calculate thermal and charge transport in the doped Hubbard model and observe a crossover separating high- and low-temperature behaviors. Distinct from the behavior at high temperatures, the Lorenz number L becomes weakly doping dependent and less sensitive to parameters at low temperatures. At the lowest numerically accessible temperatures, L roughly approaches the Wiedemann-Franz constant L 0 , even in a doped Mott insulator that lacks well-defined quasiparticles. Decomposing the energy current operator indicates a compensation between kinetic and potential contributions, which may help to clarify the interpretation of transport experiments beyond Boltzmann theory in strongly correlated metals. Close to absolute zero, the ratio of thermal and charge conductivities of many materials has been found to be proportional to the temperature. This behavior, referred to as the Wiedemann-Franz law, is expected if the same quasiparticles are the carriers of both heat and charge transport. In strongly correlated materials, however, quasiparticles may no longer be well defined. W. Wang et al . undertook a comprehensive numerical study of heat and charge transport within the doped Hubbard model, which incorporates strong interactions. Surprisingly, they found that as they lowered the temperature as far as their numerical methods allowed, the system approached the Wiedemann-Franz law limit. —Jelena Stajic Determinant quantum Monte Carlo methods are used to study heat and charge transport in the doped Hubbard model