强关联电子系统中的热输运测量

Thermal Transport Measurements in Strongly Correlated Electronic Systems

当考虑电子间的库伦排斥相互作用,以及电荷、自旋和轨道之间的相互耦合时,诸多超越了近自由电子框架的新奇量子态涌现而出,如非常规超导态和量子自旋液体等。对这些新奇物态的认知不仅会拓展现有的知识框架,也有望引发新一轮的量子科技革命。因此,对强关联物理的研究是当下凝聚态物理领域的前沿课题。铜基高温超导体的母体是一种莫特绝缘体,在传统的能带论之下被预言为金属态。然而电子间的强关联行为使得它表现出绝缘体的性质。由于莫特绝缘体中库伦相互作用致使能隙打开并冻结其中的电荷自由度,所以在该体系中难以开展电输运性质的测量研究。作为一种对于元激发(不仅包括电子,还包括磁振子、自旋子等)敏感的探针,热输运测量在强关联电子系统的研究中发挥着重要的作用。本文回顾了近些年在非常规超导、重费米子系统和量子自旋液体研究中一些有趣的纵向热输运性质的研究成果,并与我们近期发表的运用横向热导率测量热霍尔现象的综述文章相互补充。

When taking into account the electronic correlations such as the onsite Coulombrepulsion and coupling between electrons, spins and orbitals, many fascinating novel quantumstates beyond the free-electron framework can emerge, e.g., unconventional superconductivityand quantum spin liquids. The understanding of these new states not only will expandthe existing territory of our knowledge, but also likely lead to revolution in quantum scienceand technology. Therefore, studying the strongly correlated physics is a cutting-edge themein condensed matter physics. The parent state of cuprate high-temperature superconductorsis a Mott insulator, an insulating state due to the strong electronic correlation, whereas theband theory predicts it to be metallic. Due to the Coulomb gap in Mott insulators, the chargedegree of freedom is often frozen, which makes electrical transport measurements inapplicable.As a probe sensitive to the elementary excitations of quasiparticles not limited to electrons,but also including magnons, spinons, as well as phonons, thermal transport measurementsplay an important role in the study of strongly correlated electronic systems. In this paper,we review some of the recent interesting results on unconventional superconductors, heavyfermions and quantum spin liquids utilizing the longitudinal thermal transport measurements,complimentary to our recent review article on the progress of the transverse thermal conductivitymeasurements on the thermal Hall effect.