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The realization of next-generation quantum-based computing and communication devices is dependent upon the advancement in thermal management. These challenges include but are not limited to sub-Kelvin temperature cooling for quantum computing and sensing and high-density thermal energy dissipation for electronics. Thermal circuit designs are limited by the conventional passive thermal components, such as thermal resistors and thermal capacitors, in contrast to a wide range of active components in the electrical domain. On the verge of the second quantum revolution, the development of materials that enable active switching of thermal transport in a wide range of temperatures and methods that provide advantages over current thermal management approaches are essential. In this thesis, I will introduce new mechanisms for controlling thermal transport in solids based on quantum phenomena.Only recently was it recognized that topological properties of electrons in certain solids can have a dominant impact on the equations of motion of electrons. We discovered an ideal Weyl semimetal system, a topological material, that is field-induced: Bi1-xSbx, with x varying from 0.04 to 0.22. We developed a theory for the topology-induced mechanism for the transport of heat by electrons, the thermal chiral anomaly, and experimentally proved its existence. Under the right conditions, the electronic thermal conductivity of a Weyl semimetal will increase linearly with the applied magnetic field. Secondly, we investigated the effect of Bose-Einstein condensation of excitons, an electron-hole pair, on the lattice thermal conductivity of an excitonic insulator. Our data showed a surprisingly high low-temperature thermal conductivity in Ta2NiSe5, an excitonic insulator, compared to those in Ta2NiS5, a conventional insulator with a similar lattice structure. We postulated the enhancement in thermal conductivity is due to the coupling of exciton condensate to the lattice.In the last chapter, we studied the effect of magnetism on the thermal transport of MnBi2Te4. We discovered an intriguing switch of the magnetic field dependence of in-plane thermal conductivity in MnBi2Te4 as the material undergoes transition through different magnetic ordering in a magnetic field. Our study of the evolution of the magnon dispersion in the magnetic field revealed a strong, switchable interaction between magnons and the lattice, which strongly affects thermal transport in this solid. |
