Unconventional Approaches to High or Tunable Thermal Conductivity in Solids

Materials with an either high or tunable thermal conductivity can find applications ranging from thermal management of microelectronics to electrification of industrial heating processes. Wide-bandgap diamond and semi-metallic graphite achieve record-high thermal conductivity values because strong covalent bonding of light carbon atoms gives rise to a large thermal conductivity contribution from phonons, the energy quanta of lattice vibrations. Such conventional criteria for a high lattice thermal conductivity have recently been upended by the establishment of a phonon band engineering approach to high-thermal conductivity semiconducting cubic boron arsenide (c-BAs) made of both light and heavy elements. This paradigm shift is not only motivating heterogeneous integration of c-BAs heat spreaders with other semiconductors for enhanced thermal and electronic performance, but also the search of other compounds with a high thermal conductivity, including semi-metallic theta-tantalum nitride (theta-TaN). Compared to this recent progress in the research of ultrahigh-thermal conductivity materials, the study of tunable solid-state thermal transport has still been largely limited to tuning of the lattice and electronic contributions through structural and magnetic phase transitions, respectively. Besides providing an update on experimental progresses and applications of high-thermal conductivity c-BA, theta-TaN, and graphitic materials, this presentation will introduce recent efforts of utilizing interlayer excitons and flat moiré electron bands to realize tunable thermal transport along and between two-dimensional heterostructures.