Disordered Materials: II

The macroscopic thermal conductivities of crystals and glasses vary strongly and with opposite trends upon heating, decreasing in crystals and increasing in glasses. These contrasts originate from different microscopic conduction mechanisms: in crystals, periodicity allows for particlelike propagation of dispersive atomic vibrational excitations; in glasses, instead, disorder blurs or destroys dispersion, and enables heat transfer through wavelike tunneling between quasi-degenerate vibrational states. Here, we rely on the recently developed unified Wigner formulation of thermal transport in crystals and glasses [1] to explore conductivity anomalies that emerge from the coexistence of propagation and tunneling conduction in solids with controlled atomic disorder [2,3]. We show that these mechanisms compensate in materials with crystalline bond order and nearly glassy bond geometry such as meteoritic tridymite [4], yielding a conductivity that is constant from the quantum to the classical regime (i.e., from below to above the Debye temperature). Our findings prove that temperature-invariant conductivities are not limited to the classical regime, and pave the way to understand or control heat-transport phenomena in solids exposed to large temperature variations.

[1] Simoncelli et al., PRX 12 (2022)

[2] Pazhedath et al., PRApplied 22 (2024)

[3] Harper et al., PRMaterials 8 (2024)

[4] Simoncelli et al., arXiv:2405.13161 (2024)