Temperature crossovers in the specific heat of amorphous magnets

Abstract

It is argued that the specific heat of amorphous solids at low temperatures can be understood to arise from a single branch of collective modes. The idea is illustrated in a model of a correlated spin glass for which magnetic anisotropies are present but they are completely frustrated by disorder. The low-energy spectrum is dominated by soft modes corresponding to propagating Halperin-Saslow spin waves at short wavelengths, evolving into a relaxation and a diffuson mode at the long wavelengths. The latter gives rise to an anomalous temperature behavior of the specific heat at $T\ll T_{\ast }$: $C\sim T$ in $d=3$ solids, $C\sim T\ln (1/T)$ in $d=2$. The temperature scale $T_{\ast }$ has a non-trivial dependence on the damping coefficient describing magnetic friction, which can be related to fluctuations of the spin-torque operator via a Green-Kubo formula. Halperin-Saslow modes can also become diffusive due to disclination motion (plastic flow). Extensions of these ideas to other systems (including disordered phases of correlated electrons in cuprate superconductors and of moiré superlattices) are discussed

8 pages, 3 figures; article for the special topic "Disordered Materials at the Atomic Scale" of JAP; comments are welcome

References in corpus (9)

• Quantum critical behavior in magic-angle twisted bilayer graphene
• Long-distance spin transport in a disordered magnetic insulator
• Colloquium: Hydrodynamics and holography of charge density wave phases
• Deformations, relaxation and broken symmetries in liquids, solids and glasses: a unified topological field theory
• Tunable non-Fermi liquid phase from coupling to two-level systems
• A new paradigm for the low-T glassy-like thermal properties of solids
• Low-Temperature Heat Transport under Phonon Confinement in Nanostructures
• Extended linear-in-$T$ resistivity due to electron-phason scattering in moiré superlattices
• Quantum confinement theory of the heat capacity of thin films