A fermion phenomenology of low-temperature strongly-noncrystalline solids

Abstract

Insisting on the relevance of spin-statistics theorem, I propose that anomalous low-energy excitations of strongly-noncrystalline solids (SNSs), observed at low temperatures T < 1 K, are fermions, which are localized and weakly interacting. This phenomenological theory rationalizes all low-energy quantum many-body states of SNSs as Goldstone bosons-phonons and half-integer-spin fermions. Fermi glass, rather than isolated two-level systems (TLSs), appears to be a consistent theory of various thermal and nonlinear response properties of SNSs. A robust consequence of this theory is nearly constant-in-energy density of fermion states near Fermi energy, which in turn implies linear-in-temperature specific heat and frequency-independent sound internal friction. Consistent parameters of Landau-Fermi glass are calculated on theoretical grounds as well as from experimental data.