A new theoretical approach to the low‐temperature specific heat of disordered solids

Abstract

Starting from a perturbation theory for the free energy of disordered solids, the anomalous temperature dependence of the specific heat can be calculated. The model under consideration is based on the two common features of a large group of disordered solids, firstly, the distorted SRO, and, secondly, the cluster-like arrangement of strongly distorted atoms which are imbedded in a crystallike matrix. The theory yields the increase of the specific heat proportional to T for very low temperatures and the anomalous high value of the P-term. The calculated values coincide very well with the experimentally determined temperature dependence for disordered covalent solids.Ausgehend von einer Storungstheorie fur die freie Energie von ungeordneten Festkorpern kann die anomale Temperaturebhangigkeit der spezifischen Warme berechnet werden. Das vorgeschlagene Modell baut auf zwei Charakteristika auf, die einer groI3en Gruppe von ungeordnehn Festkorpern gemeinsam sinddie gestorte Nahordnung und die clusterartige Anordnung der stark gestorten Atome, die in eine kristallartige Matrix eingebettet sind. Die Theorie beschreibt den Anstieg der spezifischen Warme proportional zu T fur sehr niedrige Temperaturen und den anonial hohen Beitrag des Ts-proportiooalen Terme. Die berechneten Werte stimmen sehr gut mit der experimentell bestimmten Temperaturabhiingigkeit fur ungeordnete kovalente Festkorper uberein.attenuation, and velocity [a, lo]. It is surprising that thermal and acoustic properties of non-crystalline materials, or of those with greatly disturbed crystallinity, depend only weakly on structure and nature of bonding: They are similar in completely different solids (as vitreous SiO,, the amorphous polymer PMMA, or the glassy metal Pd-Si-Cu). I n addition to this, highly disordered crystals may also show part of the behaviour charscteristic of glassy materials a t low temperatures [ I l l .

Megahertz-Rate Semi-Device-Independent Quantum Random Number Generators Based on Unambiguous State Discrimination

“…Given two non-orthogonal states of polarization, the optimal USD measurement can be realized using a partial polarizer (i.e. polarization dependent losses) [47]. Encodings using frequency or spatial modes could also be considered.…”