Low-Temperature Heat Capacity Anomalies in Ordered and Disordered Phases of Normal and Deuterated Thiophene

We measured the specific heat C_p of normal (C₄H₄S) and deuterated (C₄D₄S) thiophene in the temperature interval of 1 ≤ T, K ≤ 25. C₄H₄S exhibits a metastable phase II₂ and a stable phase V, both with frozen orientational disorder (OD), whereas C₄D₄S exhibits a metastable phase II₂, which is analogous to the OD phase II₂ of C₄H₄S and a fully ordered stable phase V. Our measurements demonstrate the existence of a large bump in the heat capacity of both stable and metastable C₄D₄S and C₄H₄S phases at temperatures of ∼10 K, which significantly departs from the expected Debye temperature behavior of C_p ≈ T³. This case study demonstrates that the identified low-temperature C_p anomaly, typically referred to as a "Boson-peak" in the context of glassy crystals, is not exclusive of disordered materials.

The quasi-low temperature behaviour of specific heat

A new mathematical approach to condensed matter physics, based on the finite temperature field theory, was recently proposed. The field theory is a scale-free formalism; thus, it denies absolute values of thermodynamic temperature and uses dimensionless thermal variables, which are obtained with the group velocities of sound and the interatomic distance. This formalism was previously applied to the specific heat of condensed matter and predicted its fourth power of temperature behaviour at sufficiently low temperatures, which was tested by experimental data for diamond lattice materials. The range of temperatures with the quartic law varies for different materials; therefore, it is called the quasi-low temperature regime. The quasi-low temperature behaviour of specific heat is verified here with experimental data for the fcc lattice materials, silver chloride and lithium iodide. The conjecture that the fourth order behaviour is universal for all condensed matter systems has also supported the data for glassy matter: vitreous silica. This law is long known to hold for the bcc solid helium-4. The characteristic temperatures of the threshold of the quasi-low temperature regime are found for the studied materials. The scaling in the specific heat of condensed matter is expressed by the dimensionless parameter, which is explored with the data for several glasses. The explanation of the correlation of the 'boson peak' temperature with the shear velocity is proposed. The critique of the Debye theory of specific heat and the Born-von Karman model of the lattice dynamics is given.

Thermodynamic Properties of Molecular Crystals Calculated within the Quasi-Harmonic Approximation

A computational study of the possibilities of contemporary theoretical chemistry as regards calculated thermodynamic properties for molecular crystals from first-principles is presented. The study is performed for a testing set of 22 low-temperature crystalline phases whose properties such as densities of phonon states, isobaric heat capacities, and densities are computed as functions of temperature within the quasi-harmonic approximation. Electronic structure and lattice dynamics are treated by plane-wave based calculations with optPBE-vdW functional. Comparison of calculated results with reliable critically assessed experimental data is especially emphasized.

Vibrational relaxation of chloroiodomethane in cold argon

Electronically exciting the C-I stretch in the molecule chloroiodomethane CH2ClI embedded in a matrix of argon at 12 K can lead to an isomer, iso-chloroiodomethane CH2Cl-I, that features a chlorine iodine bond. By temporally probing the isomer at two different frequencies of 435 nm and 485 nm, multiple timescales for isomerization and vibrational energy relaxation were inferred [T. J. Preston, et al., J. Chem. Phys. 135, 114503 (2011)]. This relaxation is studied theoretically using molecular dynamics by considering 2 and 3 dimensional models. Multiple decay rate constants of the same order of magnitude as the experiment are observed. These decay rate constants are interpreted within the context of the Landau-Teller theory. Sensitivity of the decay rate constants on the bath and system parameters shed more light into the mechanism of vibrational energy relaxation.

Phenomenon and manifestation of the `Author's Effect of Showcasing' (AES): a literature science study, I. Emergence, causes and traces of the phenomenon in the literature, perception and notion of the effect

The `Author's Effect of Showcasing' (AES) is the activity of publishing authors who shape by free will the formal reference stock of their communications cited directly and item by item, placing this formal reference stock into the showcase of science — consciously or unconsciously. This first paper of the study demonstrates the emergence, causes and traces of the AES phenomenon in the journal literature of the natural sciences already in the mature Little Science age, and the continuous existence of the phenomenon ever since. The perception and cognition of the effect is shown on the basis of the relevant findings of the present author's previous, manual fact-finding reference investigations based on autopsy, processing around 27,600 journal communications and reference stocks containing more than 322,000 citations. Finally, a summarizing definition of the notion of the effect is given. In a second paper, the manifestation of the AES phenomenon will be demonstrated and analysed in the theoretically most homogeneous domain of the scientific literature.

Similarities in the Cp/T3 peaks in amorphous and crystalline metals

A low-temperature peak in C(p)/T(3) vs is ubiquitous to glasses. It arises from an abundance of low-frequency vibrations, the origin of which remains unclear. A comparable C(p)/T(3) vs peak is observed in crystals due to the dispersion of acoustic phonons and/or the excitation of optical phonons. We compared the C(p)/T(3) vs peaks in metallic and oxide glasses to elemental crystals by analyzing specific heat, phonon density of states, and elastic constant data. We observe no clear distinction in the peak temperature or amplitude between metallic glasses and crystals. Surprisingly, the peak is larger in single crystal Pd(40)Cu(40)P(20) than in glassy Pd(40)Cu(40)P(20).