Low-temperature specific heat of orientational glasses

This review summarizes specific heat data measured at low temperatures (T<1 K) on orientational glasses. Three species of mixed molecular crystals exhibiting orientational disorder are considered, namely (KBr)_1–x (KCN) _x , (NaCN)_1–x (KCN) _x (Rb)_1–x (NH₄) _x H₂PO₄. For intermediate concentrations of the anisotropic components, glass-like excitations have been observed. It is demonstrated that with respect to thermal properties, orientational disorder leads to the same universal behaviours than for structural disorder, i.e. a specific heat which varies below 1 K and for times 10^–4 s–10 s as:C _p(T,t)T ¹×ln(t). The variation of the glass-like anomaly with compositional disorder is also discussed. It is concluded that the low-energy excitations are related to orientational degrees of freedom which are frozen at low temperatures but still perform reorientations via quantum tunneling motions.     

Low-temperature specific heat of TlCrS2

The specific heat of the ferromagnetic semiconductor TlCrS₂ is investigated experimentally, and the thermodynamic parameters are calculated. It is demonstrated that the temperature dependence of the magnetic specific heat of the TlCrS₂ compound is characteristic of quasi-two-dimensional magnetic systems.     

Low-temperature specific heat of compacted vitreous silica

We present low-temperature specific-heat measurements of two types of irreversibly compacted vitreous silica (Suprasil W and Suprasil I, differing in their OH⁻ content). In the whole temperature range investigated (0.1 K<T<35 K), the specific heatC is reduced by up to 50% compared to that of uncompacted samples but exhibits a similar temperature dependence, with the characteristic maximum inC/T ³ shifted to higher temperatures. This coherent change ofC, which is roughly the same for both types of vitreous silica, gives strong evidence that the low-energy excitations characteristic of amorphous materials have a common structural origin. Possible relations to the microscopic changes upon compaction are discussed, giving support to the coupled-rotation model of SiO₄ tetrahedra. Phenomenologically, the change ofC upon compaction can be understood by the soft-potential model. The relationship between height and position of theC/T ³ maximum observed in normal and compacted states for both types of vitreous silica and, surprisingly, also for α-quartz hints at a correlation between the mechanisms leading to theC/T ³ maximum for amorphous and crystalline materials with similar short-range order.     

Low-temperature specific heat of USb and UTe

We have measured the low-temperature specific heat c_p of single-crystalline samples of USb and UTe between 0.1 and 12 K. From the experimental data we deduce values for the electronic specific-heat parameter γ of 0.2 mJ/mole K² and 10.3 mJ/mole K² for USb and UTe, respectively. c_p data below 1 K reveal the onset of nuclear specific heat with decreasing temperature. In our temperature range, this contribution is much stronger for USb than for UTe.     

Low-temperature specific heat of CeAl3 and related compounds

Low-temperature measurements of the specific heat are reported for Ce_1−xLa_xAl₃ and Y_1−xTh_xAl₃. The observed maxima for Ce_1−xLa_xAl₃ are attributed to crystalline field effects. The marked variations in the electronic density of states for Y_1−xTh_xAl₃ are ascribed to influences of Brillouin zones. Results are related to the Kondo sideband model.     

Low-temperature specific heat of CeAl2 at high pressures

Abstract

We have obtained new data of the low-temperature specific heat of CeAl₂ under pressure with the aim to complete the phase diagram and to solve an existing discrepancy between results of magnetic and thermodynamic measurements.     

Low-temperature specific heat and thermal conductivity of neutron-irradiated lithium fluoride

Exposure of LiF to radiation within a reactor reduces the low-temperature thermal conductivity and creates an excess specific heat. These properties are similar to those observed in samples exposed only to γ-irradiation and, for our sample, could be accounted for by the integrated γ-exposure alone. The low-temperature behavior can be explained by invoking various kinds of defects such as fluttering dislocations or clusters (extended defects) having a spectrum of shapes and sizes. The two-level-states found in reactor-irradiated SiO₂ cannot be identified in the irradiated LiF.     

Low-temperature specific heat of the heavy-fermion superconductor PrOs4Sb12

We report the magnetic field dependence of the specific-heat C of single crystals of the first Pr-based heavy-fermion superconductor Pr(Os4Sb12. The variation of C at low temperature and the magnetic phase diagram inferred from C, the resistivity and magnetization provide compelling evidence of a doublet ground state. Two distinct superconducting anomalies in C indicate an unconventional superconducting state, where the splitting may arise from a weak lifting of the ground state degeneracy. In combination this identifies Pr(Os4Sb12 as a strong contender for quadrupolar pairing, i.e., superconductivity that is neither electron-phonon nor magnetically mediated.     

Low-temperature specific heat spectra considering nonextensive long-range correlated quasiperiodic DNA molecules

We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q-gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum.     

Phase transition,structural, mechanical and thermal properties of erbium pnictides under pressure

In this article, we have investigated the high-pressure structural phase transition of erbium pnictides (ErX; X?=?N, P and As). An extended interaction potential model has been developed (including the zero-point energy effect in three-body interaction potential model). Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses have been predicted successfully. The elastic constants, their combinations and pressure derivatives are also reported. The pressure behaviour of elastic constants, bulk modulus and shear modulus have been presented and discussed. Moreover, the thermophysical properties such as molecular force constant (f), infrared absorption frequency (υ ₀), Debye temperature (θ _D) and Grunneisen parameter (γ) have also been predicted.