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 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.     

Low-temperature specific heat of Er2Ba4Cu7O15-δ

The magnetic ordering of Er ions in Er₂Ba₄Cu₇O_15-δ (δ = 0:7 and δ = 0:08) has been studied by low temperature heat capacity measurements. The Néel temperature T _N of Er₂Ba₄Cu₇O_15-δ is almost independent of the oxygen concentration (TN = 0:54K for δ = 0:08 and T _N = 0:50K for δ = 0:7). While an anisotropic two-dimensional (2D) Ising model describes the experimental data very well for Er₂Ba₄Cu₇O_14:92, this model cannot be applied to the oxygen reduced sample Er₂Ba₄Cu₇O_14:3. By using a model consisting of 1D-Ising chains and of 2D-Ising clusters of Er³⁺ ions we could fit the specific heat data of Er₂Ba₄Cu₇O_14:3 accurately. Our measurements show clearly that with the reduction of the oxygen content the in-plane anisotropy of the magnetic exchange coupling increases.     

Low-temperature heat capacity of metals

The low-temperature heat capacities of transition metals and alloys were reviewed by Heiniger, Bucher, and Muller¹ in 1966, with particular emphasis on the dependence of the electronic heat capacity on the number of conduction electrons. Nuclear contributions to the heat capacity of metals and alloys have been reviewed recently by Lounasmaa.² The most recent general review of the low-temperature heat capacities of metals, however, was that by Keesom and Pearlman³ in 1956. Since that time there have been important advances in experimental techniques and also in theory related to certain of the heat capacity contributions.