Entropy of solid He4: the possible role of a dislocation glass

Solid He4 is viewed as a nearly perfect Debye solid. Yet, recent calorimetry indicates that its low-temperature specific heat has both cubic and linear contributions. These features appear in the same temperature range ($T \sim 200$ mK) where measurements of the torsional oscillator period suggest a supersolid transition. We analyze the specific heat to compare the measured with the estimated entropy for a proposed supersolid transition with 1% superfluid fraction. We find that the experimental entropy is substantially less than the calculated entropy. We suggest that the low-temperature linear term in the specific heat is due to a glassy state that develops at low temperatures and is caused by a distribution of tunneling systems in the crystal. It is proposed that small scale dislocation loops produce those tunneling systems. We argue that the reported mass decoupling is consistent with an increase in the oscillator frequency as expected for a glass-like transition.Comment: 4 pages latex file with 4 eps figure file

Internal loss of superconducting resonators induced by interacting two level systems

In a number of recent experiments with microwave high quality superconducting coplanar waveguide (CPW) resonators an anomalously weak power dependence of the quality factor has been observed. We argue that this observation implies that the monochromatic radiation does not saturate the Two Level Systems (TLS) located at the interface oxide surfaces of the resonator and suggests the importance of their interactions. We estimate the microwave loss due to interacting TLS and show that the interactions between TLS lead to a drift of their energies that result in a much slower, logarithmic dependence of their absorption on the radiation power in agreement with the data

Nonequilibrium spectral diffusion due to laser heating in stimulated photon echo spectroscopy of low temperature glasses

A quantitative theory is developed, which accounts for heating artifacts in three-pulse photon echo (3PE) experiments. The heat diffusion equation is solved and the average value of the temperature in the focal volume of the laser is determined as a function of the 3PE waiting time. This temperature is used in the framework of nonequilibrium spectral diffusion theory to calculate the effective homogeneous linewidth of an ensemble of probe molecules embedded in an amorphous host. The theory fits recently observed plateaus and bumps without introducing a gap in the distribution function of flip rates of the two-level systems or any other major modification of the standard tunneling model.Comment: 10 pages, Revtex, 6 eps-figures, accepted for publication in Phys. Rev.

Mechanical Relaxation in Glasses and at the Glass Transition

The Gilroy-Phillips model of relaxational jumps in asymmetric double-well potentials, developed for the Arrhenius-type secondary relaxations of the glass phase, is extended to a formal description of the breakdown of the shear modulus at the glass transition, the flow process.Comment: 13 pages, 11 figures, 49 ref

Thermodynamic properties of small amorphous and crystalline Silica particles at low temperatures

We have measured the low-temperature ($T \le 1$K) specific heat and heat release of small amorphous and crystalline SiO2 particles embedded in Teflon and of Vycor. The temperature and time dependence of these properties have been interpreted in terms of the tunneling model. We found that the particle size influences the density of states of tunneling systems of the composite. The smaller the size of the particles the larger is the density of states of tunneling systems P0. Quartz grains with dimensions in the micrometer range show similar glass-like properties as vitreous silica. In comparison with bulk vitreous silica, Vycor shows a much larger P0 in agreement with the behavior we found for small SiO2 particles. We discuss the implication of our results on the origin of the universal low-temperature properties of glasses