Pressure measurements of the solid hydrogen quadrupolar glass

We report measurements of the pressure and (?P/?T)_V in samples of solid hydrogen of orthohydrogen concentrations of 40–55% and 150 mK ? T ? 1 K. No evidence of a first or second order phase transition is seen at temperatures associated with the formation of a quadrupolar glass.     

Lower phase transition temperature of solid hydrogen sulphide

The lower phase transition temperature of solid hydrogen sulphide is measured accurately using the polarizing microscope technique. A temperature difference is observed between one phase transition and its reverse. It is suggested that this may be due to hysteresis effect in the phase transition as a result of change of structure.     

Specific heat of solid deuterium in the region of the proposed rotational glass phase

The specific heat of solid deuterium of 33% paradeuterium concentration has been measured for 1 K > T > 0.115K by a thermal relaxation technique. No evidence of a phase transition was found in the samples in the temperature range associated with the molecular rotational glass phase. No thermal remanence effects were observed for characteristic measurements times greater than 30 seconds. Integration of the specific heat indicates that rotational entropy of the solid below 0.35 Kelvin equals about 10% of the free rotator entropy, in agreement with ?P/?T)_V studies of solid H₂.     

On quantum effects on the surface of solid hydrogen

The low-frequency spectrum of hypothetical superfluidity on the free surface of a quantum crystal of hydrogen is determined. In the quantum-rough state of the surface, crystallization waves with a quadratic spectrum should propagate. In the atomically smooth state, the spectrum is linear. Crystallization waves propagating along elementary steps are also considered.     

On the α-γ phase transition in solid nitrogen

The α-γ transition is discussed starting from the elastic stability conditions of the α-N₂ phase. The α phase can be shown to become unstable on increasing pressure. The energy potential surface near the phase transition point has been calculated using an ab initio intermolecular potential. The probable path of the transition is traced on the surface.     

On hydrogen localization in the β′ phase of VO0.2

The results of an investigation of the dynamics of hydrogen atoms in the body-centered tetragonal lattice of the interstitial β′ phase of vanadium-oxygen by the method of inelastic scattering of slow neutrons are reported. It is concluded on the basis of an analysis of the structure of the alloy investigated that hydrogen in the lattice is localized in tetrahedral interstices with the point symmetry of an almost ideal tetrahedron. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 326–328 (10 March 1998)     

On the magnetic ordering in β phase and α-β phase transition in solid oxygen

The symmetry-allowed configurations of magnetic spins in the β phase of solid oxygen have been calculated in the framework of the general molecular field approximation. The three-sublattice configuration has been found to be most stable while the two-sublattice structure (the α phase) requires the elastic deformation which accompanies the α-β structural phase transition.     

The signature of the nuclear quadrupole interaction in continuous phase transitions

A correlation between the largest component of the electric field gradient (EFG) tensor, V_zz, and its asymmetry parameter η is discovered in a series of compounds which exhibt phase transitions. It is shown that all the EFG tensor components depend linearly on a single control parameter. A convenient way to unravel this correlation from V_zz, η-data is presented.     

Deuteron quadrupole coupling constants in crystals with symmetrical hydrogen bonds

Deuteron quadrupole coupling constants for the free formic and trifluoroacetic acid molecules, for their acid anions and for the maleate anion were calculated using the INDO method. The results are compared with experimental values for potassium deuterium maleate and bistrifluoroacetate.     

Study of the hydrogen solid solution in thulium

Solid solutions of hydrogen in thulium are investigated, mainly by X-ray determinations in the temperature range 20–500°C. Several observations lead us to distinguish between two variaties α and α¹. In the range of existence of the α¹ phase, below the transition temperature of 120°C, the hydrogen interstitials induce in the metal lattice a behaviour different from that of the α phase, as concerns the phase equilibrium, the additional resistivity, and the lattice anisotropy.Several simple models are proposed for the explanation of this anomaly, encountered also in other heavy rate earth-hydrogen systems.     

Frozen glass phase in the multi-index matching problem

The multi-index matching is an NP-hard combinatorial optimization problem; for two indices it reduces to the well understood bipartite matching problem that belongs to the polynomial complexity class. We use the cavity method to solve the thermodynamics of the multi-index system with random costs. The phase diagram is much richer than for the case of the bipartite matching problem: it shows a finite temperature phase transition to a completely frozen glass phase, similar to what happens in the random energy model. We derive the critical temperature, the ground-state energy density, and properties of the energy landscape and compare the results to numerics based on exact analysis of small systems.     

Search for superfluidity in solid hydrogen

A torsional oscillator study of solid para-hydrogen has been carried out down to 20 mK in a search for evidence of superfluidity. We found evidence of a possible phase transition, marked by an abrupt increase in the resonant period of oscillation and onset of extremely long relaxation times as the temperature was raised above 60 mK. In contrast to solid 4He, the change in the period for para-hydrogen is not a consequence of irrotational superflow. The long relaxation times observed suggest the effect is related to the motion of residual ortho-hydrogen molecules in the solid.