Supercooling molecular hydrogen down through the superfluid transition

Recent calculations by Vorobev and Malyshenko [JETP Lett. 71, 39 (2000)] show that molecular hydrogen may stay liquid and superfluid in strong electric fields of the order of 4x10(7) V/cm. I demonstrate that strong local electric fields of similar magnitude exist beneath a two-dimensional layer of electrons localized in the image potential above the surface of solid hydrogen. Even stronger local fields exist around charged particles (ions or electrons) if the surface or bulk of a solid hydrogen crystal is statically charged. Measurements of the frequency shift of the 1 --> 2 photoresonance transition in the spectrum of a two-dimensional layer of electrons above a positively or negatively charged solid hydrogen surface performed in the temperature range 7-13.8 K support the prediction of electric field induced surface melting. The range of surface charge density necessary to stabilize the liquid phase of molecular hydrogen at the temperature of superfluid transition is estimated.     

Coexistence of superfluid and solid helium in aerogel

The results of recent neutron scattering studies of solid helium in silica aerogel are discussed. Previously I.V. Kalinin et al., Pis’ma Zh. éksp. Teor. Fiz. 87 (1), 743 (2008) [JETP Lett. 87 (1), 645 (2008)], we detected the existence of a superfluid phase in solid helium at a temperature below 0.6 K and a pressure of 51 bar, although, according to the phase diagram, helium should be in the solid state under these conditions. This work is a continuation of the above studies whose main goal was to examine the detected phenomenon and to establish basic parameters of the existence of a superfluid phase. We have determined the temperature of the superfluid transition from solid to superfluid helium, T _C = 1.3 K, by analyzing experimental data. The superfluid phase excitation parameters (lifetime, intensity, and energy) have a temperature dependence similar to that of bulk helium. The superfluid phase coexists with the solid phase in the entire measured temperature range from T = 0.05 K to T _C and is a nonequilibrium one and disappears at T _C.     

Superfluidity and dimerization in a multilayered system of fermionic polar molecules

We consider a layered system of fermionic molecules with permanent dipole moments aligned perpendicular to the layers by an external field. The dipole interactions between fermions in adjacent layers are attractive and induce interlayer pairing. Because of the competition for pairing among adjacent layers, the mean-field ground state of the layered system is a dimerized superfluid, with pairing only between every other layer. We construct an effective Ising-XY lattice model that describes the interplay between dimerization and superfluid phase fluctuations. In addition to the dimerized superfluid ground state, and high-temperature normal state, at intermediate temperature, we find an unusual dimerized "pseudogap" state with only short-range phase coherence. We propose light-scattering experiments to detect dimerization.     

Observation of a superfluid phase in solid helium

Evidence of a superfluid liquid phase present in polycrystalline helium at a temperature of 0.2 K and a pressure of 51 bar has been obtained by means of inelastic neutron scattering. The superfluid component is absent at a temperature of 0.6 K and the same pressure. Thus, a “solid helium-superfluid helium” phase transition has been discovered. The sample of solid helium in a porous medium (silica aerogel) has been prepared with the use of a capillary blocking technique. The shape of the structure factor of the superfluid phase indicates the presence of clusters or the effects of a restricted geometry. The results may be used to explain the nonclassical rotational inertia phenomenon in solid helium (often referred to as supersolidity, Nature, 2004).     

Evolution of the optical properties of Pb<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>Sc<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> (PBSN-6) solid solution single crystals caused by a static electric field

The electric-field-induced variation of the optical properties (small-angle light scattering, birefringence) of PBSN-6 solid solutions was studied. It was found that in the absence of an electric field, the cubic nonpolar matrix contains, at temperatures below the dielectric permittivity maximum, spontaneously polarized regions of the ferroelectric phase not less than 10⁴ Å in size. It was shown that a weak electric field (～0.4 kV/cm) is capable of inducing a kinetic phase transition to the ferroelectric state, with the temperature of this transformation depending on the sample heating rate. The destruction of the induced state was accompanied by a sharp peak in the temperature dependence of the small-angle light scattering intensity (indicating the percolation nature of the transition) and was independent of the sample heating rate. The boundaries of stability of the induced state in various modes of application of an external electric field were determined, and the E-T phase diagram was constructed.     

Roton dipole moment

The roton excitation in the superfluid ⁴He does not possess a stationary dipole moment. However, a roton has an instantaneous dipole moment, such that at any given moment one can find it in the state either with positive or with negative dipole moment projection on its momentum direction. The instantaneous value of electric dipole moment of roton excitation is evaluated. The result is in reasonable agreement with recent experimental observation of the splitting of microwave resonance absorption line at roton frequency under external electric field.     

Pressure Effects on Solid State Phase Transformation of Aluminium Bronze in Cooling Process

Effects of high pressure （6 CPa） on the solid state phase transformation kinetic parameters of aluminum bronze during the cooling process axe investigated, based on the measurement and calculation of its solid state phase transformation temperature, duration and activation energy and the observation of its microstructures. The results show that high pressure treatment can reduce the solid phase transformation temperature and activation energy in the cooling process and can shorten the phase transformation duration, which is favorable when forming fine-grained aluminum bronze.     

固氢金属化转变压力的理论计算

 利用简单金属的赝势理论方法计算了固氢的金属转变压力,并探讨了金属氢可能的晶体结构及力、热物性。计算结果表明,在绝对零度条件下,分子态固氢（HCP结构）向原子相金属氢（FCC结构）的转变压力p_t=465.95 GPa。     

Diverse solid and supersolid phases of bosons in a triangular lattice

We investigate the ground state of bosons with long-range interactions in the large U limit on a triangular lattice. By mapping this system to the spin-1/2 XXZ model in a magnetic field, we can apply the spin wave theory to this study. We demonstrate how to construct the phase diagrams within the spin wave theory. The phase diagrams are given in an extensive parameter region, where, besides the superfluid phase, diverse solid and supersolid phases are shown to exist in this model. Especially, we find that the phase diagram obtained in this method is consistent with the one obtained previously using numerical techniques in the Ising limit. This confirms the effectiveness of our method. We analyze the stability of all the obtained supersolids and show that they will not be ruined by the quantum fluctuations. We observe that the quantum fluctuations in the stripe supersolid phase could be enhanced by the external field. We also discuss the relevance of our result with the experiment that may be realized with ultracold bosonic polar molecules in a triangular optical lattice.     

Electronic states in a Pöschl–Teller-like quantum well: Combined effects of electric field, hydrostatic pressure, and temperature

The work is devoted to present a theoretical study of the influences of external probes, such as applied electric field and hydrostatic pressure, on the electron and hole states in a Pöschl–Teller quantum well. The calculations have been done in the framework of the variational method. The dependence of the ground state energy of an electron and/or hole confined in the quantum well has been obtained as a function of the applied electric field and hydrostatic pressure. Different values of the asymmetry parameters of the Pöschl–Teller potential as well as temperature have been considered. It is shown that as a result of the increase in the electric field there is an augment of the ground state energy, and also that by increasing the quantum well width the effects of applied electric field are strengthened. It is obtained from the calculations that the ground state energy is a decreasing (increasing) function of the hydrostatic pressure (temperature). It is found that in the high pressure regime the energy grows with pressure, which is a previously unknown result. In the case of holes, the energy is always an increasing function both of the pressure and the temperature. Besides, the behavior of the photoluminescence peak energies associated to transitions between the ground states of electrons and heavy holes in the system is also reported.     

Effects of an alternating electric field on the transparency of a thin field of the smectic phase of p-type n-Octylhydroxybenzoic acid

An experimental study was made of the transparency of the smectic phase of p-type n-octylhydroxybenzoic acid as a function of the intensity and frequency of an electric field. A significant thermal hysteresis was found: at a given temperature, the smectic phase obtained by heating from the solid crystalline state is less sensitive to the electric field than the phase produced by cooling from the isotropic liquid. The transparency changes are explained on the basis of the appearance, growth, and destruction of domain structure in the electric field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 22–26, September, 1970.     

Stabilization of homogeneously precessing domains by large magnetic fields in superfluid 3He-B

We have studied the catastrophic relaxation in superfluid 3He-B as a function of magnetic field for a sample pressure of 31 bars. "Catastrophic relaxation" refers to a novel magnetic relaxation process which rapidly disrupts the homogeneous precession of nuclear spins in NMR experiments on the B phase. The catastrophe was observed through its effect on the evolution of a long-lived coherent dynamic state, the homogeneously precessing domain. Our measurements reveal that the onset of catastrophic relaxation is suppressed to lower temperatures by a strong magnetic field.     

Influence of electric field,hydrostatic pressure and temperature on the electronic states in a Pöschl-Teller quantum well

Influence of the electric field and hydrostatic pressure on the electronic states in a Pöschl-Teller quantum well is studied. In the framework of variational method the dependences of the ground state energy on the electric field and hydrostatic pressure are calculated for different values of the potential parameters and the temperature. It is shown that the increase in the electric field leads to the increase in the ground state energy, while the increase in the well width leads to the strengthening of the electric field effect. The ground state energy decreases with increasing pressure and increases with increasing temperature.     

Unusual liquid state of hard-core bosons on the pyrochlore lattice

We study the physics of hard-core bosons with unfrustrated hopping (t) and nearest-neighbor repulsion (V) on the three dimensional pyrochlore lattice. At half-filling, we demonstrate that the small V/t superfluid state eventually becomes unstable at large enough V/t to an unusual insulating state which displays no broken lattice translation symmetry. Equal time and static density correlators in this insulator are well described by a mapping to electric field correlators in the Coulomb phase of a U(1) lattice gauge theory, allowing us to identify this insulator with a U(1) fractionalized Mott-insulating state. The possibility of observing this phase in suitably designed atom-trap experiments with ultracold atoms is also discussed, as are specific experimental signatures.     

Equations of state and phase diagrams of hydrogen isotopes

A new form of the semiempirical equation of state proposed for the liquid phase of hydrogen isotopes is based on the assumption that its structure is formed by cells some of which contain hydrogen molecules and others contain hydrogen atoms. The values of parameters in the equations of state of the solid (molecular and atomic) phases as well as of the liquid phase of hydrogen isotopes (protium and deuterium) are determined. Phase diagrams, shock adiabats, isentropes, isotherms, and the electrical conductivity of compressed hydrogen are calculated. Comparison of the results of calculations with available experimental data in a wide pressure range demonstrates satisfactory coincidence.     

电场中(MgO)2吸附H2的理论研究

电场诱导MgO材料吸附H2是一种有效的储氢方法,而较高的场强制约其广泛应用。本文在B3LYP/CC-PVTZ水平上对电场中 (MgO)2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005 a. u. 的电场,就能使其对单个H2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV. 该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法。计算还表明电场中(MgO)2最多能吸附8个H2,相应的质量密度达到16.7 wt%。     

Tuning the tricritical point with spin-orbit coupling in polarized fermionic condensates

We investigate a two-component atomic Fermi gas with population imbalance in the presence of Rashba-type spin-orbit coupling (SOC). As a competition between SOC and population imbalance, the finite-temperature phase diagram reveals a large variety of new features, including the expanding of the superfluid state regime and the shrinking of both the phase separation and the normal regimes. For sufficiently strong SOC, the phase separation region disappears, giving way to the superfluid state. We find that the tricritical point moves toward a regime of low temperature, high magnetic field, and high polarization as the SOC increases.     

Electrical properties of AgSnSbSe<Subscript>3</Subscript> under different external effects

The electrical properties of the chalcogenide AgSnSbSe₃ have been investigated over a wide range of variations in external parameters, such as the temperature, the pressure, and the frequency of the electric field. It has been found that the temperature dependence of the permittivity and the dependence of the electrical resistivity on the hydrostatic pressure exhibit anomalies that are characteristic of structural phase transitions. The influence of the frequency on dielectric properties of the material has been analyzed.     

电场中(MgO)2吸附H2的理论研究

电场诱导MgO材料吸附H2是一种有效的储氢方法,而较高的场强制约其广泛应用。本文在B3LYP/CC-PVTZ水平上对电场中 (MgO)2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005 a. u. 的电场,就能使其对单个H2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV. 该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法。计算还表明电场中(MgO)2最多能吸附8个H2,相应的质量密度达到16.7 wt%。     

电场中(MgO)_2吸附H_2的理论研究

电场诱导MgO材料吸附H_2是一种有效的储氢方法,而较高的场强制约其广泛应用.本文在B3LYP/CC-PVTZ水平上对电场中(MgO)_2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005a.u.的电场,就能使其对单个H_2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV.该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法 .计算还表明电场中(MgO)_2最多能吸附8个H_2,相应的质量密度达到16.7 wt%.