Effect of charging energy on transition temperature of granular superconductors

The effect of the zero-point fluctuations of the phase on the transition temperature T_c of a granular superconductor is calculated using a model which takes into account the short-range part of the charging energy. A self-consistent mean field theory predicts a critical value of the ratio of the Josephson coupling constant to the charging energy and the existence of two values of T_c, indicating the possibility of reentrance into normal state at the lower one.     

Hydrogen isotope replacement reactions on rhenium

The existence of a mobile equilibrium at room temperature between part of the hydrogen adsorbed on rhenium and gaseous hydrogen is demonstrated by the easy exchange of isotopes between the adsorbed layer and the gas phase. The adsorbed gas is desorbed as a mixture of homonuclear molecules (of H₂ or D₂)and of the isotopically mixed species (HD). However, the replacement reactions are not symmetrical; there is a greater proportion of HD in the desorbed gas when deuterium is replaced by hydrogen than in the converse reaction. This kinetic isotope effect is attributed to differences between the zero-point energies of the various hydrogen containing species.Quantatitive agreement between the shapes of the experimentally observed desorption curves and calculated curves is obtained if the zero-point energy of the bond between a surface rhenium atom and deuterium is assigned the value 2.6 kcal mole^?1.     

Fluctuation of Mesoscopic RLC Circuit at Finite Temperature

We consider the fluctuation of mesoscopic RLC circuit at finite temperature since a resistance always produces Joule heat when the circuit is working. By virtue of the thermo field dynamics and the coherent thermo state representation we show that the quantum mechanical zero-point fluctuations of both charge and current increase with the rising temperature and the resistance value.     

Defects in silicon: the role of vibrational entropy

Vibrational free energies are calculated from first-principles in the same Si periodic supercells routinely used to perform defect calculations. The specific heat, vibrational entropy, and zero-point energy obtained in defect-free cells are very close to the measured values. The importance of the vibrational part of the free energy is studied in the case of two defect problems: the relative energies of the H₂ and H₂^∗ dimers and the binding energy of a copper pair. In both cases, the vibrational entropy term causes total energy differences to change by about 0.2 eV between 0 and 800 K. We also comment on the rotational entropy in the case of H₂ and the configurational entropy in the case of the Cu pair. These examples illustrate the importance of extending first-principles calculations of defects in semiconductors to include free energy contributions.     

Temperature dependence of Johnson noise

Johnson noise is usually considered to measure the absolute, thermodynamic temperature. A careful analysis of data on copper to 1.7 mK suggests that a kinetic temperature T_o coth T_o/T is measured, where T_o = 1.98 mK, and so reflects a zero-point energy.     

The lattice energy of magnesium hydride

The lattice energy of MgH₂ has been calculated using a Born-Mayer model. The result is U₀ = ?2906.5 kJ mol^?1 which may be compared with the Born-Haber cycle value of ?2721.3 kJ mol^?1. This difference indicates that there is an appriciable covalent contribution to the bonding. The importance of the zero-point energy contribution to the lattice energy in the case of the light metal hydrides is discussed.     

基于第一性原理的固氦零点振动能的量子理论计算

基于第一性原理,运用原子团簇理论和Hartree-Fock Self-Consistent-Field从头算法计算了高压固氦hcp结构在平衡位置r=1.75-2.6附近的原子相互作用能,并使用1stOpt软件拟合出固氦的零点振动频率,得到零点振动能、Gruneisen系数及零点振动压强,最后与实验值做了比较.结果表明:固氦晶体在其各自平衡位置附近的运动可近似为简谐振动;固氦晶体的零点振动频率随着摩尔体积的增大而减小;零点振动能占多体相互总能的比例超过5%,已不可忽略,其比例随摩尔体积的增加而增大;零点振动能随原子间距和摩尔体积的增大而减小;Gruneisen系数随着摩尔体积的增大而增大,并始终处于1和2之间;零点振动引起的压强与实验值曲线趋势完全一致,但比实验值稍小,零点振动压强对总压强的贡献随着摩尔体积的增大由8%增大到50%左右,由此引起的零点振动压强值的贡献越来越大.     

基于第一性原理的固氦零点振动能的量子理论计算

基于第一性原理,运用原子团簇理论和Hartree-Fock Self-Consistent-Field从头算法计算了高压固氦hcp结构在平衡位置r=1.75-2.6Å附近的原子相互作用能,并使用1stOpt软件拟合出固氦的零点振动频率,得到零点振动能、Gruneisen系数及零点振动压强,最后与实验值做了比较.结果表明：固氦晶体在其各自平衡位置附近的运动可近似为简谐振动;固氦晶体的零点振动频率随着摩尔体积的增大而减小;零点振动能占多体相互总能的比例超过5%,已不可忽略,其比例随摩尔体积的增加而增大;零点振动能随原子间距和摩尔体积的增大而减小;Gruneisen系数随着摩尔体积的增大而增大,并始终处于1和2之间;零点振动引起的压强与实验值曲线趋势完全一致,但比实验值稍小,零点振动压强对总压强的贡献随着摩尔体积的增大由8%增大到50%左右,由此引起的零点振动压强值的贡献越来越大.     

Manifestation of quantum statistics in vibrational dynamics of poly(ethylene) crystals

The temperature dependences of the transverse expansion ?_⊥(T) and the longitudinal contraction ?_‖(T) (with respect to the axes of chain molecules) in large-sized poly(ethylene) (PE) crystal grains (100×60×60 nm) are measured using x-ray diffraction in the temperature range 5–380 K. The temperature dependence of the elongation of the molecular skeleton ?_C(T) is obtained by Raman spectroscopy. It is found that the dependences ?_⊥(T), ?_‖(T), and ?_C(T) exhibit a similar specific nonlinear behavior. Analysis of these dependences indicates that the nonlinearity is associated with the quantum statistics of transverse vibrations. The energies and amplitudes of zero-point (at T=0) transverse (torsional and bending) vibrations and the relevant zero-point components ?_‖(0) and ?_C(0) are estimated. It is revealed that the zero-point components make a considerable contribution to the dynamics of the PE crystal up to the melting temperature (～400 K).     

Electric field induced phase transition in first order ferroelectrics with large zero point energy

An electric field induced phase transition in first order ferroelectrics with very large zero point energy is studied on the framework of the effective field approach. It is well known that when the zero point energy of a system is relatively large, the ferroelectric behaviour is depressed and no phase transition can be observed. The critical value Ω_cf of zero point energy for whom the phase transition disappears turns out to be dependant on the order of transition. For zero point energies larger than this critical value, a phase transition may be induced applying an external electric field. This temperature dependence of the induced polarization shows a discontinuous step when the applied electric field is weak, but becoming a continuous one at a strong applied electric field. Another critical value of zero point energy Ω_cp>Ω_cf is deduced for which no phase transition at all can be attained.     

NMR and magnetic studies on 7 K anomaly in Tl3H(SO4)2

Measurements of the spin-lattice relaxation time, NMR absorption line and magnetization have been carried out on the Tl₃H(SO₄)₂ crystal below 50 K. The anomaly at around 7 K was: (1) the spin-lattice relaxation times of ¹H and ²⁰⁵Tl nuclei increase steeply with decreasing temperature below 7 K, (2) the NMR absorption lines below 7 K shift to the high-magnetic field side in comparison with that above 7 K, and (3) the ¹H NMR line width exhibits a drastic increase of the line width with decreasing temperature below 7 K. These results indicate that the magnetic dipole fluctuation of the proton changes at 7 K. On the other hand, there are no remarkable anomalies of magnetic susceptibility at around 7 K. From these results it is deduced that the anomaly at around 7 K is caused by the change in quantum mechanical process of the proton from proton tunneling to zero-point vibration of hydrogen in the hydrogen bond with the decrease of temperature.     

Lattice-dynamical functions of solids at very high pressures

Abstract

Vibrational spectra of face-centered cubical (f.c.c.) solids are investigated at the pressure region, where the quantum-statistical model for the electron energy is applicable. Phonon dispersion curves are obtained for different values of the specific volume. The integration of the phonon spectra over the Brillouin zone yields the zero-point vibrational energy, the Debye temperature, the Gruneisen coefficient, mean-square amplitude of zero-point and thermal vibration, the melting temperature. All quantities under consideration are calculated from the universal functions of the reduced volume, using the scaling relations for given atomic number 2.     

Effect of covalency,zero-point energy and charge transfer on the phase-transition,elastic and thermophysical properties of Ca-chalcogenides under compression

The pressure induced phase-transition, elastic and thermophysical properties of Ca-chalcogenides have been investigated by means of many body potential. The modified charge transfer potential consists of long-range Coulomb and charge-transfer interactions modified by covalency and short-range overlap repulsion extended up to second neighbours and zero-point energy effects. Another charge-transfer model excludes covalency and zero-point energy effects. These chalcogenides undergo first-order phase-transition at P _T = 39.23, 36.30 and 31.20 GPa and their equation of state show volume collapse of 10.12, 7.61 and 4.55% for CaS, CaSe and CaTe, respectively, which are in good agreement with the experiments. The elastic and thermophysical properties of these compounds have also been computed at normal and high pressures. Both the models are capable of explaining the Cauchy-discrepancy (C₁₂ ≠ C₄₄), elastic, phase-transition and thermophysical properties successfully.     

Thermal Squeezed State Representation of Scalar Field and Energy Density in Semiclassical Theory of Gravity

The semiclassical theory of gravity is studied in terms of representation of scalar field in thermal coherent state and thermal squeezed state formalisms. For the FRW cosmological model with a minimal scalar field, the semiclassical Einstein equation reduces to zero-point energy term plus a finite temperature term and classical term in thermal coherent state. In thermal squeezed vacuum state it reduces to quantum term in addition to the finite temperature term and zero-point energy term. The present study can account for nonclassical state and finite temperature effect contributions to energy density in semiclassical theory of gravity.     

Extremely large binding energy of biexcitons in an organic-inorganic quantum-well material (C4H9NH3)2PbBr4

We have confirmed biexciton formation in an organic-inorganic hybrid quantum-well material (C₄H₉NH₃)₂PbBr₄ by photoluminescence and two-photon absorption measurements. The biexciton has extremely large binding energy, 60 meV, which to our knowledge is the largest value ever reported for a semiconductor. By analyzing the spectrum of biexciton luminescence, the biexciton gas temperature was found to be much higher than the bath temperature due to a higher local temperature arising from the large biexciton binding energy.     

Studies of dielectric and impedance properties of KCa2V5O15 ceramics

A polycrystalline sample, KCa₂V₅O₁₅, with tungsten bronze structure was prepared by a mixed-oxide method at low temperature (i.e., at 630 °C). A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscopy (SEM). Two dielectric anomalies at 131 and 275 °C were observed in the temperature dependency of dielectric response at various frequencies, which may be attributed to the ferroelastic-ferroelectric and ferroelectric-paraelectric transitions, respectively. The nature of variation of the electrical conductivity, and value of activation energy of different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies). The impedance plots showed only bulk contributions, and non-Debye type of relaxation process occurs in the material. A hopping mechanism of electrical transport processes in the system is evident from the modulus analysis. The activation energy of the compound (calculated both from loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers.     

The NMR indirect nuclear spin–spin coupling constant of the HD molecule

We present new calculated and experimental values of the NMR indirect nuclear spin–spin coupling constant in HD. In the quantum-chemical ab initio calculations, the full configuration-interaction (FCI) method is used, yielding an equilibrium value of 41.22?Hz in the basis-set limit. Adding a calculated zero-point vibrational correction of 1.89?Hz and a temperature correction of 0.20?Hz at 300?K, we obtain a total calculated spin–spin coupling constant of J _FCI(HD)?=?43.31(5)?Hz at 300?K. This result is within the error bars of the experimental gas-phase NMR value, J _exp(HD)?=?43.26(6)?Hz, obtained by extrapolating values measured in HD–He mixtures to zero density.     

Theoretical study of the surface structure and vibrations of solid argon

The influence of zero-point oscillations on the equilibrium structures and the vibrational modes for the (001), (110) and (111) surfaces of solid Ar is investigated at zero temperature. The surface structures are determined by minimizing the total energy, the static lattice energy plus zero-point energy, where the zero-point energy is evaluated from Einstein frequencies. It is found that the interlayer distances near the surface are larger than the values for bulk argon and are also larger than the distances predicted by minimizing only the static lattice energy. Based upon the surface structures determined by each of these two different minimization schemes, the phonon dispersion curves have been calculated for 21 layer slabs. The qualitative features of the dispersion curves in each case are very similar but there is a significant overall reduction in the frequencies calculated using the structures determined by minimizing the total energy, including the zero-point contribution. The rms vibrational amplitudes of atoms near the surface are calculated from the Einstein frequencies and their values relative to the bulk amplitude are the same as those evaluated by Allen and De Wette [Phys. Rev. 179 (1969) 873] from the lattice dynamics of slabs.     

Structural and electrical characteristics of rare earth simple perovskite oxide La0.57Nd0.1Pb0.33Mn0.8Ti0.2O3

Polycrystalline La_0.57Nd_0.1Pb_0.33Mn_0.8Ti_0.2O₃ (LNPMT) is prepared by the solid-state reaction technique. The formation of single phase material was confirmed by X-ray diffraction studies, and it was found to be a rhombohedral phase at room temperature. The impedance plane plot shows semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The frequency dependent conductivity spectra follow the universal power law. The activation energy deduced from analysis of the imaginary part of electric modulus and imaginary impedance is found to be ∼75 meV. Such a value of activation energy indicates that the conduction mechanism for the sample is due to electron hopping. The imaginary part of the electric modulus suggests that the relaxation describes the same mechanism at various temperatures.     

Coulomb repulsion-induced hyperbolic pairing as a mechanism of high-T c superconductivity

The hyperbolic metric of the dispersion law (the effective mass tensor components of carriers are opposite in sign) in the vicinity of the Fermi contour in high-T _c superconducting cuprates in the case of repulsive interaction gives rise to a superconducting state characterized by the condensate of pairs with a large total momentum (hyperbolic pairing). The gain in the energy of the superconducting state over the normal state is due to the fact that a change in the kinetic energy of pairs (because of the negative light component of the effective mass) dominates over the change in the potential energy (corresponding to energy loss). The shift of the chemical potential upon the transition to the superconducting phase is substantial in this case. With increasing repulsive interaction, the superconducting gap δ_K increases and the resulting gain in energy changes to an energy loss at a certain critical value of the repulsive potential. The low temperature T _c of the superconducting transition and the large value of δ _K in this region of potential values are the reasons for the high value of the 2δ_K/T _c ratio and for the developed quantum fluctuations that are observed in underdoped cuprate superconductors.