Effect of in-plane vortex coupling on Hall conductivity in high-Tc superconducting thin films

The controversial pinning dependence of the Hall conductivity (σ_xy) is studied in the vortex-liquid phase of high-T_c superconducting thin films. A strong pinning dependence of σ_xy is found to be triggered by a crossover from a regular liquid to the glassy liquid (GL) where vortices remain coupled in ab-plane. This result suggests that a non-linear effect in the GL region needs to be considered to account for the behavior of σ_xy in the whole vortex-liquid phase.     

Thermodynamics of SU(3) lattice gauge theory

The pressure and the energy density of the SU(3) gauge theory are calculated on lattices with temporal extent N_τ = 4, 6 and 8 and spatial extent N_σ = 16 and 32. The results are then extrapolated to the continuum limit. In the investigated temperature range up to five times T_c we observe a 15% deviation from the ideal gas limit. We also present new results for the critical temperature on lattices with temporal extent N_τ = 8 and 12. At the corresponding critical couplings the string tension is calculated on 32⁴ lattices to fix the temperature scale. An extrapolation to the continuum limit yields T_c/√σ = 0.629(3). We furthermore present results on the electric and magnetic condensates as well as the temperature dependence of the spatial string tension. These observables suggest that the temperature dependent running coupling remains large even at T ≅ 5T_c. For the spatial string tension we find √σ_s/T=0.566(13)g²2(T) with g² (5T_c) ≅ 1.5.     

Pressure dependence of the Grüneisen parameter of sodium and potassium

Temperature changes associated with adiabatic pressure changes (?T/?P)_s have been measured for sodium and potassium at room temperature (297 K) under hydrostatic pressures up to 32 kbar. For both metals a large decrease in the value of (?T/?P)_s is observed as the pressure increases. The Grüneisen parameter γ is related to (?T/?P)_s by γ = B_s(?T/?T)_s/T where B_s is the adiabatic bulk modulus. Available data for the pressure dependence of B_s and the isothermal bulk modulus B_T are used to predict the pressure and volume dependence of γ.     

Universal explicit expression for quantum Hall conductance at any temperatures and chemical potentials

This paper generalises the theorem already obtained [Solid State Commun. 127 (2003) 505] for the high mobility, dissipationless, integer quantum Hall systems at T=0 K to the T>0 K situations. The results obtained are again suitable at both microscopic and macroscopic scales. In comparison [Solid State Commun. 127 (2003) 505], this generalised form gives a universal explicit expression for the Hall conductance σ_xy(μ,T) between any two points selected in such a system as a function of chemical potential and temperature. Further, thermal deviation Δσ_xy(μ,T) from the exact quantised values of σ_xy(μ,T) and the minimum slopes of Hall plateaux in the T>0 cases, observed already in experiments, are also derived in theory. Similar to those in the T=0 K case [Solid State Commun. 127 (2003) 505], the overall quantum Hall behaviour of the system can again be obtained from this theory by simply selecting two points on the two Hall contacts.     

Temperature dependence of the energy separation between Γ and L minima in n-type GaSb

Energy separation ΔE_c between Λ and L minima of GaSb conduction band is deduced from temperature dependence of tunneling current in p−n junctions. ΔE_c is found to inceasing vx. temperature with a coefficient d(ΔE_c/dT) of about - 2.10^-4eV/dgK.     

Nonmonotonic temperature dependence of the Hall resistance of a 2D electron system in silicon

For a 2D electron system in silicon, the temperature dependence of the Hall resistance ρ_xy(T) is measured in a weak magnetic field in the range of temperatures (1–35 K) and carrier concentrations n where the diagonal resistance component exhibits a metallic-type behavior. The temperature dependences ρ_xy(T) obtained for different n values are nonmonotonic and have a maximum at T_max ～ 0.16T_F. At lower temperatures T < T_max, the change δρ_xy(T) in the Hall resistance noticeably exceeds the interaction quantum correction and qualitatively agrees with the semiclassical model, where only the broadening of the Fermi distribution is taken into account. At higher temperatures T > T_max, the dependence ρ_xy(T) can be qualitatively explained by both the temperature dependence of the scattering time and the thermal activation of carriers from the band of localized states.     

Superconducting and normal state properties of dilute alloys of LaSn3 containing Ce impurities

The dependence of the superconducting transition temperature T_c on Ce impurity concentration and the specific heat jump at T_c as a function of T_c are reported for the system ($\text{La}$Ce)Sn₃. The experimental results are analyzed using a theory due to Kaiser concerning the effect on superconductivity of nonmagnetic localized resonant impurity states This analysis yields values for the intraatomic Coulomb repulsion parameter U_eff and the Ce local density of states at the Fermi level N_? (E_F). The results of low temperature normal state heat capacity and magnetic susceptibility measurements which give independent estimates of N_? (E_F) are also reported. A large pressure dependence of the T_c of ($\text{La}$Ce)Sn₃ alloys was observed for pressures up to 20 kbar. This behavior is similar to that previously observed in several other superconducting matrix-Ce impurity systems in which the Ce solute 4f electron shell undergoes a continuous-pressure induced demagnetization.     

X-ray diffraction study of a structural phase transition in (NbSe4)3I

The second-order structural phase transition was observed by X-ray diffraction technique in (NbSe₄)₃I. The transition temperature (T_c) was 274.2 K. No evidence of the formation of the charge-density wave was found out. Temperature dependence of the intensity of (0,5,12) reflection obeys the Landau theory of the second kind of phase transition near T_c. Temperature dependence of the integral breadth of (0,0,12) reflection indicates the effect of the soft-phonon mode below T_c. The existence of the structural phase transition, probably not associated with charge-density-wave formation, suggests the unique nature of (NbSe₄)Z₃I in the new series of compounds (MSe₄)_xI (M=Nb, Ta).     

Carrier concentration dependence and temperature dependence of mobility in silicon (100) N-channel inversion layers at low temperatures

The carrier concentration (N_s) dependence of electron mobility in Si (100) inversion layers has been measured at temperatures T = 1.5?70K for high- and low-mobility MOSFETs. An extrinsic term is observed in the T-dependent part of the scattering probability, τ^?1_T. At T = 4.4 K, τ^?1_T depends on N_s as N^?1.9_s in low mobility samples. In high-mobility samples, τ^?1_T increases with increasing N_s in high N_s region while τ^?1_T ∝ N^?1.6_s in low N_s region. The N_s-dependence of τ^?1_T becomes weaker with increasing T in both of low- and high-mobility samples. At N_s = 3 × 10¹² cm^?2, τ^?1_T depends on T as T^1.8 in low-mobility samples and τ^?1_T ∝ T^2.0 in high- mobility samples at T 5 K.     

Electronic structure of new multiple band Pt-pnictide superconductors APt3P

We report LDA calculated band structure, densities of states and Fermi surfaces for recently discovered Pt-pnictide superconductors APt₃P (A = Ca, Sr, La), confirming their multiple band nature. Electronic structure is essentially three dimensional, in contrast to Fe pnictides and chalcogenides. LDA calculated Sommerfeld coefficient agrees rather well with experimental data, leaving little space for very strong coupling super-conductivity, suggested by experimental data on specific heat of SrPt₃P. Elementary estimates show, that the values of critical temperature can be explained by rather weak or moderately strong coupling, while the decrease in superconducting transition temperature T _c from Sr to La compound can be explained by corresponding decrease in total density of states at the Fermi level N(E _F). The shape of the density of states near the Fermi level suggests that in SrPt₃P electron doping (such as replacement Sr by La) decreases N(E _F) and T _c , while hole doping (e.g., partial replacement of Sr with K, Rb or Cs, if possible) would increase N(E _F) and possibly T _c .     

Proton conductivity and ferroelectric phase transition in hydrogen-bonded ferroelectric NH4IO3

We report on the ac dielectric permittivity (ε) and the electric conductivity (σ_ω), as function of the temperature 300?K?T4IO₃. The main feature of our measured parameters is that, the compound undergoes a ferroelectric phase transition of an improper character, at (368?±?1)K from a high temperature paraelectric phase I (Pm2₁ b) to a low temperature ferroelectric phase II (Pc21n). The electric conduction seems to be protonic. The frequency dependent conductivity has a linear response following the universal power law (σ_{( ω )}?=?A(T)ω ^{s (T)}). The temperature dependence of the frequency exponent s suggests the existence of two types of conduction mechanisms.     

Temperature dependence of the spectral weight in p- and n-type cuprates: A study of normal state partial gaps and electronic kinetic energy

The optical conductivity of CuO₂ (copper-oxygen) planes in p- and n-type cuprates thin films at various doping levels is deduced from highly accurate reflectivity data. The temperature dependence of the real part σ₁ (ω) of this optical conductivity and the corresponding spectral weight allow to track the opening of a partial gap in the normal state of n-type Pr_2−xCe_xCuO₄ (PCCO) but not of p-type Bi₂Sr₂CaCu₂O_8+δ (BSCCO) cuprates. This is a clear difference between these two families of cuprates, which we briefly discuss. In BSCCO, the change of the electronic kinetic energy E_kin—deduced from the spectral weight—at the superconducting transition is found to cross over from a conventional BCS behavior (increase of E_kin below T_c) to an unconventional behavior (decrease of E_kin below T_c) as the free carrier density decreases. This behavior appears to be linked to the energy scale over which spectral weight is lost and goes into the superfluid condensate, hence may be related to Mott physics.     

Antiferromagnetic exchange mechanism of superconductivity in cuprates

The theory of superconducting pairing due to antiferromagnetic exchange is considered. The strong dependence of the superconducting transition temperature T _c on the lattice constant a observed recently in mercury superconductors is explained within the framework of this theory. Calculations have been performed based on the two-band p-d Hubbard model in the strong correlation limit. The large excitation energy Δ_pd for the antiferromagnetic exchange of two particles from different Hubbard subbands results in the suppression of the retardation effects and in the pairing of all the particles in the conduction subband with the Fermi energy E _F ?Δ_pd:T _c ?E _F exp(?1/λ), where λ∝J. The dependence T _c (a) and the isotope effect are explained by the dependence of the exchange interaction J on a and on zero-point vibrations of oxygen ions.     

Proton conduction in CsHSO4–mesoporous silica composite electrolytes

Novel proton-conducting composites were prepared by incorporating molten CsHSO₄ (CHS) into two types of mesoporous silica, MCM-41 with a one-dimensional (1-D) hexagonal structure and MCM-48 with a three-dimensional (3-D) cubic structure. Their proton conductivities (σ) were measured to examine effects of the incorporation and the dimensionality of the mesopores on their conductivity. Incorporation of proper amounts of MCMs maintained high proton conductivities as high as ~ 10^? 3 S cm^? 1 at temperatures above the superprotonic phase-transition temperature (T_s: 414 K) of CHS and improved the conductivity by 2 to 3 orders of magnitude at temperatures below T_s. In the case of MCM-41, more than 40 mol% mixing, however, caused steep drops in σ in both temperature ranges. On the other hand, the CHS/MCM-48 composite showed a linear increase in σ below T_s and a gradual decrease in σ above T_s with an increase in the MCM-48 content at least up to 60 mol%. X-ray diffraction (XRD) analysis revealed that CHS filled in the MCM mesopores became X-ray crystallographically amorphous and the amount of the amorphous phase increased with an increase in the MCM contents. In the case of the CHS/MCM-48 composites, the activation energy (E_a) for proton conduction below T_s drastically came close to that above T_s by mixing with MCM-48 up to 30 mol%. This indicates that the proton can transport similarly to the conduction mechanism in the superprotonic phase even below T_s. These results suggest that CHS adopts a highly proton-conducting amorphous phase in the mesopores at temperatures below T_s, and that MCM-48 with the 3-D cubic structure is more suitable for formation of high proton-conducting percolation paths.     

On the dependence of the single-spin asymmetry of charged pions on kinematical variables

The experimental single-spin asymmetry (A _N ) of charged pions produced in proton-proton and proton-nucleus collisions is analyzed phenomenologically as a function of kinematical variables. It is shown that the c.m. pion threshold energy (E ₀ ^c.m. ) above which |A _N | is positive depends on the reaction energy √s and on the particle-production angle θ ^c.m.. The dependence of the single-spin asymmetry on the kinematical variables in the region specified by the inequalities 0.7 < p _T < 2.7 GeV/c and E ^c.m. > E ₀ ^c.m. exhibits a scaling behavior. The dependence of A _N on √s proves to be significant at moderate and low energies. Formulas that make it possible to predict the behavior of A _N for charged pions over a broad region of kinematical variables are derived.     

Gamma rays and neutrons following preequilibrium 165Ho(p, xcnypγ) reactions at Ep = 60 MeV

Neutrons and γ-rays following 60 MeV proton bombardment of ¹⁶⁵Ho were measured in coincidence with discrete γ-rays characteristic of the reaction channels (residual nuclei). The cross sections for the (p, xcnγ) reactions with x = 2–6, the γ-ray multiplicities, and the energy and angular distributions of the emitted neutrons were analyzed in terms of the preequilibrium and equilibrium deexcitation processes. Characteristic behaviours of the preequilibrium process were found in the (p, 2nγ) and (p, 4nγ) reactions where the sum E_T, = ∑^xE_i of the energies E_i of the emitted neutrons was large, while those of the equilibrium process were typical for the (p, 6ny) reaction with small E_T. The reactions are well reproduced by the expression σ. ≈0.35∑_xσ (2, x?2) + 0.4∑_xσ(1, χ?1)+ 0.25∑_xσ(0, x), where σ(n_p, n_c) stands for emission of n_p neutrons at the preequilibrium stage followed by evaporation of n_c neutrons at the equilibrium stage.     

Injection and thermodepolarization currents in GaSe <Co> single crystals

The current-voltage characteristics (CVC) at different temperatures, the temperature dependence of electric conductivity [σ(T)] and the currents of thermostimulated depolarization (TSD) have been studied in GaSe <0.05 at.% Co> on a combined basis.The location depth (E_t=0.57eV) and the concentration of traps (N_t=2.7x10¹²cm^?3) have been determined from the temperature dependence of the trapping factor. In the course of TSD investigations, levels with location depths of 0.28±0.02 and 0.57±0.03 eV have been revealed. It is noted that traps with the energy of 0.57±0.03 eV are found both with TSD measurements and on the basis of the temperature dependence of the electric conductivity and the trapping factor.It has been established that the hole centres above the valence band are responsible for the CVC, σ(T) and TSD. The location depths, concentrations and trapping cross-sections of these centres have been determined.     

High-temperature phase transitions in the improper ferroelectric KIO3

The ac conductivity (σ_ac) and dielectric permittivity (?) are determined in the temperature range 300?K?T3 compound. The results indicated that the compound behaves as an improper ferroelectric and undergoes a ferroelectric phase transition from a high temperature rhombohedral phase I to a low temperature monoclinic phase II at T _c?=?(486?±?1)?K. A second structural phase transition was observed around 345?K. The conductivity varies with temperature range and for T?>?428?K intrinsic conduction prevails. Different activation energies in the different temperature regions were calculated. The frequency dependence of σ(ω) was found to follow the universal dynamic response [σ(ω)∝(ω) ^s(T)]. The thermal behaviour of the frequency exponent s(T) suggests the hopping over the barrier model rather than the quantum mechanical tunneling model for the conduction mechanism.     

Inclusive π electroproduction in the deep inelastic region

Using 20.5 GeV electrons on protons, we measured inclusive π⁰'s (of transverse momentum, p_T, from 0 to 1.4 GeV/c) produced by virtual photons of energy, ν, from 4 to 16.5 GeV and four-momentum squared, q², from ?1.8 to ?8.5 (GeV/c)². Comparing with charged pion data, we find , supporting the quark model. Photon knockout of a quark is favored as the interpretation of these data because of scaling in z = E_π/ν and similarity in z-dependence of other pion production data. Consistent with this interpretation are the dependence of 〈p_T〉 on q², the azimuthal dependence, and fits to the constituent interchange model. We also observe a possible p_T^?4 dependence at large |q²| over a limited p_T range.     

Giant thermal hysteresis of sound velocity and internal friction in a La0.8Sr0.2MnO3 single crystal

Temperature dependences of the velocity of longitudinal sound V ₁ and the internal friction Q ^?1 are studied for a La_0.8Sr_0.2MnO₃ single crystal in the temperature range 5–350 K. The latter includes the temperature of the structural phase transition T _s ≈95 K (from the Pnma orthorhombic low-temperature phase to the $R\bar 3c$ rhombohedral high-temperature one) and the Curie point T _c =308 K. Near the temperatures T _s and T _c , the curves V ₁(T) and Q ^?1(T) exhibit pronounced singularities. Outside the vicinities of T _s and T _c , the velocity of sound monotonically decreases with increasing temperature. A thermal hysteresis of giant width is observed in the aforementioned dependences. The hysteresis is attributed to the following mechanism: when the crystal under study is heated starting at temperatures T<T _s , some regions occupied by the Pnma low-temperature phase are retained in the $R\bar 3c$ matrix up to the temperature T=350 K.