3He Effect on 2D Superfluidity in 3He–4He Mixture Films on Planar Gold

There have been a number of experiments exploring the nature of 2D superfluidity and the configuration of ³He–⁴He mixture films on various substrates. To date, a possible film-structure at T=0 is that of a simple layer model, ³He/superfluid ⁴He/solid-like ⁴He/substrate, in which the submonolayer superfluidity is strongly affected by the coverage of the ³He overlayer. Yet the mechanism is not been fully understood. In this paper, we report a QCM study at 60 MHz for the ³He effect on the superfluidity of mixture films on flat gold, mainly focusing on the anomalous depletion of the temperature dependence of the superfluid density σ _s. In the measurements, we kept the ³He coverage constant (n ₃= 0, 3.6, 7.2, 19.0, 57.2, or 92.8 μmol/m²) and then incrementally added ⁴He. We observed the evolution of the ³He effect on σ _s(T) with increasing ³He coverage; this depletion of σ _s(T) rapidly increases and then saturates near n ₃～1 layer. From the analysis of the linear-temperature region in the plot of the dissipation peak temperature T _p as a function of the superfluid ⁴He coverage n _4s and comparison with previous studies on Mylar and porous gold, we found a universal function for the strength of the ³He effect for all substrates.     

Low-temperature characteristics of Matsushita carbon resistors with and without magnetic fields

The resistance versus temperature (RT) characteristics and magnetoresistance (MR) of 1/8 W nominal 68 Ω and 100 Ω Matsushita carbon resistors of grade ERC-18SG have been measured at temperatures between 8 and 0.05 K, in magnetic fields up to 84kOe (84 × 10⁶/4 π Am⁻¹). In both carbon resistors, the RT behaviour is expressed as R(T) = R₂exp{(T₂/T)^1/2} in the high temperature region and as R(T) = R₄exp{(T₄/T)^1/4} in the low temperature region. These relationships are explained as due to variable-range hopping conduction with and without the changing energy between isolated metallic grains, respectively. Negative and positive MR's have been observed in low and high magnetic fields, respectively. The negative MR increases with decreasing temperature at very low temperatures < 0.1 K. These phenomena are discussed in terms of the theory based on the strong Anderson localization.     

Spin Coherence Time T 2 in Metallic P-doped Si at Very Low Temperature

We report NMR measurements of transverse relaxation rate 1/T ₂ of the ³¹P nuclear spins in metallic Si:P (concentration of dopant P, n=18×10¹⁸ and 56×10¹⁸ cm^?3) at temperatures between 45 mK and 5 K in a magnetic field of 7 T. Above 1.4 K, 1/T ₂ is constant independent of temperature as well as concentration and is determined by magnetic dipolar interaction between the ³¹P and ²⁹Si nuclear spins. As temperature decreases below 1.4 K, 1/T ₂ increases over the dipolar-determined value by an order of magnitude and levels off around 0.6 K. The concentration dependence of 1/T ₂ at low temperatures suggests that 1/T ₂ below 1.4 K is determined by the coupling between the ³¹P nuclear spins. We understand 1/T ₂ at low temperatures originates from the RKKY interaction. We explain the temperature dependence of 1/T ₂ between 0.6 K and 1.4 K by the motional-narrowing expression of 1/T ₂ with a temperature-dependent correlation time of the fluctuating local field due to the RKKY interaction.     

Electronic Inhomogeneity and Possible Pseudogap Behavior of Spin Susceptibility in the Electron-Doped Superconductor Sr0.93La0.07CuO2: 63Cu NMR Study

The magnetic susceptibility, NMR spectra, nuclear spin-lattice relaxation rate (T ₁ ^?1)_α and the echo-decay rate (T ₂ ^?1) of ⁶³Cu were measured for the electron-doped infinite-layer superconductor Sr_0.93La_0.07CuO₂/T _c ^onset = 42.4 K). The results obtained revealed a clear tendency toward frustrated phase separation in this nominally underdoped high-T _c material. Above T _c the ⁶³Cu Knight shift is found to decrease upon cooling giving an evidence for a pseudogap-like decrease of the spin susceptibility. It is shown that unusual anisotropy of the ⁶³Cu Knight shift in the electron-doped CuO₂ layer can be understood as a “compensation effect” between the isotropic hyperfine coupling, mediated by the 4s Fermi-contact and 3d core-polarization exchange interactions, and the anisotropic on-site spin-dipolar hyperfine interaction of the Cu nuclei with the itinerant carriers, whose states near the Fermi energy have a sizeable admixture of Cu(4p_z) and/or Cu(3d_z ²) orbitals.     

The penetration depth of HgBa2CuO4+δ with 0.07 ≤ δ ≤ 0.35

The magnetic penetration depth λ(T) of three HgBa₂CuO_4+δ samples with 0.16 < δ ≤ 0.27 has been determined from the reversible magnetization. The obtained λ follows a BCS-like correlation of 1/λ² ∝ 1?(T/T_c)² over whole measured temperature range in an underdoped sample with T_c ～ 90 K, but deviates significantly from similar fits in an overdoped sample with the same T_c and an optimum doped sample, whose 1/λ² 's depends on T nearly linearly below T_c/2. This asymmetry between the underdoped and overdoped samples suggests that the T-dependence of 1/λ² is affected by doping in a complicated way.     

AC susceptibility study of YBCO

The temperature dependence of ac susceptibility of YBCO bulk samples was measured as a function of ac field amplitude and frequency. Analysis of the temperature dependence of the ac susceptibility near the transition temperature (T _c ) has been done employing the simplified Kim model. We have obtained an empirical function for the penetration field H _p = H _α (1?t) ^β , t = T=T _c . Best fitting to data was obtained with parameters H _α ≈ 6:2 × 10³ A/m and β ≈ 1.50. The experimental value agrees well with the model calculations. In addition, as the frequency increases, the peak temperature (T _p ) shifts to higher temperature. This effect can be interpreted in terms of flux creep. The field dependence of activation energy obtained from the Arrhenius plots for the frequency (f) and (T _p ) can be described as U ∝ (H _ac )^?β′ with β′ ≈ 0:38 for YBCO.     

Hall effect in detwinned single crystals of YBa2(Cu1−x Zn x )3O7 −δin the mixed state

The effect of zinc doping on the mixed-state Hall effect in detwinned single crystals of YBa₂Cu₃O_{7 ?δ} has been studied. We observe a sign reveral of the Hall effect in crystals with a superconducting transition temperature (T _c) as low as 71 K. The Hall conductivity in the mixed state follows theC ₁/H+C ₂ H field dependence. The absolute value of the coefficientC ₁ increases faster than (1–T/T _c) with decreasing temperature.C ₂ increases rapidly asT falls belowT _c. The temperature dependence of the ratioC ₁/C ₂ scales approximately asT/T _c for different levels of zinc doping.     

Effect of gold doping on the superconducting critical temperature and transition width in single-crystal YBa2Cu3Oδ (YBCO)

Single-crystal YBa₂Cu₃O_?δ (YBCO) has been made with some of the copper atoms in the copper-oxygen chains replaced by gold. The samples were made by a flux method. The gold concentration was determined by EDX (energy-dispersive X-ray spectroscopy) as a function of the nominal (i.e., flux) composition. Up to about 4.8% of all the copper atoms can be replaced by gold. The effect of the gold doping on the superconducting transition temperature (T _c ) and the transition width (ΔT _c ) were determined.     

Kinetic Growth Properties of the Interface in Phase-Separated 3He-4He Liquid Mixtures: Crossover Between the Hydrodynamic and Ballistic Regimes

We developed a method to measure the transmission coefficient of sound for the interface between the c- and d-phases of a phase-separated ³He-⁴He liquid mixture at various temperatures and sound frequencies. From the data the kinetic growth coefficient of the interface ξ _ω(T), describing phase-conversion processes at the interface, can be determined.We have extended the experiment down to 6 mK with sound of 9, 14, and 32 MHz. The main specific features observed are as follows: (i) ξ _ω(T) showsa maximum at T _max(ω), (ii) above T _max(ω), ξ _ω(T) decreases with the increase of temperature as ξ _ω(T)=Aω ^5/2/T ³, and (iii) below T _max(ω), ξ _ω(T)decreases with the decrease of temperature and the frequency-dependence seems to disappear. That is, T _max(ω) corresponds to the crossover temperature between the hydrodynamic and ballistic regimes for ξ _ω(T).     

Percolation and electronic properties of superconducting (YBa2Cu3O7−δ )1−x Ag x ceramics and thick films

We present the percolation and electronic properties of (Y₁Ba₂Cu₃O_7?δ )_1?xAg_x compounds in which silver fills the intergranular space without reducing T_c, which remains at 92 ± 1 K. Normal-state resistivity is decreased by up to two orders of magnitude when adding up to 50 wt.% Ag (T _c=87 K), and samples exhibit improved contact resistance, better mechanical properties, and resistance to water. We analyzed the percolation properties of these compounds and found that the critical indicest, s are in agreement with percolation theory, butp _c is higher than expected, probably due to the effect of holes. TheJ _c estimated from magnetization reaches 5 · 10⁴A/cm² (atT = 4.2K,H = 0) and shows enhancement of 15–50% by addition of ～ 10 wt.% Ag, which exists also in samples having a higherJ _c due to preparation conditions (temperature). We present preliminary results on the 2D percolation problem in (Y₁Ba₂Cu₃O[_7?δ )_1?xAg_x samples, obtained by preparing Y₁Ba₂Cu₃O_7?δ thick films using the spin-on technique. Preliminary results show good adhesion but a reduced T_c of Y₁Ba₂Cu₃O_7?δ films compared with bulk samples.     

High Field ESR Study of the New Low Dimensional S=1/2 System: Cu(NO3)2⋅H2O

Cu(NO₃)₂?H₂O is a new S=1/2 system based on transition metal nitrates and contains two-dimensional Cu²⁺ (S=1/2) layers. We studied single crystalline samples by means of high field (HF) ESR and NMR. Cu²⁺ HF-ESR and ¹H-NMR data reveal pronounced spin-spin correlations at temperatures much higher than the antiferromagnetic ordering temperature T _N ～3.6 K. These observations clearly suggest a two-dimensional character of magnetic interactions in Cu(NO₃)₂?H₂O. We discuss the obtained results by considering the possible exchange paths between inequivalent Cu-sites in this compound.     

Spin exchange rate constant for collisions of metastable helium atoms with rubidium atoms

The spin exchange rate constant C _se in the He(2³S₁)-Rb(5²S_1/2) system has been measured for the first time in experiments on the optical orientation of metastable helium atoms in the presence of rubidium atoms. In the temperature interval T = 293–348 K, this value is C _se = (1.8 ± 0.4) × 10^?9 cm³ s^?1. The chemiionization rate constant, which has been simultaneously measured in collisions of these particles, is C _ci = (3.1 ± 0.6) × 10^?9 cm³ s^?1.     

Thermodynamic properties of InP

The emf of an electrochemical cell of the type (?) W, In(l) | ZnCl₂ + KCl + NaCl + InCl | (InP(s) + P(black)), W(+) has been measured in the temperature range 500–600 K. The change in the chemical potential of this cell (Δμ_In=?52.50 + 19.01 × 10^?3 T kJ/mol) corresponds to the reaction In(l) + P(black) → InP(s). The standard enthalpy of formation of InP from solid indium and white phosphorus is determined to be Δ_f H ⁰(298 K) = ?69.3 ± 3 kJ/mol. We have performed thermodynamic analysis of the literature data for the In-P system, with consideration for different phosphorus allotropes.     

Structural, electrical, and optical properties of copper indium diselenide thin film prepared by thermal evaporation method

Stoichiometric compound of copper indium diselenide (CuInSe₂) was synthesized by direct reaction of high-purity elemental copper, indium and selenium in an evacuated quartz ampoule. The phase structure and composition of the synthesized pulverized material analyzed by X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDAX) revealed the chalcopyrite structure and stoichiometry of elements. Thin films of CuInSe₂ were deposited onto organically cleaned soda lime glass substrates held at different temperatures (i.e. 300 K to 573 K) using thermal evaporation technique. CuInSe₂ thin films were then thermally annealed in a vacuum chamber at 573 K at a base pressure of 10^− 2 mbar for 1 h. The effect of substrate temperature (T_s) and thermal annealing (T_a) on structural, compositional, morphological, optical and electrical properties of films were investigated using XRD, transmission electron microscopy, EDAX, atomic force microscopy (AFM), optical transmission measurements and Hall effect techniques. XRD and EDAX studies of CuInSe₂ thin films revealed that the films deposited in the substrate temperature range of 423-573 K have preferred orientation of grains along the (112) plane and near stoichiometric composition. AFM analysis indicates that the grain size increases with increase of T_s and T_a. Optical and electrical characterizations of films suggest that CuInSe₂ thin films have high absorption coefficient (10⁴ cm^− 1) and resistivity value in the interval 10^− 2-10¹ Ω cm influenced by T_s and T_a.     

Thermodynamic properties of (TeO2) n (WO3)1 − n glasses in the range 0–650 K

The heat capacity of (TeO₂) _n (WO₃)_{1 ? n} tellurite glasses with n = 0.75, 0.78, 0.85, and 0.90 has been determined using precision adiabatic calorimetry (6–350 K) and dynamic scanning calorimetry (320–650 K), and the thermodynamic characteristics of their glassy state and devitrification have been evaluated. The experimental heat capacity data have been used to calculate the standard thermodynamic functions of the glassy and supercooled liquid states at temperatures from T → 0 to 650 K: heat capacity C _p ⁰ (T), enthalpy H ⁰(T) — H ⁰(0), entropy S ⁰(T), and Gibbs function G ⁰(T) — H ⁰(0). The character of structural heterodynamicity of the tellurite glasses has been assessed by processing the low-temperature heat capacity data using the multifractal formulation of the Debye theory of heat capacity of solids. The composition dependences of the devitrification temperature and 298.15-K thermodynamic functions have been obtained, and the 298.15-K C _p ⁰ of tellurium dioxide has been estimated. The thermal and thermodynamic properties of the (TeO₂) _n (WO₃)_{1 ? n} tellurite glasses have been compared with those of (TeO₂) _n (ZnO)_{1 ? n} glasses.     

Effect of Short-Range Ferromagnetic Ordering on the Electrical Transport Properties of (La0.9Bi0.1)2/3Ca1/3MnO3 in the Magnetic Field up to 40 T

The temperature and magnetic field dependence of the resistance of polycrystalline sample (La_0.9Bi_0.1)_2/3Ca_1/3MnO₃ was investigated in pulsed high magnetic field up to 40 T over a wide temperature region. In order to describe the magnetotransport properties of the sample, an extended Mott hopping conduction model was employed. Instead of B _J (gμ _B J(T)B/k _B T) in the ferromagnetic (FM) state and $B_{J}^{2}(g\mu_{B}J(T)B/k_{B}T)$ in the paramagnetic (PM) state, the magnetic field dependence of the resistance could scale nicely with the Brillouin function B _J (gμ _B J(T)B/k _B T) in all the given temperatures (above and below the Curie temperature T _c ). The deduced value of the average spin moment J(T) increases with the increasing of the temperature and reaches the maximum value (～35) around T _c . The large value of J(T) indicate the presence of magnetic clusters in the sample which is induced by the short-range ferromagnetic ordering, however, compared to the un-doped compound La_2/3Ca_1/3MnO₃, the value of J(T) is much smaller, which might be ascribe to the location of the 6s² lone pair electrons of Bi³⁺ ions in the sample (La_0.9Bi_0.1)_2/3Ca_1/3MnO₃.     

Studies on Low-Field and Room-Temperature Magnetoresistance in La2/3(Ca1−x Sr x )1/3MnO3 Perovskites

The polycrystalline perovskites La_2/3(Ca_1?x Sr _x )_1/3MnO₃ (x=0,0.2,0.4,0.6,0.8,1) were successfully prepared by a modified method of solid-state reactions, in which the ingredient mixture with ethanol as a liquid milling medium to form suspension was milled by high-energy ball milling for 10 h and sintered in air at 1400 °C for 10 h. The microstructure, electrical transport, and low-field magnetoresistance (LFMR) of the perovskites were investigated to study the room-temperature magnetoresistance (RTMR) behavior. The results reveal that the metal-to-insulator transition temperature (T _MI) increased with increasing doping level x, and the peak values of the magnetoresistance (MR) near T _MI dropped with the more Ca²⁺ substituted. A single-phase La_2/3Ca_1/3MnO₃ showed T _MI at 263 K and the peak MR of 23 % in the applied field of 3 kOe near T _MI. The LFMR effect at room temperature could be obtained by controlling the doping Sr²⁺-substituted Ca²⁺ level. When x=0.29, transition temperature (T _MI) was 305.30 K, and the MR effect was recorded up to 12.9 % at 298.55 K and 3 kOe. Finally, the possible mechanism is discussed.     

Determination of the surface tension of liquid stainless steel

The surface tensions (σ) and temperature dependencies (dσ/dT) of several commercial 4-series ferritic stainless steels have been measured using the sessile drop technique on an Al₂O₃ plate over the temperature range 1789 to 1883 K in an atmosphere of high purity (P _{O 2} < 10^?19 MPa) argon gas. Precise densities of liquid stainless steels have also been obtained using the modified sessile drop method in order to calculate accurate values of the surface tension. The surface tensions of liquid stainless steels decreased markedly with increasing sulphur concentration in the steels. The variation of surface tensions of liquid stainless steels can be described by the following equation σ = 1790 ? 182 ln (1 + 260a _S) (mN/m) when only S is considered or σ = 1820 ? 304 ln (1 + 383a _O) ? 182ln (1 + 260a _S) (mN/m) when both S and O are considered. The equations apply to the following compositional ranges: mass%O = 0.0022–0.0064, mass%S = 0.0008–0.05. The temperature coefficient of the surface tension (dσ/dT) of liquid stainless steel was found to change from negative to positive at a sulphur concentration of about 30 mass ppm in the steel. Nitrogen was found to have little effect on the surface tension of liquid stainless steel.     

Combined effect of substrate temperature and laser energy density on laser ablated BiFeO3 thin films

Bismuth ferrite (BiFeO₃) thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates by laser ablation deposition at various substrate temperature (T _sub) and laser energy density (D _L). The combined effect of T _sub and D _L on crystalline phase, preferential orientation and surface morphology of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T _sub and D _L simultaneously. BiFeO₃ thin films with single phase could be prepared at T _sub-D _L of 893 K?1 J/cm², 943 K?2 J/cm² and 963 K?3 J/cm², respectively. Film deposited at T _sub = 963 K and D _L = 3 J/cm² exhibited better ferroelectric property due to the combination of high (111) preferential orientation, dense surface morphology and less Fe²⁺ content.     

Superconducting state in M3C60: Strong vs. weak coupling

The superconducting state in the doped fullerenes is due to strong coupling (e.g.,λ≈2.1 for Rb₃C₆₀) to low-frequency intramolecular modes Ω?Ω _L ≈250 cm^?1 (Ω≡〈Ω²〉^1/2). The analysis is based on an equation describingT _c for any strength of the coupling and on recent isotope effect and NMR data.