Transport properties in single phase superconductor Ba2YCu3O9-δ

The electrical resistivity and the thermopower are measured on the single phase superconductor Ba₂YCu₃O₉-δ (δ=2.1). The results indicate that the temperature dependences of the resistance and thermopower exhibit typical metallic behaviour, and the sample conducts via electrons at high temperatures. The behaviour of the thermopower can be described with Mott's semi-classical model. The specific heat of electrons in normal state has been estimated 780mJ/K·mole at 200K, i.e. γ=3.9mJ/K²·mole. Unusual phonon-drag effect is observed above the superconducting transition temperature T_c. Below T_c, the electrical resistivity and the thermopower all drop to zero corresponding to a superconducting ground state.     

Prediction of Re ɛ fromK 13 decays in an extended cabibbo model

With the help of an extended Cabibbo model for the weak hadronic vector current which includes the 10 and ¯10 representations to account for possibleΔS=-ΔQ transitions, a prediction is made for the quantity (1-¦x¦²)/¦1?x¦² wherex=A(K⁰→π^üe^?¯v)/A(¯K⁰→π^üe^?¯v) using the experimental branching ratio Γ(K^?→ π⁰e^?¯v/Γ(K _L ⁰ →π^üe^?¯v). From the known charge asymmetry in the decay of the long lived kaon one then obtains Re?.     

Measurement of the ratio axial vector to vector coupling constant ¦g 1/f 1¦ in Λ→p e − ¯v decay

In a stoppingK ^? exposure of the Saclay 81 cm hydrogen bubble chamber, we have obtained a sample of 352 kinematically determined Λ→pe ^?¯v dacays. From the electron-neutrino angular distribution of these events, we find the ratio of the axial vector to vector coupling constants ¦g ₁/f ₁¦=0.74 _?0.09 ^+0.12 . This result is in good agreement with Cabibbo's theory. The method of analysis is insensitive to the relative strength of weak magnetism.     

Heavy fermion behaviour of the nonmagnetic CeCu4Al compound

We present measurements of the temperature dependence of the electrical resistivity, the thermopower and the specific heat of the hexagonal compound CeCu₄Al. At high temperatures, the electrical resistivity is characterized by a nearly temperature independent behaviour, followed by a continuous increase below 100K. No maximum has been found down to 1.7 K. The thermopower shows a positive maximum at about 30 K. As in CeCu₆ no negative values are observable in the range from 4.2 K up to a room temperature. The specific heat data between 7 and 15 K reveal a γ value around 280 mJ mol^-1 K^-2. Below this temperature range the specific heat c_p/T shows a rapid rise and crosses the value of 1 J mol^-1 K^-2 at about 1.45 K.     

C-axis thermoelectric transport in low stage SbCl5 graphite intercalation compounds

c-axis thermal conductivity, electrical resistivity and thermopower measurements performed on stages-2, 3 and 4 SbCl₅-graphite intercalation compounds in the temperature range 3 < T < 300 K are reported. Contrary to the electrical resistivity and thermopower data, the temperature variation of the thermal conductivity is qualitatively different from that previously observed on other intercalation compounds.     

Structure-mediated transition in the behavior of elastic and inelastic properties of beach tree bio-carbon

Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T _carb ranging from 600 to 1600°C have been studied. The dependences E(T _carb) and δ(T _carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, ΔE ～ AΔT _carb and Δδ ～ BΔT _carb, with A ≈ 13.4 MPa/K and B ≈ ?2.2 × 10^?6 K^?1 for T _carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ ?3.0 × 10^?7 K^?1 for T _carb > 1000°C. The transition observed in the behavior of E(T _carb) and δ(T _carb) at T _carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T _carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T _carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature.     

Magnetotransport parameters of La0.67Ca0.33MnO3 films grown on neodymium gallate substrates

Weakly mechanically stressed 40-nm-thick La_0.67Ca_0.33MnO₃ films have been grown coherently on a (001)NdGaO₃ substrate by laser evaporation. The electrical resistivity ρ of the La_0.67Ca_0.33MnO₃ film reaches a maximum at a temperature T _C ≈ 255 K. At temperatures below 0.6T _C, the temperature dependences of ρ are well approximated by the relation ρ = ρ_def + C ₁ T ² + C ₂ T ^4.5, in which the first term on the right-hand side accounts for the contribution of structural defects to electrical resistivity, and the second and third terms stand for those of the electron-electron and electron-magnon interactions, respectively. The parameters ρ_def ≈ 1 x 10^?4 Ω cm and C ₁ ≈ 7.7 × 10^?9 Ω cm K^?2 do not depend on temperature and magnetic field H. The coefficient C ₂ decreases with increasing H to reach about 4.9 × 10^?15 Ω cm K^?4.5 at μ₀ H = 14 T.     

Kinetic effects in manganites La1 − x Ag y MnO3 (y ≤ x)

We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La_{1 ? x} Ag _y MnO₃ (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρ_FM(T) = ρ₀ + AT ² + BT ^4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.     

Transport properties of CeCu6 single crystals

The electrical resistivity ? and the thermoelectric power of CeCu₆ single crystals are strongly anisotropic. The inverse of the temperature of the Kondo resistivity maximum (T_max) roughly scales the linear temperature coefficient B of ? as well as the residual value (?₀ ÷ B ÷ 1/T_max). Along the [1 0 0] direction ? follows a T² Fermi-liquid law between 30 and 90 mK. The thermoelectric power is positive over the investigated temperature range (1–300 K) and shows two contributions.     

新型超导体MgB2的热电势和电阻率研究

测量了MgB₂的热电势和电阻率与温度的依赖关系.在100K—300K区间,热电势呈近似线性温度依赖关系,其斜率为正,表明载流子为空穴型且与能带贡献的图像相一致.与此对应,在此温区电阻率呈T²依赖关系.在100K以下,热电势和电阻率各自转变了其高温区的温度依赖关系.热电势在超导转变温度T_c(零电阻366K)到100K间有一宽峰,具有声子曳引峰的特征,表明电子-声子相互作用很强.估算了一些重要的参数,如带米能E_F、能带宽度 关键词： 新型超导体 热电势 电阻率     

Correlation between transport properties and quasielastic linewidths of Ce and Yb compounds with unstable 4f-shell

From an analysis of available data it is shown that there is experimental evidence for a rather general correlation of electrical resistivity, ϱ, and thermopower with the quasielastic linewidth of the neutron spectra, Γ_QE, for intermetallic Ce- and Yb-compounds with an unstable 4f-shell. At high temperatures, k_BT > Γ_QE, the 4f-contribution to the resistivity, Δϱ, scales with Γ⁻¹_QE. For Ce-compounds, which show a resistivity maximum, the measured strong temperature dependence of Γ_QE corresponds to the temperature dependence of the resistivity above the resistivity maximum over a few hundred K. Empirical expressions for resistivity and thermopower are presented, which not only yield the observed correlation for k_BT > Γ_QE, but which also describe the low temperature decrease of the two quantities: Fits for the resistivities and the thermopowers of a large number of Ce- and Yb-compounds are is very good agreement with the data over a large range of temperatures. The correlation as well as the empirical expressions for resistivity and thermopower are discussed within a model of M. Weger, which has recently been proposed to account for the so called “resistivity saturation” observed in materials with narrow bands.     

P–V–T equation of state of rhodium oxyhydroxide

A high pressure X-ray diffraction study of RhOOH was carried out up to 17.44?GPa to investigate the compression behavior of an oxyhydroxide with an InOOH-related structure. A fit to the third-order Birch–Murnaghan equation of state gave K₀?=?208?±?6?GPa, and K′?=?9.4?±?1.3. The temperature derivative of the bulk modulus was found to be ?K/?T?=??0.06?±?0.02?GPa K^?1. The refined parameters for volume thermal expansion were α₀?=?2.7?±?0.3?×?10^?5 K^?1; α₁?=?1.7?±?1.1?×?10^?8 K^?2 in the polynomial form (α(T)?=?α_0?+?α₁(T?300)). Our results show that RhOOH is very incompressible, and has a higher bulk modulus than other InOOH-structured oxyhydroxides (e.g. δ-AlOOH, ε-FeOOH, and γ-MnOOH).     

Temperature dependence of the contribution to the transport coefficients of nearly ferromagnetic metals from electron-paramagnon scattering

We present calculations of the temperature dependence of the contribution from electron-paramagnon scattering to the electrical and thermal resistivity of a simple model of a nearly ferromagnetic metal. The purpose of the work is to explore the behavior of these quantities when the temperature is the order of or greater than the spin fluctuation temperature T_sf. As the temperature T is raised from zero through T_sf, the electrical resistivity varies more slowly with temperature than the T² law characteristic of the regime T?T_sf. When T?T_sf, the electrical resistivity becomes proportional to T, although this asymptotic behavior is approached very slowly. The Lorenz number rises monotonically with temperature, and appears to approach the ideal Sommerfeld value when T?T_sf, although this limit is also approached slowly.     

First observation of a particle-antiparticle asymmetry in the decay of neutral kaons into π0π0

CP violation has been observed as a time-dependent rate asymmetry between the decays ${?erline K}^0 ?ghtarrow ?^{0} ?^{0}$ and K⁰ → π⁰π{0}, where the neutral kaons are produced with definite and individually known strangeness in ${?r p}p ?ghtarrow{?erline K}^0 K^+?^- $ or p?p → K⁰ K^? π⁺. A special technique for the data analysis has been developed. The values obtained for ?₀₀ and ¦ η₀₀¦ are in agreement with those of previous measurements of CP violation.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

In-situ X-ray diffraction study on β-CrOOH at high pressure and high-temperature

ABSTRACT

High pressure hydrous phases with distorted rutile-type structure have attracted much interest as potential water reservoirs in the Earth’s mantle. An in-situ X-ray diffraction study of β-CrOOH was performed at high pressures of up to 6.2?GPa and high-temperatures of up to 700?K in order to clarify the temperature effect on compression behaviors of β-CrOOH. The P-V-T data fitted to a Birch–Murnaghan equation of state yielded the following results: isothermal bulk modulus K_T0?=?191(4)?GPa, temperature derivative (?K_T/?T)_P?=??0.04(2)?GPa?K^?1, and volumetric thermal expansion coefficient α?=?3.3(2)?×?10^?5?K^?1. In this study, at 300?K, the a-axis became less compressible at pressures above 1–2?GPa. We found that the pressure where the slopes of a/b and a/c ratios turned positive increased with temperature. This is the first experimental study indicating the temperature dependence of the change in the axial compressibility in distorted rutile-type M³⁺OOH.     

Spin-lattice relaxation of the Vk-center in LiF

The angular and temperature dependences of the spin-lattice relaxation (SLR) rate of V_k-centers in LiF doped with Mg or Ag have been investigated. In the temperature interval 4.2–100 K the results can be fitted by the formula $\text{τ}{}^{\mathrm{?1}}\text{= A(θ)T + Be}{}^{\mathrm{<mtext>?\Delta </mtext><mtext>T</mtext>}}$ with A(0°) = 0.11 sec^?1K^?1, A(90°) = 1.3 sec^?1K^?1, B = 3 × 10⁵sec^?1 and Δ = (175 ± 15)K.A mechanism for the SLR is considered, assuming the modulation of the hyperfine interaction by phononinduced transitions between the ground and excited states of the resonant molecular vibrations of the V_k-center. This mechanism is found to explain the value, the temperature dependence and the isotropy of τ^?1 in the interval T = 20–100 K.The one-phonon SLR mechanisms of the V_k-center in the T < 10 K region are discussed.     

Effect of electron irradiation on the structure and properties of the MgB2 superconductor

This paper reports on the results of an investigation into the effect of irradiation of the Bardeen-Cooper-Schriefer superconductor MgB₂ by electrons with a mean energy ē ～ 10 MeV at low doses (0 ≤ Φt ≤ ～5 × 10¹⁶ cm^?2) on the lattice parameters, the intensity and width of diffraction lines, the superconducting transition temperature T _c , and the temperature dependence of the resistivity ρ(T) in the normal state. The results of structural investigations have revealed regularities in the defect formation in the magnesium and boron sublattices of the MgB₂ compound as a function of the electron fluence. At the initial stage, irradiation leads to the formation of vacancies, originally in the magnesium sublattice and then in the boron sublattice. For fluences Φt ≥ ～1 × 10¹⁶ cm^?2, vacancies are formed in both sublattices. The evolution of the electrical and physical properties [T _c , ρ_{273 K}, residual resistivity ratio RRR = ρ_{273 K}/ρ_{50 K}, parameters of the dependence ρ(T)] under electron irradiation is in agreement with the regularities revealed in the formation of radiation-induced defects in the crystal lattice of the MgB₂ compound.     

The resistivity of fine platinum wires

We have measured the resistivity of pure platinum wires ranging in diameter from 16 mil to 0.3 mil in the temperature range 1.2 to 4.2°K, and observed size-dependent deviations from Matthiessen’s rule. The temperature dependent portion of the resistivity is dominated in this temperature range by a term of the formAT ², whereA increases from about 12×10^?12 Ω cm/°K² for the thickest wires to 18×10^?12 Ω cm/°K² for the thinnest ones. There is an additional resistivity contribution which appears to increase more rapidly thanT ⁵, and which also evidences some increase with decreasing wire diameter. The observed deviations from Matthiessen’s rule display temperature and size variations consistent with the theory ofBlatt andSatz, and the magnitude of the deviations can be accounted for by this theory taking into account only that portion of the electrical resistivity produced by electron-phonon scattering. Thus the data are consistent with arguments suggesting that interband electron-electron scattering does not lead to size-dependent deviations from Matthiessen’s rule.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.