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1.
We present the result of our accurate measurements of the a- and b-axis resistivity (ρa and ρb), magnetoconductivity Δσ/σ, Hall coefficient RH, and the a-axis thermopower Sa in untwinned YBa2Cu3Oy single crystals in a wide range of doping (6.45≤y≤7.0). The systematics of our data reveals a number of novel 60-K-phase anomalies in the charge transport: (i) temperature dependences of ρa show anomalous overlap below ∼130 K for 6.65≤y≤6.80, (ii) Hall mobility μH shows an enhancement near y?6.65, which is reflected in an anomalous y dependence of σxy, (iii) with decreasing temperature RH shows a marked drop upon approaching Tc only in samples with 6.70≤y≤6.85, (iv) superconducting fluctuation magnetoconductivity is anomalously enhanced near y?6.7, and (v) Hc2 is anomalously reduced near y?6.70. We discuss that the fluctuating charge stripes might be responsible for these anomalies in the charge transport.  相似文献   

2.
Thermopower of the ambient pressure organic superconductor β-(BEDT-TTF)2I3 has been studied. Measurements performed on, respectively, crystals of needle formed morphology and on flake-like crystals with hexagon shape showed equal thermopower results. S was measured along the a-axis as well as along the b′-axis. Marked anisotropy is observed in the entire temperature region studied. The temperature dependence, as represented by dS/dT, is, however, nearly isotropic. On the basis of an analysis of anisotropic thermopower we attribute the isotropic part of S to a term depending on the bond-properties and the anisotropic part of S to the scattering mechanism. The analysis yields transfer integrals of the order of 0.12 eV along both a- and b′-axes.  相似文献   

3.
In this paper, based on a discussion about the Wigner-Yanase-Dyson (WYD) skew information, the measure Fa,α(ρab) for correlations in terms of the WYD skew information is introduced and discussed. The following conclusions are obtained. For a classical-quantum state ρab, Fa,α(ρab)=0 if and only if ρab is a product state; Fa,α(ρab) is locally unitary invariant and convex on the set of states with the fixed marginal ρa; Fa,α(ρab) decreases under local random unitary operation on Hb; For a quantum-classical state ρab, Fa,α(ρab) decreases under local operation on Hb; Lastly, Fa,α(ρab) is computed for the pure states and the Bell-diagonal states, respectively.  相似文献   

4.
We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b(a) = b_0 a + b_e(1-a), where at the earlytime the coupling is given by a constant b_e and today the coupling is described by another constant b_0. We explore six specific models with(i) Q = b(a)H_0ρ_0,(ii) Q = b(a)H_0ρ_(de),(iii) Q = b(a)H_0ρ_c,(iv) Q = b(a)Hρ_0,(v) Q = b(a)Hρ_(de), and(vi) Q = b(a)Hρ_c.The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements,and the Hubble constant direct measurement. We find that, for all the models, we have b_0 0 and b_e 0 at around the 1σ level,and b_0 and b_e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.  相似文献   

5.
Thermopower measurements are reported for two similar amorphous alloys, one with α= ρ-1 dρ/dT<0, the other with α>0. The thermopower is negative and only approximately linear in temperature for both samples. The sign and relative magnitudes of the thermopower are in disagreement with the diffraction model neglecting the energy dependence of the t-matrix as has been widely done to explain the thermopower of amorphous metals with α<0.  相似文献   

6.
Grain boundaries grown by the biepitaxial technique do not show Fraunhofer-type critical current I c vs. magnetic field H a dependences, which are a hallmark of standard Josephson junctions. To clarify the reason for this unusual behavior, we have fabricated asymmetric 45° grain boundaries using the bicrystal technique and analyzed their I c (H a) characteristics. These characteristics crisply show a number of remarkable features, which suggest that due to the particular orientation of these junctions, their I c (H a) dependence is intrinsically non-Fraunhofer. Conventional models, relying on standard tunneling and a superconducting order parameter with s-wave symmetry, do not account for the I c (H a) characteristics observed.  相似文献   

7.
Current-voltage characteristics I(V) with a tunneling character have been observed in selected (“electroresistive”) ceramic manganites R1−xAxMnO3 (R=La, Y; A=Ca, Ba). In this contribution, an I(V) model calculation based on spin-dependent transfer and a bipolar serial array of grains containing deGennes magnetic states are presented. The basic elements of the characteristic are so recovered, including its magnetic field (H) dependence, which in turn allows one to identify this array with a series of spin-dependent tunneling diodes connected in opposition. Besides, we find that the tunneling currents are only significant under space charge bending of the bands near the boundaries, that the electrochemical potential becomes H-field sensitive because of the spin-dependent electron state bandwidth b cos(q(H)/2) and that any slight randomness in the magnetic system will lead to hysteresis effects in the tunneling characteristic.  相似文献   

8.
The thermopower of (TMTSF)2PF6 has been measured along the a-axis as well as along the b-axis. Marked anisotropy is seen in the whole temperature region studied. Close to 100 K, an anomaly is attributed to cross over from dominating one-dimensionality to dominating two-dimensionality. Precursor effects seen in Sa near Tc are attributed to SDW fluctuations. Well below Tc, both thermopower components exhibit typical semiconducting properties.  相似文献   

9.
The transport coefficients of tellurium-doped n-Bi1 ? x Sb x semiconducting alloys (0.07 ≤ x ≤ 0.15) are studied for single-crystal samples in the temperature range 1.5 ≤ T ≤ 40 K and in magnetic fields 0 ≤ H < 20 kOe. The theory developed in this study attributes the specific features in the behavior of the transport coefficients observed in a magnetic field to a strong anisotropy of the electron spectrum and anisotropy in the electron relaxation time. It is found that the dependences of the transport coefficients on the magnetic field for HC 3 can be theoretically expressed through one anisotropy parameter δ, and those for HC 2, by means of several anisotropy parameters, namely, γ, η, ζ, and m 3/m 1. It is established that the anisotropy parameter δ in the n-Bi-Sb semiconducting alloys can be estimated from measurements of the electrical resistivity ρ22(∞)/ρ22(0) ? δ and the Hall coefficient R 12.3(∞)/R 12.3(H → 0) ? δ in a magnetic field HC 3. It is shown that the observed increase in the thermoelectric efficiency by a factor of 1.5–2.0 in the transverse magnetic fields HC 3 and HC 2 originates from the nonmonotonic dependence of the diffusion component of the thermopower Δα22(H)(?TC 1) on the magnetic field. The nonmonotonic dependence of the diffusion thermopower in n-Bi-Sb semiconducting alloys is associated with the strong anisotropy of the electron spectrum, the anisotropy in the electron relaxation time, and the many-valley pattern of the spectrum.  相似文献   

10.
The energy minimum of a linear chain of four hydrogen atomsH4 was investigated in dependence on the inner atomic distancea and the ?surface” distanceb. An energy minimum was obtained for someab. Some comments of methodological character are added.  相似文献   

11.
Hangdong Wang 《Physics letters. A》2009,373(44):4092-4095
In this Letter, the single crystals of Ba5Co5ClO13 were grown by the flux method successfully. Their structure, magnetic and transport properties were studied. A large anisotropy of the magnetic and transport properties has been detected in this compound. Below the TN∼108 K, the magnetic susceptibility exhibits an antiferromagnetic peak in χc and an upturn transition in χab. We suggest that this behavior is consistent with the competition of the ferromagnetic (FM) intra-blocks coupling and antiferromagnetic (AFM) inter-blocks coupling in this compound. The temperature dependence of the resistivity displays a hump in ρab and a kink in ρc around TN, suggesting the strong coupling between the transport and magnetic properties. Above and below the transition, the transport properties in ab plane follow the three-dimensional (3D) variable range hopping (VRH) mechanism.  相似文献   

12.
We present a theoretical study of the length dependence of both conductance and thermopower of organometallic vanadium-benzene molecules (V nBzn+1) sandwiched between magnetic Co(100) electrodes. We show that the molecules with n≥3 are efficient spin filters. Namely, we find that the zero bias conductance of the majority electrons is small and decays exponentially with increasing length of the molecule and is in the tunneling regime while the minority electrons show metallic conductance. We show furthermore that the thermopower strongly depends on the length of the molecules and can even change sign as a function of length and temperature.  相似文献   

13.
The effect of neutron-bombardment-induced atomic disorder on the galvanomagnetic properties of Sr2RuO4 single crystals has been experimentally studied in a broad range of temperatures (1.7–380 K) and magnetic fields (up to 13.6 T). The disorder leads to the appearance of negative temperature coefficients for both the in-plane electric resistivity (ρa) and that along the c axis (ρc), as well as the negative magnetoresistance Δρ, which is strongly anisotropic to the magnetic field orientation (Ha and Hc), with the easy magnetization direction along the c axis and a weak dependence on the probing current direction in the low-temperature region. The experimental ρa(T) and ρc(T) curves obtained for the initial and radiation-disordered samples can be described within the framework of a theoretical model with two conductivity channels. The first channel corresponds to the charge carriers with increased effective masses (~10m e , where m e is the electron mass) and predominantly electron-electron scattering, which leads to the quadratic temperature dependences of ρa and ρc. The second channel corresponds to the charge carriers with lower effective masses exhibiting magnetic scattering at low temperatures, which leads to the temperature dependence of the ρa, c(T) ∝ 1/T type.  相似文献   

14.
The concentration and temperature dependences of the thermopower of composites containing Co nanoparticles embedded in the Al2O n dielectric matrix are investigated. Below the percolation threshold, i.e., in the tunneling conduction region, the absolute values of the thermopower of the composites under investigation are less than those above the percolation threshold. It is revealed that, in the tunneling conduction region, the slope of the temperature dependences of the thermopower changes at a temperature of ~205 K. This can indicate that the thermopower is sensitive to a change in the mechanism of conduction from the Mott law ln(σ) ∝ (1/T)1/4 to a power relation that corresponds to the model of inelastic resonant tunneling through a chain of localized states in the dielectric matrix. The introduction of oxygen in the course of sputtering brings about a decrease in the absolute values of the thermopower; however, the character of variation in the concentration and temperature dependences of the thermopower remains unchanged.  相似文献   

15.
A peak is detected on the dependence of the diffusion-induced thermopower on transverse magnetic field in degenerate semiconducting alloys n-Bi1?x Sbx (0.07≤x≤0.15) doped with tellurium donor impurity. The temperature gradient is directed along the bisector axis C 1 of the monocrystalline sample and the magnetic field is along the triad axis C 3. The electron spectrum of the Bi-Sb alloys under investigation consists of three equivalent ellipsoids with distinctly different effective masses along the axes of the ellipsoid (m /m ). A simple kinetic theory shows that the presence of the peak on the diffusion thermopower is a manifestation of this strong anisotropy in the electron spectrum and of the additive contribution of all three ellipsoids to electron transport. The nonmonotonic dependence of thermopower on the transverse magnetic field makes it possible to determine the electron relaxation time, while the temperature dependence of this relaxation time can be used to separate the relaxation time for electrons scattered from ionized impurities and from acoustic phonons.  相似文献   

16.
Derrida  B.  Douçot  B.  Roche  P.-E. 《Journal of statistical physics》2004,115(3-4):717-748
We calculate the first four cumulants of the integrated current of the one-dimensional symmetric simple exclusion process of N sites with open boundary conditions. For large system size N, the generating function of the integrated current depends on the densities ρ a and ρ b of the two reservoirs and on the fugacity z, the parameter conjugated to the integrated current, through a single parameter. Based on our expressions for these first four cumulants, we make a conjecture which leads to a prediction for all the higher cumulants. In the case ρ a =1 and ρ b =0, our conjecture gives the same universal distribution as the one obtained by Lee, Levitov, and Yakovets for one-dimensional quantum conductors in the metallic regime.  相似文献   

17.
Self-Consistent Field (SCF) and Configuration Interaction (CI) studies are performed on the bending mode of the water molecule using a double zeta plus polarization basis set. The ab initio points are fitted to a three-parameter double minimum potential consisting of a quadratic plus Lorentzian terms. The vibration-rotation energies are then evaluated using the large amplitude Hamiltonian developed by P. R. Bunker and co-workers at various levels of approximations. It is found that the calculated frequencies improve significantly as one proceeds from approximate Hb00(ρ) to rigid bender Hb0(ρ) [P. R. Bunker and J. M. R. Stone, J. Mol. Spectrosc.41, 310–332 (1972)] to semirigid bender Hb0(r, ρ) [P. R. Bunker and P. M. Landsberg, J. Mol. Spectrosc.67, 374–385 (1977)] Hamiltonian. With Hb0(r, ρ), the ab initio calculated bending frequency ν2 differs from the observed value (1595 cm?1) by 30 cm?1 and the barrier height is 12 229 cm?1. It is also shown that ν2 and its first four overtones are better calculated by 45–98 cm?1 when the ab initio potential is used directly instead of the three-parameter analytic potential fitted to ab initio data. Finally, rotation bending energy levels are calculated for v2 ≤ 3 and J ≤ 10 on the basis of a nonrigid bender Hamiltonian of A. R. Hoy and P. R. Bunker [J. Mol. Spectrosc.74, 1–8 (1979)], using the ab initio quadratic force field of P. Hennig, W. P. Kraemer, G. H. F. Diercksen, and G. Strey, [Theor. Chim. Acta47, 233–248 (1978)]. These results show that the accuracy of calculated force constants and frequencies is critically dependent not only on the size of the basis set but also on the number and spacing of the ab initio points used to derive the force field.  相似文献   

18.
The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C6H13O2NHClH2O (termed form II) has been determined using three-dimensional photographic data. This differs conformationally from the hydrochloride derivative (termed form I, Trommel and Bijvoet 1954) reported earlier. The crystal belongs to the orthorhombic space group P212121 with cell dimensions,a=5.87±0.01,b=24.77±0.02 andc=6.85±0.01 ? and four molecules per cell,ρ obs=1.240 g/cm3,ρ cal=1.238 g/cm3,μ for CuKa=32.6 cm−1. Contribution No. 420 from the Department of Crystallography and Biophysics, University of Madras, Madras 600025.  相似文献   

19.
Co–Al2O3 granular films with a narrow distribution in cluster size of Co clusters embedded in Al2O3 matrix were prepared by sequential deposition based on self-organized growth. Resistivity dependence of giant magnetoresistance (GMR) was studied. The GMR takes a maximum of 5.2% at room temperature and 9.4% at 13 K and 5700 Gs when the resistivity of the sample is 4×105–7×105 μΩ cm. The temperature dependence of resistivities and GMR were discussed especially. A temperature dependence of conductance ρ∼exp[T1/(T+T0)] was found, which indicates the dominant conduction mechanism is fluctuation-induced tunneling. A linear relationship of GMR versus T was observed, GMR=akT, in applied magnetic field 5700 Gs. The remarkable character of temperature dependence of GMR should be due to the special microstructure that the clusters are monodispersed in the films.  相似文献   

20.
The thermopower of Andreev interferometers, which are doubly connected loops in which one arm is a superconductor and one arm is a normal metal, oscillates as a function of magnetic field with a fundamental period corresponding to a flux quantum h / 2 e through the area of the loop. While the magnetoresistance of an Andreev interferometer is symmetric with respect to the magnetic field, the thermopower can be either symmetric or antisymmetric, depending on the topology of the sample. The temperature dependence of the thermopower oscillations is nonmonotonic. This nonmonotonic behavior does not appear to be related to the reentrance observed by many groups in the conductance of normal-metal/superconductor (NS) structures.  相似文献   

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