Normal-state Transport Properties Research Articles

The phase diagram of Pr xY 1- xBa 2Cu 3O 7-δ - oxygen depletion versus Pr doping

We investigated the Pr xY 1- x Ba 2Cu 3O 7-δ system, system, varying both the Pr and oxygen content and measured the resistivity as function of composition and temperature. Including literature data on T N , a phase diagram was constructed, which shows the variation of T c and of T N in the ( x , δ ) plane. In Pr xY 1-xBa 2Cu 3O 7-δ , one finds close similarity between the dependence of the normal state transport properties: T c , T N , ϱ( T), R H ( T) etc., on doping by Pr and “doping” by oxygen vacancies.

The effect of oxygen depletion on the in-plane resistivity and Hall coefficient of crystalline thin films of YBa 2(Cu 1−xZn x) 3O 7−δ

The different effects of in-plane or out-of-plane doping on the normal state transport properties of fully oxygenated YBCO are fairly well established. Little is known, however, about the effects of in-plane impurities on oxygen deficient or underdoped YBCO. To address this issue we report measurements of R H(T) and ϱ ab(T) of laser ablated crystalline thin films of YBa 2(Cu 1−xZn x) 3O 7−δ with 0 ≤ x ≤ 0.02 and 0 ≤ δ ≤ 0.28, and discuss our results in relation to recent specific heat measurements by Loram and co-workers.

Out-of-plane transport in thick single-crystal YBa 2Cu 3O 7−δ

A 2.5-mm thick single-crystal YBa 2Cu 3O 7−δ was successfully grown by a modified Czochralski technique, and various transport properties were measured and analyzed. Since the sample is sufficiently thick along the c axis, the out-of-plane data were measured as precisely as the in-plane data. The measured c-axis Hall coefficient is negative and essentially independent of temperature, while the c-axis Seebeck coefficient is positive and roughly proportional to temperature. The result strongly suggests that the normal-state transport properties of YBa 2Cu 3O 7 are, at least qualitatively, consistent with the uniform RVB theory. This also indicates that the electronic states for YBa 2Cu 3O 7 exhibit a highly two-dimensional nature, even if YBa 2Cu 3O 7 has the least anisotropy between in- and out-of-plane resistivities among high- T c cuprates.

Scaling of the Hall coefficient and resistivity in underdoped and overdoped RBa2Cu3Oy films.

We have studied the normal-state transport properties, the resistivity ρ(T), and the Hall coefficient RH(T) on two sets of samples of RBa2Cu3Oy compounds (R=Y,Sm) away from optimal doping. In the overdoped regime, RH(T) obtained from Ca-doped SmBa2Cu3Oy shows a saturation at high temperature. While RH(T) decreases with T at low temperature, it becomes temperature independent when the temperature exceeds a certain value T*H. This characteristic T*H decreases with doping, and is only visible in our experimental temperature range when the samples are sufficiently doped. By assuming a universal functional form for all doping levels, the temperature dependence of the Hall coefficient can be scaled. Another characteristic temperature T*ρ can be seen from the resistivity data in the underdoped regime, obtained from the oxygen-deficient YBa2Cu3Oy samples. Above T*ρ, ρ(T) increases almost linearly with T, whereas below, it deviates from the linear behavior. We discuss the relationship between these two characteristic temperatures T*H and T*ρ for different doping levels. For the underdoped samples, the resistivity is fitted well by the relation ρ(T)≊aRH(T)T2+b.

Charge excitation and the normal-state transport properties in the flux-binding phase of the t-J model.

Elementary excitations are discussed in the flux-binding phase [Weng, Sheng, and Ting, Phys. Rev. B 49, 607 (1994)] of the [ital t]-[ital J] model. It is shown that the density and current constraints in the gauge-theory description will dramatically modify the charge excitations. An effective Lagrangian for the normal state of the flux-binding phase is derived, and based on it the transport properties are studied. We find that the resistivity is linearly temperature dependent with a relaxation rate [h bar]/[tau][congruent]2[ital k][sub [ital B]][ital T], and the Hall coefficient involves a second relaxation rate with the cotangent Hall angle following a [ital T][sup 2] law. Furthermore, the thermopower exhibits a strong doping dependence. All these features are in good agreement with the transport measurements of the high-[ital T][sub [ital c]] copper oxide compounds.

Normal-state transport properties of fullerene superconductors

The normal-state transport properties of alkali-metal-doped fullerene crystals are explored. The Hall effect has been measured in KxC60 from room temperature toT c . The electrical resistivityρ for K3C60 and Rb3C60 has been measured over a wide temperature range (20–650 K), and notable differences are observed for the materials at both low and high temperatures. The electrical resistivity of Rb3C60 has been measured in hydrostatic pressures up to 9 kbar. The resistivity is highly pressure sensitive. The transport results give an insight into the normal-state conduction mechanism and thus have consequences for the superconductivity mechanism.

Velocity renormalization near the Mott transition in a perfectly ordered lattice (II)

We consider a medium-density electron gas, near the Wigner-Mott transition, immersed in a medium with a background dielectric constant ε 0( q, ω)that is very large at q = 0, ω = 0, but falls sharply with increasing q and/or ω. We consider the dependence of the screening parameter for state k on the energy of this state. We find that the electronic velocity is enhanced considerably at k = k F , somewhat similar to the enhancement found by Lindhard in 1954 for an unscreened electron gas. We use parameters applicable to high- T c cuprates. We find that the maximum of v(k) around k F is very sharp, the width being a few meV, somewhat smaller than the frequency at which the dielectric constant ε 0( q, ω) drops. We relate this velocity peak to the normal-state transport properties of the cuprates and several other systems, and to the superconductivity. We point out specific experiments that suggest a large enhancement of v F.

Charge dynamics in (La, Sr)2CuO4: from underdoping to overdoping

The normal state transport properties (resistivity, Hall effect) of La2−xSrxCuO4 have been studied over wide ranges of Sr doping and temperature. The familiar T-linear resistivity and the strongly T dependent Hall effect RH(T) are found only near the optimal hole concentration (x ≈ 0.15–0.18). The charge dynamics changes significantly in the non-superconducting overdoped range with RH(T) becoming constant above a characteristic temperature T*, and p(T) ∝ Tn (n > 1; n ≈ 1.5±0.1). The temperature scale T*, decreasing with increasing hole concentration, provides a link between transport and magnetic properties.

Superconducting/non-superconducting phase boundary in the low temperature tetragonal phase of (La,RE)-Sr-Cu-O

From measurements of the structural, superconducting and normal state transport properties of rare earth doped La2−xSrxCuO4 we find a phase boundary between a superconducting and a non-superconducting state of the low temperature tetragonal phase. This phase boundary is determined by the magnitude of the buckling of the Cu-O-Cu bonds in the CuO2 layers, suggesting the importance of spin-orbit coupling for the electronic properties of these compounds.

Normal-state effective action for the flux-binding phase of the t-J model

Abstract The normal-state transport properties are studied for the flux-binding phase of the t-J model, within the framework of gauge theory. We find that the resistivity is linearly temperature dependent with a relaxation rate h /τ ⋍ 2 k B T . We also show that the Hall coefficient involves a second relaxation rate and the contangent Hall angle follows a T2 law. Furthermore, the thermopower exhibits a strong doping dependence. All these features are in good agreement with the transport measurements of the high-Tc copper oxide compounds.

Superconducting fluctuations: paraconductivity, excess Hall effect and magnetoconductivity in 2223-BiSrCaCuO thin films

We report a detailed study of the influence of thermodynamic fluctuations of the superconducting order parameter on various normal-state transport properties in 2223-(Bi,Pb)SrCaCuO thin films at temperatures near the superconducting transition. Measurements of the electrical resistivity, the magnetoresistance and the Hall effect were analyzed with regard to fluctuation contributions, using theories for 2-dimensional, layered superconductors. We obtained a consistent set of parameters, which fit all magneto-transport measurements above 118 K, but observed a remarkable enhancement of both excess Hall effect and negative magnetoconductivity closer to T c , whereas the zero-field fluctuation conductivity follows the theoretical predictions down to 110 K. No significant contributions from the indirect (Maki-Thompson) fluctuation process were found.

Hall effect measurements on YBa2Cu 3O7− δ-films with different oxygen defficiency

We have investigated the puzzling normal-state transport properties of epitaxial YBa 2Cu 3 O 7− δ thin films. The Hall coefficient R H( B, T, δ) and the resistance ϱ xx (B,T,δ) were measured for an oxygen deficiency δ from 0.05 to 0.5. The temperature dependence of the cotangent of the Hall angle cot ϑ H = ϱ xx (T)/(R H(T) B z) fits the relation cot ϑ = αT 2 + C. The value of α at B=1 Tesla for the film with the highest critical temperature T c is α=40×10 −3 K −2. This is in good agreement with reported data.

Superconducting and normal-state transport properties in bulk YBaCuO, doped with Zn

We have investigated the resistivity, the Hall number, n H, and the Hall conductivity, σ H, in bulk YBa 2 (Cu 1−xZn x) 3O 7−δ within the range of Zinc content 0< x<0.06. The magnetic field values were up to 5 T and the temperature range 20 K–300 K. The superconducting transition temperature Tc, as well as, the slope of the normalized resitivity in the normal-state decrease with increasing Zn concentration. The T 3 dependence of σ H 1, with a change of the slope around 230 K–240 K is correlated with the T-dependence of the carrier concentration.

Transport properties of YBaCuO and BiSrCaCuO thin films in the thermodynamic fluctuation range

Thin films of YBaCuO have been fabricated by pulsed-laser deposition in oxygen atmosphere on MgO substrates. Films of the 2223-phase of BiSrCaCuO, stabilized by Pb-addition in the ceramic targets, were prepared by DC-magnetron sputtering. The effect of thermodynamic fluctuations of the superconducting order parameter on the normal state transport properties was investigated by measurements of the electrical resistivity, the magnetoresistance and the Hall effect. Analyzing the results in terms of Aslamazov-Larkin and Maki-Thompson theories and their extensions for 2-dimensional, layered superconductors, we obtain a consistent set of parameters from which the c-axis coherence lengths ξ c(0) = 1.5 A ̊ in YBaCuO and ξ c(0) = 1.7 A ̊ in 2223-(Bi,Pb)SrCaCuO are deduced. A significant contribution from the Maki-Thompson process was found in YBaCuO, but no such effects in the (Bi,Pb)SrCaCuO films.

Theory of normal and superconducting properties of fullerene-based solids

Recent experiments on the normal state and superconducting properties of fullerene-based solids are used to constrain the proposal theories of the electronic nature of these materials. In general, models of superconductivity based on electron pairing induced by phonons are consistent with electronic band theory and analyses of the measured normal state transport properties. The experiments on normal state transport properties also yield estimates of the parameters characterizing these type II superconductors. It is argued that, at this point, a ‘standard model’ of phonons interacting with itinerant electrons may be a good first approximation for explaining the properties of the metallic fullerenes.

Anisotropic transport properties of single-crystal La2-xSrxCuO4: Evidence for the dimensional crossover.

The anisotropic normal-state transport properties, resistivity and thermopower, are investigated for high-quality single crystals of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ in the compositional range 0.10\ensuremath{\le}x\ensuremath{\le}0.30. The results indicate that charge transport in the material with superconducting compositions is two-dimensional. A crossover from two to three dimensions is observed at high temperature or on entering the nonsuperconducting overdoped region.

Electron-phonon coupling in high temperature superconductors: The connection to superconducting behavior

Abstract The results of recent calculations of the frequency, linewidths, and coupling strengths to carriers on the Fermi surface for several phonons in La1.85Sr0.15CuO4 (LSCO) [our work] and YBa2Cu3O7 (YBCO) [by the Stuttgart group] are discussed and related to experiment. The estimates of the electron-phonon coupling constant are X = 1.35 for LSCO based on 11 phonons, and λ = 1.7 for YBCO based on 17 phonons. These coupling strengths are large enough to make the electron-phonon interaction a central feature in normal state transport properties and a likely candidate for the pairing mechanism for high temperature superconductivity. The strong coupling arises from features that are generic in the high temperature superconducting cuprates: a modest (certainly not large) density of states at the Fermi level which results in weak screening; a confinement of the metallic electrons to layers separated by dielectric regions, which further weakens screening and results in Madelung-like contributions to electron-phonon matrix elements; the site energies of the Cu d states and the O p states are roughly equal, leading to strong hybridization and highly metallic bands at the Fermi level.

Normal state transport properties in superconducting oxides RBa2Cu3O7- delta (R=Y, Gd, Sm, Nd, and Dy)

The resistivity, Hall coefficient, magnetoresistance and thermoelectric power of the sintered superconducting oxides RBa2Cu3O7- delta (R=Y, Gd, Sm, Nd and Dy) have been measured in the temperature range 80 to 300 K. It is observed that the superconducting transition temperature does not change upon replacing Y by rare earth ions. The resistivity and thermoelectric power increases with temperature increase in the normal state in all the samples. A correlation between the Hall coefficient and thermoelectric power, along with the assumption that the holes introduced in the top full band by the doping of oxygen atoms are the current carriers, reveals the effective mass of the carriers to be temperature dependent. The temperature variations of the resistivity, Hall coefficient and thermoelectric power have been explained well by the temperature-dependent effective mass of holes and hole-phonon scattering. The concentration, mobility, effective mass and Fermi energy of carriers have been calculated.

Doping dependence of normal-state transport properties in La- and Pb-doped Bi2Sr2CuOy.

We report measurements of the electrical resistivity, thermoelectric power, and Hall coefficient on La- and Pb-doped ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CuO}}_{\mathit{y}}$ compounds as a function of temperature. Both insulating and overdoped nonsuperconducting-metal samples have been obtained. Analysis of the electrical resistivity in the insulating region suggests that the conduction is governed by a variable-range-hopping mechanism in the low-temperature region. As the system changes from a superconductor to an overdoped nonsuperconducting-metal, the resistivity undergoes a change from a linear temperature dependence to a power-law temperature dependence with exponent n\ensuremath{\sim}1.5. This n\ensuremath{\sim}1.5 behavior occurs over a wide temperature range. Remarkable changes associated with the insulator--superconductor-- nonsuperconducting-metal transition are also observed both in the thermoelectric power and the Hall coefficient. A significant difference is that the thermoelectric power becomes negative at the higher doping level, while the Hall coefficient remains positive. We explain the experimental results from a two-carrier model by assuming that the Cu 3${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$ electrons undergo a change from a localized state to a partially delocalized state with an increase in the number of dopant O 2p holes.

Crystal Growth and Transport Properties of Ba-Doped Bi(Pb)2Sr2Ca2Cu3Oy Compounds

Ba-doped Bi(Pb)2Sr2Ca2Cu3Oy compounds with several different Ba content have been prepared by sintering method, and their transport properties in normal state and superconducting mixed state were measured in detail. The results of the resistance measurements showed a slight increase of transition temperature by Ba doping. A limited small amount of Ba atom was contained into the layered structure of 2223 phase in spite of large nominal addition. With increasing nominal Ba content, Ba-rich impurity phase appears but the 2223 layered crystal still grows more clearly and in larger scale. The growth of the Ba-rich impurity phase seems to assist the growing of the 2223 layered phase finely.