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A procedure for determining the electrical resistivity of anisotropic materials is presented. It offers several improvements to the well-known Montgomery method. One improvement, in particular, is the ability to obtain the electrical resistivity for all three axes of an orthorhombic crystal analytically, rather than using the iterative approach suggested by Montgomery for the third axis. All necessary equations are derived and their application in determining the tensor components of the electrical resistivity is explained in detail. Measurements on isotropic specimens were executed in order to test the foundations of the method. Measurements on anisotropic samples are compared with measurements obtained by using the standard four-probe method, revealing good agreement. [ABSTRACT FROM AUTHOR]

Electrical resistivity measurements were performed as functions of temperature, magnetic field, and anglebetween the magnetic field and thec-axis of a URuSisingle crystal. The resistivity exhibits a two-fold oscillation as a function ofat high temperatures, which undergoes a 180-phase shift (sign change) with decreasing temperature at around 35 K. The hidden order transition is manifested as a minimum in the magnetoresistance and amplitude of the two-fold oscillation. Interestingly, the resistivity also showed four-fold, six-fold, and eight-fold symmetries at the hidden order transition. These higher order symmetries were also detected at low temperatures, which could be a sign of the formation of another pseudogap phase above the superconducting transition, consistent with recent evidence for a pseudogap from point-contact spectroscopy measurements and NMR. Measurements of the magnetisation of single crystalline URuSiwith the magnetic field applied parallel and perpendicular to the crystallographicc-axis revealed regions with linear temperature dependencies between the hidden order transition temperature and about 25 K. ThisT-linear behaviour of the magnetisation may be associated with the formation of a precursor phase or ‘pseudogap’ in the density of states in the vicinity of 30–35 K. [ABSTRACT FROM PUBLISHER]

Single crystals of the "cage compounds" SmTr2Zn20) (Tr = Fe, Co, Ru) and SmTr2Cd20 (Tr = Ni, Pd) have been investigated by means of electrical resistivity, magnetization, and specific-heat measurements. The compounds SmFe2Zn20, SmRu2Zn20, and SmNi2Cd20 exhibit ferromagnetic order with Curie temperatures of Tc = 47.4, 7.6, and 7.5 K, respectively, whereas SmPd2Cd20 is an antiferromagnet with a Néel temperature of TN = 3.4 K. No evidence for magnetic order is observed in SmCo2Zn20 down to 110 mK. The Sommerfeld coefficients γ are found to be 57 mJ/mol K2 for SmFe2Zn20, 79.5 mJ/molK2 for SmCo2Zn20, 258 mJ/molK2 for SmRu2Zn20, 165 mJ/molK2 for SmNi2Cd20, and 208 mJ/molK2 for SmPd2Cd20. Enhanced values of y and a quadratic temperature dependence of the electrical resistivity at low temperature for SmRu2Zn20 and SmPd2Cd20 suggest an enhancement of the quasiparticle masses due to hybridization between localized 4 f and conduction electron states. [ABSTRACT FROM AUTHOR]

Cooperative Ce and Yb valence fluctuations have recently been proposed as the mechanism responsible for stabilizing correlated electron phenomena in Cei-xRxCoIn5 over an unexpectedly large range of concentrations. In order to better understand the origins and character of this stability, we have measured the effect of applied pressure on relevant energy scales such as the superconducting critical (Tc) and Kondo-lattice coherence (T*) temperatures of Cei-xRxCoIn5 with R = Yb, Y, and Gd. Electrical resistivity measurements were performed under applied pressure on samples doped with intermediate-valent Yb and stable-valent Gd and Y, and the responses of Tc and T* to increased pressure in these systems are compared. The character of Tc(P) and T*(P) in Cei-xRxCoIn5 depends only on their respective ambient-pressure values Tc(0) and T*(0), independent of the electronic configuration of R or concentration x. The consequences of this result are discussed within the context of possible cooperative valence fluctuations in Cei-xYbxCoIn5. [ABSTRACT FROM AUTHOR]

Temperature-dependent magnetization, specific-heat, and electrical-resistivity measurements were performed on single crystals of PrNi2Cd20 and PrPd2Cd20. Neither compound shows any evidence for magnetic order above 2 K. Magnetization measurements suggest that Pr ions assume a nonmagnetic Γ1 singlet or non-Kramers Γ3 doublet ground state. A broad peak, which is identified as a Schottky anomaly, is observed in the specific heat at low temperature. Low-lying excitations involving the 4 f electrons persist down to 2 K for both PrNi2Cd20 and PrPd2Cd20 and related features are also observed in the magnetization and electrical resistivity. [ABSTRACT FROM AUTHOR]

Measurements of electrical resistivity under applied pressure were performed on single-crystalline samples of LaFeAsO grown in a molten NaAs flux. We observe a smooth suppression of spin-density wave order under nearly hydrostatic applied pressures up to 2.6 GPa and in quasihydrostatic pressures up to 14.7 GPa. Similar to some of the other reports on single and polycrystalline samples of LaFeAsO, these crystals exhibit a resistivity that increases as temperature is lowered. By fitting an Arrhenius law to the the semiconducting-like temperature dependence of the electrical resistivity, we extract an energy gap that is suppressed with pressure and vanishes near 10 GPa. This is accompanied by the emergence of a metallic temperature dependence of the electrical resistivity. A similar behavior is also observed in diamond anvil cell experiments carried out to ~37 GPa. Complete transitions to a bulk superconducting phase are not observed in any of the experiments. [ABSTRACT FROM AUTHOR]

We present the effect of yttrium substitution on superconductivity in the La1-xYxO0.5F0.5BiS2 system. Polycrystalline samples with nominal Y concentrations up to 40% were synthesized and characterized via electrical resistivity, magnetic susceptibility, and specific-heat measurements. Y substitution reduces the lattice parameter a and unit-cell volume V, and a correlation between the lattice parameter c, the LaO-La bond angle, and the superconducting critical temperature Tc is observed. The chemical pressure induced by Y substitution for La produces neither the high-Tc superconducting phase nor the structural phase transition seen in LaO0.5F0.5BiS2 under externally applied pressure. [ABSTRACT FROM AUTHOR]

Measurements of magnetization, specific heat, electrical resistivity, Hall effect, and magnetoresistance on single crystalline samples of LaFeAsO grown in a NaAs flux are reported. While this material is known to be a semimetal, the temperature dependence of the electrical resistivity data presented herein is reminiscent of semiconducting behavior and exhibits distinct features associated with a structural transition and spin density wave (SDW) order. Low-temperature x-ray diffraction measurements have confirmed that the structural transition in these samples occurs near 140 K, compared to a transition temperature of 156 K observed in polycrystalline samples. Magnetoresistance and Hall coefficient measurements were performed in magnetic fields up to 9 T applied perpendicular to the basal plane using a van der Pauw configuration. The charge carrier density and mobility indicate that electrons are the majority charge carriers and exhibit features indicative of the structural transition and SDW formation. Isotherms of magnetoresistivity measured as a function of magnetic field can be scaled onto a single curve. [ABSTRACT FROM AUTHOR]

Electrical resistivity measurements as a function of temperature between 1 and 300 K were performed at various pressures up to 3 GPa on the superconducting layered compounds LnO0.5F0.5BiS2 (Ln = La, Ce). At atmospheric pressure, LaO0.05F0.5BiS2 and CeO0.05F0.5BiS2 have superconducting critical temperatures Tc of 3.3 and 2.3 K, respectively. For both compounds, the superconducting critical temperature Tc initially increases, reaches a maximum value of 10.1 K for LaO0.5F0.5BiS2 and 6.7 K for CeO0.5F0.5BiS2, and then gradually decreases with increasing pressure. Both samples also exhibit transient behavior in the region between the lower Tc phase near atmospheric pressure and the higher Tc phase at higher pressures. This region is characterized by a broadening of the superconducting transition, in which Tc and the transition width ΔTc are reversible with increasing and decreasing pressure. There is also an appreciable pressure-induced and hysteretic suppression of semiconducting behavior up to the pressure at which the maximum value of Tc is found. At pressures above the value at which the maximum in Tc occurs, there is a gradual decrease of Tc and further suppression of the semiconducting behavior with pressure, both of which are reversible. [ABSTRACT FROM AUTHOR]

We report a strategy to induce superconductivity in the BiS2-based compound LaOBiS2. Instead of substituting F for O, we increase the charge-carrier density (electron dope) via substitution of tetravalent Th+4, Hf+4, Zr+4, and Ti+4 for trivalent La+3. It is found that both the LaOBiS2 and ThOBiS2 parent compounds are bad metals and that superconductivity is induced by electron doping with Tc values of up to 2.85 K. The superconducting and normal states were characterized by electrical resistivity, magnetic susceptibility, and heat capacity measurements. We also demonstrate that reducing the charge-carrier density (hole doping) via substitution of divalent Sr+2 for La+3 does not induce superconductivity. [ABSTRACT FROM AUTHOR]

Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1-xMxPt4Ge12(M=Ce and Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x>0.2. Temperature-dependent specific heat data at low temperatures for La1-xCexPt4Ge12 show a change from power-law to exponential behavior, which may be an indication for multiband superconductivity in LaPt4Ge12. A similar crossover was observed in the Pr1-xCexPt4Ge12 system. However, the suppression rates of the superconducting transition temperatures Tc(x) in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt4Ge12 and unconventional in PrPt4Ge12. In comparison, a nearly linear and smooth evolution of Tc with increasing Th was observed in the La1-xThxPt4Ge12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt4Ge12 and ThPt4Ge12 compounds. [ABSTRACT FROM AUTHOR]

Electrical resistivity measurements on La1-xSmxO0.5F0.5BiS2(x=0.1,0.3,0.6,0.8) have been performed under applied pressures up to 2.6 GPa from 2 K to room temperature. The superconducting transition temperature Tc of each sample significantly increases at a Sm-concentration-dependent pressure Pt, indicating a pressure-induced phase transition from a low-Tc to a high-Tc phase. At ambient pressure, Tc increases dramatically from 2.8 K at x=0.1 to 5.4 K at x=0.8; however, the Tc values at P>Pt decrease slightly with x, and Pt shifts to higher pressures with Sm substitution. In the normal state, semiconducting-like behavior is suppressed, and metallic conduction is induced with increasing pressure in all of the samples. These results suggest that the pressure dependence of Tc for the BiS2-based superconductors is related to the lattice parameters at ambient pressure and enable us to estimate the evolution of Tc for SmO0.5F0.5BiS2 under pressure. [ABSTRACT FROM AUTHOR]

We investigated the onset of the many-body coherence in the f-orbital single crystalline alloys Ce1-xYbxCoIn5 (0≤x≤0.775) through thermodynamic and magnetotransport measurements. Our study shows the evolution of the many-body electronic state as the Kondo lattice of Ce moments is transformed into an array of Ce impurities. Specifically, we observe a crossover from the predominantly localized Ce moment regime to the predominantly itinerant Yb f-electronic states regime for about 60% of Yb doping. Our analysis of the residual resistivity data unveils the presence of correlations between Yb ions, while from our analysis of specific heat data we conclude that for 0.65≤x≤0.775, Yb f electrons strongly interact with the conduction electrons while the Ce moments remain completely decoupled. The sublinear temperature dependence of resistivity across the whole range of Yb concentrations suggest the presence of a unconventional scattering mechanism for the conduction electrons. [ABSTRACT FROM AUTHOR]