Underdoped YBa2Cu3O7−δ single crystals exhibit a large, positive c-axis magnetoresistance that is strikingly linear over a wide magnetic field range up to 60 T. This linear magnetoresistance is observed at the temperatures near or below Tc, one sufficient magnetic field has been applied to suppress superconductivity. The measurements are done in the longitudinal geometry, with current and magnetic field both along the c-axis (I∥B∥c). The linear magnetoresistance can be large, giving as much as a 35% increase in resistance between 30 T and 60 T. It also exhibits very strong temperature dependence, increasing by as much as an order of magnitude as the temperature is reduced from 100 K to 10 K.

We present the resistively determined upper critical field H-c2(rho)(T) and the irreversibility lines H-irr(rho)(T) of various high-T-c cuprates, deduced from measurements in 61-T pulsed magnetic fields applied parallel to the c axis. The shape of both H-c2(rho)(T) and H-irr(rho)(T) depends monotonically on the anisotropy or the material and none of the samples show saturation of H-rho(T) at low temperatures. The anomalous positive curvature d(2)H(rho)/dT(2) >0 is the strongest in materials with the largest normal state anisotropy, regardless of whether anisotropy is varied by changing the carrier concentration or by comparing a variety of optimally doped compounds. [S0163-1829(99)10341-2].

We present a study of in-plane normal-state magnetotransport in single-crystal ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\mathrm{\ensuremath{\delta}}}$ in 60-T pulsed magnetic fields. In optimally doped samples ${(T}_{c}\ensuremath{\sim}80$ K) the weak-magnetic-field regime extends to fields as high as 60 T, but in overdoped samples ${(T}_{c}\ensuremath{\sim}30$ K) we are able to leave the weak-field regime, as shown by the behavior of both the magnetoresistance and the Hall resistance. Data from samples of both dopings provide constraints on the class of model necessary to describe normal-state transport in the cuprates.

We present a study of in-plane normal-state magnetotransport in single-crystal Tl2Ba2CuO6+delta in 60-T pulsed magnetic fields. In optimally doped samples (T-c similar to 80 K) the weak-magnetic-field regime extends to fields as high as 60 T, but in overdoped samples (T-c similar to 30 K) we an able to leave the weak-field regime, as shown by the behavior of both the magnetoresistance and the Hall resistance. Data from samples of both dopings provide constraints on the class of model necessary to describe normal-state transport in the cuprates.

We present a study of in-plane normal state magneto-transport in single crystal Tl-2201 in 60T pulsed magnetic fields. In optimally doped samples (Tc ~ 80K) the weak-magnetic-field regime extends to fields as high as 60T, but in overdoped samples (Tc ~ 30K) we are able to leave the weak field regime, as shown by the behavior of both the magnetoresistance and the Hall resistance. Data from samples of both dopings provide constraints on the class of model necessary to describe normal state transport in the cuprates.

The normal-state Hall coefficient R-H and the in-plane resistivity rho(ab) are measured in La-doped Bi2Sr2CuOy (T-c similar or equal to 13 K) single crystals and La2-xSrxCuO4 thin films by suppressing superconductivity with 61-T pulsed magnetic fields. In

The results of low-temperature normal-state resistivity measurements of La 2−x Sr x CuO 4 (LSCO) and Bi 2 Sr 2−x La x CuO y (Bi-2201) using 61-T pulsed magnetic fields are summarized. Measurements of LSCO with various Sr doping reveal (1) an insulator-to-metal crossover in the normal state that takes place near optimum doping and (2) unusual log(1/ T ) divergence of both ϱ ab and ϱ c of insulating underdoped samples. In particularly clean Bi-2201 crystals, metallic in-plane resistivity and insulating c -axis resistivitiy are found to coexist down to the lowest experimental temperature. Recent measurements of the low-temperature normal-state Hall effect on Bi-2201 find an essentially temperature-independent Hall coefficient below 20 K, which suggest that the unusual insulating behavior does not come from conventional disorder-enhanced electron interactions.

Low-temperature anisotropic normal-state resistivity is measured in La2−xSrxCuO4 single crystals by suppressing the superconductivity with a 61-T pulsed magnetic field. The logarithmic temperature dependence of both ϱab and ϱc first reported in Phys. Rev. Lett.75, 4662 (1995) is observed in a much cleaner x=0.08 sample, as well as in samples with x=0.15 which is near optimum doping, but slighly underdoped. This extension of the original observation suggests that the unusual insulating behavior is a generic property of the low-temperature normal-state of underdoped La2−xSrxCuO4 once superconductivity is suppressed.

Interactions between localized and itinerant electrons give rise to a variety of classes of materials, including the heavy fermion metals and the Kondo insulators. In the Kondo insulators, a broad, half-filled conduction band is intersected by a nearly dispersionless f-level. Hybridization and correlations give rise to a low temperature quenching of the localized spins accompanied by a loss of carriers. Extremely high magnetic fields should destroy the Kondo interaction (antiferromagnetic coupling to the localized moment). For this reason, the authors have measured, in pulsed magnetic fields of 61 T, the longitudinal, transverse, and Hall resistivity of Ce{sub 3}Bi{sub 4}Pt{sub 3}. Samples with very different disorder reveal that magnetic fields above {approximately}20T suppress extrinsic low temperature behavior. A large negative magnetoresistance is found to be governed by spin interactions (longitudinal and transverse magnetoresistance are essentially identical). The negative magnetic resistance is accompanied by an equally dramatic increase in the number of carriers measured by the Hall resistivity. The data are consistent with the linear collapse of a spin excitation gap which closes at {approximately}50T. However, roughly constant carrier density from {approximately}50T to 61T suggests that the metallic behavior above 50T results from collapse of a coherence gap rather than simple energymore » band crossing.« less