Nondestructive Testing Using Magnetic Field Visualization Technique

This paper describes a new technique to detect cracks or flaws in conducting or ferromagnetic materials using a magnetic field visualization system. In this system there are two sources for magnetic field generation, i.e. electrical current and magnetization. And the magnetic field generated by the source could give us useful information on cracks or flaws included in the material. Thus, visualization of magnetic field would enable us to identify the shape and size of cracks. We developed a preliminary system to verify the validity of the speculation and applied it to both ferromagnetic and conducting materials with flaws. The applicability of magnetic visualization has been confirmed to be an effective method in NDE and diagnosis of magnetic equipments in the present experiment. Furthermore, combination of this method with numerical prediction could demonstrate more potential capability in the field of NDE</p

Non-generality of the Kadowaki-Woods ratio in correlated oxides

An explicit expression for the Kadowaki-Woods ratio in correlated metals is derived by invoking saturation of the (high-frequency) Fermi-liquid scattering rate at the Mott-Ioffe-Regel limit. Significant deviations observed in a number of oxides are quantitatively explained due to variations in carrier density, dimensionality, unit cell volume and the number of individual sheets in the Brillouin zone. A generic re-scaling of the original Kadowaki-Woods plot is also presented.Comment: 9 pages of text, 1 table, 2 figure

Effect of controlled disorder on quasiparticle thermal transport in Bi2_2Sr2_2CaCu2_2O8_8

Low temperature thermal conductivity, $\kappa$, of optimally-doped Bi2212 was studied before and after the introduction of point defects by electron irradiation. The amplitude of the linear component of $\kappa$ remains unchanged, confirming the universal nature of heat transport by zero-energy quasiparticles. The induced decrease in the absolute value of $\kappa$ at finite temperatures allows us to resolve a nonuniversal term in $\kappa$ due to conduction by finite-energy quasiparticles. The magnitude of this term provides an estimate of the quasiparticle lifetime at subkelvin temperatures.Comment: 5 pages including 2 .eps figuer

Linear-T resistivity and change in Fermi surface at the pseudogap critical point of a high-Tc superconductor

A fundamental question of high-temperature superconductors is the nature of the pseudogap phase which lies between the Mott insulator at zero doping and the Fermi liquid at high doping p. Here we report on the behaviour of charge carriers near the zero-temperature onset of that phase, namely at the critical doping p* where the pseudogap temperature T* goes to zero, accessed by investigating a material in which superconductivity can be fully suppressed by a steady magnetic field. Just below p*, the normal-state resistivity and Hall coefficient of La1.6-xNd0.4SrxCuO4 are found to rise simultaneously as the temperature drops below T*, revealing a change in the Fermi surface with a large associated drop in conductivity. At p*, the resistivity shows a linear temperature dependence as T goes to zero, a typical signature of a quantum critical point. These findings impose new constraints on the mechanisms responsible for inelastic scattering and Fermi surface transformation in theories of the pseudogap phase.Comment: 24 pages, 6 figures. Published in Nature Physics. Online at http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys1109.htm

Small-polaron hopping conductivity in bilayer manganite La1.2_{1.2}Sr1.8_{1.8}Mn2_{2}O7_{7}

We report anisotropic resistivity measurements on a La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ single crystal over a temperature $T$ range from 2 to 400 K and in magnetic fields $H$ up to 14 T. For $T\geq 218$ K, the temperature dependence of the zero-field in-plane $\rho_{ab}(T)$ resistivity obeys the adiabatic small polaron hopping mechanism, while the out-of-plane $\rho_{c}(T)$ resistivity can be ascribed by an Arrhenius law with the same activation energy. Considering the magnetic character of the polarons and the close correlation between the resistivity and magnetization, we developed a model which allows the determination of $\rho_{ab,c}(H,T)$. The excellent agreement of the calculations with the measurements indicates that small polarons play an essential role in the electrical transport properties in the paramagnetic phase of bilayer manganites.Comment: 4 pages, 3 figures, to appear in Physical Review

Low-temperature electronic heat transport in La_{2-x}Sr_{x}CuO_{4} single crystals: Unusual low-energy physics in the normal and superconducting states

The thermal conductivity \kappa is measured in a series of La_{2-x}Sr_{x}CuO_{4} (x = 0 - 0.22) single crystals down to 90 mK to elucidate the evolution of the residual electronic thermal conductivity \kappa_{res}, which probes the extended quasiparticle states in the d-wave gap. We found that \kappa_{res}/T grows smoothly, except for a 1/8 anomaly, above x = 0.05 and shows no discontinuity at optimum doping, indicating that the behavior of \kappa_{res}/T is not governed by the metal-insulator crossover in the normal state; as a result, \kappa_{res}/T is much larger than what the normal-state resistivity would suggest in the underdoped region, which highlights the peculiarities in the low-energy physics in the cuprates.Comment: 5 pages, 3 figures, final version published in PRL. Discussions have been modified and an analysis of the phonon term has been adde

Absence of residual quasiparticle conductivity in the underdoped cuprate YBa2Cu4O8

We report here measurements of the in-plane thermal conductivity K(T) of the underdoped cuprate YBa2Cu4O8 (Y124) below 1K. K(T) is shown to follow a simple, phononic T^3 dependence at the lowest temperatures for both current directions, with a negligible linear, quasiparticle contribution. This observation is in marked contrast with behavior reported in optimally doped cuprates, and implies that extended zero-energy (or low energy) low-energy quasiparticles are absent in YBa2Cu4O8 at low temperatures.Comment: RevTex, 4 pages, 2 figures, Revised versio