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J. L. Tallon

Publications and source records attributed to J. L. Tallon.

60 records · Page 4Linked to original sources
arXiv1999

Heat capacity and transport studies of the ferromagnetic superconductor RuSr2GdCu2O8

Resistivity, thermoelectric power and heat capacity are investigated in the ferromagnetic superconductor RuSr2GdCu2O8 with and without Zn substitution. The thermodynamic signatures of the ordering of the Ru moments and the paramagnetic Gd moments as well as the onset of superconductivity are all clearly seen and quantified. The materials are shown to exhibit bulk superconductivity which coexists with spatially-uniform ferromagnetism. They appear to be typical underdoped superconducting cuprates in which the pseudogap dominates normal-state transport, thermodynamic and substitutional properties. However, a field-induced increase in Tc could suggest some degree of triplet pairing.

cond-mat.supr-con↗
arXiv1999

Magneto-Transport Properties of the Rutheno-Cuprate RuSr_2GdCu_2O_8

RuSr_2GdCu_2O_8 (Ru-1212) is a triple perovskite containing both CuO_2 and RuO_2 layers. It has attracted a great deal of interest recently because it displays electronic ferromagnetism and superconductivity coexisting on a microscopic scale, with T_Curie of 135K and T_c up to 50K. We report magnetisation and magnetoresistance (MR) data that exhibit effects due to the interaction between the ferromagnetic ruthenium moments and the conduction electrons. The MR is negative at temperatures above T_Curie, and is proportional to the square of the applied field well above this temperature. Below T_Curie the MR displays a positive peak at fields of around 15 kOe, but at high fields it becomes negative again, and approximately linear. We analyse the high temperature data in terms of spin-disorder scattering theory and extract a value for the exchange interaction between the carriers in the CuO_2 planes and the Ru spins.

cond-mat.supr-con↗
arXiv1999

Evidence for a Two-stage Melting Transition of the Vortex Matter in Bi2Sr2Ca1Cu2O8+d Single Crystals obtained by Muon Spin Rotation

From muon spin rotation measurements on under- to overdoped Bi-2212 crystals we obtain evidence for a two-stage transition of the vortex matter as a function of temperature. The first transition is well known and related to the irreversibility line (IL). The second one is located below the IL and has not been previously observed. It occurs for all three sets of crystals and is unrelated to the vortex mobility. Our data are consistent with a two-stage melting scenario where the intra-planar melting of the vortex lattice and the inter-planar decoupling of the vortex lines occur independently.

cond-mat.supr-con↗
arXiv1999

Effects of carrier concentration on the superfluid density of high-T_c cuprates

The absolute values and temperature, T, dependence of the in-plane magnetic penetration depth, $λ_{ab}$, of La_{2-x}Sr_xCuO_4 and HgBa_2CuO_{4+δ} have been measured as a function of carrier concentration. We find that the superfluid density, $ρ_s$, changes substantially and systematically with doping. The values of $ρ_{s}(0)$ are closely linked to the available low energy spectral weight as determined by the electronic entropy just above T_c and the initial slope of $ρ_{s}(T)/ρ_{s}(0)$ increases rapidly with carrier concentration. The results are discussed in the context of a possible relationship between $ρ_s$ and the normal-state (or pseudo) energy gap.

cond-mat.supr-con↗
arXiv1999

Coexistence of ferromagnetism and superconductivity in the hybrid ruthenate-cuprate compound RuSr_2GdCu_2O_8 studied by muon spin rotation (μSR) and DC-magnetization

We have investigated the magnetic and the superconducting properties of the hybrid ruthenate-cuprate compound RuSr_{2}GdCu_{2}O_{8} by means of zero-field muon spin rotation- (ZF-$μ$SR) and DC magnetization measurements. The DC-magnetisation data establish that this material exhibits ferromagnetic order of the Ru-moments ($μ(Ru) \approx 1 μ_{B}$) below T_{Curie} = 133 K and becomes superconducting at a much lower temperature T_c = 16 K. The ZF-$μ$SR experiments indicate that the ferromagnetic phase is homogeneous on a microscopic scale and accounts for most of the sample volume. They also suggest that the magnetic order is not significantly modified at the onset of superconductivity.

cond-mat.supr-con↗