Absence of orbital currents in superconducting YBa

A detailed zero-and transverse-field muon spin rotation investigation of magnetism and the magnetoelectric coupling in Cu 2 OSeO 3 is reported. An internal magnetic field B int (T = 0) = 85.37(25) mT was found, in agreement with a ferrimagnetic state below T c = 57.0(1) K. The temperature dependence of the magnetic order parameter is well described by the relation2 )β with an effective exponentβ 0.39(1), which is close to the critical exponent β 1/3 for a three-dimensional (3D) magnetic system. Just above T c the muon relaxation rate follows the power law λ(T ) ∝ (T /T c − 1) −ω withω = 1.06(9), which is characteristic for 3D ferromagnets. Measurements of B int (T ) with and without an applied electrostatic field E = 1.66 × 10 5 V/m suggest a possible electric-field effect of magnitude B V = B V (0 V) − B V (500 V) = −0.4(4) mT.

We investigated the superconducting state of the noncentrosymmetric superconductors Li2Pd x Pt3−x B with superconducting transition temperature T c=5.16(8) K (x=2.25), 3.56(8) K (x=1.5) and 2.60 K (x=0) by means of muon-spin rotation (μSR) and specific heat experiments. The μSR relaxation rate σ sc was found to be constant at low temperatures for all the compounds. Data taken at different magnetic fields show that the magnetic penetration depth λ is field-independent for Li2Pd2.25Pt0.75B and Li2Pt3B. The electronic contribution to the specific heat measured in Li2Pd1.5Pt1.5B and Li2Pt3B increases exponentially at the lowest temperatures. These features suggest that the whole family of Li2PdxPt3−xB comprises single-gap s-wave superconductors across the entire doping regime.

The effect of pressure on the copper and praseodymium magnetic order in the system Nd 1−x Pr x Ba 2 Cu 3 O 7−δ with x = 0.3, 0.5, 0.7, and 1 was investigated by means of the muon spin rotation technique. It was found that the effect of pressure on the Néel temperatures of both copper and praseodymium is positive for the whole range of Pr concentrations (0.3 < x < 1) studied. These findings are in contrast with a number of previous reports and clarify some of the puzzles related to the effect of pressure on superconductivity and magnetism in the praseodymium-substituted R 1−x Pr x Ba 2 Cu 3 O 7−δ systems, where R is a rare-earth element.