Effects of Vortex Pinning on the Temperature Dependence of the Magnetic Field Distributions in Superconductors

The temperature and applied-magnetic-field dependence of the second moments of the magnetic-field distributions as measured by mu SR for YBCO and BSCCO have been fit for four different intrinsic-field-distribution models (d-wave, 2-fluid, empirical, and BCS). It is found that if a pinning potential becomes important at about 20 K, all of the models can fit the data reasonably well. The fits and the associated fitting parameters are presented

Muon Spin Rotation study of the (TMTSF)2ClO4(TMTSF)_2ClO_4 system

We report a study of the organic compound $(TMTSF)_2 ClO_4$ in both a sample cooled very slowly through the anion ordering temperature (relaxed state) and a sample cooled more rapidly (intermediate state). For the relaxed state the entire sample is observed to be superconducting below about T_c ~ 1.2 K. The second moment of the internal field distribution was measured for the relaxed state yielding an in-plane penetration depth of ~ 12000 Angstroms. The intermediate state sample entered a mixed phase state, characterized by coexisting macroscopic sized regions of superconducting and spin density wave (SDW) regions, below T_c ~ 0.87 K. These data were analyzed using a back-to-back cutoff exponential function, allowing the extraction of the first three moments of the magnetic field distribution. Formation of a vortex lattice is observed below 0.87 K as evidenced by the diamagnetic shift for the two fields in which we took intermediate state data.Comment: 6 pages, 3 figures, to be submitted to Physica

Thermodynamic properties of excess-oxygen-doped La2CuO4.11 near a simultaneous transition to superconductivity and long-range magnetic order

We have measured the specific heat and magnetization {\it versus} temperature in a single crystal sample of superconducting La$_{2}$CuO$_{4.11}$ and in a sample of the same material after removing the excess oxygen, in magnetic fields up to 15 T. Using the deoxygenated sample to subtract the phonon contribution, we find a broad peak in the specific heat, centered at 50 K. This excess specific heat is attributed to fluctuations of the Cu spins possibly enhanced by an interplay with the charge degrees of freedom, and appears to be independent of magnetic field, up to 15 T. Near the superconducting transition $T_{c}$($H$=0)= 43 K, we find a sharp feature that is strongly suppressed when the magnetic field is applied parallel to the crystallographic c-axis. A model for 3D vortex fluctuations is used to scale magnetization measured at several magnetic fields. When the magnetic field is applied perpendicular to the c-axis, the only observed effect is a slight shift in the superconducting transition temperature.Comment: 8 pages, 8 figure

Muon spin relaxation in CeCu/sub 2/Si/sub 2/ and muon Knight shift in various heavy-fermion systems

Positive muon spin precession has been observed in varius heavy-fermion systems in the transverse external magnetic field. In the superconductor CeCu/sub 2.1/Si/sub 2/, the relaxation rate of muon spins increases rapidly with decreasing temperature below T/sub c/. This is interpreted as the results of the inhomogeneous fields due to the imperfect penetration of the external field into the type-II superconducting state. The magnetic-field penetration depth lambda is derived from the observed muon spin relaxation rate. lambda is about 1200 A at T approx. 0.5T/sub c/, and the temperature dependence of lambda is consistent with the relation expected for a BCS superconductor. We have also measured the muon Knight shift K/sub ..mu../ in the normal (or paramagnetic) state of various heavy-fermion systems. K/sub ..mu../ is large and negative (about -1000 approx. -3000 ppM at T = 10 K) for CeCu/sub 2/Si/sub 2/, UPt/sub 3/ and CeAl/sub 3/, while more complicated signals are measured in CePb/sub 3/ and CeB/sub 6/. The negative muon Knight shift in the non-magnetic heavy-fermion systems is discussed in terms of the Kondo-coupling between the conduction- and f-electrons

Static magnetic ordering of CeCu/sub 2. 1/Si/sub 2/ found by muon spin relaxation

Zero- and longitudinal-field muon spin relaxation measurements on a poly-crystal sample of a heavy-fermion superconductor CeCu/sub 2.1/Si/sub 2/ (T/sub c/ = 0.7 K) have revealed an onset of static magnetic ordering below T )approximately) 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1 ..mu../sub B/ per formula unit