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We present measurements of the magnetic field dependence of the penetration depth Lambda(H) for untwinned YBa_2Cu_3O_6.95 for temperatures from 1.2 to 70 K in dc fields up to 42 gauss and directions 0, 45 and 90 degrees with respect to the crystal b-axis. The experiment uses an ac susceptometer with fields applied parallel to the ab-plane of thin platelet samples. The resolution is about 0.15 Angstroms in zero dc field, degrading to 0.2 or 0.3 Angstroms at the higher fields. At low temperatures the field dependencies are essentially linear in H, ranging from 0.04 Angstroms/gauss for Delta-Lambda_a to 0.10 Angstroms/gauss for Delta-Lambda_b, values comparable to the T=0 Yip and Sauls prediction for a d-wave superconductor. However, the systematics versus temperature and orientation do not agree with the d-wave scenario probably due, in part, to residual sample problems.
Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 microV/cm. We defined Ic(sf) as the
The microwave power, dc magnetic field, frequency and temperature dependence of the surface resistance of MgB2 films and powder samples were studied. Sample quality is relatively easy to identify by a number of characteristics, the most clear being t
Muon-spin rotation spectroscopy has been used to measure the internal magnetic field distribution in NbSe2 for Hc1 << H < 0.25 Hc2. The deduced profiles of the supercurrent density indicate that the vortex-core radius in the bulk decreases sharply wi
Multiferroic BiFeO3 undergoes a transition from a distorted spiral phase to a G-type antiferromagnet above a critical field H_c that depends on the orientation m of the field. We show that H_c(m) has a maximum when oriented along a cubic diagonal par
We present measurements of temperature and magnetic field dependence of the critical current and excess current in a carbon nanotube Josephson quantum dot junction. The junction is fabricated in a controlled environment which allows for extraction of