I. Hellmann

Field and Temperature Dependence of the Superfluid Density in LaFeAsO1 xFx Superconductors: A Muon Spin Relaxation Study

We present zero field and transverse field muon spin relaxation experiments on the recently discovered Fe-based superconductor LaFeAsO1-xFx (x=0.075 and x=0.1). The temperature dependence of the deduced superfluid density is consistent with a BCS s-wave or a dirty d-wave gap function, while the field dependence strongly evidences unconventional superconductivity. We obtain the in-plane penetration depth of lambda ab(0)=254(2) nm for x=0.1 and lambda ab(0)=364(8) nm for x=0.075. Further evidence for unconventional superconductivity is provided by the ratio of Tc versus the superfluid density, which is close to the Uemura line of high-Tc cuprates.

Magnetic properties of vanadium oxide nanotubes probed by static magnetization and 51V NMR

Measurements of the static magnetic susceptibility and of the nuclear magnetic resonance of multiwalled vanadium-oxide nanotubes are reported. In this nanoscale magnet the structural low-dimensionality and mixed valency of vanadium ions yield a complex temperature dependence of the static magnetization and the nuclear relaxation rates. Analysis of the different contributions to the magnetism allows to identify individual interlayer magnetic sites as well as strongly antiferromagnetically coupled vanadium spins (S = 1/2) in the double layers of the nanotubes wall. In particular, the data give strong indications that in the structurally well-defined vanadium-spin chains in the walls, owing to an inhomogeneous charge distribution, antiferromagnetic dimers and trimers occur. Altogether, about 30% of the vanadium ions are coupled in dimers, exhibiting a spin gap of the order of 700 K, the other ~ 30% comprise individual spins and trimers, whereas the remaining \~ 40% are nonmagnetic.

Upper critical field, penetration depth, and depinning frequency of the high-temperature superconductor LafeAsO0.9F0.1 studied by microwave surface impedance

Temperature-dependent and magnetic-field-dependent measurements of the microwave surface impedance of superconducting

Structure and electronic properties of Li-doped vanadium oxide nanotubes

{\text{LaFeAsO}}_{0.9}{\text{F}}_{0.1}

Single-crystal growth of LiMnPO4 by the floating-zone method

({T}_{c}\ensuremath{\approx}26\text{ }\text{K})

Vanadium dioxide nanobelts: Hydrothermal synthesis and magnetic properties

reveal a very large upper critical field

Static susceptibility and heat capacity studies on V3O7·H2O7 nanobelts

({B}_{c2}\ensuremath{\approx}56\text{ }\text{T})

Single-crystal growth of LiMnPO 4 by the floating-zone method

and a large value of the depinning frequency

Synthesis and characterization of V 3O 7 H 2O nanobelts

({f}_{0}\ensuremath{\approx}6\text{ }\text{GHz})