1,021 research outputs found
Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB
We examine the superconducting anisotropy
of a metallic high- superconductor MgB by measuring the magnetic
torque of a single crystal. The anisotropy does not depend
sensitively on the applied magnetic field at 10 K. We obtain the anisotropy
parameter . The torque curve shows the sharp
hysteresis peak when the field is applied parallel to the boron layers. This
comes from the intrinsic pinning and is experimental evidence for the
occurrence of superconductivity in the boron layers.Comment: REVTeX 4, To be published in Physical Review
Measurement of Positronium hyperfine splitting with quantum oscillation
Interference between different energy eigenstates in a quantum system results
in an oscillation with a frequency which is proportional to the difference in
energy between the states. Such an oscillation is observable in polarized
positronium when it is placed in a magnetic field. In order to measure the
hyperfine splitting of positronium, we perform the precise measurement of this
oscillation using a high quality superconducting magnet and fast
photon-detectors. A result of ~GHz is obtained which is consistent with both theoretical
calculations and previous precise measurements.Comment: 4 figures accepted by Phys. Lett.
Precise measurement of HFS of positronium
The ground state hyperfine splitting in positronium, , is sensitive to high order corrections of QED. A new
calculation up to has revealed a discrepancy
between the QED prediction and the experimental results. This discrepancy might
either be due to systematic problems in the previous experiments or to
contributions beyond the Standard Model. We propose an experiment to measure
employing new methods designed to remedy the systematic
errors which may have affected the previous experiments. Our experiment will
provide an independent check of the discrepancy. The measurement is in progress
and a preliminary result of has been obtained. A measurement with a
precision of O(1) ppm is expected within a few years.Comment: 5 pages, 6 figures, contributed to POSMOL 2009, will be published in
J. Phys.: Conf. Serie
Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO
The temperature () dependent metal-insulator transition (MIT) in VO is
investigated using bulk sensitive hard x-ray ( 8 keV) valence band, core
level, and V 2 resonant photoemission spectroscopy (PES). The valence
band and core level spectra are compared with full-multiplet cluster model
calculations including a coherent screening channel. Across the MIT, V 3
spectral weight transfer from the coherent ( final)
states at Fermi level to the incoherent ( final)
states, corresponding to the lower Hubbard band, lead to gap-formation. The
spectral shape changes in V 1 and V 2 core levels as well as the valence
band are nicely reproduced from a cluster model calculations, providing
electronic structure parameters. Resonant-PES finds that the
states resonate across the V 2 threshold in
addition to the and states. The results support
a Mott-Hubbard transition picture for the first order MIT in VO.Comment: 6 pages, 3 figures. to be published in Phys. Rev.
Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems
Muon spin rotation and relaxation (SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materialsComment: 24 pages, 15 figures, submitted to J. Phys.: Condens. Matte
Determination of the Upper Critical Field of a Single Crystal LiFeAs: The Magnetic Torque Study up to 35 Tesla
We report on the upper critical field B_c2 of a superconducting LiFeAs single
crystal with T_c~16 K, determined from magnetic torque measurements in
dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B_c2 at 0.3 K
is obtained to be 26.4 T and 15.5 T for the applied field B_a||ab and B_a||c,
respectively. The anisotropy parameter = is ~ 3 at
T_c and decreases to 1.7 as , showing rather isotropic
superconductivity. While B_c2 is orbitally-limited for B_a||c, the
spin-paramagnetic effect is evident in the temperature dependence of B_c2 for
B_a||abComment: 4 pages, 4 figures, revised version to be published in J. Phys. Soc.
Jpn. as a letter articl
Tunable terahertz emission from the intrinsic Josephson junctions in acute isosceles triangular Bi2Sr2CaCu2O8+delta mesas
In order to determine if the mesa geometry might affect the properties of the coherent terahertz (THz) radiation emitted from the intrinsic Josephson junctions in mesas constructed from single crystals of the high-temperature superconductor, Bi2Sr2CaCu2O8+delta, we studied triangular mesas. For equilateral triangular mesas, the observed emission was found to be limited to the single mesa TM(1,0) mode. However, tunable radiation over the range from 0.495 to 0.934 THz was found to arise from an acute isosceles triangular mesa. This 47% tunability is the widest yet observed from the outer current-voltage characteristic branch of such mesas of any geometry. Although the radiation at a few of the frequencies in the tunable range appear to have been enhanced by cavity resonances, most frequencies are far from such resonance frequencies, and can only be attributed to the ac-Josephson effect
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