1,603 research outputs found
A second phase transition and superconductivity in the beta-pyrochlore oxide KOs2O6
Another phase transition that is probably of first order is found in the
beta-pyrochlore oxide superconductor KOs2O6 with a superconducting transition
temperature Tc of 9.6 K. It takes place at Tp=7.5 K in the superconducting
state in a zero magnetic field. By applying magnetic fields of up to 140 kOe,
the Tc gradually decreased to 5.2 K, while Tp changed little, eventually
breaking through the Hc2 line at approximately 65 kOe in the H-T diagram. Both
the normal-state resistivity and Hc2 change slightly but significantly across
the second phase transition. It is suggested that the transition is associated
with the rattling of potassium ions located in an oversized cage of osmium and
oxide ions.Comment: 10 pages including 6 figures; to be published in the Proceedings of
HFM2006(J. Phys.: Condens. Matter
Anisotropic uniaxial pressure response of the Mott insulator Ca2RuO4
We have investigated the in-plane uniaxial pressure effect on the
antiferromagnetic Mott insulator Ca2RuO4 from resistivity and magnetization
measurements. We succeeded in inducing the ferromagnetic metallic phase at
lower critical pressure than by hydrostatic pressure, indicating that the
flattening distortion of the RuO6 octahedra is more easily released under
in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the
pressure responses of various magnetic phases: Although the magnetization
increases monotonically with pressure diagonal to the orthorhombic principal
axes, the magnetization exhibits peculiar dependence on pressure along the
in-plane orthorhombic principal axes. This peculiar dependence can be explained
by a qualitative difference between the uniaxial pressure effects along the
orthorhombic a and b axes, as well as by the presence of twin domain
structures.Comment: Accepted for publication in Phys. Rev.
P-14. Effects of fatty acids on cytosolic TAG accumulation in primary cultured bovine mammary epithelial cells(Abstracts of the International Symposium on Recent Advances in Animal Science(IS-RAAS),Joint meeting of 2^<nd> IS-AS and 3^<rd> IS-IFS)
NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6
We report nuclear magnetic resonance studies on the beta-pyrochlore oxide
superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused
by fluctuations of electric field gradient, which we ascribe to highly
anharmonic low frequency oscillation (rattling) of K ions. A phenomenological
analysis shows a crossover from overdamped to underdamped behavior of the
rattling phonons with decreasing temperature and its sudden sharpening below
the superconducting transition temperature Tc. Absence of the Hebel-Slichter
peak in the relaxation rate at the O sites below Tc also indicates strong
electron-phonon coupling.Comment: 4 pages, 3 figure
Strong-Coupling Theory of Rattling-Induced Superconductivity
In order to clarify the mechanism of the enhancement of superconducting
transition temperature due to anharmonic local oscillation of a
guest ion in a cage composed of host atoms, i.e., {\it rattling}, we analyze
the anharmonic Holstein model by applying the Migdal-Eliashberg theory. From
the evaluation of the normal-state electron-phonon coupling constant, it is
found that the strong coupling state is developed, when the bottom of a
potential for the guest ion becomes wide and flat. Then, is
enhanced with the increase of the anharmonicity in the potential, although
is rather decreased when the potential becomes a double-well type
due to very strong anharmonicity. From these results, we propose a scenario of
anharmonicity-controlled strong-coupling tendency for superconductivity induced
by rattling. We briefly discuss possible relevance of the present scenario with
superconductivity in -pyrochlore oxides.Comment: 8 pages, 6 figure
Anomalous In-Plane Anisotropy of the Onset of Superconductivity in (TMTSF)2ClO4
We report the magnetic field-amplitude and field-angle dependence of the
superconducting onset temperature Tc_onset of the organic superconductor
(TMTSF)2ClO4 in magnetic fields H accurately aligned to the conductive ab'
plane. We revealed that the rapid increase of the onset fields at low
temperatures occurs both for H // b' and H // a, irrespective of the carrier
confinement. Moreover, in the vicinity of the Pauli limiting field, we report a
shift of a principal axis of the in-plane field-angle dependence of Tc_onset
away from the b' axis. This feature may be related to an occurrence of
Fulde-Ferrell-Larkin-Ovchinnikov phases.Comment: 4 pages, 4 figure
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