6 research outputs found
Synthesis of superconducting pyrochlore RbOs2O6
RbOs2O6, the third superconducting pyrochlore oxide (known so far), has been
synthesized by encapsulation and by high pressure techniques. Suitable post
chemical treatment of the as-prepared sample allowed us to eliminate the
impurity phases. Bulk superconductivity with Tc=6.4 K was observed in
magnetisation and specific heat measurements. The transition temperature of
RbOs2O6 was found to be the same for both preparation methods. Structural
investigations showed that Rb atoms occupy the 8b site in the pyrochlore
lattice with a lattice parameter of 10.1137(1) A.Comment: 12 pages, 5 figures, correction to one author name and Figure
Thermal Conductivity of the Pyrochlore Superconductor KOs2O6: Strong Electron Correlations and Fully Gapped Superconductivity
To elucidate the nature of the superconducting ground state of the
geometrically frustrated pyrochlore KOs2O6 (Tc=9.6K), the thermal conductivity
was measured down to low temperatures (~Tc/100). We found that the
quasiparticle mean free path is strikingly enhanced below a transition at
Tp=7.5K, indicating enormous electron inelastic scattering in the normal state.
In a magnetic field the conduction at T ->0K is nearly constant up to ~0.4Hc2,
in contrast with the rapid growth expected for superconductors with an
anisotropic gap. This unambiguously indicates a fully gapped superconductivity,
in contrast to the previous studies. These results highlight that KOs2O6 is
unique among superconductors with strong electron correlations.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
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
Unprecedented Superconductivity in the beta-Pyrochlore Osmate KOs2O6
Superconductivity in the potassium osmium oxide KOs2O6 crystallizing in the
beta-pyrochlore structure is studied by means of electrical resistivity,
magnetic susceptibility and specific heat. It is the second superconductor in
the family of pyrochlore oxides, following the alfa-type pyrochlore oxide
Cd2Re2O7 which is believed to be a conventional s-wave superconductor. The
superconducting transition temperature Tc of KOs2O6 is 9.6 K, almost one order
higher than the Tc = 1.0 K of Cd2Re2O7. Moreover, the superconductivity of
KOs2O6 is remarkably robust under high magnetic fields, with a large upper
critical magnetic field Hc2 of about 38 T, which seems to exceed Pauli's limit
expected for conventional superconductivity. This is also in contrast to the
case of Cd2Re2O7, in which the Hc2 is 0.29 T, much smaller than the
corresponding Pauli's limit. These distinct contrasts strongly suggest that the
mechanism of superconductivity is essentially different between the two
pyrochlore oxides.Comment: This paper has been withdrawn by the authors, due to a crucial error
in the magnitude of magnetic fields used in the experiment