1,394 research outputs found
Total suppression of superconductivity by high magnetic fields in YBa2 Cu3O6.6
We have studied in fields up to 60T the variation of the transverse
magnetoresistance (MR) of underdoped YBCO6.6 crystals either pure or with Tc
reduced down to 3.5K by electron irradiation. We evidence that the normal state
MR is restored above a threshold field H'c(T), which is found to vanish at
T'c>>Tc. In the pure YBCO6.6 sample a 50 Tesla field is already required to
completely suppress the superconducting fluctuations at Tc. While disorder does
not depress the pseudogap temperature, it reduces drastically the phase
coherence established at Tc and weakly H'c(0), T'c and the onset Tnu of the
Nernst signal which are more characteristic of the 2D local pairing.Comment: 4 pages, 4 figure
An electronic instability in bismuth far beyond the quantum limit
We present a transport study of semi-metallic bismuth in presence of a
magnetic field applied along the trigonal axis extended to 55 T for electric
conductivity and to 45 T for thermoelectric response. The results uncover a new
field scale at about 40 T in addition to the previously detected ones. Large
anomalies in all transport properties point to an intriguing electronic
instability deep in the ultraquantum regime. Unexpectedly, both the sheer
magnitude of conductivity and its metallic temperature dependence are enhanced
by this instability.Comment: 5 pages, 4 figure
Competing ferromagnetism in high temperature copper oxide superconductors
The extreme variability of observables across the phase diagram of the
cuprate high temperature superconductors has remained a profound mystery, with
no convincing explanation of the superconducting dome. While much attention has
been paid to the underdoped regime of the hole-doped cuprates because of its
proximity to a complex Mott insulating phase, little attention has been paid to
the overdoped regime. Experiments are beginning to reveal that the
phenomenology of the overdoped regime is just as puzzling. For example, the
electrons appear to form a Landau Fermi liquid, but this interpretation is
problematic; any trace of Mott phenomena, as signified by incommensurate
antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility
shows a ferromagnetic upturn. Here we show and justify that many of these
puzzles can be resolved if we assume that competing ferromagnetic fluctuations
are simultaneously present with superconductivity, and the termination of the
superconducting dome in the overdoped regime marks a quantum critical point
beyond which there should be a genuine ferromagnetic phase at zero temperature.
We propose new experiments, and make new predictions, to test our theory and
suggest that effort must be mounted to elucidate the nature of the overdoped
regime, if the problem of high temperature superconductivity is to be solved.
Our approach places competing order as the root of the complexity of the
cuprate phase diagram.Comment: The expanded published version with very minor difference
Multiple Quantum Oscillations in the de Haas van Alphen Spectra of the Underdoped High Temperature Superconductor YBa_2Cu_3O_6.5
By improving the experimental conditions and extensive data accumulation, we
have achieved very high-precision in the measurements of the de Haas-van Alphen
effect in the underdoped high-temperature superconductor
YBaCuO. We find that the main oscillation, so far believed
to be single-frequency, is composed of three closely spaced frequencies. We
attribute this to bilayer splitting and warping of a single quasi-2D Fermi
surface, indicating that \emph{c}-axis coherence is restored at low temperature
in underdoped cuprates. Our results do not support the existence of a larger
frequency of the order of 1650 T reported recently in the same compound [S.E.
Sebastian {\it et al}., Nature {\bf 454}, 200 (2008)]
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
- …