407 research outputs found
Low temperature vortex liquid states induced by quantum fluctuations in the quasi two dimensional organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}
We report the transport properties in the vortex liquid states induced by
quantum fluctuations at low temperature in the layered organic superconductor
kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}. A steep drop of the resistivity observed
below about 1 K separates the liquid state into two regions. In the low
resistance state at lower temperature, a finite resistivity with weak
temperature dependence persists down to 100 mK at least. The finite resistivity
in the vortex state at T ~= 0 K indicates the realization of quantum vortex
liquid assisted by the strong quantum fluctuations instead of the thermal one.
A possible origin for separating these liquid states is a remnant vortex
melting line at the original position, which is obscured and suppressed by the
quantum fluctuations. A non-linear behavior of the in-plane resistivity appears
at large current density in only the low resistance state, but not in another
vortex liquid state at higher temperature, where the thermal fluctuations are
dominant. The transport properties in the low resistance state are well
understood in the vortex slush concept with a short-range order of vortices.
Thus the low resistance state below 1 K is considered to be a novel quantum
vortex slush state.Comment: 7 pages, 5 figure
Relaxor ferroelectricity induced by electron correlations in a molecular dimer Mott insulator
We have investigated the dielectric response in an antiferromagnetic
dimer-Mott insulator beta'-(BEDT-TTF)2ICl2 with square lattice, compared to a
spin liquid candidate kappa-(BEDT-TTF)2Cu2(CN)3. Temperature dependence of the
dielectric constant shows a peak structure obeying Curie-Weiss law with strong
frequency dependence. We found an anisotropic ferroelectricity by pyrocurrent
measurements, which suggests the charge disproportionation in a dimer. The
ferroelectric actual charge freezing temperature is related to the
antiferromagnetic interaction, which is expected to the charge-spin coupled
degrees of freedom in the system.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Tunneling conductance in normal metal - triplet superconductor junction
We calculate the tunneling conductance spectra of a normal metal / insulator
/ triplet superconductor from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formula. For the triplet superconductor we
assume one special p-wave order parameter having line nodes and two two
dimensional -wave order parameters with line nodes breaking the
time-reversal symmetry. Also we examine nodeless pairing potentials. The
tunneling peaks are due to the formation of bound states for each surface
orientation at discrete quasiparticles trajectory angles. The tunneling spectra
can be used to distinguish the possible candidate pairing states of the
superconductor SrRuO.Comment: 4 pages with 3 figures, presented at the second Euroconference on
Vortex Matter in Superconductors, 15-25 September 2001, Crete, Greec
Two-band superconductivity featuring different anisotropies in the ternary iron silicide LuFeSi
We report detailed studies of the upper critical field and low-temperature
specific heat in the two-gap superconductor LuFeSi. The
anisotropy of the upper critical field suggests that the active band is
quasi-one-dimensional. Low-temperature specific heat in magnetic fields reveals
that the virtual in the passive band is almost isotropic. These
results strongly indicate that the two bands have two different anisotropies,
similar to the typical two-gap superconductor MgB, and their interplay
may be essential to the two-gap superconductivity in LuFeSi.Comment: 5 pages, 5 figure
Fluctuation properties of strength function associated with the giant quadrupole resonance in 208Pb
We performed fluctuation analysis by means of the local scaling dimension for
the strength function of the isoscalar (IS) giant quadrupole resonance (GQR) in
208Pb where the strength function is obtained by the shell model calculation
including 1p1h and 2p2h configurations. It is found that at almost all energy
scales, fluctuation of the strength function obeys the Gaussian orthogonal
ensemble (GOE) random matrix theory limit. This is contrasted with the results
for the GQR in 40Ca, where at the intermediate energy scale about 1.7 MeV a
deviation from the GOE limit was detected. It is found that the physical origin
for this different behavior of the local scaling dimension is ascribed to the
difference in the properties of the damping process.Comment: 10 pages, 14 figures, submitted to Physical Review
Tunneling current in triplet f-wave superconductors with horizontal lines of nodes
We calculate the tunneling conductance spectra of a
normal-metal/insulator/triplet superconductor using the
Blonder-Tinkham-Klapwijk (BTK) formulation. Possible states for the
superconductor are considered with horizontal lines of nodes, breaking the time
reversal symmetry. These results would be useful to discriminate between
pairing states in superonductor SrRuO and also in UPt.Comment: 12 pages, 7 figure
Charge current in ferromagnet - triplet superconductor junctions
We calculate the tunneling conductance spectra of a ferromagnetic metal /
insulator / triplet superconductor from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formula. For the triplet superconductor, we
assume one special -wave order parameter, having line nodes, and two two
dimensional -wave order parameters with line nodes, breaking the time
reversal symmetry. Also we examine nodeless pairing potentials. The evolution
of the spectra with the exchange potential depends solely on the topology of
the gap. The weak Andreev reflection within the ferromagnet results in the
suppression of the tunneling conductance and eliminates the resonances due to
the anisotropy of the pairing potential. The tunneling spectra splits
asymmetrically with respect to under the influence of an external
magnetic field. The results can be used to distinguish between the possible
candidate pairing states of the superconductor SrRuO.Comment: 15 pages with 8 figure
Dynamics vs electronic states of vortex core of high-T_c superconductors investigated by high-frequency impedance measurement
Dynamics of vortices reflects the electronic states of quasiparticles in the
core. To understand this, we investigated the following three issues. (1) We
investigated the complex surface impedance, Zs, of YBa2Cu3Oy as a function of
magnetic field, H. The total features were well expressed by the Coffey-Clem
model. From the data, we estimated the viscosity and pinning frequency, which
were found to be independent of frequency. In particular, the obtained
viscosity definitely shows that the core of vortex of YBa2Cu3Oy is moderately
clean. This result suggests that new physics will show up, for the physics of
quantum moderately clean vortex core is unknown at all. (2) An anomaly found in
the surface reactance at the first order transition (FOT) of vortex lattice was
investigated in Bi2Sr2CaCu2Oy with various doping levels. As a result, the
anomaly was found only in the samples exhibiting the FOT. On the other hand, we
did not observe the anomaly in YBa2Cu3Oy. These suggest that the anomaly is due
to the change in the electronic states of the vortices characteristic of
materials with very strong anisotropy. (3) We measured H dependence of both the
thermal conductivity \kappa(H) and Zs(H) in exactly the same pieces of crystal.
We could not find any anomaly in Zs(H) even at the onset of the plateau. This
result suggests that the origin of the plateau in \kappa(H) is not a drastic
phase transition but is rather gradual crossover.Comment: 6 pages, 5 figures, Proceedings of Plasma2000(Sendai), to be
published in Physica
Bulk and surface low-energy excitations in YBa2Cu3O7-d studied by high-resolution angle-resolved photoemission spectroscopy
We have performed high-resolution angle-resolved photoemission spectroscopy
on YBa2Cu3O7-delta (Y123; delta = 0.06; Tc = 92 K). By accurately determining
the Fermi surface and energy band dispersion, we solve long-standing
controversial issues as to the anomalous electronic states of Y-based high-Tc
cuprates. We unambiguously identified surface-bilayer-derived bonding and
antibonding bands, together with their bulk counterparts. The surface bands are
highly overdoped (hole concentration x = 0.29), showing no evidence for the gap
opening or the dispersion anomaly in the antinodal region, while the bulk bands
show a clear dx2-y2-wave superconducting gap and the Bogoliubov
quasiparticle-like behavior with a characteristic energy scale of 50-60 meV
indicative of a strong electron-boson coupling in the superconducting state.
All these results suggest that the metallic and superconducting states coexist
at the adjacent bilayer of Y123 surface.Comment: Accepted for publication in Phys. Rev.
Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO chain system CaYCuO
We have succeeded in growing large-size single-crystals of
CaYCuO with and measured the
magnetic susceptibility, specific heat and magnetization curve, in order to
study the magnetic ground state in the edge-sharing CuO chain as a function
of hole concentration and magnetic field. In , it has been
found that an antiferromagnetically ordered phase with the magnetic easy axis
along the b-axis is stabilized and that a spin-flop transition occurs by the
application of magnetic fields parallel to the b-axis. The antiferromagnetic
transition temperature decreases with increasing and disappears around 1.4. Alternatively, a spin-glass phase appears around . At where the hole concentration is 1/3 per Cu, it appears that a
spin-gap state is formed owing to the formation of spin-singlet pairs. No sign
of the coexistence of an antiferromagnetically ordered state and a spin-gap one
suggested in CaCuO has been found in
CaYCuO.Comment: 13 pages, 12 figures, 1 tabl
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