58 research outputs found
High pressure effects in fluorinated HgBa2Ca2Cu3O(8+d)
We have measured the pressure sensitivity of Tc in fluorinated
HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying
pressures up to 30 GPa. We obtained that Tc increases with increasing pressure,
reaching different maximum values, depending on the F doping level, and
decreases for a further increase of pressure. A new high Tc record (166 K +/- 1
K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample
near the optimum doping level. Our results show that all our samples are at the
optimal doping, and that fluorine incorporation decreases the crystallographic
-parameter concomitantly increasing the maximum attainable Tc. This effect
reveals that the compression of the axes is one of the keys that controls
the Tc of high temperature superconductors.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Electronic structure and Fermi surface tolopogy of NaCoO
We construct an effective Hamiltonian for the motion of T2g highly correlated
states in NaxCoO2. We solve exactly a multiband model in a CoO6 cluster with
electronic occupation corresponding to a nominal Co valence of either +3 or +4.
Using the ensuing ground states, we calculate the effective O mediated hopping
t=0.10 eV between many-body T2g states, and estimate the direct hopping t'~0.04
eV. The trigonal splitting 3D=0.315 eV is taken from recent quantum chemistry
calculations. The resulting effective Hamiltonian is solved using a generalized
slave-boson mean-field approximation. The results show a significant band
renormalization and a Fermi surface topology that agrees with experiment, in
contrast to predictions using the local-density approximation.Comment: 4 pages, 2 figure
Carrier doping to a partially disordered state in the periodic Anderson model on a triangular lattice
We investigate the effect of hole and electron doping to half-filling in the
periodic Anderson model on a triangular lattice by the Hartree-Fock
approximation at zero temperature. At half-filling, the system exhibits a
partially disordered insulating state, in which a collinear antiferromagnetic
order on an unfrustrated honeycomb subnetwork coexists with nonmagnetic state
at the remaining sites. We find that the carrier doping destabilizes the
partially disordered state, resulting in a phase separation to a doped metallic
state with different magnetic order. The partially disordered state is
restricted to the half-filled insulating case, while its metallic counterpart
is obtained as a metastable state in a narrow electron doped region.Comment: 4 pages, 2 figure
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Mott-Hubbard quantum criticality in paramagnetic CMR pyrochlores
We present a correlated {\it ab initio} description of the paramagnetic phase
of TlMnO, employing a combined local density approximation (LDA)
with multiorbital dynamical mean field theory (DMFT) treatment. We show that
the insulating state observed in this colossal magnetoresistance (CMR)
pyrochlore is determined by strong Mn intra- and inter-orbital local
electron-electron interactions. Hybridization effects are reinforced by the
correlation-induced spectral weight transfer. Our result coincides with optical
conductivity measurements, whose low energy features are remarkably accounted
for by our theory. Based on this agreement, we study the disorder-driven
insulator-metal transition of doped compounds, showing the proximity of
TlMnO to quantum phase transitions, in agreement with recent
measurements.Comment: 4 pages, 4 figure
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS 2 and 2H-TaSe 2
We present measurements of the superconducting and charge density wave
critical temperatures (Tc and TCDW) as a function of pressure in the transition
metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility
measurements show that Tc increases from temperatures below 1 K up to 8.5 K at
9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the
pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in
transition from incommensurate CDW to commensurate CDW. Above this pressure,
the commensurate TCDW slowly decreases coexisting with superconductivity within
our full pressure range.Comment: Published in Phys. Rev B 93, 184512 (2016
Interlayer Magnetic Frustration in Quasi-stoichiometric Li1-xNi1+xO2
Susceptibility, high-field magnetization and submillimeter wave electron spin
resonance measurements of layered quasi-stoichiometric Li1-xNi1+xO2 are
reported and compared to isomorphic NaNiO2. A new mechanism of magnetic
frustration induced by the excess Ni ions always present in the Li layers is
proposed. We finally comment on the possible realization of an orbital liquid
state in this controversial compound.Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, Rapid Com
Partial Disorder and Metal-Insulator Transition in the Periodic Anderson Model on a Triangular Lattice
Ground state of the periodic Anderson model on a triangular lattice is
systematically investigated by the mean-field approximation. We found that the
model exhibits two different types of partially disordered states: one is at
half filling and the other is at other commensurate fillings. In the latter
case, the kinetic energy is lowered by forming an extensive network involving
both magnetic and nonmagnetic sites, in sharp contrast to the former case in
which the nonmagnetic sites are rather isolated. This spatially extended nature
of nonmagnetic sites yields a metallic partially-disordered state by hole
doping. We discuss the mechanism of the metal-insulator transition by the
change of electronic structure.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
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