17,827 research outputs found
Local moment, itinerancy and deviation from Fermi liquid behavior in NaCoO for
Here we report the observation of Fermi surface (FS) pockets via the
Shubnikov de Haas effect in NaCoO for and 0.84,
respectively. Our observations indicate that the FS expected for each compound
intersects their corresponding Brillouin zones, as defined by the previously
reported superlattice structures, leading to small reconstructed FS pockets,
but only if a precise number of holes per unit cell is \emph{localized}. For
the coexistence of itinerant carriers and localized spins on a paramagnetic triangular superlattice leads at low temperatures
to the observation of a deviation from standard Fermi-liquid behavior in the
electrical transport and heat capacity properties, suggesting the formation of
some kind of quantum spin-liquid ground state.Comment: 4 pages, 4 figure
Three-loop HTL QCD thermodynamics
The hard-thermal-loop perturbation theory (HTLpt) framework is used to
calculate the thermodynamic functions of a quark-gluon plasma to three-loop
order. This is the highest order accessible by finite temperature perturbation
theory applied to a non-Abelian gauge theory before the high-temperature
infrared catastrophe. All ultraviolet divergences are eliminated by
renormalization of the vacuum, the HTL mass parameters, and the strong coupling
constant. After choosing a prescription for the mass parameters, the three-loop
results for the pressure and trace anomaly are found to be in very good
agreement with recent lattice data down to , which are
temperatures accessible by current and forthcoming heavy-ion collision
experiments.Comment: 27 pages, 11 figures; corresponds with published version in JHE
Shubnikov de Haas effect in the metallic state of NaCoO
Shubnikov de Haas oscillations for two well defined frequencies,
corresponding respectively to areas of 0.8 and 1.36% of the first Brillouin
zone (FBZ), were observed in single crystals of NaCoO. The
existence of Na superstructures in NaCoO, coupled with this
observation, suggests the possibility that the periods are due to the
reconstruction of the large Fermi surface around the point. An
alternative interpretation in terms of the long sought-after
pockets is also considered but found to be incompatible
with existing specific heat data.Comment: 5 pages 4 figure
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
Polarization Relaxation Induced by Depolarization Field in Ultrathin Ferroelectric BaTiO Capacitors
Time-dependent polarization relaxation behaviors induced by a depolarization
field were investigated on high-quality ultrathin
SrRuO/BaTiO/SrRuO capacitors. The values were
determined experimentally from an applied external field to stop the net
polarization relaxation. These values agree with those from the electrostatic
calculations, demonstrating that a large inside the ultrathin
ferroelectric layer could cause severe polarization relaxation. For numerous
ferroelectric devices of capacitor configuration, this effect will set a
stricter size limit than the critical thickness issue
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