41,746 research outputs found
Multiple phase transitions in single-crystalline NaFeAs
Specific heat, resistivity, susceptibility and Hall coefficient measurements
were performed on high-quality single crystalline NaFeAs. This
compound is found to undergo three successive phase transitions at around 52,
41, and 23 K, which correspond to structural, magnetic and superconducting
transitions, respectively. The Hall effect result indicates the development of
energy gap at low temperature due to the occurrence of spin-density-wave
instability. Our results provide direct experimental evidence of the magnetic
ordering in the nearly stoichiometric NaFeAs.Comment: 4 pages, 4 figure
The Range of Validity for the Kelvin Force
In a recent Letter, Luo, Du and Huang reported a novel convective instability
driven by a force rarely studied before -- that exerted by an external magnetic
field on a strongly magnetizable liquid. The associated physics is surprisingly
rich and promises many more interesting results for the future. Unfortunately,
the analysis starts from a misconception and employs the Kelvin force outside
its range of validity. Since few would recognize this as a mistake, and since
its consequence in the given experiment is particularly direct and critical,
this is a point well worth being clarified, and clearly understood.Comment: 1 pag
Mixed-Spin Pairing Condensates in Heavy Nuclei
We show that the Bogoliubov-de Gennes equations for nuclear ground-state wave
functions support solutions in which the condensate has a mixture of
spin-singlet and spin-triplet pairing. We find that such mixed-spin condensates
do not occur when there are equal numbers of neutrons and protons, but only
when there is an isospin imbalance. Using a phenomenological Hamiltonian, we
predict that such nuclei may occur in the physical region within the proton
dripline. We also solve the Bogoliubov-de Gennes equations with variable
constraints on the spin-singlet and spin-triplet pairing amplitudes. For nuclei
that exhibit this new pairing behavior, the resulting energy surface can be
rather soft, suggesting that there may be low-lying excitations associated with
the spin mixing.Comment: 4+ pages, 3 figures, 1 table; 1 reference added; v2 corresponds to
the published versio
Angular-dependent Magnetoresistance Oscillations in NaCoO Single Crystal
We report measurements of the c-axis angular-dependent magnetoresistance
(AMR) for a NaCoO single crystal, with a magnetic field of 10 T
rotating within Co-O planes. Below the metal-insulator transition temperature
induced by the charge ordering, the oscillation of the AMR is dominated by a
two-fold rotational symmetry. The amplitudes of the oscillation corresponding
to the four- and six-fold rotational symmetries are distinctive in low
temperatures, but they merge into the background simultaneously at about 25 K.
The six-fold oscillation originates naturally from the lattice symmetry. The
observation of the four-fold rotational symmetry is consistent with the picture
proposed by Choy, et al., that the Co lattice in the charge ordered state will
split into two orthorhombic sublattice with one occupied by Co ions and
the other by Co ions. We have also measured the c-axis AMR for
NaCoO and NaCoO single crystals, and found no
evidence for the existence of two- and four-fold symmetries.Comment: 4 pages, 6 figures. Submitted to PR
Beating of the oscillations in the transport coefficients of a one-dimensionally periodically modulated two-dimensional electron gas in the presence of spin-orbit interaction
Transport properties of a two-dimensional electron gas (2DEG) are studied in
the presence of a perpendicular magnetic field , of a {\it weak}
one-dimensional (1D) periodic potential modulation, and of the spin-orbit
interaction (SOI) described only by the Rashba term. In the absence of the
modulation the SOI mixes the spin-up and spin-down states of neighboring Landau
levels into two new, unequally spaced energy branches. The levels of these
branches broaden into bands in the presence of the modulation and their
bandwidths oscillate with the field . Evaluated at the Fermi energy, the
-th level bandwidth of each series has a minimum or vanishes at different
values of the field . In contrast with the 1D-modulated 2DEG without SOI,
for which only one flat-band condition applies, here there are two flat-band
conditions that can change considerably as a function of the SOI strength
and accordingly influence the transport coefficients of the 2DEG. The
phase and amplitude of the Weiss and Shubnikov-de Haas (SdH) oscillations
depend on the strength . For small values of both oscillations
show beating patterns. Those of the former are due to the independently
oscillating bandwidths whereas those of the latter are due to modifications of
the density of states, exhibit an even-odd filling factor transition, and are
nearly independent of the modulation strength. For strong values of
the SdH oscillations are split in two
Doping evoluton of antiferromagnetic order and structural distortion in LaFeAsOF
We use neutron scattering to study the structural distortion and
antiferromagnetic (AFM) order in LaFeAsOF as the system is doped
with fluorine (F) to induce superconductivity. In the undoped state, LaFeAsO
exhibits a structural distortion, changing the symmetry from tetragonal (space
group ) to orthorhombic (space group ) at 155 K, and then
followed by an AFM order at 137 K. Doping the system with F gradually decreases
the structural distortion temperature, but suppresses the long range AFM order
before the emergence of superconductivity. Therefore, while superconductivity
in these Fe oxypnictides can survive in either the tetragonal or the
orthorhombic crystal structure, it competes directly with static AFM order.Comment: reference update
Fermi surface topology and low-lying quasiparticle structure of magnetically ordered Fe1+xTe
We report the first photoemission study of Fe1+xTe - the host compound of the
newly discovered iron-chalcogenide superconductors. Our results reveal a pair
of nearly electron- hole compensated Fermi pockets, strong Fermi velocity
renormalization and an absence of a spin-density-wave gap. A shadow hole pocket
is observed at the "X"-point of the Brillouin zone which is consistent with a
long-range ordered magneto-structural groundstate. No signature of Fermi
surface nesting instability associated with Q= pi(1/2, 1/2) is observed. Our
results collectively reveal that the Fe1+xTe series is dramatically different
from the undoped phases of the high Tc pnictides and likely harbor unusual
mechanism for superconductivity and quantum magnetic order.Comment: 5 pages, 4 Figures; Submitted to Phys. Rev. Lett. (2009
Metric adjusted skew information: Convexity and restricted forms of superadditivity
We give a truly elementary proof of the convexity of metric adjusted skew
information following an idea of Effros. We extend earlier results of weak
forms of superadditivity to general metric adjusted skew informations.
Recently, Luo and Zhang introduced the notion of semi-quantum states on a
bipartite system and proved superadditivity of the Wigner-Yanase-Dyson skew
informations for such states. We extend this result to general metric adjusted
skew informations. We finally show that a recently introduced extension to
parameter values of the WYD-information is a special case of
(unbounded) metric adjusted skew information.Comment: An error in the literature is pointed ou
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