19,633 research outputs found
Phase transition of a Bose gas in a harmonic potential
We consider a dilute Bose gas confined by a harmonic potential. We define an
appropriate thermodynamic limit and analyze the properties of the phases and
phase transition in this limit. Critical properties in the presence of the
potential are found to be different from, though simply related, to those in
the usual translationally invariant case. We argue that the properties of
magnetically trapped rubidium\cite{Wieman} and sodium\cite{ketterle} gases (in
which Bose-Einstein condensation has been recently observed) are well
approximated by our thermodynamic limit except in a narrow window of
temperature around the critical temperature. We also consider the effect of the
confining potential on the non-equilibrium dynamics following a rapid quench to
the ordered side and give a scaling description of the late time universal
dynamics.Comment: 10 page
Momentum Distribution for Bosons with Positive Scattering Length in a Trap
The coordinate-momentum double distribution function is calculated in the local density approximation for bosons with
positive scattering length in a trap. The calculation is valid to the first
order of . To clarify the meaning of the result, it is compared for a
special case with the double distribution function of
Wigner.Comment: Latex fil
Spectral Weights, d-wave Pairing Amplitudes, and Particle-hole Tunneling Asymmetry of a Strongly Correlated Superconductor
The spectral weights (SW's) for adding and removing an electron of the
Gutzwiller projected d-wave superconducting (SC) state of the t-J-type models
are studied numerically on finite lattices. Restrict to the uniform system but
treat exactly the strong correlation between electrons, we show that the
product of weights is equal to the pairing amplitude squared, same as in the
weakly coupled case. In addition, we derive a rigorous relation of SW with
doping in the electron doped system and obtain particle-hole asymmetry of the
conductance-proportional quantity within the SC gap energy and, also, the
anti-correlation between gap sizes and peak heights observed in tunneling
spectroscopy on high Tc cuprates.Comment: 4 Revtex pages and 4 .eps figures. Published versio
The infrared conductivity of NaCoO: evidence of gapped states
We present infrared ab-plane conductivity data for the layered cobaltate
NaCoO at three different doping levels (, and 0.75). The
Drude weight increases monotonically with hole doping, . At the lowest
hole doping level =0.75 the system resembles the normal state of underdoped
cuprate superconductors with a scattering rate that varies linearly with
frequency and temperature and there is an onset of scattering by a bosonic mode
at 600 \cm. Two higher hole doped samples ( and 0.25) show two
different-size gaps (110 \cm and 200 \cm, respectively) in the optical
conductivities at low temperatures and become insulators. The spectral weights
lost in the gap region of 0.50 and 0.25 samples are shifted to prominent peaks
at 200 \cm and 800 \cm, respectively. We propose that the two gapped states of
the two higher hole doped samples (=0.50 and 0.25) are pinned charge ordered
states.Comment: 4 pages, 3 figure
^{59}Co NMR evidence for charge ordering below T_{CO}\sim 51 K in Na_{0.5}CoO_2
The CoO layers in sodium-cobaltates NaCoO may be viewed as
a spin triangular-lattice doped with charge carriers. The underlying
physics of the cobaltates is very similar to that of the high cuprates.
We will present unequivocal Co NMR evidence that below ,
the insulating ground state of the itinerant antiferromagnet
NaCoO () is induced by charge ordering.Comment: Phys. Rev. Lett. 100 (2008), in press. 4 figure
Anomalous broadening of the spin-flop transition in the reentrant spin-glass phase of LaSrCuO ()
The magnetization in a lightly doped LaSrCuO ()
single crystal was measured. Spin-flop transition was clearly observed in the
hole doped antiferromagnetically ordered state under increasing magnetic fields
perpendicular to the CuO plane. In the spin-glass phase below 25K, the
spin-flop transition becomes broad but the step in the magnetization curve
associated with the transition remains finite at the lowest temperature. We
show in this report that, at low temperature, the homogeneous antiferromagnetic
order is disturbed by the re-distribution of holes, and that the spatial
variance of the local hole concentration around increases.Comment: to be published to Physical Review
Bose-Einstein Condensation of Atoms in a Trap
We point out that the local density approximation (LDA) of Oliva is an
adaptation of the Thomas-Fermi method, and is a good approximation when
,
the LDA leads to a quantitative result (14') easily checked by experiments.
Critical remarks are made about the physics of the many body problem in terms
of the scattering length .Comment: 9 pages, latex. one figure, available from author
Suppression of the commensurate spin-Peierls state in Sc-doped TiOCl
We have performed x-ray scattering measurements on single crystals of the
doped spin-Peierls compound Ti(1-x)Sc(x)OCl (x = 0, 0.01, 0.03). These
measurements reveal that the presence of non-magnetic dopants has a profound
effect on the unconventional spin-Peierls behavior of this system, even at
concentrations as low as 1%. Sc-doping suppresses commensurate fluctuations in
the pseudogap and incommensurate spin-Peierls phases of TiOCl, and prevents the
formation of a long-range ordered spin-Peierls state. Broad incommensurate
scattering develops in the doped compounds near Tc2 ~ 93 K, and persists down
to base temperature (~ 7 K) with no evidence of a lock-in transition. The width
of the incommensurate dimerization peaks indicates short correlation lengths on
the order of ~ 12 angstroms below Tc2. The intensity of the incommensurate
scattering is significantly reduced at higher Sc concentrations, indicating
that the size of the associated lattice displacement decreases rapidly as a
function of doping.Comment: 7 pages, 5 figure
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