7,253 research outputs found
Criteria of off-diagonal long-range order in Bose and Fermi systems based on the Lee-Yang cluster expansion method
The quantum-statistical cluster expansion method of Lee and Yang is extended
to investigate off-diagonal long-range order (ODLRO) in one- and
multi-component mixtures of bosons or fermions. Our formulation is applicable
to both a uniform system and a trapped system without local-density
approximation and allows systematic expansions of one- and multi-particle
reduced density matrices in terms of cluster functions which are defined for
the same system with Boltzmann statistics. Each term in this expansion can be
associated with a Lee-Yang graph. We elucidate a physical meaning of each
Lee-Yang graph; in particular, for a mixture of ultracold atoms and bound
dimers, an infinite sum of the ladder-type Lee-Yang 0-graphs is shown to lead
to Bose-Einstein condensation of dimers below the critical temperature. In the
case of Bose statistics, an infinite series of Lee-Yang 1-graphs is shown to
converge and gives the criteria of ODLRO at the one-particle level.
Applications to a dilute Bose system of hard spheres are also made. In the case
of Fermi statistics, an infinite series of Lee-Yang 2-graphs is shown to
converge and gives the criteria of ODLRO at the two-particle level.
Applications to a two-component Fermi gas in the tightly bound limit are also
made.Comment: 21 pages, 10 figure
Ferromagnetism of cold fermions loaded into a decorated square lattice
We investigate two-component ultracold fermions loaded into a decorated
square lattice, which are described by the Hubbard model with repulsive
interactions and nearest neighbor hoppings. By combining the real-space
dynamical mean-field theory with the numerical renormalization group method, we
discuss how a ferromagnetically ordered ground state in the weak coupling
regime, which originates from the existence of a dispersionless band, is
adiabatically connected to a Heisenberg ferrimagnetic state in the strong
coupling limit. The effects of level splitting and hopping imbalance are also
addressed.Comment: 8 pages, 7 figure
Half-Quantum Vortices in Thin Film of Superfluid He
Stability of a half-quantum vortex (HQV) in superfluid He has been
discussed recently by Kawakami, Tsutsumi and Machida in Phys. Rev. B {\bf 79},
092506 (2009). We further extend this work here and consider the A phase of
superfluid He confined in thin slab geometry and analyze the HQV realized
in this setting. Solutions of HQV and singly quantized singular vortex are
evaluated numerically by solving the Ginzburg-Landau (GL) equation and
respective first critical angular velocities are obtained by employing these
solutions. We show that the HQV in the A phase is stable near the boundary
between the A and A phases. It is found that temperature and magnetic
field must be fixed first in the stable region and subsequently the angular
velocity of the system should be increased from zero to a sufficiently large
value to create a HQV with sufficiently large probability. A HQV does not form
if the system starts with a fixed angular velocity and subsequently the
temperature is lowered down to the A phase. It is estimated that the
external magnetic field with strength on the order of 1 T is required to have a
sufficiently large domain in the temperature-magnetic field phase diagram to
have a stable HQV.Comment: 5 pages, 5 figure
Oscillatory Spin Polarization and Magneto-Optic Kerr Effect in Fe3O4 Thin Films on GaAs(001)
The spin dependent properties of epitaxial Fe3O4 thin films on GaAs(001) are
studied by the ferromagnetic proximity polarization (FPP) effect and
magneto-optic Kerr effect (MOKE). Both FPP and MOKE show oscillations with
respect to Fe3O4 film thickness, and the oscillations are large enough to
induce repeated sign reversals. We attribute the oscillatory behavior to
spin-polarized quantum well states forming in the Fe3O4 film. Quantum
confinement of the t2g states near the Fermi level provides an explanation for
the similar thickness dependences of the FPP and MOKE oscillations.Comment: to appear in Phys. Rev. Let
Supersolid state in fermionic optical lattice systems
We study ultracold fermionic atoms trapped in an optical lattice with
harmonic confinement by combining the real-space dynamical mean-field theory
with a two-site impurity solver. By calculating the local particle density and
the pair potential in the systems with different clusters, we discuss the
stability of a supersolid state, where an s-wave superfluid coexists with a
density-wave state of checkerboard pattern. It is clarified that a confining
potential plays an essential role in stabilizing the supersolid state. The
phase diagrams are obtained for several effective particle densities.Comment: 7 pages, 5 figures, Phys. Rev. A in pres
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