3,320 research outputs found
Exact Groundstates of Rotating Bose Gases close to a Feshbach Resonance
We study the groundstates of rotating Bose gases when interactions are
affected by a nearby Feshbach resonance. We show that exact groundstates at
high angular momentum can be found analytically for a general and realistic
model for the resonant interactions. We identify parameter regimes where the
exact groundstates are exotic fractional quantum Hall states, the excitations
of which obey non-abelian exchange statistics.Comment: 4 page
Bridge between Abelian and Non-Abelian Fractional Quantum Hall States
We propose a scheme to construct the most prominent Abelian and non-Abelian
fractional quantum Hall states from K-component Halperin wave functions. In
order to account for a one-component quantum Hall system, these SU(K) colors
are distributed over all particles by an appropriate symmetrization. Numerical
calculations corroborate the picture that the proposed scheme allows for a
unification of both Abelian and non-Abelian trial wave functions in the study
of one-component quantum Hall systems.Comment: 4 pages, 2 figures; revised version, published in Phys. Rev. Let
The structure of spinful quantum Hall states: a squeezing perspective
We provide a set of rules to define several spinful quantum Hall model
states. The method extends the one known for spin polarized states. It is
achieved by specifying an undressed root partition, a squeezing procedure and
rules to dress the configurations with spin. It applies to both the
excitation-less state and the quasihole states. In particular, we show that the
naive generalization where one preserves the spin information during the
squeezing sequence, may fail. We give numerous examples such as the Halperin
states, the non-abelian spin-singlet states or the spin-charge separated
states. The squeezing procedure for the series (k=2,r) of spinless quantum Hall
states, which vanish as r powers when k+1 particles coincide, is generalized to
the spinful case. As an application of our method, we show that the counting
observed in the particle entanglement spectrum of several spinful states
matches the one obtained through the root partitions and our rules. This
counting also matches the counting of quasihole states of the corresponding
model Hamiltonians, when the latter is available.Comment: 19 pages, 7 figures; v2: minor changes, and added references.
Mathematica packages are available for downloa
Series of Abelian and Non-Abelian States in C>1 Fractional Chern Insulators
We report the observation of a new series of Abelian and non-Abelian
topological states in fractional Chern insulators (FCI). The states appear at
bosonic filling nu= k/(C+1) (k, C integers) in several lattice models, in
fractionally filled bands of Chern numbers C>=1 subject to on-site Hubbard
interactions. We show strong evidence that the k=1 series is Abelian while the
k>1 series is non-Abelian. The energy spectrum at both groundstate filling and
upon the addition of quasiholes shows a low-lying manifold of states whose
total degeneracy and counting matches, at the appropriate size, that of the
Fractional Quantum Hall (FQH) SU(C) (color) singlet k-clustered states
(including Halperin, non-Abelian spin singlet states and their
generalizations). The groundstate momenta are correctly predicted by the FQH to
FCI lattice folding. However, the counting of FCI states also matches that of a
spinless FQH series, preventing a clear identification just from the energy
spectrum. The entanglement spectrum lends support to the identification of our
states as SU(C) color-singlets but offers new anomalies in the counting for
C>1, possibly related to dislocations that call for the development of new
counting rules of these topological states.Comment: 12 pages with supplemental material, 20 figures, published versio
Specific Heat of Disordered He
Porous aerogel is a source of elastic scattering in superfluid 3He and
modifies the properties of the superfluid, suppressing the transition
temperature and order parameter. The specific heat jumps for the B-phase of
superfluid 3He in aerogel have been measured as a function of pressure and
interpreted using the homogeneous and inhomogeneous isotropic scattering
models. The specific heat jumps for other p-wave states are estimated for
comparison.Comment: Manuscript prepared for LT 2
Fractional Chern Insulators beyond Laughlin states
We report the first numerical observation of composite fermion (CF) states in
fractional Chern insulators (FCI) using exact diagonalization. The ruby lattice
Chern insulator model for both fermions and bosons exhibits a clear signature
of CF states at filling factors 2/5 and 3/7 (2/3 and 3/4 for bosons). The
topological properties of these states are studied through several approaches.
Quasihole and quasielectron excitations in FCI display similar features as
their fractional quantum hall (FQH) counterparts. The entanglement spectrum of
FCI groundstates shows an identical fingerprint to its FQH partner. We show
that the correspondence between FCI and FQH obeys the emergent symmetry already
established, proving the validity of this approach beyond the clustered states.
We investigate other Chern insulator models and find similar signatures of CF
states. However, some of these systems exhibit strong finite size effects.Comment: 9 pages with supplementary material, 13 figures, published versio
Dissipation signatures of the normal and superfluid phases in torsion pendulum experiments with 3He in aerogel
We present data for energy dissipation factor (Q^{-1}) over a broad
temperature range at various pressures of a torsion pendulum setup used to
study 3He confined in a 98% open silica aerogel. Values for Q^{-1} above T_c
are temperature independent and have a weak pressure dependence. Below T_c, a
deliberate axial compression of the aerogel by 10% widens the range of
metastability for a superfluid Equal Spin Pairing (ESP) state; we observe this
ESP phase on cooling and the B phase on warming over an extended temperature
region. While the dissipation for the B phase tends to zero as T goes to 0,
Q^{-1} exhibits a peak value greater than that at T_c at intermediate
temperatures. Values for Q^{-1} in the ESP phase are consistently higher than
in the B phase and are proportional to \rho_s/\rho until the ESP to B phase
transition is attained. We apply a viscoelastic collision-drag model, which
couples the motion of the helium and the aerogel through a frictional
relaxation time \tau_f. Our dissipation data is not sensitive to the damping
due to the presumed small but non-zero value of \tau_f. The result is that an
additional mechanism to dissipate energy not captured in the collision-drag
model and related to the emergence of the superfluid order must exist. The
extra dissipation below T_c is possibly associated with mutual friction between
the superfluid phases and the clamped normal fluid. The pressure dependence of
the measured dissipation in both superfluid phases is likely related to the
pressure dependence of the gap structure of the "dirty" superfluid. The large
dissipation in the ESP state is consistent with the phase being the A or the
Polar with the order parameter nodes oriented in the plane of the cell and
perpendicular to the aerogel anisotropy axis.Comment: 12 pages, 7 figure
Magnetic degeneracy and hidden metallicity of the spin density wave state in ferropnictides
We analyze spin density wave (SDW) order in iron-based superconductors and
electronic structure in the SDW phase. We consider an itinerant model for
Fe-pnictides with two hole bands centered at and two electron bands
centered at and in the unfolded BZ. A SDW order in such a
model is generally a combination of two components with momenta and
, both yield order in the folded zone. Neutron
experiments, however, indicate that only one component is present. We show that
or order is selected if we assume that only one hole band
is involved in the SDW mixing with electron bands. A SDW order in such 3-band
model is highly degenerate for a perfect nesting and hole-electron interaction
only, but we show that ellipticity of electron pockets and interactions between
electron bands break the degeneracy and favor the desired or
order. We further show that stripe-ordered system remains a metal for
arbitrary coupling. We analyze electronic structure for parameters relevant to
the pnictides and argue that the resulting electronic structure is in good
agreement with ARPES experiments. We discuss the differences between our model
and model of localized spins.Comment: reference list updated, typos are correcte
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