49 research outputs found
Interaction-induced chiral p_x \pm i p_y superfluid order of bosons in an optical lattice
The study of superconductivity with unconventional order is complicated in
condensed matter systems by their extensive complexity. Optical lattices with
their exceptional precision and control allow one to emulate superfluidity
avoiding many of the complications of condensed matter. A promising approach to
realize unconventional superfluid order is to employ orbital degrees of freedom
in higher Bloch bands. In recent work, indications were found that bosons
condensed in the second band of an optical chequerboard lattice might exhibit
p_x \pm i p_y order. Here we present experiments, which provide strong evidence
for the emergence of p_x \pm i p_y order driven by the interaction in the local
p-orbitals. We compare our observations with a multi-band Hubbard model and
find excellent quantitative agreement
Tunable gauge potential for neutral and spinless particles in driven lattices
We present a universal method to create a tunable, artificial vector gauge
potential for neutral particles trapped in an optical lattice. The necessary
Peierls phase of the hopping parameters between neighboring lattice sites is
generated by applying a suitable periodic inertial force such that the method
does not rely on any internal structure of the particles. We experimentally
demonstrate the realization of such artificial potentials, which generate
ground state superfluids at arbitrary non-zero quasi-momentum. We furthermore
investigate possible implementations of this scheme to create tuneable magnetic
fluxes, going towards model systems for strong-field physics
Orbital superfluidity in the -band of a bipartite optical square lattice
The successful emulation of the Hubbard model in optical lattices has
stimulated world wide efforts to extend their scope to also capture more
complex, incompletely understood scenarios of many-body physics. Unfortunately,
for bosons, Feynmans fundamental "no-node" theorem under very general
circumstances predicts a positive definite ground state wave function with
limited relevance for many-body systems of interest. A promising way around
Feynmans statement is to consider higher bands in optical lattices with more
than one dimension, where the orbital degree of freedom with its intrinsic
anisotropy due to multiple orbital orientations gives rise to a structural
diversity, highly relevant, for example, in the area of strongly correlated
electronic matter. In homogeneous two-dimensional optical lattices, lifetimes
of excited bands on the order of a hundred milliseconds are possible but the
tunneling dynamics appears not to support cross-dimensional coherence. Here we
report the first observation of a superfluid in the -band of a bipartite
optical square lattice with -orbits and -orbits arranged in a
chequerboard pattern. This permits us to establish full cross-dimensional
coherence with a life-time of several ten milliseconds. Depending on a small
adjustable anisotropy of the lattice, we can realize real-valued striped
superfluid order parameters with different orientations or a
complex-valued order parameter, which breaks time reversal
symmetry and resembles the -flux model proposed in the context of high
temperature superconductors. Our experiment opens up the realms of orbital
superfluids to investigations with optical lattice models.Comment: 5 pages, 5 figure
Topological semimetal in a fermionic optical lattice
Optical lattices play a versatile role in advancing our understanding of
correlated quantum matter. The recent implementation of orbital degrees of
freedom in chequerboard and hexagonal optical lattices opens up a new thrust
towards discovering novel quantum states of matter, which have no prior analogs
in solid state electronic materials. Here, we demonstrate that an exotic
topological semimetal emerges as a parity-protected gapless state in the
orbital bands of a two-dimensional fermionic optical lattice. The new quantum
state is characterized by a parabolic band-degeneracy point with Berry flux
, in sharp contrast to the flux of Dirac points as in graphene. We
prove that the appearance of this topological liquid is universal for all
lattices with D point group symmetry as long as orbitals with opposite
parities hybridize strongly with each other and the band degeneracy is
protected by odd parity. Turning on inter-particle repulsive interactions, the
system undergoes a phase transition to a topological insulator whose
experimental signature includes chiral gapless domain-wall modes, reminiscent
of quantum Hall edge states.Comment: 6 pages, 3 figures and Supplementary Informatio
Quantum phase transition to unconventional multi-orbital superfluidity in optical lattices
Orbital physics plays a significant role for a vast number of important
phenomena in complex condensed matter systems such as high-T
superconductivity and unconventional magnetism. In contrast, phenomena in
superfluids -- especially in ultracold quantum gases -- are commonly well
described by the lowest orbital and a real order parameter. Here, we report on
the observation of a novel multi-orbital superfluid phase with a {\it complex}
order parameter in binary spin mixtures. In this unconventional superfluid, the
local phase angle of the complex order parameter is continuously twisted
between neighboring lattice sites. The nature of this twisted superfluid
quantum phase is an interaction-induced admixture of the p-orbital favored by
the graphene-like band structure of the hexagonal optical lattice used in the
experiment. We observe a second-order quantum phase transition between the
normal superfluid (NSF) and the twisted superfluid phase (TSF) which is
accompanied by a symmetry breaking in momentum space. The experimental results
are consistent with calculated phase diagrams and reveal fundamentally new
aspects of orbital superfluidity in quantum gas mixtures. Our studies might
bridge the gap between conventional superfluidity and complex phenomena of
orbital physics.Comment: 5 pages, 4 figure
Novel Arenavirus Sequences in Hylomyscus sp. and Mus (Nannomys) setulosus from CĂ´te d'Ivoire: Implications for Evolution of Arenaviruses in Africa
This study aimed to identify new arenaviruses and gather insights in the evolution of arenaviruses in Africa. During 2003 through 2005, 1,228 small mammals representing 14 different genera were trapped in 9 villages in south, east, and middle west of Côte d'Ivoire. Specimens were screened by pan-Old World arenavirus RT-PCRs targeting S and L RNA segments as well as immunofluorescence assay. Sequences of two novel tentative species of the family Arenaviridae, Menekre and Gbagroube virus, were detected in Hylomyscus sp. and Mus (Nannomys) setulosus, respectively. Arenavirus infection of Mus (Nannomys) setulosus was also demonstrated by serological testing. Lassa virus was not found, although 60% of the captured animals were Mastomys natalensis. Complete S RNA and partial L RNA sequences of the novel viruses were recovered from the rodent specimens and subjected to phylogenetic analysis. Gbagroube virus is a closely related sister taxon of Lassa virus, while Menekre virus clusters with the Ippy/Mobala/Mopeia virus complex. Reconstruction of possible virus–host co-phylogeny scenarios suggests that, within the African continent, signatures of co-evolution might have been obliterated by multiple host-switching events
Support for and resistance against large stadia: the role of lifestyle and other socio-economic factors
From the Olympics to the World Cup, mega sporting events are a source of enjoyment for tens of thousands of people, but can also be a source of intense debate and controversy. This insightful new Handbook addresses a number of central questions, including: How are host cities selected and under what economic conditions? How are these events organized, and how is local resistance overcome? Based on historical and empirical experience, what are the pitfalls for the organizers of these events? What are the potential economic benefits, including any international image effects? How can the costs be minimized and the benefits maximized for host cities and countries? How do these mega events impact the challenges of globalization and what is their environmental legacy
Measuring and quantifying lifestyles and their impact on public choices: the case of professional football in Munich
Lifestyle data are rarely used in multivariate economic and social studies because the data describe the probability of having a categorical attribute. We propose a novel conversion of lifestyle data into metric scale values. Examining the 2001 referendum on the Allianz-Arena in Munich, our analysis demonstrates that refined indicators of value and strata orientation outperform the typical oriented indicators of economic wealth, in terms of capturing the spatial distribution of support and opposition to the project