21 research outputs found
Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors
It was recently proposed to use the stray magnetic fields of superconducting
vortex lattices to trap ultracold atoms for building quantum emulators. This
calls for new methods for engineering and manipulating of the vortex states.
One of the possible routes utilizes type-1.5 superconducting layered systems
with multi-scale inter-vortex interactions. In order to explore the possible
vortex states that can be engineered, we present two phase diagrams of
phenomenological vortex matter models with multi-scale inter-vortex
interactions featuring several attractive and repulsive length scales. The
phase diagrams exhibit a plethora of phases, including conventional 2D lattice
phases, five stripe phases, dimer, trimer, and tetramer phases, void phases,
and stable low-temperature disordered phases. The transitions between these
states can be controlled by the value of an applied external field.Comment: 16 pages, 20 figure
Magnetism and pairing of two-dimensional trapped fermions
The emergence of local phases in a trapped two-component Fermi gas in an
optical lattice is studied using quantum Monte Carlo simulations. We treat
temperatures that are comparable or lower than those presently achievable in
experiments and large enough systems that both magnetic and paired phases can
be detected by inspection of the behavior of suitable short-range correlations.
We use the latter to suggest the interaction strength and temperature range at
which experimental observation of incipient magnetism and d-wave pairing are
more likely and evaluate the relation between entropy and temperature in
two-dimensional confined fermionic systems.Comment: 4 pages + supplementary materia
Kaleidoscope of exotic quantum phases in a frustrated XY model
The existence of quantum spin liquids was first conjectured by Pomeranchuk
some 70 years ago, who argued that frustration in simple antiferromagnetic
theories could result in a Fermi-liquid-like state for spinon excitations. Here
we show that a simple quantum spin model on a honeycomb lattice hosts the long
sought for Bose metal with a clearly identifiable Bose surface. The complete
phase diagram of the model is determined via exact diagonalization and is shown
to include four distinct phases separated by three quantum phase transitions
Interaction effects and quantum phase transitions in topological insulators
We study strong correlation effects in topological insulators via the Lanczos
algorithm, which we utilize to calculate the exact many-particle ground-state
wave function and its topological properties. We analyze the simple,
noninteracting Haldane model on a honeycomb lattice with known topological
properties and demonstrate that these properties are already evident in small
clusters. Next, we consider interacting fermions by introducing repulsive
nearest-neighbor interactions. A first-order quantum phase transition was
discovered at finite interaction strength between the topological band
insulator and a topologically trivial Mott insulating phase by use of the
fidelity metric and the charge-density-wave structure factor. We construct the
phase diagram at as a function of the interaction strength and the
complex phase for the next-nearest-neighbor hoppings. Finally, we consider the
Haldane model with interacting hard-core bosons, where no evidence for a
topological phase is observed. An important general conclusion of our work is
that despite the intrinsic nonlocality of topological phases their key
topological properties manifest themselves already in small systems and
therefore can be studied numerically via exact diagonalization and observed
experimentally, e.g., with trapped ions and cold atoms in optical lattices.Comment: 13 pages, 12 figures. Published versio
Pangolins in global camera trap data: Implications for ecological monitoring
Despite being heavily exploited, pangolins (Pholidota: Manidae) have been subject to limited research, resulting in a lack of reliable population estimates and standardised survey methods for the eight extant species. Camera trapping represents a unique opportunity for broad-scale collaborative species monitoring due to its largely non-discriminatory nature, which creates considerable volumes of data on a relatively wide range of species. This has the potential to shed light on the ecology of rare, cryptic and understudied taxa, with implications for conservation decision-making. We undertook a global analysis of available pangolin data from camera trapping studies across their range in Africa and Asia. Our aims were (1) to assess the utility of existing camera trapping efforts as a method for monitoring pangolin populations, and (2) to gain insights into the distribution and ecology of pangolins. We analysed data collated from 103 camera trap surveys undertaken across 22 countries that fell within the range of seven of the eight pangolin species, which yielded more than half a million trap nights and 888 pangolin encounters. We ran occupancy analyses on three species (Sunda pangolin Manis javanica, white-bellied pangolin Phataginus tricuspis and giant pangolin Smutsia gigantea). Detection probabilities varied with forest cover and levels of human influence for P. tricuspis, but were low (<0.05) for all species. Occupancy was associated with distance from rivers for M. javanica and S. gigantea, elevation for P. tricuspis and S. gigantea, forest cover for P. tricuspis and protected area status for M. javanica and P. tricuspis. We conclude that camera traps are suitable for the detection of pangolins and large-scale assessment of their distributions. However, the trapping effort required to monitor populations at any given study site using existing methods appears prohibitively high. This may change in the future should anticipated technological and methodological advances in camera trapping facilitate greater sampling efforts and/or higher probabilities of detection. In particular, targeted camera placement for pangolins is likely to make pangolin monitoring more feasible with moderate sampling efforts
Pangolins in Global Camera Trap Data: Implications for Ecological Monitoring
Despite being heavily exploited, pangolins (Pholidota: Manidae) have been subject to limited research, resulting in a lack of reliable population estimates and standardised survey methods for the eight extant species. Camera trapping represents a unique opportunity for broad-scale collaborative species monitoring due to its largely non-discriminatory nature, which creates considerable volumes of data on a relatively wide range of species. This has the potential to shed light on the ecology of rare, cryptic and understudied taxa, with implications for conservation decision-making. We undertook a global analysis of available pangolin data from camera trapping studies across their range in Africa and Asia. Our aims were (1) to assess the utility of existing camera trapping efforts as a method for monitoring pangolin populations, and (2) to gain insights into the distribution and ecology of pangolins. We analysed data collated from 103 camera trap surveys undertaken across 22 countries that fell within the range of seven of the eight pangolin species, which yielded more than half a million trap nights and 888 pangolin encounters. We ran occupancy analyses on three species (Sunda pangolin Manis javanica, white-bellied pangolin Phataginus tricuspis and giant pangolin Smutsia gigantea). Detection probabilities varied with forest cover and levels of human influence for P. tricuspis, but were low (M. javanica and S. gigantea, elevation for P. tricuspis and S. gigantea, forest cover for P. tricuspis and protected area status for M. javanica and P. tricuspis. We conclude that camera traps are suitable for the detection of pangolins and large-scale assessment of their distributions. However, the trapping effort required to monitor populations at any given study site using existing methods appears prohibitively high. This may change in the future should anticipated technological and methodological advances in camera trapping facilitate greater sampling efforts and/or higher probabilities of detection. In particular, targeted camera placement for pangolins is likely to make pangolin monitoring more feasible with moderate sampling efforts