240 research outputs found
Stability of trapped fermionic gases with attractive interactions
We present a unified overview, from the mean-field to the unitarity regime,
of the stability of a trapped Fermi gas with short range attractive
interactions. Unlike in a system of bosons, a Fermi gas is always stable in
these regimes, no matter how large the particle number. However, when the
interparticle spacing becomes comparable to the range of the interatomic
interactions, instability is not precluded.Comment: 5 pages, 4 figure
Design principles for shift current photovoltaics
While the basic principles and limitations of conventional solar cells are
well understood, relatively little attention has gone toward maximizing the
potential efficiency of photovoltaic devices based on shift currents. In this
work, we outline simple design principles for the optimization of shift
currents for frequencies near the band gap, derived from the analysis of a
general effective model. The use of a novel sum rule allows us to express the
band edge shift current in terms of a few model parameters and to show it
depends explicitly on wavefunctions via Berry connections in addition to
standard band structure. We use our approach to identify two new classes of
shift current photovoltaics, ferroelectric polymer films and single-layer
orthorhombic monochalcogenides such as GeS. We introduce tight-binding models
for these systems, and show that they exhibit the largest shift current
responsivities at the band edge reported so far. Moreover, exploring the
parameter space of these models we find photoresponsivities that can exceed
mA/W. Our results show how the study of the shift current via effective
models allows one to improve the possible efficiency of devices based on this
mechanism and better grasp their potential to compete with conventional solar
cells.Comment: 10 pages, 4 figures, AC and BMF share equal contributions. Published
in Nature Communication
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