74 research outputs found
Fermion pairing in mixed-dimensional atomic mixtures
We investigate the quantum phases of mixed-dimensional cold atom mixtures. In
particular, we consider a mixture of a Fermi gas in a two-dimensional lattice,
interacting with a bulk Fermi gas or a Bose-Einstein condensate in a
three-dimensional lattice. The effective interaction of the two-dimensional
system mediated by the bulk system is determined. We perform a functional
renormalization group analysis, and demonstrate that by tuning the properties
of the bulk system, a subtle competition of several superconducting orders can
be controlled among -wave, -wave, -wave, and
-wave pairing symmetries. Other instabilities such as a
charge-density wave order are also demonstrated to occur. In particular, we
find that the critical temperature of the -wave pairing induced by the
next-nearest-neighbor interactions can be an order of magnitude larger than
that of the same pairing induced by doping in the simple Hubbard model. We
expect that by combining the nearest-neighbor interaction with the
next-nearest-neighbor hopping (known to enhance -wave pairing), an even
higher critical temperature may be achieved.Comment: 10 pages, 10 figure
Observing light-induced Floquet band gaps in the longitudinal conductivity of graphene
We propose optical longitudinal conductivity as a realistic observable to
detect light-induced Floquet band gaps in graphene. These gaps manifest as
resonant features in the conductivity, when resolved with respect to the
probing frequency and the driving field strength. We demonstrate these features
via a dissipative master equation approach which gives access to a frequency-
and momentum-resolved electron distribution. This distribution follows the
light-induced Floquet-Bloch bands, resulting in a natural interpretation as
occupations of these bands. Furthermore, we show that there are population
inversions of the Floquet-Bloch bands at the band gaps for sufficiently strong
driving field strengths. This strongly reduces the conductivity at the
corresponding frequencies. Therefore our proposal puts forth not only an
unambiguous demonstration of light-induced Floquet-Bloch bands, which advances
the field of Floquet engineering in solids, but also points out the control of
transport properties via light, that derives from the electron distribution on
these bands
Laser operation based on Floquet-assisted superradiance
We demonstrate the feasibility of utilizing the recently established
Floquet-assisted superradiance for laser operation. In particular, we show the
robustness of this state against key imperfections. We consider the effect of a
finite linewidth of the driving field, modelled via phase diffusion. We find
that the linewidth of the light field in the cavity narrows drastically across
the FSP transition, reminiscent of a line narrowing at the laser transition.
Next, we demonstrate that the FSP is robust against inhomogeneous broadening,
while displaying a reduction of light intensity. We show that the depleted
population inversion of near-resonant Floquet states leads to hole burning in
the inhomogeneously broadened Floquet spectra. Finally, we show that the FSP is
robust against dissipation processes, with coefficients up to values that are
experimentally available. We conclude that the FSP presents a robust mechanism
that is capable of realistic laser operation
Detecting light-induced Floquet band gaps of graphene via trARPES
We propose a realistic regime to detect the light-induced topological band
gap in graphene via time-resolved angle-resolved photoelectron spectroscopy
(trARPES), that can be achieved with current technology. The direct observation
of Floquet-Bloch bands in graphene is limited by low-mobility,
Fourier-broadening, laser-assisted photoemission (LAPE), probe-pulse
energy-resolution bounds, space-charge effects and more. We characterize a
regime of low driving frequency and high amplitude of the circularly polarized
light that induces an effective band gap at the Dirac point that exceeds the
Floquet zone. This circumvents limitations due to energy resolutions and band
broadening. The electron distribution across the Floquet replica in this limit
allow for distinguishing LAPE replica from Floquet replica. We derive our
results from a dissipative master equation approach that gives access to
two-point correlation functions and the electron distribution relevant for
trARPES measurements
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