We use a functional integral formulation to study the finite temperature crossover from cooperative Cooper pairing independent bound state formation and condensation. show inadequacy of mean field results for normal properties obtained at saddle point level as coupling increases. The importance quantum (temporal) fluctuations is pointed out an interpolation scheme ${\mathit{T}}_{\mathit{c}}$ derived this view. time-dependent Ginzburg-Landau (TDGL) equation near shown describe damped mode in...

We determine the phase diagram of a quasi-one-dimensional superconductor (weakly coupled chains system with an open Fermi surface) in magnetic field. The usual Ginzburg-Landau regime is followed, when field increased, by cascade superconducting phases separated first-order transitions, which ends strong reentrance phase. These new show novel kind symmetry laminar type. Zeeman splitting does not completely suppress very field, ground state being this case Larkin-Ovchinnikov-Fulde-Ferrell state.

We analyze the phase diagram of uniform superfluidity for two-species fermion mixtures from Bardeen-Cooper-Schrieffer to Bose-Einstein condensation (BEC) limit as a function scattering parameter and population imbalance. find at zero temperature that imbalance versus is asymmetric unequal masses, having larger stability region when lighter fermions are in excess. In addition, we topological quantum transitions associated with disappearance or appearance momentum space regions quasiparticle...

We discuss the evolution from BCS to BEC superfluids in presence of spin-orbit coupling, and show that this is just a crossover balanced case. The dependence several thermodynamic properties, such as chemical potential, order parameter, pressure, entropy, isothermal compressibility spin susceptibility tensor on coupling interaction parameter at low temperatures are analyzed. studied both case equal Rashba Dresselhaus (ERD) Rashba-only (RO) coupling. Comparisons between two cases reveal...

We discuss ultracold Fermi gases in two dimensions, which could be realized a strongly confining one-dimensional optical lattice. obtain the temperature versus effective interaction phase diagram for an $s$-wave superfluid and show that, below certain critical ${T}_{c}$, spontaneous vortex-antivortex pairs appear all coupling strengths. In addition, we that evolution from weak-to-strong is smooth, system forms square lattice at lower ${T}_{M}$.

Abstract We discuss standard and tighter upper bounds on the critical temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> </mml:mrow> </mml:math> of two-dimensional superfluids superconductors versus particle density n or filling factor ν for continuum lattice systems from Bardeen–Cooper–Schrieffer (BCS) to Bose regime. consider only one-band Hamiltonians, where transition normal...

We consider the evolution of superfluid properties a three dimensional p-wave Fermi gas from weak (BCS) to strong (BEC) coupling as function scattering volume. analyse order parameter, quasi-particle excitation spectrum, chemical potential, average Cooper pair size and momentum distribution in ground state ($T = 0$). also discuss critical temperature $T_{\rm c}$, potential number unbound, bound fermions normal T_{\rm c}$). Lastly, we derive time-dependent Ginzburg-Landau equation for $T...

We discuss the emergence of rings zero-energy excitations in momentum space for superfluid phases ultracold fermions when spin-orbit effects, Zeeman fields, and interactions are varied. show that containing nodes possess nontrivial topological invariants, phase transitions between distinct belong to Lifshitz class. Upon crossing boundaries, existing massless Dirac gapless annihilate produce bulk zero-mode Majorana at then become massive gapped phase. characterize these tunable via several...

We discuss topological phase transitions in ultra-cold Fermi superfluids induced by interactions and artificial spin orbit fields. construct the diagram for population imbalanced systems at zero finite temperatures, analyze spectroscopic thermodynamic properties to characterize various transitions. For balanced systems, evolution from BCS BEC presence of spin-orbit effects is only a crossover as system remains fully gapped, even though triplet component order parameter emerges. However,...

The use of multicore optical fibers is emerging as a key solution to implement space-division multiplexing, essential for overcoming the capacity limits conventional single-mode fibers. However, next-generation high-capacity networks will require new devices compatible with these In this work, we present an all-fiber architecture high-speed core-selective switch, crucial efficient signal distribution in networks. device leverages interference achieve rapid core-switching within 0.7 μs-three...

The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this to happen three basic conditions need be satisfied. First, an indirect must exist when in its normal state. Second, superconductivity not destroyed due proximity ferromagnetic boundaries. Third, roughness $F/S$ interfaces small. appearance superconducting gap causes reduction existent This temperature dependent, being...

We study the superfluid and insulating phases of bosons in double-well optical lattices, focus on specific example a two-legged ladder, which is currently accessible experiments. obtain zero-temperature phase diagram using both mean-field time-evolving block decimation techniques. find that approach describes correct boundaries only when intrachain hopping sufficiently small comparison to on-site repulsion. show dependence interchain or tilt between double wells. Mott-insulator at unit...

We have experimentally observed the emergence of spontaneous antiferromagnetic spatial order in a sodium spinor Bose-Einstein condensate that was quenched through magnetic phase transition. For negative values quadratic Zeeman shift, gas initially prepared F = 1, mF 0 state collapsed into dynamically evolving superposition all 3 spin projections, 0, +/-1. The quench gave rise to rich, nonequilibrium behavior where both nematic and waves were generated. characterized spatiotemporal evolution...

We analyze the phase diagram of superfluidity for two-species fermion mixtures from Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit as a function scattering parameter, population imbalance, and mass anisotropy. identify regions corresponding normal, or uniform nonuniform superfluid phases, discuss topological quantum transitions in BCS, unitarity, BEC limits. derive Ginzburg-Landau equation near critical temperature, show that it describes dilute mixture paired...

We investigate the effects of quantum fluctuations on low-energy collective modes two-dimensional (2D) $s$-wave Fermi superfluids from BCS to Bose limit. compare our results recent Bragg scattering experiments in 2D box potentials, with very good agreement. show that phase and modulus pairing order parameter are absolutely necessary give physically acceptable chemical potential dispersion relation mode throughout evolution. Furthermore, we demonstrate change concave convex as interactions...

Orbital angular momentum can be used to implement high capacity data transmission systems that applied for classical and quantum communications. Here we experimentally study the generation properties of so-called perfect vortex beams Laguerre-Gaussian in ring-core optical fibers. Our results show when using a single preparation stage, present less ring-radius variation allows coupling higher power into ring core fiber. These lead lower requirements establish fiber-based communications links...

The low-temperature evolution from BCS to Bose-Einstein condensation (BEC) for a two-dimensional d-wave superconductor is discussed at the saddle point (mean field) level. A systematic study of changes thermodynamic properties presented as function charge carrier density and fixed interaction. It has been found that when interaction strength large enough, there critical below which single quasiparticle excitation spectrum develops gap. At higher carriers lower (towards regime) gapless...

We consider a single copper oxide plane with infinite Hubbard U on the sites and direct oxygen-oxygen copper-oxygen overlaps as model for high-${\mathit{T}}_{\mathit{c}}$ materials. Using slave-boson representation, we find region of parameter space charge-transfer-type metal-insulator transition at zero doping, i.e, half-filling in mean-field limit. Performing 1/N expansion calculate photoemission inverse-photoemission spectra near both n-type p-type materials using sudden approximation.

The phase diagrams of low density Fermi-Fermi mixtures with equal or unequal masses and populations are described at zero finite temperatures in the strong attraction limit. In this limit, mixture can be by a weakly interacting Bose-Fermi mixture, where bosons correspond to Feshbach molecules fermions excess atoms. First, we discuss three four fermion scattering processes, use exact boson-fermion boson-boson lengths generate terms underlying fermion-fermion length. dimensions, addition...

We consider p-wave pairing of single hyperfine state and s-wave two states ultracold atomic gases trapped in quasi-two-dimensional optical lattices. First, we analyse superfluid properties symmetries the strictly weak coupling BCS regime where discuss order parameter, chemical potential, critical temperature, compressibility density as a function filling factor for tetragonal orthorhombic Second, superfluids evolution from to BEC at low temperatures ($T \approx 0$), changes quasiparticle...

We analyze the evolution of two-band superfluidity from Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit. When interband interaction is tuned negative positive values, a quantum phase transition occurs 0-phase $\ensuremath{\pi}$-phase state, depending on relative two order parameters. Furthermore, population imbalances between bands can be created by tuning intraband or interactions. also find undamped low-energy collective excitations corresponding in-phase and...

We review aspects of the evolution from Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein condensation (BEC) in two dimensions, which have now become relevant systems with low densities, such as gated superconductors Li x ZrNCl, magic-angle twisted trilayer graphene, FeSe, FeSe 1− S , and ultracold Fermi superfluids. emphasize important role played by chemical potentials determining crossovers or topological quantum phase transitions during BCS–BEC one-band two-band superfluids...

We use the functional integral approach to study low energy collective excitations in a continuum model of neutral two-band superfluids at T=0 for all couplings with separable pairing interaction. In long wavelength and frequency limit, we recover Leggett's analytical results weak coupling (BCS) s-wave pairing, further obtain strong (BEC) both two three dimensional systems. also analyse numerically behavior out-of-phase {\it exciton} (finite frequency) mode in-phase phonon} (Goldstone) from...

The ground state phase diagram of fermion mixtures in optical lattices is analyzed as a function interaction strength, filling factor, and tunneling parameters. In addition to standard superfluid, phase-separated or coexisting superfluid--excess-fermion phases found homogeneous harmonically trapped systems, fermions have several insulating phases, including molecular Bose-Mott insulator (BMI), Fermi-Pauli (band) (FPI), BMI-FPI mixture Bose-Fermi checkerboard (BFC). BMI the counterpart atomic...