arXiv subjects

Umberto Toniolo

Publications and source records attributed to Umberto Toniolo.

4 recordsLinked to original sources

arXiv2018

Reduced quantum anomaly in a quasi-2D Fermi superfluid: The significance of the confinement-induced effective range of interactions

A two-dimensional (2D) harmonically trapped interacting Fermi gas is anticipated to exhibit a quantum anomaly and possesses a breathing mode at frequencies different from a classical scale invariant value $ω_{B}=2ω_{\perp}$, where $ω_{\perp}$ is the trapping frequency. The predicted maximum quantum anomaly ($\sim10\%$) has not been confirmed in experiments. Here, we theoretically investigate the zero-temperature density equation of state and the breathing mode frequency of an interacting Fermi superfluid at the dimensional crossover from three to two dimensions. We find that the simple model of a 2D Fermi gas with a single $s$-wave scattering length is not adequate to describe the experiments in the 2D limit, as commonly believed. A more complete description of quasi-2D leads to a much weaker quantum anomaly, consistent with the experimental observations. We clarify that the reduced quantum anomaly is due to the significant confinement-induced effective range of interactions, which is overlooked in previous theoretical and experimental studies.

cond-mat.quant-gas↗

arXiv2018

Breathing mode frequency of a strongly interacting Fermi gas across the 2D-3D dimensional crossover

We address the interplay between dimension and quantum anomaly on the breathing mode frequency of a strongly interacting Fermi gas harmonically trapped at zero temperature. Using a beyond mean-field, Gaussian pair fluctuation theory, we employ periodic boundary conditions to simulate the dimensionality of the system and impose a local density approximation, with two different schemes, to model different trapping potentials in the tightly-confined axial direction. By using a sum-rule approach, we compute the breathing mode frequency associated with a small variation of the trapping frequency along the weakly-confined transverse direction, and describe its behavior as functions of the dimensionality, from two- to three-dimensions, and of the interaction strength. We compare our predictions with previous calculations on the two-dimensional breathing mode anomaly and discuss their possible observation in ultracold Fermi gases of $^{6}$Li and $^{40}$K atoms.

cond-mat.quant-gas↗

arXiv2017

Dimensional crossover in a strongly interacting ultracold atomic Fermi gas

We theoretically explore the crossover from three dimensions (3D) to two (2D) in a strongly interacting atomic Fermi superfluid through confining the transverse spatial dimension. Using the gaussian pair fluctuation theory, we determine the zero-temperature equation of state and Landau critical velocity as functions of the spatial extent of the transverse dimension and interaction strength. In the presence of strong interactions, we map out a dimensional crossover diagram from the location of maximum critical velocity, which exhibits distinct dependence on the transverse dimension from 2D to quasi-2D, and to 3D. We calculate the dynamic structure factor to characterize the low-energy excitations of the system and propose that the intermediate quasi-2D regime can be experimentally probed using Bragg spectroscopy.

cond-mat.quant-gas↗

arXiv2016

Larkin-Ovchinnikov superfluidity in a two-dimensional imbalanced atomic Fermi gas

We present an extensive study of two-dimensional Larkin-Ovchinnikov (LO) superfluidity in a spin-imbalanced two-component atomic Fermi gas. In the context of Fulde-Ferrell-Larkin- Ovchinnikov (FFLO) phase, we explore a wide and generic class of pairing gap functions with ex- plicit spatial dependency. The mean-field theory of such phases is applied through the Bogoliubov-de Gennes equations in which the pairing gap can be determined self-consistently. In order to systemat- ically explore the configuration space we consider both the canonical and grand canonical ensembles where we control the polarization or chemical potentials of the system, respectively. The mean-field calculations enable us to understand the nature of the phase transitions in the fully paired Bardeen- Cooper-Schrieffer (BCS) state, exotic LO phase, and partially polarized free Fermi gas. The order of the phase transitions has been examined and in particular we find a weak first-order phase transition between the exotic inhomogeneous LO phase and the BCS phase. In comparison to the three-dimensional case, where the phase diagram is dominated by a generic separation phase, we predict a broader parameter space for the spatially inhomogeneous LO phase. By computing the superfluid density of the LO phase at different polarization, we show how the superfluidity of the system is suppressed with increasing spin polarization.

cond-mat.quant-gas↗