Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G34: Atoms in Reduced Dimensions and Novel Geometries |
Hide Abstracts |
Sponsoring Units: DAMOP Chair: Lincoln Carr, Colorado School of Mines Room: 704 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G34.00001: Magnetism on the Lieb Lattice Fr\'ederic H\'ebert, Vladimir Iglovikov, Richard Scalettar, George Batrouni The fermionic Hubbard model on a square lattice is known to exhibit antiferromagnetism at half-filling for arbitrarily weak interactions, due to the nesting of its Fermi surface and the divergence of the density of states. This talk presents a determinant Quantum Monte Carlo study of the magnetic properties of the Hubbard model on the ``Lieb lattice,'' which is obtained from the square lattice by removing 1/4 of the sites in a regular pattern. This model exhibits a flat band at half-filling, surrounded by two dispersive bands. The non interacting states at half-filling are localized, which allows us to study the magnetic properties of a system that does not have a Fermi surface, although there is an infinite density of states at half-filling. Other magnetic phases may also appear away from half-filling. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G34.00002: Quantum Monte Carlo Study of Superconductivity on the Lieb Lattice Vladimir Iglovikov, Richard Scalettar, Fr\'ederic H\'ebert, George Batrouni The attractive fermion Hubbard model on a square lattice is known to have a finite temperature (Kosterlitz-Thouless) transition to a superconducting ground state away from half-filling. This talk presents determinant Quantum Monte Carlo results for pairing correlations on a ``Lieb lattice,'' which is obtained from the square lattice by regular pattern removal of 1/4 of the sites. The Lieb lattice has two dispersing bands, and one flat band. We will show how superconductivity differs when the chemical potential lies in the flat band. For large values of the on-site attractive interaction, the fermions form tightly bound bosonic pairs. In that limit, our work addresses the nature of Bose-Einstein condensation when the non-interacting band structure has no wave-vector which minimizes the energy. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G34.00003: FFLO pairing correlations in a trapped quasi one-dimensional Fermi gas Dominique Gautreau, Stephen Kudla, Daniel Sheehy Recent work has pursued the possibility of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase of imbalanced Fermi gases in one dimension, in which an imposed population imbalance between two species of interacting fermion leads to spatially-modulated local pairing correlations. While experiments at Rice (Liao et al, Nature 467, 567 (2010)) show consistency with the expected bulk phase diagram using the local density approximation, little is known about how the FFLO pairing correlations will be revealed experimentally. Using a simple variational wavefunction ansatz for the FFLO state of a trapped 1D gas, in which the population imbalance leads to an imbalance in pairing among harmonic oscillator states, we compute predicted experimental signatures of the FFLO phase in a trapped one-dimensional fermionic atomic gas. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G34.00004: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G34.00005: Heat capacity and sound velocities of low dimensional Fermi gases P. Salas, M.A. Solis We report the heat capacity ratio and sound velocities for an interactionless Fermi gas immersed in periodic structures such as penetrable multilayers or multitubes created by one (planes) or two perpendicular (tubes) external Dirac comb potentials. The isobaric specific heat of the fermion gas presents the dimensional crossover previously observed in the isochoric specific heat [1] - from 3D to 2D or to 1D -. The quotient between the two quantities has a prominent bump related to the confinement, and as the temperature increases, it goes towards the monoatomic classical gas value 5/3. We present the isothermal and the adiabatic sound velocities of the fermion gas which show anomalous behavior at temperatures below $T_F$ due to the dimensionality of the system, while at higher temperatures again we recover the behavior of a classical Fermi gas. Furthermore, as the temperature goes to zero the sound velocity has a finite value, as expected.\\[4pt] [1] P. Salas and M.A. Sol\'is, ``Trapping effect of periodic structures on the thermodynamic properties of a Fermi gas,'' J. Low Temp, Phys. (2013) DOI 10.1007/s10909-013-0939-x. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G34.00006: Spin imbalance in 1D trapped attractive Fermi atoms: T\textgreater 0 quantum Monte Carlo results ChangMo Yang, D.M. Ceperley Spin imbalance in a one-dimensional system of fermions with short-ranged attractive interactions is studied with continuous-space path-integral Monte Carlo simulation. Following closely the experiment with ${}^6$Li atoms~[1], the pair momentum distribution is calculated at various spin polarizations. FFLO-type pairing is confirmed at the experimental temperature and coupling strength. We compare our results to those of other numerical methods~[2-4] and discuss the prospects for experimental detection.\\[4pt] [1] Y.-A. Liao et al.,~\textit{Nature},~467, 567 (2010).\\[0pt] [2] H. Lu et al.,~\textit{Phys.~Rev.~Lett.},~108, 225302 (2012).\\[0pt] [3] F. Heidrich-Meisner et al.,~\textit{Phys.~Rev.~A},~81, 023629 (2010).\\[0pt] [4] M. Takahashi,~\textit{Prog.~Theor.~Phys,}~46, 1388 (1971).\\[0pt] [5] M. Casula et al.,~\textit{Phys.~Rev.~A},~78, 033607, (2008). [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G34.00007: Quasi-two-dimensional Fermi gases Meera Parish, Andrea Fischer, Jesper Levinsen We consider a two-component gas of fermionic atoms confined to a quasi-two-dimensional geometry by a harmonic trapping potential in the transverse direction. We construct a mean field theory of the BCS-BEC crossover that allows us to extrapolate to an infinite number of transverse harmonic oscillator levels. Even when the interactions are weak and the Fermi energy is less than the confinement frequency, we find that the higher transverse levels can substantially modify fermion pairing. We also investigate the effect of confinement on few-body correlations, and we demonstrate the existence of a universal tetramer for mass ratios $> 5.0$. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G34.00008: Pairing correlations in a trapped quasi one-dimensional Fermi gas Stephen Kudla, Dominique Gautreau, Daniel Sheehy We utilize a BCS-type variational wavefunction to study attractively-interacting quasi one-dimensional fermionic atomic gases, motivated by cold-atom experiments that access this regime using a anisotropic harmonic trapping potential (characterized by $\omega_x = \omega_y\gg \omega_z$) that confines the gas to a cigar-shaped geometry. To handle the presence of the trap along the $z$ direction, we construct our variational wavefunction from the harmonic oscillator Hermite functions that are the eigenfunctions of the single-particle problem. Using an analytic determination of the effective interaction among Hermite function states along with a numerical calculation of the resulting variational equations, we make specific experimental predictions for how local pairing correlations will be revealed in experimental probes like the local density, the momentum distribution, and the momentum correlation function. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G34.00009: Finite-temperature dynamical structure factor of the one-dimensional Bose gas: From the Gross-Pitaevskii equation to the Kardar-Parisi-Zhang universality class of dynamical critical phenomena Austen Lamacraft, Manas Kulkarni We study the finite-temperature dynamical structure factor S(k,$\omega$) of a one-dimensional Bose gas using numerical simulations of the Gross-Pitaevskii equation appropriate to a weakly interacting system. The line shape of the phonon peaks in S(k,$\omega$) has a width proportional to $|$k$|^{3/2}$ at low wave vectors. This anomalous width arises from resonant three-phonon interactions, and reveals a remarkable connection to the Kardar-Parisi-Zhang universality class of dynamical critical phenomena. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G34.00010: Casimir interaction between mobile impurities in one-dimensional quantum liquids Michael Schecter, Alex Kamenev At zero temperature virtual phonons of a quantum liquid scatter off impurities and mediate a long-range interaction, analogous to the Casimir effect. At finite temperature, moving impurities also experience a correlated friction due to coherent exchange of real phonons. In one dimension the effect is universal and the induced interaction decays as $1/r^3$, much slower than the van der Waals interaction $\sim1/r^6$ where $r$ is the impurity separation. The magnitude of the effect is characterized by the product of impurity-phonon scattering amplitudes, which are seen to vanish for the class of integrable impurity models. By tuning the parameters near integrability one can thus observe an attractive interaction turned into a repulsive one. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G34.00011: Spreading of correlations in the XXZ chain at finite temperatures Lars Bonnes, Andreas L\"auchli In a quantum quench, for instance by abruptly changing the interaction parameter in a spin chain, correlations can spread across the system but have to obey a speed limit set by the Lieb-Robinson bound. This results into a causal structure where the propagation front resembles a light-cone. One can ask how fast a correlation front actually propagates and how its velocity depends on the nature of the quench. This question is addressed by performing global quenches in the XXZ chain initially prepared in a finite-temperature state using minimally entangled typical thermal states (METTS). We provide numerical evidence that the spreading velocity of the spin correlation functions for the quench into the gapless phase is solely determined by the value of the final interaction and the amount of excess energy of the system. This is quite surprising as the XXZ model is integrable and its dynamics is constrained by a large amount of conserved quantities. In particular, the spreading velocity seems to interpolate linearly from a universal value at $T=\infty$ to the spin wave velocity of the final Hamiltonian in the limit of zero excess energy for $\Delta_{\mathrm{final}} > 0$. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G34.00012: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G34.00013: Order-by-disorder of interacting bosons on the dice lattice under a synthetic gauge field Matjaz Payrits, Ryan Barnett We consider a gas of interacting bosons in the two-dimensional dice lattice in the presence of a half-elementary magnetic flux threading each plaquette. The single particle spectrum of the system consists of three doubly-degenerate completely flat bands, which indicates a large ground state degeneracy. It is shown how this degeneracy is partially lifted in the superfluid regime at the mean-field level. Furthermore, it is shown how quantum and thermal fluctuations conclusively remove the remaining accidental degeneracy between the mean field states, thus selecting a unique state up to overall symmetries. This can be elegantly described by means of the distribution of condensate vortices in the Kagom\'{e} vortex lattice, which is dual to the dice lattice. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G34.00014: Collective Excitations in Quasi-2D and 3D Condensates Dan Lobser, Andrew Barentine, Heather Lewandowski, Eric Cornell Collective motion of a Bose-Einstein condensate has been a system of interest since the discovery of BEC. Boltzmann proved that the monopole mode of a thermal gas in an isotropic, harmonic and 3D trap is undamped [1, 2]. BECs are not classical gases and their weakly interacting nature causes damping in a 3D monopole mode. However, experimental limitations have precluded studies of this behavior in very spherical traps. Quantum gases confined to lower dimensions exhibit remarkable physical properties such as the Berezkinskii-Kosterlitz-Thouless transition or the Tonks-Girardeau gas. Confinement effects in a quasi-2D condensate are predicted to shift the frequency of the monopole mode [3]. One correction in particular connects a small frequency shift with certain quantum corrections [4]. Current results of our studies in 2D and 3D will be presented. \\[4pt] [1] ``Transverse Breathing Mode of an Elongated Bose-Einstein Condensate,'' F. Chevy, V. Bretin, P. Rosenbusch, K. W. Madison, and J. Dalibard, Phys. Rev. Lett. 88 250402 (2002). \\[0pt] [2] L. Boltzmann, Wissenschaftliche Abhandlungen, edited by F. Hasenorl (Barth, Leipzig, 1909), Vol. II \\[0pt] [3] Olshanii et al., Phys. Rev. Lett. 105, 095302 (2010) \\[0pt] [4] Hu, et al., Phys. Rev. Lett. 107, 110401 (2011) [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G34.00015: Universal high frequency high momentum behavior of dynamic structure factor in one dimensional interacting boson gas Ran Qi, Michael Pustilnik, Shina Tan We study the short-distance and short-time structure of density-density correlation in one dimensional repulsively interacting boson gas. A compact universal formula is obtained for the high frequency high momentum asymptotic behavior of dynamic structure factor. We observe non-monotonous behavior in the dependence of DSF on interacting strength and qualitative change in the singular behavior in different region of $q^2/\omega$. Possible experimental applications are discussed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2023 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700