Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V3: Correlated Phases in Fermi Gases of Ultracold Atoms |
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Sponsoring Units: DCMP DAMOP Room: 301/302 |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V3.00001: A Mott insulator of fermionic atoms in an optical lattice Invited Speaker: In a solid material strong interactions between the electrons can lead to surprising properties. A prime example is the Mott insulator, where the suppression of conductivity is a result of interactions and not the consequence of a filled Bloch band. The proximity to the Mott insulating phase in fermionic systems is the origin for many intriguing phenomena in condensed matter physics, most notably high-temperature superconductivity. Compared to real materials, a fermionic quantum gas trapped in an optical lattice offers a very pure realisation of the Hubbard model, giving a new approach to understand the physics of strongly correlated systems. We report on the formation of a Mott insulator of a repulsively interacting two-component Fermi gas in an optical lattice. It is signalled by three features: a drastic suppression of doubly occupied lattice sites, a strong reduction of the compressibility inferred from the response of double occupancy to atom number increase, and the appearance of a gapped mode in the excitation spectrum. In collaboration with Robert J\"ordens, Niels Strohmaier, and Daniel Greif, ETH Zurich; Kenneth G\"unter, ETH Zurich, ENS Paris; Leticia Tarruell and Tilman Esslinger, ETH Zurich. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 9:12AM |
V3.00002: The phase-diagram of a superfluid two-component Fermi gas Invited Speaker: What is the benefit of realizing superfluidity in a gas a million times more dilute than air? Such systems consist of well-separated atoms which can be observed and manipulated with the control and precision of atomic physics, and which can be treated with first-principles calculations. By implementing scattering resonances, we have realized the strong-coupling limit of the Bardeen Schrieffer-Cooper (BCS) mechanism and observed a normalized transition temperature of 20\% of the Fermi temperature, higher than in any superconductor. When the population of the two spin states is imbalanced, pairing is frustrated; and superfluidity is quenched at the Chandrasekhar-Clogston limit. When the fermions can form molecules, we observe the emergence of bosonic behavior, and an imbalanced two-component Fermi system can be described as a boson-fermion mixture. Pairing correlations have been studied by rf spectroscopy, determining the fermion pair size and the pairing gap energy in a resonantly interacting superfluid. These studies illustrate a new approach to condensed-matter physics where many-body Hamiltonians are realized in dilute atomic gases. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:48AM |
V3.00003: Trapping and cooling fermionic atoms into the Mott and N\'eel states Invited Speaker: Atomic gases cooled to Nanokelvin temperatures are a new exciting tool to study a broad range of quantum phenomena. In particular, the outstanding degree of control which has been achieved over these quantum systems facilitates access to strongly correlated quantum many body physics. For example, optical lattices have been created to mimic condensed matter systems. We perform a theoretical study of a fermionic gas with two repulsively interacting hyperfine states confined to an optical lattice. We determine a generic state diagram in the presence of a harmonic confining potential. We discuss implications for current experiments. Further we outline different strategies to reach the antiferromagnetic phase. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:24AM |
V3.00004: Polarized Fermi condensates Invited Speaker: We theoretically investigate the polarized two-component Fermi gas, which is the simplest fermion system displaying both superfluidity and ``magnetism''. In particular, we show that the elusive Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulated superfluid phase may be realized by embedding the polarized Fermi gas in an array of weakly-coupled parallel 1D ``tubes'' produced by a two-dimensional optical lattice. We argue that the most promising regime for observing the FFLO phase is in the quasi-1D regime, where the atomic motion is largely 1D but there is weak tunneling in the transverse directions that stabilizes long range order. Moreover, within this system, there is an additional phase transition in the FFLO phase, where the quasiparticle spectrum changes from gapless near the 3D limit to gapped in the quasi-1D regime. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 11:00AM |
V3.00005: A Three-Component Degenerate Fermi Gas. Invited Speaker: We have realized a three-component Fermi gas consisting of the three lowest spin states ($|1\rangle$, $|2\rangle$, $|3\rangle$) of the $^6$Li atom. Interactions in this system are governed by three different scattering lengths ($a_{12}$, $a_{23}$, $a_{13}$) between the three states, which all exhibit broad and overlapping Feshbach resonances. This enables us to tune the interactions of the system to become both strongly repulsive and strongly attractive, making it a generic three-component system. It is therefore ideally suited to study predictions of exotic phases such as color superconductivity that are expected for example inside of neutron stars. It is also possible to tune the scattering lengths to very small values simultaneously, which facilitates the preparation of the mixture: Starting from a degenerate mixture of atoms in states $|1\rangle$ and $|2\rangle$, we simultaneously apply radio frequencies resonant with the $|1\rangle$-$|2\rangle$ and $|2\rangle$-$|3\rangle$ transitions. This causes the three states to be mixed. To obtain an incoherently mixed sample within a few hundred milliseconds we apply a small magnetic field gradient along the weak axis of our trap. In first experiments we studied the collisional stability of our gas with respect to the magnetic field [1]. We observe an intriguing three-body loss resonance that occurs where all two-body scattering lengths are negative and no two-body bound state exists. The mixture is stable where the scattering lengths are relatively small, which is an important prerequisite for the preparation of the gas. The stable gas is also a good starting point for experiments in the strongly interacting regime, where we aim to observe many-body effects. Progress on this effort will be reported. \\[4pt] [1] T.B. Ottenstein et al., Phys. Rev. Lett. 101, 203202. [Preview Abstract] |
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