Polaron-to-Polaron Transitions in the Radio-Frequency Spectrum of a Quasi-Two-Dimensional Fermi Gas

Zhang, Y.; Ong, Willie; Arakelyan, Ilya; Thomas, J. E.

doi:10.1103/physrevlett.108.235302

Cited by 159 publications

(203 citation statements)

References 18 publications

(14 reference statements)

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“…Here, we note an interesting feature of the mean-field treatment above. One finds that for a certain parameter regime, no mean-field solution can be found due to a singularity in the self-consistency (17). The singularity arises when the denominator of the right-hand side of Eq.…”

Section: Effective Mass Of the Polaronmentioning

confidence: 99%

“…(17). Note that we did not include the mean-field energy of the interactions between condensed bosons and the impurity E MF = 2πa IB,σ n 0 μ in the binding energy.…”

Section: Binding Energy Of the Polaronmentioning

confidence: 99%

“…The set of self-consistency conditions (17) can then be reformulated as a single scalar equation for :…”

Section: B Mean-field Polaron Solutionmentioning

confidence: 99%

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Radio-frequency spectroscopy of polarons in ultracold Bose gases

Shashi¹,

Grusdt²,

Abanin³

et al. 2014

Phys. Rev. A

108

182

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Recent experimental advances enabled the realization of mobile impurities immersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here, we consider impurities with two or more internal hyperfine states, and study their radio-frequency (rf) absorption spectra, which correspond to transitions between two different hyperfine states. We calculate rf spectra for the case when one of the hyperfine states involved interacts with the BEC, while the other state is noninteracting, by performing a nonperturbative resummation of the probabilities of exciting different numbers of phonon modes. In the presence of interactions, the impurity gets dressed by Bogoliubov excitations of the BEC, and forms a polaron. The rf signal contains a δ-function peak centered at the energy of the polaron measured relative to the bare impurity transition frequency with a weight equal to the amount of bare impurity character in the polaron state. The rf spectrum also has a broad incoherent part arising from the background excitations of the BEC, with a characteristic power-law tail that appears as a consequence of the universal physics of contact interactions. We discuss both the direct rf measurement, in which the impurity is initially in an interacting state, and the inverse rf measurement, in which the impurity is initially in a noninteracting state. In the latter case, in order to calculate the rf spectrum, we solve the problem of polaron formation: a mobile impurity is suddenly introduced in a BEC, and dynamically gets dressed by Bogoliubov phonons. Our solution is based on a time-dependent variational ansatz of coherent states of Bogoliubov phonons, which becomes exact when the impurity is localized. Moreover, we show that such an ansatz compares well with a semiclassical estimate of the propagation amplitude of a mobile impurity in the BEC. Our technique can be extended to cases when both initial and final impurity states are interacting with the BEC.

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Section: Effective Mass Of the Polaronmentioning

confidence: 99%

“…(17). Note that we did not include the mean-field energy of the interactions between condensed bosons and the impurity E MF = 2πa IB,σ n 0 μ in the binding energy.…”

Section: Binding Energy Of the Polaronmentioning

confidence: 99%

See 1 more Smart Citation

Radio-frequency spectroscopy of polarons in ultracold Bose gases

Shashi¹,

Grusdt²,

Abanin³

et al. 2014

Phys. Rev. A

108

182

View full text Add to dashboard Cite

show abstract

mentioning

confidence: 99%

“…Experiments have focused on a polaronic interpretation of radio frequency [21] and thermodynamic data. Theory has focused either on the very low temperature region (both the ground state [22,23] and Kosterlitz Thouless regimes [24,25]), on possible LOFF phases [26] and on the polaronic limit [27,28] where the spin imbalance is extreme.…”

mentioning

confidence: 99%

Two-dimensional spin-imbalanced Fermi gases at nonzero temperature: Phase separation of a noncondensate

Boyack

Levin

2016

Phys. Rev. A

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We study a trapped two-dimensional spin-imbalanced Fermi gas over a range of temperatures. In the moderate temperature regime, associated with current experiments, we find reasonable semiquantitative agreement with the measured density profiles as functions of varying spin imbalance and interaction strength. Our calculations show that, in contrast to the three-dimensional case, the phase separation which appears as a spin balanced core, can be associated with non-condensed fermion pairs. We present predictions at lower temperatures where a quasi-condensate will first appear, based on the pair momentum distribution and following the protocols of Jochim and collaborators. While these profiles also indicate phase separation, they exhibit distinctive features which may aid in identifying the condensation regime.Ultracold Fermi gases are a valuable resource for learning about highly correlated superfluids. Their utility comes from their tunability [1] which allows the dimensionality, band structure, interaction strength, and spin imbalance to be freely varied. With these various parameters one can, in principle, simulate a number of important condensed matter systems ranging from preformed pair and related effects in the high T c cuprates [2-4] to intrinsic topological superfluids [5][6][7] and other exotic pairing states.In this paper we focus on recent experiments [8,9] of two-dimensional (2D) spin-imbalanced Fermi gases. These address the interesting conflict between the tendency towards enhanced pairing (which is associated with two dimensionality [10]), and spin imbalance which acts to greatly undermine pairing. These imbalance effects are believed [11] to have related effects in studies of color superconductivity and quark-gluon plasmas. In condensed matter systems, lower dimensional imbalanced superfluids are thought to be ideal for observing more exotic phases, such as the elusive LOFF state [12], or algebraic order [13,14].The approach we use has been rather successful in addressing 2D low temperature quasi-condensation [15] in balanced gases. In this paper we present predictions for future very low temperature experiments on spinimbalanced gases. Importantly, our calculations, which find no true long range order, are consistent with the Mermin-Wagner theorem [16]. Following the experiments of Jochim and collaborators [17,18], we show how quasicondensation is reflected in the pair-momentum distribution which has a strong peak at low momentum. This peak, which we study throughout the crossover from BCS to BEC, disappears somewhat abruptly at a fixed temperature, T qc , which denotes quasi-condensation. We find T qc varies only weakly with the polarization.A central finding in this paper is that 2D spinimbalanced systems in a trap exhibit a new form of phase separation involving non-condensed pairs appearing primarily in the center region of the trap. This is to be contrasted with 3D gases [19,20] where the phase separation is associated with a true condensate. In the 2D polarized case, because almost all the ...

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