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Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture

Christoph Kohstall, Matteo Zaccanti, Michael Jag +5 more

arXiv:1112.0020NatureMay 1, 2012486 citations

Spectral Theory of the Fermi Polaron

Marcel Griesemer, Ulrich Linden

arXiv:1805.07229Annales Henri PoincaréApr 17, 201911 citations

Thermally stable p-wave repulsive Fermi polaron without a two-body bound state

Hui Hu, Jia Wang, Xia-Ji Liu

Abstract We theoretically investigate the polaron physics of an impurity immersed in a two-dimensional Fermi sea, interacting via a p-wave interaction at finite temperature. In the unitary limit with a divergent scattering area, we find a well-defined repulsive Fermi polaron at short interaction range, which shows a remarkable thermal stability with increasing temperature. The appearance of such a stable repulsive Fermi polaron in the resonantly interacting limit can be attributed to the existence of a quasi-bound dressed molecule state hidden in the two-particle continuum, although there is no bound state in the two-particle limit. We show that the repulsive Fermi polaron disappears when the interaction range increases or when the scattering area is tuned to the weakly interacting regime. The large interaction range and small scattering area instead stabilize attractive Fermi polarons.Abstract We theoretically investigate the polaron physics of an impurity immersed in a two-dimensional Fermi sea, interacting via a p-wave interaction at finite temperature. In the unitary limit with a divergent scattering area, we find a well-defined repulsive Fermi polaron at short interaction range, which shows a remarkable thermal stability with increasing temperature. The appearance of such a stable repulsive Fermi polaron in the resonantly interacting limit can be attributed to the existence of a quasi-bound dressed molecule state hidden in the two-particle continuum, although there is no bound state in the two-particle limit. We show that the repulsive Fermi polaron disappears when the interaction range increases or when the scattering area is tuned to the weakly interacting regime. The large interaction range and small scattering area instead stabilize attractive Fermi polarons.

arXiv:2311.10238AAPPS bulletinNov 16, 20236 citations

The Moving Fermi Polaron

Ijaz Durrani

Jun 26, 20260 citations

Repulsive Fermi Polarons in a Resonant Mixture of Ultracold Li6 Atoms

Francesco Scazza, Giacomo Valtolina, Pietro Massignan +7 more

We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

arXiv:1609.09817Physical Review LettersFeb 21, 2017267 citations

Fermi polarons and beyond

Meera M. Parish, Jesper Levinsen

These lecture notes give a brief introduction to the so-called Fermi-polaron problem, which explores the behaviour of a mobile impurity introduced into an ideal Fermi gas. While this problem has been considered now for more than a decade in ultracold atomic gases, it continues to generate surprises and insights as new quantum mixtures emerge, both in atomic gases and in the solid state. Here we summarise the basic theory for the Fermi polaron with a focus on the three-dimensional case, although the results can be straightforwardly generalised to two dimensions. Our aim is to provide a pedagogical treatment of the subject and we thus cover fundamental topics such as scattering theory and renormalisation. We discuss the ground state of the Fermi polaron and how it is connected to the phase diagram of the spin-imbalanced Fermi gas, and we also give a brief overview of the energy spectrum and non-equilibrium dynamics. Throughout, we highlight how the static and dynamic behaviour of the Fermi polaron is well described using intuitive variational approaches.These lecture notes give a brief introduction to the so-called Fermi-polaron problem, which explores the behaviour of a mobile impurity introduced into an ideal Fermi gas. While this problem has been considered now for more than a decade in ultracold atomic gases, it continues to generate surprises and insights as new quantum mixtures emerge, both in atomic gases and in the solid state. Here we summarise the basic theory for the Fermi polaron with a focus on the three-dimensional case, although the results can be straightforwardly generalised to two dimensions. Our aim is to provide a pedagogical treatment of the subject and we thus cover fundamental topics such as scattering theory and renormalisation. We discuss the ground state of the Fermi polaron and how it is connected to the phase diagram of the spin-imbalanced Fermi gas, and we also give a brief overview of the energy spectrum and non-equilibrium dynamics. Throughout, we highlight how the static and dynamic behaviour of the Fermi polaron is well described using intuitive variational approaches.

arXiv:2306.01215Jun 2, 20234 citations

The Scattering and Coherence of a Fermi Polaron

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