Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms

Jo, Gyu-Boong; Lee, Ye-Ryoung; Choi, Jaehoon; Christensen, Caleb A.; Kim, Tony H.; Thywissen, Joseph H.; Pritchard, David E.; Ketterle, Wolfgang

doi:10.1126/science.1177112

Cited by 305 publications

(451 citation statements)

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“…In particular, it is an open question whether the repulsive 3D gas exhibits a Stoner type instability to a ferromagnetic state, as indicated by a renormalized Hartree-Fock calculation [18]. Experimental support for the existence of such an instability has been provided by the observation of a sudden decrease in the three-body loss rate and a minimum in the kinetic energy of the gas at a critical value k F a = 1.9 ± 0.1 of the interaction parameter [19]. Recent variational [20] and numerical calculations [21,22] in fact find that the ground state energy of the unpolarized Fermi liquid state exceeds that of a saturated ferromagnet for sufficiently strong repulsion.…”

Section: Introductionmentioning

confidence: 99%

“…Recall, that A(E)A(E ′ )/g 2 1 is just the matrix element of the contact operator ψ † ↑ ψ † ↓ ψ ↓ ψ ↑ (R) in these states, which is given in equation (19). The Wilson coefficient of the contact operator, up to order |x|, is therefore given by (1 + 2m r g 1 |x|).…”

Section: Short Distance Expansion Of the Pair Distribution Functionmentioning

confidence: 99%

“…The repulsive normal Fermi liquid at positive scattering lengths therefore corresponds to a metastable branch of the 3D balanced Fermi gas with contact interactions. In the experiment [19], the gas is initially prepared in the weakly interacting limit k F a ≪ 1 and then the interactions are quickly ramped to the strongly repulsive regime k F a ≫ 1 in order to avoid production of bound dimers [43]. An analysis of the dynamic competition between a putative formation of ferromagnetic domains within an RPA-approximation and the formation of pairs indicates that the growth rate of the latter instability is always faster [44].…”

Section: Absence Of Ferromagnetism For Zero Range Interactionsmentioning

confidence: 99%

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Tan relations in one dimension

2011

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We derive exact relations that connect the universal C/k 4 -decay of the momentum distribution at large k with both thermodynamic properties and correlation functions of two-component Fermi gases in one dimension with contact interactions. The relations are analogous to those obtained by Tan in the three-dimensional case and are derived from an operator product expansion of the one-and two-particle density matrix. They extend earlier results by Olshanii and Dunjko [1] for the bosonic Lieb-Liniger gas. As an application, we calculate the pair distribution function at short distances and the dimensionless contact in the limit of infinite repulsion. The ground state energy approaches a universal constant in this limit, a behavior that also holds in the three-dimensional case. In both one and three dimensions, a Stoner instability to a saturated ferromagnet for repulsive fermions with zero range interactions is ruled out at any finite coupling.

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Section: Introductionmentioning

confidence: 99%

Section: Short Distance Expansion Of the Pair Distribution Functionmentioning

confidence: 99%

Section: Absence Of Ferromagnetism For Zero Range Interactionsmentioning

confidence: 99%

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Tan relations in one dimension

2011

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“…The long lifetime of the repulsive polaron in our system, which we ascribe to the finite effective range of the interparticle interaction, may be a key factor to overcome the problem of decay into molecular excitations [11,19] in the experimental investigation of metastable many-body states that rely on repulsive interactions. In particular, the creation of states with two fermionic components phase-separating on microscopic or macroscopic scales [5][6][7][8]10, 11] appears to be an intriguing near-future prospect.…”

mentioning

confidence: 99%

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

Kohstall

Zaccanti

Jag

et al. 2012

Nature

498

678

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Ultracold Fermi gases with tuneable interactions represent a unique test bed to explore the many-body physics of strongly interacting quantum systems [1-4]. In the past decade, experiments have investigated a wealth of intriguing phenomena, and precise measurements of groundstate properties have provided exquisite benchmarks for the development of elaborate theoretical descriptions. Metastable states in Fermi gases with strong repulsive interactions [5-11] represent an exciting new frontier in the field. The realization of such systems constitutes a major challenge since a strong repulsive interaction in an atomic quantum gas implies the existence of a weakly bound molecular state, which makes the system intrinsically unstable against decay. Here, we exploit radio-frequency spectroscopy to measure the complete excitation spectrum of fermionic 40 K impurities resonantly interacting with a Fermi sea of 6 Li atoms. In particular, we show that a welldefined quasiparticle exists for strongly repulsive interactions. For this "repulsive polaron" [9, 12, 13] we measure its energy and its lifetime against decay. We also probe its coherence properties by measuring the quasiparticle residue. The results are well described by a theoretical approach that takes into account the finite effective range of the interaction in our system. We find that a non-zero range of the order of the interparticle spacing results in a substantial lifetime increase. This major benefit for the stability of the repulsive branch opens up new perspectives for investigating novel phenomena in metastable, repulsively interacting fermion systems.Landau's theory of a Fermi liquid [14] and the underlying concept of quasiparticles lay at the heart of our understanding of interacting Fermi systems over a wide range of energy scales, including liquid 3 He, electrons in metals, atomic nuclei, and the quark-gluon plasma. In the field of ultracold Fermi gases, the normal (non-superfluid) phase of a strongly interacting system can be interpreted in terms of a Fermi liquid [15][16][17][18]. In the population-imbalanced case, quasiparticles coined Fermi polarons are the essential building blocks and have been studied in detail experimentally [16] for attractive interactions. Recent theoretical work [9,12,13] has suggested a novel quasiparticle associated with repulsive interactions. The properties of this repulsive polaron are of fundamental importance for the prospects of repulsive many-body states. A crucial question for the feasibility of future experiments is the stability against decay into molecular excitations The vertical lines at 1/(κ F a) = ±1 indicate the width of the strongly interacting regime. The inset illustrates our rf spectroscopic scheme where the impurity is transferred from a noninteracting spin state |0 to the interacting state |1 . [11,12,19]. Indeed, whenever a strongly repulsive interaction is realized by means of a Feshbach resonance [20], a weakly bound molecular state is present into which the system may rapidly decay.Our system consi...

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“…It dates back to the Stoner's ferromagnetic (FM) instability [20], Hertz-Millis theory [21,22] to describe magnetic transition in itinerant Fermi systems without SOC, upto recent doping dependent charge and spin orderings in high temperature superconductors [23,24]. In cold atom systems, there were both experimental [25] and theoretical work [26] on possible itinerant FM in a purely repulsively interacting two component Fermi systems. But so far, possible dramatic effects of the SOC on the magnetic orders and transitions in the itinerant fermionic systems have not been discussed.…”

Section: Introductionmentioning

confidence: 99%

Itinerant magnetic phases and quantum Lifshitz transitions in a three-dimensional repulsively interacting Fermi gas with spin-orbit coupling

Zhang

Liu

2016

Phys. Rev. B

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Magnetic phenomena in itinerant electron systems has been at the forefront in material science. Here we show that the Weyl spin-orbit couplings (SOC) in 3 dimensional repulsively interacting itinerant Fermi systems opens up a platform to host new itinerant magnetic phases, excitations and phase transitions. A putative Ferromagnetic state (FM) is always unstable against a stripe Spiral spin density wave (S-SDW) or a stripe Longitudinal-SDW at small or large SOC strengths respectively. The stripe ordering wavevector is given by the nesting momentum of the two SOC split Fermi surfaces with the same or opposite helicities at small or large SOC strengths respectively. The LSDW is accompanied by a charge density wave (CDW) with half of its pitch. The transition from the paramagnet to the SSDW or LSDW+CDW is described by quantum Lifshitz type actions, in sharp contrast to the Hertz-Millis types for itinerant electron systems without SOC. The collective excitations and FS re-constructions inside the SSDW and LSDW+CDW are also studied. The effects of a harmonic trap in cold atom experiments are briefly discussed. In view of recent groundbreaking experimental advances in generating 2d SOC in cold atoms, these phenomena can be observed in current or near future cold atom experiments even at very weak interactions. They may also be relevant to some itinerant magnetic materials with a strong SOC.

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Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms

Cited by 305 publications

References 35 publications

Tan relations in one dimension

Tan relations in one dimension

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

Itinerant magnetic phases and quantum Lifshitz transitions in a three-dimensional repulsively interacting Fermi gas with spin-orbit coupling

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