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Attractive and repulsive Fermi polarons in two dimensions

机译：二维的吸引和排斥费米极化子

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摘要

The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasipartide plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresis-tance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasipartides known as Fermi polarons The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasipartides-repulsive polarons- the lifetime of which determines the possibility of stabilizing repulsively interacting Fermi systems.
机译：环境中单一杂质的动力学是多体物理学中的一个基本问题。在固态状态下，众所周知的情况是杂质与硼化浴耦合（例如晶格振动）；杂质及其伴随的晶格畸变形成一个新的实体，极化子。该准partideide在高转变温度超导体的光谱功能以及锰矿中的巨大磁阻中起着重要作用。对于铁离子浴中的杂质，研究已经考虑了重的或固定的杂质，这些杂质表现出安德森正交性灾难和近藤效应。最近，移动杂质已经成为研究的重点，并且发现它们形成了称为费米极化子的新准粒子。费米极化子问题构成了两个重要的量子多体问题的极端但在概念上简单的限制：交叉分子Bose-Einstein冷凝物和BCS（Bardeen-Cooper-Schrieffer）与自旋不平衡配对的超流体之间具有吸引作用，而Stoner的流动铁磁性则具有排斥作用。已经提出，这样的量子相（以及其他难以捉摸的外来状态）可能在局限于二维的费米气体中实现。它们的稳定性和可观察性与二维费米气体中费米极化子的理论辩论密切相关。在这里，我们创建并研究二维自旋不平衡费米气体中的费米极化子，并使用动量分辨光发射光谱法测量其光谱函数。对于有吸引力的相互作用，我们找到了极化子与紧密结合的二聚体之间有争议的配对过渡的证据，这为不平衡，强耦合的二维费米气体的基本配对机理提供了见解。此外，对于斥力相互作用，我们研究了新型拟粒子-斥力极化子，其寿命决定了稳定斥力相互作用费米系统的可能性。

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  • 来源
    《Nature》 |2012年第7400期|p.619-622B1|共5页
  • 作者

    Marco Koschorreck; Daniel Pertot; Enrico Vogt; Bernd Froehlich; Michael Feld; Michael Koehl;

  • 作者单位

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

    Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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