Liquid and Crystal Phases of Dipolar Fermions in Two Dimensions

Matveeva, N. M.; Giorgini, S.

doi:10.1103/physrevlett.109.200401

Cited by 60 publications

(126 citation statements)

References 32 publications

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“…The particular form of this interaction leads to surprising new features not present in other systems, like stripe phases in two-dimensional (2D) Bose systems [10]. Similar phases in Fermi systems have also been predicted [11,12], although these are more controversial [13]. One of the most interesting phenomenon recently reported in the field of dipolar quantum gases is the formation of self-bound droplets when a gas of trapped 164 Dy atoms is brought to the regime of mean field collapse [14,15].…”

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Droplets of Trapped Quantum Dipolar Bosons

et al. 2016

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Strongly interacting systems of dipolar bosons in three dimensions confined by harmonic traps are analyzed using the exact Path Integral Ground State Monte Carlo method. By adding a repulsive two-body potential, we find a narrow window of interaction parameters leading to stable groundstate configurations of droplets in a crystalline arrangement. We find that this effect is entirely due to the interaction present in the Hamiltonian without resorting to additional stabilizing mechanisms or specific three-body forces. We analyze the number of droplets formed in terms of the Hamiltonian parameters, relate them to the corresponding s-wave scattering length, and discuss a simple scaling model for the density profiles. Our results are in qualitative agreement with recent experiments showing a quantum Rosensweig instability in trapped Dy atoms.Dipolar effects in quantum gases have been considered of major experimental and theoretical interest in the last decade since the initial studies of dilute clouds of Cr atoms, which present a relatively large magnetic dipolar moment. In the pioneering experiments of Ref.[1], the two-body scattering length of a cloud of 52 Cr atoms was drastically reduced by bringing it close to a Feshbach resonance. In this way, dipolar effects were enhanced and interesting new features, not observed before in other species like Rb or Cs, appeared. The long range and anisotropic character of the dipolar interaction has been largely explored since then, leading to interesting new phenomena such as d-wave superfluidity or d-wave collapse [2,3]. All these experiments have opened new perspectives on the field of dipolar quantum physics, and new systems with stronger dipolar interactions have since then been explored. The most promising ones, consisting initially in ultracold polar molecules of K and Rb or Cs and Rb, are unfortunately problematic due to the inherent difficulty to bring them down to the quantum degeneracy limit, although recent progress have been achieved with NaK [4] The anisotropy of the dipolar interaction plays a fundamental role on the behavior of the system, with different regimes and phases depending on the geometry and dimensionality. The particular form of the dipole-dipole potential makes the interaction be attractive or repulsive depending on the relative orientation of the dipoles, according to the expressionwhere C dd sets the strength of the interaction that is proportional to the square of the (magnetic or electric) dipolar moment, p j is the dipolar moment itself, and r is the relative position vector of the two interacting dipoles. The particular form of this interaction leads to surprising new features not present in other systems, like stripe phases in two-dimensional (2D) Bose systems [10]. Similar phases in Fermi systems have also been predicted [11,12], although these are more controversial [13]. One of the most interesting phenomenon recently reported in the field of dipolar quantum gases is the formation of self-bound droplets when a gas of trapped 164 Dy atoms...

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Droplets of Trapped Quantum Dipolar Bosons

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“…Examples of quantum solids include, Wigner crystals (Wigner, 1934;Ceperley and Alder, 1980;Drummond et al, 2004;Militzer and Graham, 2006;Drummond and Needs, 2009), vortex lattices (Safar et al, 1992;Cooper, Wilkin, and Gunn, 2001;Abo-Shaeer et al, 2001), dipole systems (Astrakharchik et al, 2007;Matveeva and Giorgini, 2012;Boninsegni, 2013a;Moroni and Boninsegni, 2014), rare-gases, molecular solids, light metals, and many other similar systems (see the next paragraphs). For the sake of focus, however, in this review we will concentrate on quantum crystals formed by atoms and small molecules.…”

Section: Introduction a Quantum Crystals: Definition And Interestsmentioning

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Simulation and understanding of atomic and molecular quantum crystals

2017

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Quantum crystals abound in the whole range of solid-state species. Below a certain threshold temperature the physical behavior of rare gases ( 4 He and Ne), molecular solids (H 2 and CH 4 ), and some ionic (LiH), covalent (graphite), and metallic (Li) crystals can be only explained in terms of quantum nuclear effects (QNE). A detailed comprehension of the nature of quantum solids is critical for achieving progress in a number of fundamental and applied scientific fields like, for instance, planetary sciences, hydrogen storage, nuclear energy, quantum computing, and nanoelectronics. This review describes the current physical understanding of quantum crystals formed by atoms and small molecules, as well as the wide palette of simulation techniques that are used to investigate them. Relevant aspects in these materials such as phase transformations, structural properties, elasticity, crystalline defects and the effects of reduced dimensionality, are discussed thoroughly. An introduction to quantum Monte Carlo techniques, which in the present context are the simulation methods of choice, and other quantum simulation approaches (e. g., path-integral molecular dynamics and quantum thermal baths) is provided. The overarching objective of this article is twofold. First, to clarify in which crystals and physical situations the disregard of QNE may incur in important bias and erroneous interpretations. And second, to promote the study and appreciation of QNE, a topic that traditionally has been treated in the context of condensed matter physics, within the broad and interdisciplinary areas of materials science.

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“…An anisotropic 2D quantum gas can be realized by tilting the polarization dipoles in a deep trap, and a stripe phase can form spontaneously 20,21 . For r D r s , dipoles will crystallize without imposing an optical lattice [22][23][24] . A bilayered dipolar Bose gas can dimerize if the polarization direction in the two layers is the same 25 .…”

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Dipolar bilayer with antiparallel polarization: A self-bound liquid

2016

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Dipolar bilayers with antiparallel polarization, i.e. opposite polarization in the two layers, exhibit liquid-like rather than gas-like behavior. In particular, even without external pressure a self-bound liquid puddle of constant density will form. We investigate the symmetric case of two identical layers, corresponding to a two-component Bose system with equal partial densities. The zerotemperature equation of state E(ρ)/N , where ρ is the total density, has a minimum, with an equilibrium density that decreases with increasing distance between the layers. The attraction necessary for a self-bound liquid comes from the inter-layer dipole-dipole interaction that leads to a mediated intra-layer attraction. We investigate the regime of negative pressure towards the spinodal instability, where the bilayer is unstable against infinitesimal fluctuations of the total density, conformed by calculations of the speed of sound of total density fluctuations.

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Liquid and Crystal Phases of Dipolar Fermions in Two Dimensions

Cited by 60 publications

References 32 publications

Droplets of Trapped Quantum Dipolar Bosons

Droplets of Trapped Quantum Dipolar Bosons

Simulation and understanding of atomic and molecular quantum crystals

Dipolar bilayer with antiparallel polarization: A self-bound liquid

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