A superconductor to superfluid phase transition in liquid metallic hydrogen

Babaev, Egor; Sudbø, Asle; Ashcroft, N. W.

doi:10.1038/nature02910

Cited by 339 publications

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“…These cannot be classified as superconductors in the usual sense; we will see below that also the superfluid mode is quite different from superfluid modes in one-component neutral systems. Previous studies of this state have, however, mostly focused on the reaction of the system to an applied magnetic field [12,14,15]; here our intention is to study the reaction of the system to rotation. The composite superfluid and superconducting modes in this system are inextricably intertwined and as we find below this has unusual manifestations in rotational response, which extend our general understanding of quantum ordered fluids.…”

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confidence: 99%

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Violation of the London law and Onsager–Feynman quantization in multicomponent superconductors

Babaev

Ashcroft

2007

Nature Phys

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Two quite fundamental principles governing the response to rotation of single-component superfluids and superconductors, the London law [1] relating the angular velocity to a subsequently established magnetic field, and the OnsagerFeynman quantization of superfluid velocity [2,3] are shown to be violated in a two-component superconductor. The manifestation of the two principles normally involves the fundamental constants alone, but this no longer holds as is demonstrated explicitly for the projected liquid metallic states of hydrogen and deuterium at high pressures. The rotational responses of liquid metallic hydrogen or deuterium identify them as a new class of dissipationless states; they also directly point to a particular experimental route for verification of their existence.Non-classical response to rotation is a hallmark of quantum ordered states such as superconductors and superfluids. The rotational responses of all presently known single-component "super" states of matter (superconductors, superfluids and supersolids) are largely described by two fundamental principles and fall into two categories according to whether the systems are composed of neutral or charged particles. For superfluid systems composed of electrically neutral particles (liquids, vapors, or even solids [4]) and for slow rotations, a fraction of the system, the superfluid fraction, remains irrotational. However in response to rotation exceeding a certain critical rotation frequency, the superfluid fraction comes into rotation by means of vortex formation. Onsager and Feynman [2,3] pointed out that the superfluid velocity (v) in these vortices in single-component systems is quantized and the circulation quantum K depends only on particle's mass m and Planck's constant h: K = (1/2π) v · dl =h/m. Here we mention that for superfluids with e.g. p-wave symmetry of the order parameter which are also invariant under simultaneous phase and spin transformations this quantization is modified [5]. We also mention that a special situation occur in a multicomponent superfluid with a dissipationless drag (Andreev-Bashkin effect) where a superfluid velocity of one condensate can carry superfluid density of another [6,7]. Below however we will consider the mixture of charged condensates only with the simplest symmetry of the order parameter coupled by a gauge field.For systems composed of charged particles and which are also superconducting (electronic Cooper pairs in metals, or protonic Cooper pairs in neutron stars) vortices are not induced by rotation; however, the rotational response of these systems is no less interesting. London showed that a uniformly rotating single component superconductor generates a persistent current in a thin layer near its surface, and this in turn produces a detectable magnetic field, the London field [1]. London related this field to the rotation frequency, Ω, according to B = −(2mc/e)Ω, where m is the electron's mass, e denotes it electric charge and c is the speed of light. This law is experimentally confirmed (see ...

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“…Then the dominant structure is a field-induced lattice of composite vortices (1, −1) (as in the case of no rotation [12,14,15]). Here the energetically most favorable way to introduce a superfluid momentum-carrying vortex is the substitution of one of the (1, −1) vortices by a (1, 0) vortex (see Fig.…”

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Violation of the London law and Onsager–Feynman quantization in multicomponent superconductors

Babaev

Ashcroft

2007

Nature Phys

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“…Recently, multicomponent superconducting systems have attracted increasing interest in areas ranging through metallic superconductors, hydrogen in extreme conditions and color superconductivity in dense QCD [9,10,11]. Below we consider a generic two-component superconductor (TCS), showing that it allows a novel type of thermodynamically stable vortices, whose electrodynamics is of Pippard type with respect to one of the order parameters and which have non-monotonic interaction energy for a wide range of parameters as an intrinsic feature.…”

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“…Analogous situations might appear in mixtures of condensates with different pairing symmetries. Another candidate for this type of superconductivity is the projected liquid metallic state of hydrogen [10] where this regime is expected to be realized under certain conditions. A similar situation might also occur in the color superconducting state in quark matter [11].…”

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Semi-Meissner state and neither type-I nor type-II superconductivity in multicomponent superconductors

2005

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Traditionally, superconductors are categorized as type-I or type-II. Type-I superconductors support only Meissner and normal states, while type-II superconductors form magnetic vortices in sufficiently strong applied magnetic fields. Recently there has been much interest in superconducting systems with several species of condensates, in fields ranging from Condensed Matter to High Energy Physics. Here we show that the type-I/type-II classification is insufficient for such multicomponent superconductors. We obtain solutions representing thermodynamically stable vortices with properties falling outside the usual type-I/type-II dichotomy, in that they have the following features: (i) Pippard electrodynamics, (ii) interaction potential with long-range attractive and shortrange repulsive parts, (iii) for an n-quantum vortex, a non-monotonic ratio E(n)/n where E(n) is the energy per unit length, (iv) energetic preference for non-axisymmetric vortex states, "vortex molecules". Consequently, these superconductors exhibit an emerging first order transition into a "semi-Meissner" state, an inhomogeneous state comprising a mixture of domains of two-component Meissner state and vortex clusters.The formation of vortices in type-II superconductors subjected to a magnetic field is one of the most remarkable phenomena occuring in condensed matter. In all type-II superconductors (i.e. superconductors where the GL parameter, which is the ratio of the magentic field penetration length to the coherence lenth, is κ > 1/ √ 2 [1]) these vortices share a set of properties: an n-quantum vortex is unstable with respect to decay into n onequantum vortices, two vortices have purely repulsive interaction, and invasion of vortices under normal conditions is a second order phase transition characterised by a critical value of the external magnetic field H c1 .Vortices as solutions of the GL equations also exist formally in a type-I superconductor (κ < 1/ √ 2), but these vortices are thermodynamically unstable. The special case κ = 1/ √ 2 is also very interesting since, at this value of κ, vortices do not interact [2,3]. One should note, however, that in real life systems the situation is more complicated; experiments [4] show that in certain materials with κ ≈ 1/ √ 2 there might exist a tiny attractive force between vortices at a certain distance. Such an interaction was reproduced in a modified one-component GL model with additional terms in the regime κ ≈ 1/ √ 2 [5]. We should also mention a long range van der Waals -type vortex attraction in layered systems produced by thermal fluctuations or disorder [6].Besides superconductivity, the vortex concept has a direct counterpart in High Energy Physics, called the Nielsen-Olesen string. Such strings have been considered in cosmology [7] where they are expected to form during a symmetry breaking phase transition in the early universe. There also exists a similar type-I/type-II division of semilocal cosmic strings in the Higgs doublet model [8].Recently, multicomponent superconducting systems hav...

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“…4 A superfluid phase has been recently predicted as well for very-high-density regimes. 5 In the quest for supercooling liquid hydrogen down to temperatures as low as 4 K where the superfluid transition is expected to take place, confinement within porous media reported on a strong reduction of the freezing point from about 14 K for the bulk liquid down to about 8 K when confined in Vycor glass that is a tenuous disordered structure. 6 Further confinement within materials having pore sizes of the order of a nanometer such as zeolites was an obvious next step.…”

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Collective excitations in liquidD2confined within the mesoscopic pores of a MCM-41 molecular sieve

et al. 2006

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We present a comparative study of the excitations in bulk and liquid D 2 confined within the pores of MCM-41. The material ͑Mobile Crystalline Material-41͒ is a silicate obtained by means of a template that yields a partially crystalline structure composed by arrays of nonintersecting hexagonal channels of controlled width having walls made of amorphous SiO 2 . Its porosity was characterized by means of adsorption isotherms and found to be composed by a regular array of pores having a narrow distribution of sizes with a most probable value of 2.45 nm. The assessment of the precise location of the sample within the pores is carried out by means of pressure isotherms. The study was conducted at two pressures which correspond to pore fillings above the capillary condensation regime. Within the range of wave vectors where collective excitations can be followed up ͑0.3ഛ Q ഛ 3.0 Å −1 ͒, we found confinement brings forward a large shortening of the excitation lifetimes that shifts the characteristic frequencies to higher energies. In addition, the coherent quasielastic scattering shows signatures of reduced diffusivity.

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A superconductor to superfluid phase transition in liquid metallic hydrogen

Cited by 339 publications

References 17 publications

Violation of the London law and Onsager–Feynman quantization in multicomponent superconductors

Violation of the London law and Onsager–Feynman quantization in multicomponent superconductors

Semi-Meissner state and neither type-I nor type-II superconductivity in multicomponent superconductors

Collective excitations in liquidD2confined within the mesoscopic pores of a MCM-41 molecular sieve

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