Neutrino superfluidity

It is shown that Dirac-type neutrinos display BCS superfluidity for any nonzero mass. The Cooper pairs are formed by attractive scalar Higgs boson exchange between left- and right-handed neutrinos; in the standard SU(2) x U(1) theory, right-handed neutrinos do not couple to any other boson. The value of the gap, the critical temperature, and the Pippard coherence length are calculated for arbitrary values of the neutrino mass and chemical potential. Although such a superfluid could conceivably exist, detecting it would be a major challenge.     

Conjectured superfluidity of deuterium

It is proposed that supercooled deuterium may suffer a phase change to the superfluid state near 3 K. A rough estimate of the possibility of the d(d, n)α³ fusion reaction due to large wavefunction overlap in the bose condensate is found to be infinitesimally small.     

Generalized Landau superfluidity criterion

An analysis of experimental data shows that, in addition to phonon-roton excitations in superfluid helium, there necessarily exist at least one branch of elementary excitations whose energy spectrum strongly depends on temperature. On this basis, the Landau superfluidity criterion is generalized for several branches of elementary excitations, taking into account that the critical velocity should vanish during the phase transition of liquid helium from the superfluid state to the normal state.     

Local superfluidity of parahydrogen clusters

We study by quantum Monte Carlo simulations the local superfluid response of small (up to 27 molecules) parahydrogen clusters, down to temperatures as low as 0.05 K. We show that at low temperature superfluidity is not confined at the surface of the clusters, as recently claimed by Khairallah et al. [Phys. Rev. Lett. 98, 183401 (2007)10.1103/PhysRevLett.98.183401]. Rather, even clusters with a pronounced shell structure are essentially uniformly superfluid. Superfluidity occurs as a result of long exchange cycles involving all molecules.     

Breached superfluidity via p-wave coupling

Anisotropic pairing between fermion species with different Fermi momenta opens two-dimensional areas of gapless excitations, thus producing a spatially homogeneous state with coexisting superfluid and normal fluids. This breached pairing state is stable and robust for arbitrarily small mismatch and weak p-wave coupling.     

Galilei invariance and superfluidity II

Continuing the (heuristic) analysis of the mathematical structure of the Landau excitations, we find that inone dimension they may be described by a vector bundle over the base space of the boosts. The total space is a direct integral of all irreducible representations (of a given class) of the Galilei group. The existence of an energy-momentum spectrum requires the action of the boosts to be non-linear. This action can also be formulated as a superselection rule.     

Nanoscale molecular superfluidity of hydrogen

We present a microscopic quantum theoretical analysis of the nanoscale superfluid properties of solvating clusters of para-H2 around the linear OCS molecule. Path-integral calculations with N=17 para-H2 molecules, constituting a full solvation shell, show the appearance of a significant superfluid response to rotation around the molecular axis at T=0.15 K. This low-temperature superfluid response is highly anisotropic and drops sharply as the temperature increases to T approximately 0.3 K. These calculations provide definitive theoretical evidence that an anisotropic superfluid state exists for molecular hydrogen in this microscopic solvation layer.     

Microscopic theory of strong superfluidity

Various forms of superfluidity in nuclei and nuclear and neutron matter are characterized by the relevance of strong nucleon-nucleon correlations, as well as by gap values, which can be a substantial fraction of the Fermi energy. We present a microscopic many-body theory of nuclear superfluidity. The influence of various physical effects is analyzed within the Green's function formalism and the Bethe-Brueckner-Goldstone expansion. In particular, dispersive effects are discussed in detail. We point out open problems that must be solved before a full understanding of nuclear superfluidity can be achieved.     

超流研究的历史回顾

回顾了超流发现的历史，介绍了超流的一些现象、理论以及新近的研究结果。强调指出超流与超导一样是一种宏观量子现象。     

Stability criteria for breached-pair superfluidity

We present simple, concrete, two-fermion models that exhibit thermodynamically stable isotropic translationally invariant gapless superfluid states (breached-pair superfluidity). The mass ratio between the components and the momentum structure of the interaction are crucial for determining the stability of such states: idealized, momentum-independent ("contact") interactions are insufficient.     

A variational approach to superfluidity

A variational approach to problems in quantum statistical mechanics is described and it is shown how to determine the best quasi-free approximation to the equilibrium state. The relation between this approximation and the Bogoliubov approximation in superfluidity is discussed.     

High-Tc spin superfluidity in antiferromagnets

We report the observation of the unusual behavior of induction decay signals in antiferromagnetic monocrystals with Suhl-Nakamura interactions. The signals show the formation of the Bose-Einstein condensation (BEC) of magnons and the existence of spin supercurrent, in complete analogy with the spin superfluidity in the superfluid (3)He and the atomic BEC of quantum gases. In the experiments described here, the temperature of the magnon BEC is a thousand times larger than in the superfluid (3)He. It opens a possibility to apply the spin supercurrent for various magnetic spintronics applications.     

On the theory of superfluidity

We investigate the properties of dispersion spectra of one-dimensional periodic Bose systems with repulsive interparticle interactions. These systems with sufficient large interactions can support metastable supercurrent states, which correspond to the local minima of the dispersion spectra at non-zero momenta. The existence of local minima in the spectra and the energy barriers, which separate the minima, can be explained in terms of Bose exchange symmetry. We extend our study to the case of higher dimensional Bose systems. We suggest that superfluidity could be understood as a Bose exchange effect.     

Pion superfluidity in nuclear matter

We utilize analogies with theories and properties of both liquid He⁴ and electrons in solids and liquids in constructing a model of nuclear matter in which the presence of stabilized pions is assumed. This model is then used to predict relationships between various thermodynamic parameters of a nuclear matter system, such as that between its “free” pion density and the characteristic transition temperature at which a Bose-Einstein condensation will commence.     

显现超流体最初端倪的分子--氦团簇

最近 ,文章作者所在的研究小组发表了数篇关于氦原子数多达二十的气相分子团簇的振动转动光谱的实验观测 .研究结果表明 ,N2 O分子和CO2 分子的氦团簇在氦原子数为 7个和 6个时就分别显示出分子超流体现象的开端 .文章简要地介绍了这些实验光谱观测的最新进展及其背景和物理意义     

New kinds of superconductivity and superfluidity

Formation of self-organized macroscopic and periodic structures in a physical system of interacting fermions are derived from first principles. The system of structureless and chargeless fermions with magnetic moments can have four different phases. Two of these phases exhibit the totally unique phenomena typical for superconductivity and superfluidity as well as various kinds of structural singularities such as disgyrations in the superfluid ³He.     

Phenomenological theory of superfluidity and superconductivity

Quantum condensation is used here as the basis for a phenomenological theory of superfluidity and superconductivity. It leads to remarkably good calculations of the transition temperaturesT _c of superfluid³He and⁴He, as well as a large number of cuprate, heavy fermion, organic, dichalcogenide, and bismuth oxide superconductors. Although this approach may apply least to the long-coherence-length metallics, reasonably good estimates are made for them and chevral superconductors.T _c for atomic H is estimated.T _c can be calculated as a function of number density or density of states and effective mass of normal carriers; or alternatively with the Fermi energy as the only input parameter. Predictions are made for a total of 26 superconductors and four superfluids. An estimate is also made for coherence lengths.     

Variational solution of a superfluidity model

We derive, using the variational principle for the free energy, the solution of a model for superfluidity proposed in a previous paper. The solution has the phase diagram and the excitation spectrum expected from a superfluid. We draw the attention to the fact that the model is obtained, as compared with the Bogoliubov model, by a milder suppressing of interactions with the zero mode fluctuations, leading to the good spectral properties of superfluidity.