Fractional-flux vortices and spin superfluidity in triplet superconductors

We discuss a novel type of fractional-flux vortices along with integer flux vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We show that under certain conditions a spin-triplet superconductor should exhibit a novel state of spin superfluidity without superconductivity.     

Microscopic Superconductivity and Room Temperature Electronics of High-Tc Cuprates

This paper points out that the Landau criterion for macroscopic superfluidity of He II is only a criterion for microscopic superfluidity of ⁴He, extends the Landau criterion to microscopic superconductivity in fermions (electron and hole) system and system with Cooper pairs without long-range phase coherence. This paper gives another three non-superconductive systems that are of microscopic superconductivity. This paper demonstrates that one application of microscopic superconductivity is to establish room temperature electronics of the high-T_c cuprates.     

Quasiclassical boundary conditions for Fermi liquids at surfaces

The general boundary conditions at surfaces are derived within the quasiclassical theory of superfluidity in Fermi liquids (superconductors, superfluid³He). These conditions supplement the transport-like equations first introduced into the theory of superconductivity by G. Eilenberger, and allow a quantitative analysis of superfluids near a wall.     

From Defiant Youth to Conformist Adulthood: The Sad Story of Liquid Helium

In this paper I discuss the properties of superfluid helium and present the different approaches to the problem of superfluidity. The gradual realization of this new liquid state brought about dramatic changes in our assessment of quantum mechanics and our reconceptualization of fluids, especially with the introduction of the notion of macroscopic quantum phenomena, which was introduced for superconductivity and superfluidity by Fritz London.     

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。     

The Superfluidity of the Charged Bosons'System

We establish a model of bosons in which a boson carries a charge-|e| and there exists a positive and homogeneous background which makes the system neutral. We show that the superfluidity may emerge in very general conditions for the model in support of some superconductivity theories based on the formation of bosonic bound state of two electrons.     

Neutron star matter superfluidity and superconductivity

The possibility of superfluidity or superconductivity in neutron or proton subsystems in the nuclear-matter region in neutron stars is investigated. The energy gap and corresponding critical temperature and critical magnetic field is calculated or estimated as function of density or Fermi momentum. In the calculations are used reaction matrix elements calculated earlier by means of Brueckner theory by the author. The final results indicate that neutron superfluidity, corresponding specifically toS-state pairing, may exist in a low-density shell in the nuclear-matter region of a neutron star. There is probably anisotropic neutron superfluidity, corresponding to the³ P ₂ or the singletD state, for higher densities. Superfluidity or superconductivity, corresponding toS-state pairing for the proton subsystem, is quite likely in most of the nuclear-matter region. The expected temperatures and magnetic fields in neutron stars seem to be well below the estimated critical temperatures or critical magnetic fields corresponding to the calculated values of the energy gap. However, similar methods have earlier predicted a much too high critical temperature for liquid³He.     

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.     

Approximate diagonalization of the energy operator of a system of interacting particles

The present work considers a method of diagonalization of the energy operator of a system of valence electrons in a simple model of a semiconductor, and in a simple model of a metal. The results obtained are used in the theory of superconductivity and in the theory of superfluidity.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 43–47, December, 1971.     

On the role of the uncertainty principle in superconductivity and superfluidity

We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.     

Microscopic theory of single particle and pair condensation of an attracting bose gas as the basis for superfluidity and superconductivity

A consistent and unified microscopic theory of superfluidity and superconductivity is developed on the basis of two-stage Fermi-Bose-liquid (FBL) (in particular case, one-stage Bose-liquid) scenarios. It is shown that these phase transition scenarios is accompanied, as a rule, by the formation of composite bosons (Cooper pair and bipolarons) with their subsequent single particle (SPC) and pair condensation (PC). A brief outline of the modified and generalized BCS-like pairing theory of fermions is presented. In an analogy to that, a detailed boson pairing theory is developed. The SPC and PC features of an attracting 3d- and 2d-BG as a function of the interboson coupling constant in the complete range 0≤T≤T _B is studied in detail. It is argued that the coexistence of the order parameters of attracting fermions Δ_F and bosons Δ_B leads to the superfluidity (in³He) and superconductivity (in superconductors) by two FBL scenarios. One of these scenarios is realized in the so-called fermion superconductors (FSC) and the other in the boson superconductors (BSC) in which the gapless superconductivity is caused by the absence of the gap Δ_SF in the excitation spectrum of bosons and not by the presence of point or line nodes of the BCS-like gap Δ_F. The new adequate definitions for basic superconducting parameters of FSC and BSC are given. The theory proposed is consistent with the experimental data available.     

Landau’s Nobel Prize in Physics

Work of Lev Landau had a profound impact on the physics in 20th century. Landau had created the paradigms that had framed the conversations on the outstanding problems in physics for decades. He had laid foundations for our understanding of quantum matter like superfluidity, superconductivity and the theory of Fermi liquid. Here we present some Nobel Archive data on the winning nomination that led to the Nobel Prize in Physics in 1962.     

Dislocations as linear topological defects

Dislocations and dislocation plasticity are considered and compared with such dissimilar physical phenomena as superfluidity of liquid helium and type II superconductivity. These phenomena share the common property that the dislocations, as well as quantum vortices in superconductors and superfluid helium, are topological defects. They arise during a phase transformation which is accompanied by spontaneous symmetry breaking caused by Bose condensation of acoustic phonons. The general problems of the evolution of ensembles of linear topological defects and the character of the spatial structures formed by them are discussed.     

Exact periodic and explicit solutions of the conformable time fractional Ginzburg Landau equation

The Ginzburg–Landau (GL) equation is one of the most important nonlinear equation in physics. It is used to model a vast variety of phenomena in physics like nonlinear waves, second order phase transitions, Bose–Einstein condensation, superfluidity, superconductivity, liquid crystals and strings in field theory. In this work, new exact, periodic and explicit solutions of a time fractional GL equation involving conformable fractional derivatives with Kerr law nonlinearity have been found. The Kerr law nonlinearity is due to the non-harmonic motion of electrons under the influence of an applied field. To determine the solution of the model, we have employed a couple of integration algorithms, solitary wave ansatz and \(\exp (-\varphi ({\chi }\))) methods. New periodic and hyperbolic soliton solutions are found as well as the constraint condition for the existence of the solution.     

Is electromagnetic gauge invariance spontaneously violated in superconductors?

We aim to give a pedagogical introduction to those elementary aspects of superconductivity which are not treated in the classic textbooks. In particular, we emphasize that global U (1) phase rotation symmetry, and not gauge symmetry, is spontaneously violated, and show that the BCS wave function is, contrary to claims in the literature, fully gauge invariant. We discuss the nature of the order parameter, the physical origin of the many degenerate states, and the relation between formulations of superconductivity with fixed particle numbers vs. well-defined phases. We motivate and to some extend derive the effective field theory at low temperatures, explore symmetries and conservation laws, and justify the classical nature of the theory. Most importantly, we show that the entire phenomenology of superconductivity essentially follows from the single assumption of a charged order parameter field. This phenomenology includes Anderson’s characteristic equations of superfluidity, electric and magnetic screening, the Bernoulli Hall effect, the balance of the Lorentz force, as well as the quantum effects, in which Planck’s constant manifests itself through the compactness of the U (1) phase field. The latter effects include flux quantization, phase slippage, and the Josephson effect.     

A possible spin-fluctuation mechanism in the emergence of superconductivity in a region of magnetic instability, using the example of PuCoGa5

The spin-fluctuation superconductivity mechanism of strongly correlated d-f electrons is considered within the Hubbard model. It is shown that the emergence of superconductivity is possible under conditions of strong spin anharmonicity. Evaluations of the superconductivity temperature in the model developed for the electron structure of PuCoGa₅ agree with the experimental data.     

Supersolidity for hard-core-bosons coupled to optical phonons

The coexistence of diagonal long-range order (DLRO) and off-diagonal long-range order (ODLRO), manifested in some systems, is still a theoretical enigma. Here, we present a novel microscopic mechanism for supersolidity or the homogeneous coexistence of charge-density-wave state (an example of DLRO) and superfluidity/superconductivity (a realization of ODLRO). We derive an effective d-dimensional Hamiltonian for a system of hard-core-bosons coupled to optical phonons in a lattice. At non-half-fillings, a superfluid/superconductor to a supersolid transition occurs at intermediate boson–phonon couplings, while at strong-couplings the system phase separates. We demonstrate explicitly that the presence of next-nearest-neighbor hopping and nearest-neighbor repulsion leads to supersolidity.     

The Fulde-Ferrell-Larkin-Ovchinnikov states in s and d-wave superconductor with spin-dependent bandwidth imbalance on square lattice

We study numerically the phase diagram for s and d-wave fermionic superfluidity/superconductivity with spin-dependent bandwidth imbalance on a two-dimensional square-lattice. We also investigate the spontaneous space symmetry breaking states at low temperatures by solving the Bogoliubov-de Gennes equations. It is found that, the spatial configuration of the order parameter,both the uni-directional Fulde-Ferrell-Larkin-Ovchinnikov(FFLO) states and the two-dimensional FFLO state may show up in the presence of finite spin-dependent bandwidth imbalance. Moreover, we calculate the spectra of local density of states, and the experimental proposals of observing such FFLO states are therefore suggested.