Superconductivity in Bilayer Cuprates

We calculate the stability of d_x²-y² wave superconducting state in bilayer cuprates within the antiferromagnetic and van Hove scenario. We find an increment ~10 K of T_c^max with the growth from one plane to a bilayer when the hole pairing induced by the spin-wave exchange is included.     

Excitons and Trions in Bilayer van der Waals Heterostructures

Physics of the Solid State - Excitons and trions in bilayer structures based on transition metal dichalcogenides are theoretically studied. Expressions for the effective potential of interparticle...     

On a Nonlinear Effect in the Superconductivity Theory

Physics of the Solid State - Based on the solution of the hydrodynamic equations and Maxwell’s equations, we show that an external quasi-homogeneous magnetic field leads to the emergence of a...     

On Superconductivity State in Pure Graphene

We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U ≌ 5t, where t is hopping term, pure graphene can be in superconductivity state.     

On Superconductivity State in Pure Graphene

We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U≌5t, where t is hopping term, pure graphene can be in superconductivity state.     

On the Zero Set of the Wave Function in Superconductivity

We consider the Ginzburg Landau functional in a multiply connected planar domain with enclosed magnetic flux. Particular attention is given to the zero set of the order parameter. We show that there exist applied fields for which the zero set is of codimension 1. Received: 8 July 1997/ Accepted: 28 January 1999     

On the Spin-Bag Theory of High Tc Superconductivity

The properties in the spin-bag mechanism of hige T_c superconductivity are studied in the SDW background. It is found that if the Coulomb repulsive potential is much smaller than the valence-band width and is not beyond a particular range determined by the bag energy, two doped holes can be pairing via sharing a common bag. The transition temperature has a maximum value of the order 200 K for reasonable parameters but is independent of doping concentration. In addition, the ratio of the energy gap to T_c is found to be the same as the BCS value. Finally, the specific heat jump at the transition temperature, the coherence length and the upper critical field are roughly estimated.     

On the Possibility of Supertasks in General Relativity

Malament-Hogarth spacetimes are the sort of models within general relativity that seem to allow for the possibility of supertasks. There are various ways in which these spacetimes might be considered physically problematic. Here, we examine these criticisms and investigate the prospect of escaping them.     

On the Possibility of Measuring the Unruh Effect

There is a persistent state of confusion regarding the nature of the Unruh effect. We will argue that, in contrast to some interpretations thereof, the effect does not represent any novel physics and that, by its very nature, the effect is fundamentally unmeasurable in all experiments of the kind that have been contemplated until now. Also, we discuss what aspects connected with this effect one might consider as possibilities to be explored empirically and what their precise meaning may be regarding the issue at hand.     

On the Coexistence of Superconductivity and Magnetic Ordering in Unconventional Superconductors

It is demonstrated that the coexistence of superconductivity and magnetic ordering, occurring, for instance, in iron-based pnictides and uranium compounds, is not forbidden by classical Maxwell’s equations and London-type equations. It predicts simply that internal magnetization is allowed but localized magnetic moments are screened at distances of the order of the London penetration depth. A microscopic theory is considered for the case of ferromagnetic ordering, described in simple terms by electron-magnon coupling. For the sake of simplicity, we assume that itinerant electrons are not responsible for the magnetic ordering, but interact with phonon and magnon excitations, leading to an alternative Cooper pair channel. The temperature dependence and the isotope effect of the superconducting gap is also analysed.     

On the Possibility to Construct Gravitational Eye

The possibility of modifying a conventional Cavendish torsion pendulum into a half-armed pendulum oscillator to measure the horizontal gravitational acceleration is discussed. A new kind of gravitational detector, gravieye, as we named, can be made by a proper combination of such oscillators to ＂see＂ remote objects and to be used, e.g. to detect the movement of huge mass at a long distance.     

On Magnetic Flux Trapping by Surface Superconductivity

The magnetic flux trapping by surface superconductivity is considered. The stability of the state localized at the cylindrical sample surface upon a change in the external magnetic field is tested. It is shown that as the magnetic field decreases, the sample acquires a positive magnetic moment due to magnetic flux trapping; i.e., the magnetization curve of surface superconductivity is “paramagnetic” by nature.     

On the Possibility of Acceleration of Polarized Protons in the Synchrotron Nuclotron

One of the main tasks of the NICA project is to produce colliding beams of polarized protons. It is planned to accelerate polarized protons from the source to the maximum energy in the existing proton synchrotron. We consider all depolarizing spin resonances in the Nuclotron and propose methods to overcome them.     

On a Possibility of the Overgrowth of Diamonds in the Hydrocarbon Atmosphere

The possibility to increase sizes of diamond crystals at least 25 μm by means of their annealing at a temperature of 1450 K in a hydrocarbon atmosphere has been studied. The initial diamond crystals are incorporated in the polyvinyl acetate layer on the surface of a silicon monocrystal and subjected to the annealing in methane atmosphere with low pressure in the presence of an external electric field with intensity up to 0.04 V/μm. Under these conditions the charged ions of methane dissociation products are accelerated and acquire the kinetic energy that is comparable with energy sufficient to form sp³-hybride bonds, which can lead to an increase in the sizes of initial seed crystallites. The obtained substrates of a composite with a typical thickness not higher than 1.2 mm, which contain a joined diamond crystal in the carbon matrix, can be used as thermal conductive and electrical insulating spacers in devices for cooling items of electronic engineering.     

Superconductivity in the palladium-silver-deuterium system

Superconducting transition temperatures up to 16 K have been observed for Pd-Ag alloys charged with deuterium or hydrogen by ion implantation at liquid helium temperatures.     

On the Possibility of the Implicit Renormalization of the Casimir Energy

We propose a procedure for renormalizing the Casimir energy that makes the steps that are used in the standard renormalization procedure, that is, regularization, subtraction, and deregularization, implicit. The proposed procedure is based on the calculation of a set of convergent sums, each of which is related to the initial divergent sum of the non-renormalized Casimir energy. Next, we construct a system of linear equations that relates this set of convergent sums to the renormalized Casimir energy. The unknown renormalized Casimir energy is obtained as a result of solving this system of equations. In this case, both the calculations of the convergent sums and the subsequent solution of the system of linear equations are performed with a certain (generally speaking, arbitrary) ordered accuracy; thus, the result is also approximate. The proposed procedure is, first, more computationally effective than the standard one, and, second, applicable not only to the problems where a transcendental equation for the spectrum can be written, but also to the problems where the spectrum is known only numerically.     

Superconductivity in the alkali metals

At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties.