Theory Of High-temperature Superconductivity Research Articles

Integrating Superconductivity in Cu Replace Lead Apatite by Nuclear Magnetic Moment Theory of RBL

Recently, scientists proclaimed superconductivity under ambient conditions of room temperature and 1 atmosphere pressure in Cu partial substituted lead apatite: Pb(10-x)Cux(PO4)6. This paper highlights the application of RBL’s stable isotope of positive and negative nuclear magnetic moments (NMMs) theory for explaining the heavy isotopic enrichment of this materials as {207Pb{10-x}63Cux(‘31PιO4)6}, where ι = 17 or 18 and the resulting superconductivity and novel room temperature atmospheric pressure superconductivity of this heavy isotopic enriched substance. On the basis of such analysis by RBL theory, the synthesis of high temperature, regular pressure superconductivity can be explained and this recent experimental observation of ambient pressure and temperature superconductivity in 207Pb{10-x}63Cux(‘31PιO4)6, where ι = 17 or 18, proves RBL’s NMMs theory of high temperature superconductivity. After 1 month on July 22, 2023 of the archiving of such data for superconductivity Pb(10-x)Cux(PO4)6 by Lee and coworkers, a huge experimental effort by hundreds of researchers around the world has attempted to replicate this room temperature, ambient pressure superconductivity in Pb(10-x)Cux(PO4)6 without success. The resulting inability to replicate the ambient superconductivity and note of some fractional component in the mixture causing the ambient superconductivity is explained by RBL’s theory as the fractional component may be clumped isotopes as in {207Pb{10-x}63Cux(‘31PιO4)6}, where ι = 17 or 18, and RBL here notes the vapor deposition process alleged by Lee and coworkers for producing the superconductivity was previously predicted by RBL to cause isotopic fractionation during solid to liquid and liquid to gas and gas to solid physical changes.

Glimpses of Greatness

P W Anderson was a theoretical physicist. He won the Nobel Prize in 1977. He catalysed Nobel Prizes for several others. His career spanned 72 years of relentless research, filled with path-breaking contributions. He focussed on ‘here and now’ phenomena of inanimate materials and built theoretical quantum models of lasting value. He communed with nature by contemplation and study of experimental results. As a founding father, he set agenda for the field of condensed matter physics, for half a century. It is a growing fertile field now, with a web of connection to different corners of science, technology, and sometimes beyond. As a person, Anderson was remarkable. He was my long time collaborator since 1984. I had a wonderful opportunity to join hands with him when he initiated the resonating valence bond (RVB) theory of high-temperature superconductivity in cuprates in early 1987.

Pairing in two dimensions and possible consequences for superconductivity: extension of Cooper's approach

Relation between the binding energy of a pair of electrons in Cooper's configuration and the magnitude of the attractive interaction between them is investigated theoretically for a two-dimensional electron gas when the electron pair has (a) zero and (b) finite center of mass momentum (CMM) first (i) in the background of a passive Fermi sea and (ii) with inclusion of the effect of Pauli exclusion principle in the presence of an active Fermi sea, at zero temperature. In the Cooper's approach (Cooper 1956 Phys. Rev. 104 1189) two pairing electrons are considered above the Fermi sea. Due to Pauli exclusion principle, these two electrons are forbidden to go into the states whose energies are less than the Fermi energy. Consequently, the role of the electrons which form the Fermi sea is passive in formation of electron pair (Fujita and Godoy 2001 Theory of High Temperature Superconductivity (Kluwer Academic Publishers)). However, in the case of an active Fermi sea, implying possible presence of multiple pairs of electrons coming out of the Fermi sea, the two electrons will have less available region in the momentum space for pair formation due to the Pauli blocking effect. In both the situations, threshold values of attractive interaction are found to exist to bind the electrons having finite CMM even with respect to the Fermi energy while with arbitrarily small value of attractive interaction they can be bound only in the case of zero CMM and that too in the presence of a passive Fermi sea. However, the presence of an active Fermi sea strongly opposes the pair formation having lower CMM. Furthermore, raising the range of the attractive interaction below and above the Fermi surface makes the pair formation more difficult due to enhanced Pauli blocking in this case. In the case of a passive Fermi sea however, with the increase in the range of the attractive interaction it becomes easier for the electron pairs to be in both Cooper pair state (CP) and true bound state (TB). These results are totally distinct from those obtained by Randeria et al (1989 Phys. Rev. Lett. 62 981, 1990 Phys. Rev. B 41 327) that a fermionic bound state in true vacuum is a necessary and sufficient condition for the Cooper pairing instability in the presence of a passive Fermi sea, independent of attractive interaction strength implying that for a potential which is attractive everywhere in two dimension, a two-body bound state exists for an arbitrarily weak attraction. Our calculations show, in the mean field approximation, that co-existence of TB state and CP state with various CMMs can occur only beyond a critical attractive interaction strength. This could lead to the formation of incoherent pairs even under strong coupling situation, which may hint onto the pseudo gap formation leading to some of the exotic features in the anomalous normal state seen in some of the exotic superconductors.

EXPERIMENTAL STUDY OF THE SUPERCONDUCTING MICROSTRIP ANTENNA AS A PROTECTIVE DEVICE OF THE RECEIVER FROM ELECTROMAGNETIC DAMAGE

The paper presents the results of experimental studies of a superconducting protective antenna, which consists of a high-temperature film deposited by a magnetron or a laser beam on a substrate. The work is carried out: - analysis of the selection criteria for the substrate type (Al2O3, Y2O3, SrTiO3, MgO) and the method for depositing a high-temperature superconducting film (HTSF) on its surface – YBaCuO - analysis of the methods of making contacts, which allow to reduce losses when passing a signal from the superconducting microstrip antenna to the waveguide path. The aim of this article is determination of the parameters of a prototype sample of a microstrip antenna device made from HTSF: transient characteristics of high-temperature superconductors, HTSF impulsive characteristics, recovery time of the superconducting state after the action of a powerful pulse on the protective device, the amplitude-frequency characteristics of the protective device in the superconducting state. This will allow to evaluate the possibility of using a microstrip antenna device made from high-temperature superconductors to protect the receiving systems from electromagnetic damage. The absence of a unified theory of high-temperature superconductivity leads to the need to select an analytical form of the functions of the amplitude-frequency characteristics of superconducting protection, and for this mathematical models are used in the programs "APPROX", "MathCAD14.0". The reliability of the obtained results of mathematical modeling of the processes of protection and recovery of the superconducting state after electromagnetic shock are confirmed in the course of experimental studies (an error of 0.15%).

Theory of high-temperature superconductivity in strongly correlated fermions system

A unified theory to explain generally the properties of high-temperature superconducting cuprates and iron pnictides etc. is presented. The theory is based on the extended d-p model emphasizing that the electronic state of superconductors can be described by the composed fermions constructed with newly defined operators. The peculiarity in the theory is that the Hamiltonian is so modified by the unitary transformation using these fermion operators as to apply the mean field approximation. It is found that the results can provide a universal explanation about the various superconducting and normal properties of high-temperature superconductors.

Theory of High-Temperature Superconductivity in Cuprates

We propose a microscopic theory of superconductivity for systems with strong electron correlations such as cuprates in the framework of the extended Hubbard model where the intersite Coulomb repulsion and electron-phonon interaction (EPI) are taken into account. The Dyson equation for the normal and pair Green functions for the Hubbard operators (HOs) is derived. Due to the unconventional commutation relations for the HOs, a specific kinematical interaction of electrons with spin and charge fluctuations with a large coupling constant of the order of the kinetic energy of electrons W emerges that results in the d-wave pairing with high- Tc. Superconductivity can be suppressed only for a large intersite Coulomb repulsion \(V \gtrsim W\). Isotope effect on Tc caused by electron-phonon interaction is weak at optimal doping and increases at low doping. The kinematical interaction is absent in the spin-fermion models and is lost in the slave-boson (-fermion) models treated in the mean-field approximation.

A study of the equation for an energy gap on the basis of the fluctuation theory of high-temperature superconductivity

The equation for an energy gap is investigated using the fluctuation theory of high-temperature superconductivity. It is shown that the proposed mechanism can explain an increase in critical temperature, T c . An explicit expression for the critical temperature is obtained using the technique of rectangular pits.

A simple mathematical model for high temperature superconductivity

There exists no established theory for high temperature superconductivity, since Müller and Bednorz's discovery in 1986, although some partial theories have been proposed. We will give a consistent mathematical theory of high temperature superconductivity based on a theory of stochastic processes of Schrödinger and Nagasawa.

Superconductivity from repulsive electronic correlations on alternant cuprate and iron-based lattices

A key question in the theory of high-temperature superconductivity is whether off-diagonal long-range order can be induced wholly or in large part by repulsive electronic correlations. Electron pairs on cuprate and the iron-based pnictide and chalcogenide alternant lattices may interact with a strong short-range Coulomb repulsion and much weaker longer range attractive tail. Here, we show that such interacting electrons can cooperate to produce a superconducting state in which time-reversed electron pairs effectively avoid the repulsive part but reside predominantly in the attractive region of the potential. The alternant lattice structure is a key feature of such a stabilization mechanism leading to the occurrence of high-temperature superconductivity with or sign alternating s-wave or s± condensate symmetries. © 2013 Wiley Periodicals, Inc.

Theory of High Temperature Superconductivity Beyond BCS with Realistic Coulomb and Fröhlich Interactions

Along with some other researches we have realised that the true origin of high-temperature superconductivity is found in the strong Coulomb repulsion combined with a significant electron–phonon interaction. Both interactions are strong (on the order of 1 eV) compared with the low Fermi energy of doped carriers which makes the conventional BCS-Eliashberg theory inapplicable in cuprates and related doped insulators. Based on our recent analytical and numerical results we argue that high-temperature superconductivity from repulsion alone is impossible for any strength of the Coulomb interaction. Major steps of the alternative polaron theory are outlined starting from the generic Hamiltonian including the unscreened (bare) Coulomb and electron–phonon interactions. The theory accounts for high superconducting critical temperatures, unconventional isotope effects and reconciles tunnelling, photoemission and quantum oscillation data.

Theory of High Temperature Superconductivity in Cuprates and Other Doped Polar Insulators

In the last two decades, there have been tremendous attempts to build an adequate theory of high-temperature superconductivity. Most studies used some model Hamiltonians with input parameters not directly related to the material. The dielectric response function of electrons in strongly correlated high-temperature superconductors is a priori unknown. Hence, one has to start with the generic Hamiltonian including unscreened Coulomb and Frohlich electron–phonon interactions operating on the same scale since any ad-hoc assumption on their range and relative magnitude might fail. Using such a generic Hamiltonian, the analytical theory of high-temperature superconductivity in doped polar insulators predicting the critical temperature in excess of a hundred Kelvin without any adjustable parameters has been built. The many-particle electron system is described by an analytically solvable polaronic t–Jp Hamiltonian with reduced hopping integral, t, allowed double on-site occupancy, large phonon-induced antiferromagnetic exchange, Jp>t, and a high-temperature superconducting state of small superlight bipolarons protected from clustering. Here, major steps of the theory are outlined suggesting that the true origin of high-temperature superconductivity is found in a proper combination of strong electron–electron correlations with a significant finite-range (Frohlich) EPI, and that the theory is fully compatible with the key experiments.

Theory of high-temperature superconductivity in cuprates

A microscopic theory of electronic spectrum and superconducting pairing in the high-temperature cuprate superconductors is presented. The theory is based on consideration of strong electron correlations within the Bogolyubov polar model. The Dyson equation is derived by using the equation of motion method for the thermodynamic Green functions in terms of the Hubbard operators. The self-energy is evaluated in the noncrossing approximation for electron scattering on spin and charge fluctuations induced by kinematic interaction. The theory demonstrates that a strong Coulomb repulsion results in the anomalous electronic spectrum and unconventional (d-wave) superconducting pairing with high T c mediated by the antiferromagnetic exchange and spin fluctuations.

Theory of high-temperature superconductivity and effective gravity

We argue that an approach involving effective gravity could play a crucial role in elucidating the properties of the high-temperature superconducting materials. In particular we propose that the high critical temperature might be naturally explained in a framework constructed as a direct condensed-matter analog of the Randall-Sundrum approach to a geometrization of the hierarchy problem in high-energy physics.

Two-time Green’s functions in superconductivity theory

Based on the method of the equations of motion for two-time Green’s functions, we derive superconductivity equations for different types of interactions related to the scattering of electrons on phonons and spin fluctuations or caused by strong Coulomb correlations in the Hubbard model. We derive an exact Dyson equation for the matrix Green’s function with the self-energy operator in the form of the multiparticle Green’s function. Calculating the self-energy operator in the approximation of noncrossing diagrams leads to a closed system of equations corresponding to the Migdal-Eliashberg strong-coupling theory. We propose a theory of high-temperature superconductivity due to kinematic interaction in the Hubbard model. We show that two pairing channels occur in systems with a strong Coulomb correlation: one due to the antiferromagnetic exchange in interband hopping and the other due to the coupling to spin and charge fluctuations in hopping within one Hubbard band.

Are we there yet?

It's more than twenty years since our journey towards a theory of high-temperature superconductivity began, but we've yet to reach our destination. The road ahead is winding, but there are new data and ideas to guide us.

Have Cuprates Earned Their Stripes?

Physicists are struggling to understand how electrons behave in cuprate superconductors, and the outcome may resolve the question of how these materials become superconducting. In his Perspective, Norman discusses work reported in the same issue by Vershinin et al. in which scanning tunneling microscopy was used to study electrons in a cuprate above the superconducting transition temperature. The researchers found that the material displays a charge modulation that gives rise to a checkerboard pattern of electrons instead of a stripe pattern seen in other experiments. More needs to be learned about this system, but it indicates that a proper theory of high-temperature superconductivity may lie somewhere between a localized electron picture and one in which the electrons are itinerant.

Theory of High Temperature Superconductivity: A Status Report

This talk briefly reviews the current experimental and theoretical developments in high Tc superconductivity, focusing on the pseudogap regime of the underdoped region of the phase diagram.We argue that the appearance of superconductivity cannot be explained based on the traditional approach of quasiparticles exchanging some bosons, and that something fundamentally different is called for.

Photoemission, Correlation and Superconductivity: New Avenues

We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.

Universal superconducting and magnetic properties of the (Ca xLa 1− x)(Ba 1.75− xLa 0.25+ x)Cu 3O y system: a μSR investigation

The (Ca x La 1− x )(Ba 1.75−xLa 0.25+ x ) Cu 3O y system is ideal for testing theories of high temperature superconductivity, since nearly the full range of doping is controlled by y, and T c max is continuously controlled by x, with minimal structural changes. We investigate this system with both transverse and longitudinal field μSR. This allows us to re-examine the Uemura relation, the nature of the spontaneous magnetic fields below T c, and the relation between their appearance temperature T g and T c max. Our major findings are: (1) the Uemura relation is respected by this system more adequately than by other cuprates, (2) T g and T c are controlled by the same energy scale, (3) the phase separation between hole poor and hole rich regions is a microscopic one, and (4) spontaneous magnetic fields appear gradually with no moment size evolution.

Theory of high-temperature superconductivity from electronic structure to d-wave pairing

A brief review on the Kamimura–Suwa (K–S) model is first given. Then it is shown that an observed peculiar doping dependence of electronic entropy is explained by the K–S model successfully. Further it is shown on the basis of the K–S model that the phonon-mediated d-wave superconductivity is possible in LSCO.