A POSSIBLE PAIRING MECHANISM FOR HTSC: TWO-DIMENSIONAL CONFINEMENT AND COULOMB OVER-SCREENING

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3472-3477 ◽  
Author(s):  
D. ARIOSA ◽  
H. BECK
Keyword(s):  
Mean Field ◽  
Three Dimensional ◽  
Critical Density ◽  
Zero Point ◽  
Coulomb Repulsion ◽  
Two Dimensional ◽  
Pairing Mechanism ◽  
Density Region ◽  
Point Energy ◽  
Localization Energy

Among all the common properties of HTCS cuprates, we build our model on two of them: their high anisotropy, and their extremely low density of charge carriers. The intra-layer pairing mechanism is provided by the two-dimensional over-screening of Coulomb repulsion.1,2 The c-axis zero point energy restricts this pairing to a low carrier density region. Below a critical density, the system behaves as a two-dimensional confined jellium where the energy gain due to charge pairing is larger than the c-axis localization energy. In the high density region, where the pairing energy cannot compensate the localization energy, the system delocalizes and crosses over to a three-dimensional regime. This competition between binding and confinement energies implies a monotonic decrease of mass anisotropy with doping. Pre-formed pairs which exist below a Mean Field (MF) temperature defined by the binding energy, account for pseudo-gap observations.3,4 The superconducting critical temperature T c is given by the Beresinskii–Kosterlitz–Thouless (BKT) transition of the two-dimensional layer, renormalized by quantum phase fluctuations (QPF).5 QPF account for the metal-insulator transition at very low doping.

Bereziskii-Kosterlitz-Thouless transition in the Weyl system PtBi2

2021 ◽  
Author(s):  
Arthur Veyrat ◽  
Valentin Labracherie ◽  
Rohith Acharya ◽  
Dima Bashlakov ◽  
Federico Caglieris ◽  
...  
Keyword(s):  
Condensed Matter ◽  
Three Dimensional ◽  
Spin Orbit Coupling ◽  
Two Dimensional ◽  
Pairing Mechanism ◽  
Critical Fields ◽  
Weyl Semimetal ◽  
Superconducting Coherence Length ◽  
Low Dimensional ◽  
Strong Spin

Abstract Symmetry breaking in topological matter became, in the last decade, a key concept in condensed matter physics to unveil novel electronic states. In this work, we reveal that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi2 lead to a Weyl semimetal band structure, with unusually robust two-dimensional superconductivity in thin fims. Transport measurements show that high-quality PtBi2 crystals are three-dimensional superconductors (Tc≈600 mK) with an isotropic critical field (Bc≈50 mT). Remarkably, we evidence in a rather thick flake (60 nm), exfoliated from a macroscopic crystal, the two-dimensional nature of the superconducting state, with a critical temperature Tc≈370 mK and highly-anisotropic critical fields. Our results reveal a Berezinskii-Kosterlitz-Thouless transition with TBKT≈310 mK and with a broadening of Tc due to inhomogenities in the sample. Due to the very long superconducting coherence length ξ in PtBi2, the vortex-antivortex pairing mechanism can be studied in unusually-thick samples (at least five times thicker than for any other two-dimensional superconductor), making PtBi2 an ideal platform to study low dimensional superconductivity in a topological semimetal.

MEAN-FIELD THEORY FOR LAYERED HIGH-TEMPERATURE SUPERCONDUCTORS

1988 ◽  
Vol 02 (05) ◽  
pp. 1059-1065 ◽  
Author(s):  
D. Baeriswyl ◽  
T. Schneider
Keyword(s):  
High Temperature Superconductors ◽  
Mean Field Theory ◽  
Mean Field ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
Interlayer Spacing ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Pairing Mechanism ◽  
The Mean

Using the mean-field approximation we study a model for quasi-two-dimensional layered superconductors. The interlayer coupling, assumed to be mediated by a small electron hopping term, is found to leave Tc practically unaffected. Consequently, a three-dimensional pairing mechanism is required to explain the observed dependence of Tc on the average interlayer spacing in the Bi and Tl compounds.

THE EMISSION OF HEAVY CLUSTERS DESCRIBED IN THE MEAN-FIELD HFB THEORY: THE CASE OF 242Cm

2008 ◽  
Vol 17 (10) ◽  
pp. 2275-2282 ◽  
Author(s):  
L. M. ROBLEDO ◽  
M. WARDA
Keyword(s):  
Mean Field ◽  
Zero Point ◽  
Point Energy ◽  
Cluster Emission ◽  
Field Techniques ◽  
Hartree Fock ◽  
Moment Operator ◽  
Collective Coordinate ◽  
The Mean ◽  
Asymmetric Fission

The emission of a nucleus of 34 Si by the parent [Formula: see text] is a process in the diffuse borderline between cluster emission and standard mass asymmetric fission. In this paper we analyze in a microscopic framework such process using the standard mean field techniques used to describe cluster emission. They include Hartree-Fock-Bogoliubov constrained calculations with the Gogny D1S interaction and the octupole moment operator as the collective coordinate to describe the process. Collective masses and all kind of zero point energy corrections are considered which allows for a parameter free estimation of the process' half-life. The agreement with experiment is quite satisfactory.

scholarly journals Bayesian reconstruction of images of objects with high-density inclusions with suppression of artifacts

2018 ◽  
Vol 145 ◽  
pp. 05017
Author(s):  
Sergei Zolotarev ◽  
Valery Vengrinovich ◽  
Mohsen Mirzavand ◽  
Mieteeg Mukhtar ◽  
Ivan Georgiev
Keyword(s):  
Tomographic Reconstruction ◽  
Three Dimensional ◽  
Original Method ◽  
High Density ◽  
X Rays ◽  
Two Dimensional ◽  
Density Region ◽  
Bayesian Reconstruction ◽  
Mathematical Algorithm ◽  
High Density Region

The technology of three-dimensional Bayesian tomographic reconstruction of homogeneous objects with high-density inclusions is developed. The approach is based on preliminary correction of projections by extracting the data corresponding to X-rays passing through a high-density region, and replacing it with synthesized data obtained by two-dimensional interpolation. An original method for selecting interpolation points is proposed and a mathematical algorithm is described that ensures the implementation of two-dimensional interpolation correction of projections.

Structural and Electronic Properties of ZnO NANOCLUSTERs: A B3LYP DFT Study

2013 ◽  
Vol 650 ◽  
pp. 29-33 ◽  
Author(s):  
D.K. Pandey ◽  
P.S. Yadav ◽  
S. Agrawal ◽  
B.K. Agrawal
Keyword(s):  
Electronic Properties ◽  
Three Dimensional ◽  
Zero Point ◽  
Point Energy ◽  
Stable Clusters ◽  
Structural And Electronic Properties ◽  
Zno Nanoclusters ◽  
The Stability ◽  
Homo Lumo ◽  
Zero Point Energy Correction

An ab initio B3LYP-DFT/6-311G(3df) study has been performed for the stability, structural and electronic properties of forty ZnmOn(m + n = p = 2 to 4) nanoclusters. We also consider the zero point energy correction. The nanoclusters containing large number of strongly electronegative O atoms for p = 3 and 4 are found to be most stable as compared to the other nanoclusters of the same configuration. The most stable clusters have linear or planer structures and not the three dimensional ones. The observed trend of decrease of the HOMO-LUMO gap with the size of the nanocluster is in conformity with the quantum confined behavior.

scholarly journals Self-consistent mean-field magnetohydrodynamics

2009 ◽  
Vol 466 (2114) ◽  
pp. 583-601 ◽  
Author(s):  
A. Courvoisier ◽  
D. W. Hughes ◽  
M. R. E. Proctor
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Mean Field Theory ◽  
Mean Field ◽  
Three Dimensional ◽  
Nonlinear Regime ◽  
Two Dimensional ◽  
Link Type ◽  
Forcing Function ◽  
Basic States

We consider the linear stability of two-dimensional nonlinear magnetohydrodynamic basic states to long-wavelength three-dimensional perturbations. Following Hughes & Proctor (Hughes & Proctor 2009 Proc. R. Soc. A 465 , 1599–1616 ( doi:10.1098/rspa.2008.0493 )), the two-dimensional basic states are obtained from a specific forcing function in the presence of an initially uniform mean field of strength . By extending to the nonlinear regime the kinematic analysis of Roberts (Roberts 1970 Phil. Trans. R. Soc. Lond. A 266 , 535–558 ( doi:10.1098/rsta.1970.0011 )), we show that it is possible to predict the growth rate of these perturbations by applying mean-field theory to both the momentum and the induction equations. If , these equations decouple and large-scale magnetic and velocity perturbations may grow via the kinematic α -effect and the anisotropic kinetic alpha instability, respectively. However, if , the momentum and induction equations are coupled by the Lorentz force; in this case, we show that four transport tensors are now necessary to determine the growth rate of the perturbations. We illustrate these situations by numerical examples; in particular, we show that a mean-field description of the nonlinear regime based solely on a quenched α coefficient is incorrect.

MAGNETIC PAIRING IN TWO-DIMENSIONAL ANTIFERROMAGNETIC XY MODEL

1989 ◽  
Vol 03 (01) ◽  
pp. 65-76
Author(s):  
K. Y. SZETO
Keyword(s):  
High Temperature ◽  
Coulomb Repulsion ◽  
Coulomb Gas ◽  
The Self ◽  
Xy Model ◽  
Two Dimensional ◽  
Pairing Mechanism ◽  
Spin Variable ◽  
Self Consistent ◽  
Magnetic Pairing

A two-dimensional Ising Coulomb gas is introduced to describe the frustrated plaquettes of the two-dimensional antiferromagnetic XY model with Coulomb repulsion. The Ising spin variable corresponds to the two possible chiralities of the frustrated plaquettes, which repel each other with a screened Coulomb potential. Using the self-consistent screening analysis, the Ising Coulomb gas is shown to have a Kosterlitz-Thouless transition from a pairing phase at low temperature to a plasma phase at high temperature. The phase diagram is obtained numerically as a function of density and relative strength of the attraction between particles of opposite chiralities and the Coulomb repulsion. Possible applications to the magnetic pairing mechanism of high temperature superconductors is discussed in the context of Li doped La 2 CuO 4. It is also argued that the Aharony et al. model of magnetic pairing with the dipolar attraction can be derived as a special case of the Ising Coulomb gas model and is superceded by a stronger attractive interaction in magnetic pairing mechanism in the self-consistent analysis.

High Resolution Microscopy of Multi-Layered Biological Crystals

1982 ◽  
Vol 40 ◽  
pp. 80-83
Author(s):  
H.A. Cohen ◽  
T.W. Jeng ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Low Dose ◽  
Three Dimensional ◽  
Data Interpretation ◽  
Two Dimensional ◽  
Biological Objects ◽  
Density Maps ◽  
Density Map ◽  
Complex Crystal ◽  
High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

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