A Simple Model for Investigation of the Pair Breaking Effect on the Parameters of HTS/FM Thin Films

A simple model was proposed for description of Cooper pair breaking effect (which is caused by transfer of spin-polarized carriers from the ferromagnetic (FM) manganite into the high temperature superconductor (HTS)) on the critical temperature and the microwave surface impedance of HTS/FM heterostructures. The model is based on the assumption on an exponential dependence of the Cooper pairs concentration (as well as number of the holes in CuO2 planes, responsible for the superconductivity) on the distance from HTS/FM interface. The model fits well the thickness dependence of HTS film parameters and is used for evaluation of the penetration depth of spin-polarized particles into HTS in the HTS/FM structures.

Download Full-text

Electron beam induced effects in Cu/GeSe2amorphous films

MRS Proceedings ◽

10.1557/proc-777-t4.7 ◽

2003 ◽

Vol 777 ◽

Author(s):

J.S. Romero ◽

A.G. Fitzgerald

Keyword(s):

Thin Films ◽

Electron Beam ◽

Simple Model ◽

Copper Concentration ◽

Negative Charge ◽

Electron Bombardment ◽

Continuous Operation ◽

Electron Radiation ◽

Crystalline Product ◽

Intense Electron

AbstractCopper migration is observed in the SEM in amorphous GeSe2/Cu thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. The phenomenon can be explained using a simple model in which the population of D- centers is considered to increase upon electron irradiation. The increase in the D- center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%-30% have been obtained. Additionally we have observed the local crystallization of amorphous GeSe2/Cu thin films in the TEM when the samples were subjected to intense electron bombardment. The crystalline product has been identified as Berzelianite (Cu2Se).

Download Full-text

Systems with Condensates and Pairing

10.1093/oso/9780198797241.003.0012 ◽

2018 ◽

Author(s):

Klaus Morawetz

Keyword(s):

Critical Parameters ◽

Einstein Condensation ◽

Cooper Pairs ◽

Pair Breaking ◽

Systematic Theory ◽

Bose Einstein Condensation ◽

T Matrix ◽

The Stability ◽

Bose Einstein

The Bose–Einstein condensation and appearance of superfluidity and superconductivity are introduced from basic phenomena. A systematic theory based on the asymmetric expansion of chapter 11 is shown to correct the T-matrix from unphysical multiple-scattering events. The resulting generalised Soven scheme provides the Beliaev equations for Boson’s and the Nambu–Gorkov equations for fermions without the usage of anomalous and non-conserving propagators. This systematic theory allows calculating the fluctuations above and below the critical parameters. Gap equations and Bogoliubov–DeGennes equations are derived from this theory. Interacting Bose systems with finite temperatures are discussed with successively better approximations ranging from Bogoliubov and Popov up to corrected T-matrices. For superconductivity, the asymmetric theory leading to the corrected T-matrix allows for establishing the stability of the condensate and decides correctly about the pair-breaking mechanisms in contrast to conventional approaches. The relation between the correlated density from nonlocal kinetic theory and the density of Cooper pairs is shown.

Download Full-text

Multiplicity, Parity and Angular Momentum of a Cooper Pair in Unconventional Superconductors of D4h Symmetry: Sr2RuO4 and Fe-Pnictide Materials

Symmetry ◽

10.3390/sym13081435 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1435

Author(s):

Victor G. Yarzhemsky

Keyword(s):

Angular Momentum ◽

Cooper Pair ◽

Point Group ◽

Group Symmetry ◽

Cooper Pairs ◽

Group Approach ◽

Angular Momentum Projection ◽

Space Group ◽

Unconventional Superconductors ◽

Even Pairs

Sr2RuO4 and Fe-pnictide superconductors belong to the same point group symmetry D4h. Many experimental data confirm odd pairs in Sr2RuO4 and even pairs in Fe-pnictides, but opposite conclusions also exist. Recent NMR results of Pustogow et al., which revealed even Cooper pairs in Sr2RuO4, require reconsideration of symmetry treatment of its SOP (superconducting order parameter). In the present work making use of the Mackey–Bradley theorem on symmetrized squares, a group theoretical investigation of possible pairing states in D4h symmetry is performed. It is obtained for I4/mmm , i.e., space group of Sr2RuO4, that triplet pairs with even spatial parts are possible in kz direction and in points M and Y. For the two latter cases pairing of equivalent electrons with nonzero total momentum is proposed. In P4/nmm space group of Fe- pnictides in point M, even and odd pairs are possible for singlet and triplet cases. It it shown that even and odd chiral states with angular momentum projection m=±1 have nodes in vertical planes, but Eg is nodal , whereas Eu is nodeless in the basal plane. It is also shown that the widely accepted assertion that the parity of angular momentum value is directly connected with the spatial parity of a pair is not valid in a space-group approach to the wavefunction of a Cooper pair.

Download Full-text

Superconducting coherence length of hole-doped cuprates obtained from electron–boson spectral density function

Scientific Reports ◽

10.1038/s41598-021-91163-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Jungseek Hwang

Keyword(s):

Spectral Density ◽

Coherence Length ◽

Cooper Pair ◽

Average Frequency ◽

Spin Fluctuations ◽

Fermi Velocity ◽

Cooper Pairs ◽

Spectroscopic Techniques ◽

Microscopic Mechanism ◽

Superconducting Coherence Length

AbstractElectron–boson spectral density functions (EBSDFs) can be obtained from measured spectra using various spectroscopic techniques, including optical spectroscopy. EBSDFs, known as glue functions, are suggested to have a magnetic origin. Here, we investigated EBSDFs obtained from the measured optical spectra of hole-doped cuprates with wide doping levels, from underdoped to overdoped cuprates. The average frequency of an EBSDF provides the timescale for the spin fluctuations to form Cooper pairs. This timescale is directly associated with retarded interactions between electrons. Using this timescale and Fermi velocity, a reasonable superconducting coherence length, which reflects the size of the Cooper pair, can be extracted. The obtained coherence lengths were consistent with those measured via other experimental techniques. Therefore, the formation of Cooper pairs in cuprates can be explained by spin fluctuations, the timescales of which appear in EBSDFs. Consequently, EBSDFs provide crucial information on the timescale of the microscopic mechanism of Cooper pair formation.

Download Full-text