scholarly journals Pauli paramagnetism of triplet Cooper pairs in a nematic superconductor

2021 ◽  
Vol 104 (21) ◽  
Author(s):  
D. A. Khokhlov ◽  
R. S. Akzyanov
Keyword(s):  
Cooper Pairs ◽  
Pauli Paramagnetism

Systems with Condensates and Pairing

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.

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

Symmetry ◽  
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.

scholarly journals On-demand thermoelectric generation of equal-spin Cooper pairs

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Felix Keidel ◽  
Sun-Yong Hwang ◽  
Björn Trauzettel ◽  
Björn Sothmann ◽  
Pablo Burset
Keyword(s):  
Cooper Pairs ◽  
Thermoelectric Generation ◽  
On Demand

The Ternary Rare Earth Chromium Nitrides Ce2CrN3 and Ln3Cr10−xN11 with Ln = La, Ce, Pr

1995 ◽  
Vol 50 (6) ◽  
pp. 905-912 ◽  
Author(s):  
Sascha Broil ◽  
Wolfgang Jeitschko
Keyword(s):  
Rare Earth ◽  
Single Crystal ◽  
Chromium Nitrides ◽  
First Approximation ◽  
Structure Factors ◽  
Square Planar ◽  
Pauli Paramagnetism ◽  
Cubic Structure ◽  
Cold Pressed ◽  
N Flux

The title compounds have been prepared by annealing cold-pressed pellets of the binary nitrides LnN and CrN. Well developed crystals were obtained by recrystallization of the binary or prereacted ternary nitrides in a Li3N flux. Their structures were determined from single-crystal diffractometer data. C e2CrN3 has a U2CrN3 type structure: Immm , a = 379.0(1), b = 340.4(1), c = 1251.7(2) pm, Z = 2, R = 0.012 for 383 structure factors and 16 variables. The atomic positions of this structure are similar to those of U2IrC2 and K2NiF4. The structure may be rationalized to a first approximation with the formula (Ce+4)2[CrN3]8−. The chromium atoms are in a distorted square-planar nitrogen coordination. The CrN4-squares are linked via corner-sharing nitrogen atoms, thus forming infinite, straight - N - CrN2- N - CrN2- chains. The cubic structure of La3Cr10−xN11 (a = 1298.2(1) pm ), Ce3Cr10−xN11 (with a small homogenity range; a = 1284.3(1)-1286.1(3) pm ), and Pr3Cr10−xN11 (a = 1289.1(2) pm ) was determined for the lanthanum compound: Fm 3̄ m , Z = 8, R = 0.027 for 189 F values and 18 variables. One chromium site was found to have an occupancy of only 80.9(5)% resulting in the composition La3Cr9.24(1)N11. The nitrogen atoms occupy four atomic sites. Three of these have octahedral environments (6 La, 3 La + 3 Cr, 2 La + 4 Cr), the fourth one is surrounded by eight chromium atoms forming a cube. The chromium atoms are tetrahedrally coordinated by nitrogen atoms, and these CrN4-tetrahedra are linked via common corners and edges to form a three-dimensionally infinite polyanionic network. In addition the chromium atoms with oxidation numbers of about 2 to 3 form numerous Cr - Cr bonds, which allow to rationalize the Pauli paramagnetism of the compound.

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

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.

Electric-Field Induced Formation of Superconducting Granular Balls

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2529-2535
Author(s):  
R. Tao ◽  
X. Xu ◽  
Y. C. Lan
Keyword(s):  
Surface Energy ◽  
Electric Field ◽  
Liquid Nitrogen ◽  
Applied Electric Field ◽  
Strong Electric Field ◽  
Particle Surface ◽  
Cooper Pairs ◽  
Surface Charges

When a strong electric field is applied to a suspension of micron-sized high T c superconducting particles in liquid nitrogen, the particles quickly aggregate together to form millimeter-size balls. The balls are sturdy, surviving constant heavy collisions with the electrodes, while they hold over 106 particles each. The phenomenon is a result of interaction between Cooper pairs and the strong electric field. The strong electric field induces surface charges on the particle surface. When the applied electric field is strong enough, Cooper pairs near the surface are depleted, leading to a positive surface energy. The minimization of this surface energy leads to the aggregation of particles to form balls.

Light emission by tunneling Cooper pairs across a vacuum gap

2000 ◽  
Vol 116 (10) ◽  
pp. 539-542 ◽  
Author(s):  
Y Uehara ◽  
T Fujita ◽  
M Iwami ◽  
S Ushioda
Keyword(s):  
Light Emission ◽  
Cooper Pairs ◽  
Vacuum Gap
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