scholarly journals Superconducting Coherence Length of Hole-doped Cuprates Obtained From Electron-boson Spectral Density Function

2021 ◽  
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

Abstract Electron{boson spectral density functions (EBSDFs) can be obtained from measured spectra using various spectroscopic techniques, including optical spectroscopy. EBSDFs, known as glue functions, 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 betweenelectrons. 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.

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.

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.

Impurity effects on the superconducting coherence length in Zn- or Ni-dopedYBa2Cu3O6.9single crystals

1999 ◽  
Vol 60 (1) ◽  
pp. 114-117 ◽  
Author(s):  
K. Tomimoto ◽  
I. Terasaki ◽  
A. I. Rykov ◽  
T. Mimura ◽  
S. Tajima
Keyword(s):  
Coherence Length ◽  
Impurity Effects ◽  
Superconducting Coherence Length

scholarly journals MECHANISM OF HIGH-Tc SUPERCONDUCTIVITY BASED MAINLY ON TUNNELING MEASUREMENTS IN CUPRATES

2005 ◽  
Vol 19 (16) ◽  
pp. 743-770 ◽  
Author(s):  
A. MOURACHKINE
Keyword(s):  
Tunneling Spectroscopy ◽  
Phase Coherence ◽  
Spin Fluctuations ◽  
Cooper Pairs ◽  
High Tc ◽  
High Tc Superconductivity ◽  
One Dimensional ◽  
Topological Excitations ◽  
Discrete Breathers

The main purpose of this brief review is to present a sketch of the mechanism of high-Tc superconductivity based mainly on tunneling measurements in cuprates. In the review, we shall mostly discuss tunneling spectroscopy in Bi 2 Sr 2 CaCu 2 O 8. Analysis of the data shows that the Cooper pairs in cuprates are topological excitations (e.g. quasi-one-dimensional bisolitons, discrete breathers etc.), and the phase coherence among the Cooper pairs appears due to spin fluctuations.

Influence of Finite Size Effects on the Fulde-Ferrell-Larkin-Ovchinnikov State

2017 ◽  
Vol 21 (3) ◽  
pp. 748-762 ◽  
Author(s):  
Andrzej Ptok ◽  
Dawid Crivelli
Keyword(s):  
Fermi Surface ◽  
Size Effects ◽  
Cooper Pair ◽  
Finite Size ◽  
Superconducting Phase ◽  
Cooper Pairs ◽  
Fflo State ◽  
Finite Size Effects ◽  
Infinite Systems ◽  
Nano Size

AbstractThe Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is the superconducting phase for which the Cooper pairs have a non-zero total momentum, depending on the splitting of the Fermi surface sheets for electrons with opposite spin. In infinite systems the momentum is a continuous function of the temperature. In this paper, we have shown how the finite size of the system, through the discretized geometry of the Fermi surface, affects the physical properties of the FFLO state by introducing discontinuities in the Cooper pair momentum. Our calculation in an isotropic system show that the superconducting state with two opposite Cooper pair momenta is more stable than state with one momentum also in nano-size systems, where finite size effects play a crucial role.

GENERALIZED BCS EQUATIONS: APPLICATIONS

2010 ◽  
Vol 24 (19) ◽  
pp. 3701-3712 ◽  
Author(s):  
G. P. MALIK
Keyword(s):  
Cooper Pair ◽  
Energy Gap ◽  
High Temperature Superconductors ◽  
Bcs Theory ◽  
Simple Extension ◽  
Cooper Pairs ◽  
Debye Temperatures ◽  
Unified Study ◽  
Interesting Candidate ◽  
Composite Superconductors

Based on the concepts of a superpropagator, multiple Debye temperatures, and equivalence of the binding energy of a Cooper pair and the BCS energy gap, the set of generalized BCS equations obtained recently via a temperature-generalized Bethe–Salpeter equation is employed for a unified study of the following composite superconductors: MgB 2, Nb 3 Sn , and YBCO. In addition, we study the Nb – Al system in which Cooper pairs as resonances have recently been reported to have been observed. Our approach seems to suggest that a simple extension of the BCS theory that accommodates the concept of Cooper pairs bound via a more than one phonon exchange mechanism may be an interesting candidate for dealing with high-temperature superconductors.

Coherence Length in a Two-Dimensional Anisotropic Model of Superconductivity

1998 ◽  
Vol 12 (32) ◽  
pp. 3475-3483 ◽  
Author(s):  
L. Bujkiewicz ◽  
L. Jacak
Keyword(s):  
Coherence Length ◽  
Order Parameter ◽  
Cooper Pair ◽  
Mean Square ◽  
Two Dimensional ◽  
Anisotropic Model ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Range Of Values

The coherence length as a mean-square radius of a Cooper pair is calculated for various forms of the anisotropic order parameter. A wide range of values of this quantity is obtained and the smallest values are of the order of magnitude of a few lattice spacings.

DYNAMICAL PROPERTIES OF MULTI-PHOTON INTERACTION BETWEEN A CAVITY FIELD AND A SINGLE-QUBIT

2013 ◽  
Vol 11 (04) ◽  
pp. 1350038 ◽  
Author(s):  
HEBA KADRY ◽  
NORDIN ZAKARIA ◽  
LEE YEN CHEONG ◽  
MAHMOUD ABDEL-ATY
Keyword(s):  
Evolution Operator ◽  
Cooper Pair ◽  
Time Dependent ◽  
Cooper Pairs ◽  
Cavity Field ◽  
Field Coupling ◽  
Single Qubit ◽  
Cooper Pair Box ◽  
The Mean ◽  
Dynamical Properties

We study the dynamical properties of a cavity field coupling to a Cooper pair box (CPB). We assumed that the CPB is prepared initially in a mixed state with a coherent state for the field. By solving the time-dependent equations using the evolution operator, it shows that mean numbers of Cooper pairs is affected by the detuning. The mean number of Cooper pairs is further enhanced by the multi-photon processes in commonly used cavity field.

Fabrication and Electric Transport in MgB2 Doped with Nanosized Carbon-Based Core-Shell Structures

2010 ◽  
Vol 663-665 ◽  
pp. 871-875
Author(s):  
Viorel Sandu ◽  
Gheorghe Virgil Aldica ◽  
Stelian Popa ◽  
Elena Cimpoiasu ◽  
Florian Dumitrache ◽  
...  
Keyword(s):  
Coherence Length ◽  
Shell Structures ◽  
Electric Transport ◽  
Metallic Core ◽  
The Core ◽  
Ceramic Samples ◽  
Plasma Sintering ◽  
Short Processing Time ◽  
Spark Plasma ◽  
Superconducting Coherence Length

We present the fabrication and electric properties of MgB2 ceramic samples doped with nanosized spheres, 4-8 nm, of graphite with a metallic core. The samples were prepared using the spark plasma sintering technique. The size of the additive is comparable to the superconducting coherence length. The short processing time limits the diffusion of the carbon while keeping the core intact. Therefore, in addition to the doping with carbon, the metallic core, which has the size smaller than the superconducting coherence length, create pinning centers which might improve the dissipationless electric transport. The results are analyzed in the framework of different pinning models.

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