scholarly journals Peculiarities in the concentration dependence of the superconducting transition temperature in the bipolaron theory of Cooper pairs

2017 ◽  
Vol 31 (11) ◽  
pp. 1750125 ◽  
Author(s):  
Victor Lakhno
Keyword(s):  
Transition Temperature ◽  
Concentration Dependence ◽  
Superconducting Transition Temperature ◽  
Superconducting Phase ◽  
Intermediate Level ◽  
Cooper Pairs ◽  
Superconducting Transition

It is shown that the bipolaron theory of Cooper pairs suggests that there is a possibility for a superconducting phase to exist at low and high levels of doping and be absent at the intermediate level of doping. The results obtained possibly to imply the universal character of 1/8 anomaly.

scholarly journals Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5830
Author(s):  
Andrzej Ślebarski ◽  
Maciej M. Maśka
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
High Temperature Superconductors ◽  
Superconducting Phase ◽  
Length Scale ◽  
Superconducting Transition ◽  
Atomic Disorder ◽  
Strong Inhomogeneity ◽  
Related Compounds

We investigated the effect of enhancement of superconducting transition temperature Tc by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La3M4Sn13, Ca3Rh4Sn13, Y5Rh6Sn18, Lu5Rh6Sn18; M= Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale ξ in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with Tc⋆>Tc (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of Tc⋆∼2Tc (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase Tc⋆ in respect to the bulk Tc one and proposed a model that explains the Tc⋆>Tc behavior in the series of nonmagnetic skutterudite-related compounds.

scholarly journals Smart meta-superconductor MgB2 constructed by the dopant phase of luminescent nanocomposite

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Yongbo Li ◽  
Honggang Chen ◽  
Mingzhong Wang ◽  
Longxuan Xu ◽  
Xiaopeng Zhao
Keyword(s):  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Ex Situ ◽  
Cooper Pairs ◽  
Superconducting Transition ◽  
Luminescence Characteristic ◽  
Dopant Content ◽  
Strong Luminescence

Abstract On the basis of the idea that the injecting energy will improve the conditions for the formation of Cooper pairs, a smart meta-superconductor (SMSC) was prepared by doping luminescent nanocomposite Y2O3:Eu3+/Ag in MgB2. To improve the superconducting transition temperature (TC) of the MgB2-based superconductor, two types of Y2O3:Eu3+/Ag, which has the strong luminescence characteristic, with different sizes were prepared and marked as m-Y2O3:Eu3+/Ag and n-Y2O3:Eu3+/Ag. MgB2 SMSC was prepared through an ex situ process. Results show that when the dopant content was fixed at 2.0 wt.%, the TC of MgB2 SMSC increased initially then decreased with the increase in the Ag content in the dopant. When the Ag content is 5%, the TC of MgB2 SMSC was 37.2–38.0 K, which was similar to that of pure MgB2. Meanwhile, the TC of MgB2 SMSC doped with n-Y2O3:Eu3+/Ag increased initially then decreased basically with the increase in the content of n-Y2O3:Eu3+/Ag, in which the Ag content is fixed at 5%. The TC of MgB2 SMSC doped with 0.5 wt.% n-Y2O3:Eu3+/Ag was 37.6–38.4 K, which was 0.4 K higher than that of pure MgB2. It is thought that the doping luminescent nanocomposite into the superconductor is a new means to improve the TC of SMSC.

Kinetic Energy Driven Charge Pairing and Superconductivity in the t–J Model

2003 ◽  
Vol 17 (22) ◽  
pp. 1151-1159
Author(s):  
Shiping Feng
Keyword(s):  
Transition Temperature ◽  
Kinetic Energy ◽  
Ground State ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Doping Concentration ◽  
Attractive Force ◽  
Hole Doping ◽  
Cooper Pairs ◽  
Superconducting Transition

The superconducting mechanism of doped cuprates is studied within the t–J model. It is shown that dressed holons interact directly through the kinetic energy by exchanging dressed spinon excitations. This interaction leads to a net attractive force between dressed holons, and the electron Cooper pairs originating from the dressed holon pairing state are due to the charge-spin recombination, and their condensation reveals the superconducting ground state. The superconducting transition temperature is determined by the dressed holon pair transition temperature, and is proportional to the hole doping concentration in the underdoped regime, in qualitative agreement with experiments.

scholarly journals SUPERCONDUCTIVITY IN NaxCoO2·yH2O DRIVEN BY THE KINETIC ENERGY

2005 ◽  
Vol 19 (01n03) ◽  
pp. 73-75 ◽  
Author(s):  
BIN LIU ◽  
YING LIANG ◽  
SHIPING FENG
Keyword(s):  
Transition Temperature ◽  
Kinetic Energy ◽  
Ground State ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Doping Concentration ◽  
Experimental Results ◽  
Cooper Pairs ◽  
Superconducting Transition ◽  
Mechanism Of Superconductivity

Within the charge-spin separation fermion-spin theory, the mechanism of superconductivity in Na x CoO 2·y H 2 O is studied. It is shown that dressed fermions interact occurring directly through the kinetic energy by exchanging magnetic excitations. This interaction leads to a net attractive force between dressed fermions(then the electron Cooper pairs), and their condensation reveals the superconducting ground state. The optimal superconducting transition temperature occurs in the electron doping concentration δ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitative agreement with the experimental results.

Epr Spectroscopy on Zn-Substituted YBa2Cu3O7

1987 ◽  
Vol 99 ◽  
Author(s):  
A. M. Ponte Goncalves ◽  
Chan-Soo Jee ◽  
D. Nichols ◽  
J. E. Crow ◽  
G. H. Myer ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Transition Temperature ◽  
Epr Spectroscopy ◽  
Superconducting Transition Temperature ◽  
Superconducting Phase ◽  
Superconducting Transition ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic ◽  
Cu Ions ◽  
Bulk Response

ABSTRACTThe temperature and concentration dependence of the electron paramagnetic resonance spectra of YBa2(Cu1−xZnx)3O7 has been measured for 0≤x≤0.16. Zn substituted on the Cu-site cause a rapid nearly linear depression of the superconducting transition temperature Tc with Tc going to zero in the vicinity of x=0.10. Only weak EPR spectra due to ≤1% of the Cu-ions are seen in the superconducting phase of YBa2Cu3O7. These spectra are most likely attributed to Cu-ions in the vicinity of grain boundaries and do not represent a bulk response. However, a strong asymmetric resonance is observed in the Zn-substituted samples with x>0.1. The EPR results obtained for YBa2(Cu1−xZnx)3O7 are discussed in terms of a possible localization of d-electrons.

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