Spin fluctuations and the superconducting state in doped insulators

1998 ◽  
Vol 87 (5) ◽  
pp. 956-966
Author(s):  
A. I. Agafonov ◽  
É. A. Manykin
Keyword(s):  
Superconducting State ◽  
Spin Fluctuations

Mechanisms

2021 ◽  
pp. 32-125
Author(s):  
Vladimir Z. Kresin ◽  
Sergei G. Ovchinnikov ◽  
Stuart A. Wolf
Keyword(s):  
Superconducting State ◽  
Degrees Of Freedom ◽  
Pair Correlation ◽  
Three Dimensional ◽  
Layered Materials ◽  
Spin Fluctuations ◽  
Strong Electron ◽  
Hubbard Hamiltonian ◽  
Electron Phonon Interaction ◽  
Phonon Mechanism

This chapter introduces the general concepts of pair correlation, and superconductivity as a strong non-adiabatic phenomenon. Phonon, electronic, and magnetic mechanisms play the major roles; each of them can serve as the origin of the superconducting state. Speaking of the phonon mechanism, it is essential that an explicit expression for Tc depend on the intensity of the electron–phonon interaction. In principle, the electron–phonon mechanism can provide high values of Tc, up to room temperature. Pioneering work by Little, who introduced the electronic mechanism, is described. The mechanism has been analysed for one-dimensional, two-dimensional, and three-dimensional systems. The plasmon mechanism can play a role for layered materials. The superconducting state can be provided by magnetic degrees of freedom. The band limit with spin fluctuations and the regime of strong electron correlations are described. The Hubbard Hamiltonian and the t − J model are the ingredients of the approach.

ANOMALOUS BEHAVIOR OF SPIN FLUCTUATIONS IN POLYCRYSTALLINE NdBa2Cu3O7

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3164-3169
Author(s):  
A. P. REYES ◽  
M. ABDELRAZEK ◽  
P. L. KUHNS ◽  
W. G. MOULTON ◽  
W. P. HALPERIN ◽  
...  
Keyword(s):  
Superconducting State ◽  
Lattice Relaxation ◽  
Anomalous Behavior ◽  
Spin Fluctuations ◽  
Spin Lattice Relaxation ◽  
Physical Origin ◽  
Spin Lattice ◽  
Fast Relaxation ◽  
Spin Freezing ◽  
Nuclear Spin Lattice Relaxation

Nuclear spin-lattice relaxation rate 1/T1 at the planar O(2,3) and bridging O(4) oxygen sites in NdBa 2 Cu 3 O 7 have been measured as a function of temperature in fields up to 42T. Data is characterized by extremely fast relaxation due to Nd. A well-defined peak is observed, indicative of spin freezing, occurring well below T c , and higher than T N , and whose physical origin is unknown. Extracted T1 data for Cu(2) shows enhanced Cu-Cu correlations in the superconducting state, suggesting a short-ranged order at lower temperatures.

scholarly journals MAGNETIC-FIELD-INDUCED SUPERCONDUCTIVITY IN LAYERED ORGANIC MOLECULAR CRYSTALS WITH LOCALIZED MAGNETIC MOMENTS

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3071-3071
Author(s):  
O. CEPAS ◽  
R. H. MCKENZIE ◽  
J. MERINO
Keyword(s):  
Magnetic Field ◽  
Superconducting State ◽  
Magnetic Moments ◽  
Spin Fluctuations ◽  
Zero Field ◽  
Field Range ◽  
Organic Molecular Crystals ◽  
Magnetic Ions ◽  
The Magnetic Field

The synthetic organic compound λ (BETS) 2 FeCl 4 undergoes successive transitions from an antiferromagnetic insulator to a metal and then to a superconductor as a magnetic field is increased. We use a Hubbard-Kondo model to clarify the role of the Fe 3+ magnetic ions in these phase transition. In the high-field regime, the magnetic field acting on the electron spins is compensated by the exchange field He due to the magnetic ions. This suggests that the field-induced superconducting state is the same as the zero-field superconducting state which occurs under pressure or when the Fe 3+ ions are replaced by non-magnetic Ga 3+ ions. We show how Hc can be extracted from the observed splitting of the Shybnikov-de Haas frequencies. Furthermore, we use this method of extracting He to predict the field range for field-induced superconductivity in other materials. We also show that at high fields the spin fluctuations of the localized spins are not important.

Observation by HVEM of the martensite transformation and the superconducting transition in Nb3Sn

1988 ◽  
Vol 46 ◽  
pp. 788-789
Author(s):  
M. A. Kirk ◽  
M. C. Baker ◽  
B. J. Kestel ◽  
H. W. Weber
Keyword(s):  
Thin Films ◽  
Low Temperature ◽  
Superconducting State ◽  
Martensite Transformation ◽  
Sputter Deposition ◽  
Diffusion Reaction ◽  
Solute Diffusion ◽  
Superconducting Transition ◽  
Twin Boundaries ◽  
Martensite Structure

It is well known that a number of compound superconductors with the A15 structure undergo a martensite transformation when cooled to the superconducting state. Nb3Sn is one of those compounds that transforms, at least partially, from a cubic to tetragonal structure near 43 K. To our knowledge this transformation in Nb3Sn has not been studied by TEM. In fact, the only low temperature TEM study of an A15 material, V3Si, was performed by Goringe and Valdre over 20 years ago. They found the martensite structure in some foil areas at temperatures between 11 and 29 K, accompanied by faults that consisted of coherent twin boundaries on {110} planes. In pursuing our studies of irradiation defects in superconductors, we are the first to observe by TEM a similar martensite structure in Nb3Sn.Samples of Nb3Sn suitable for TEM studies have been produced by both a liquid solute diffusion reaction and by sputter deposition of thin films.

KONDO EFFECT AND LOCALIZED SPIN FLUCTUATIONS IN THE Zn-TRANSITION METAL SYSTEM

1971 ◽  
Vol 32 (C1) ◽  
pp. C1-221-C1-223
Author(s):  
P. J. FORD ◽  
C. RIZZUTO ◽  
E. SALAMONI ◽  
P. ZANI
Keyword(s):  
Transition Metal ◽  
Kondo Effect ◽  
Spin Fluctuations ◽  
Metal System ◽  
Transition Metal System

TRANSVERSE SPIN FLUCTUATIONS IN γ - Mn (37 % Fe) ALLOY

1988 ◽  
Vol 49 (C8) ◽  
pp. C8-183-C8-184 ◽  
Author(s):  
J. J. Milczarek ◽  
K. Mikke ◽  
E. Jaworska
Keyword(s):  
Spin Fluctuations ◽  
Transverse Spin

scholarly journals Specific heat of Zn-dopedYBa2Cu3O6.95:Possible evidence for Kondo screening in the superconducting state

2000 ◽  
Vol 61 (5) ◽  
pp. 3604-3609 ◽  
Author(s):  
D. L. Sisson ◽  
S. G. Doettinger ◽  
A. Kapitulnik ◽  
R. Liang ◽  
D. A. Bonn ◽  
...  
Keyword(s):  
Specific Heat ◽  
Superconducting State ◽  
Kondo Screening
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