Spin fluctuations, Fermi surface hotspots and nesting in PuCoGa5

2014 ◽  
Vol 1683 ◽  
Author(s):  
Matthias J. Graf ◽  
Tanmoy Das ◽  
Jian-Xin Zhu
Keyword(s):  
Spin Fluctuation ◽  
Pairing Symmetry ◽  
Spin Fluctuations ◽  
Gap Functions ◽  
Fermi Surfaces ◽  
Unconventional Superconductors ◽  
Magnetic Spin ◽  
The Many ◽  
Superconducting Pairing ◽  
Strong Spin

ABSTRACTSurprisingly little is known about the mechanism and symmetry of superconducting pairing in PuCoGa5. A common thread with other unconventional superconductors is the presence of spin fluctuations in the normal state, which in this particular case is controlled by strong spin–orbit coupling split bands. The many and anisotropic Fermi surfaces make the guessing of the potential spin-fluctuation nesting vector and resulting symmetry of the pairing function a nontrivial task. To provide much needed guidance for the identification of the pairing symmetry in this multiband superconductor, we perform first-principles based magnetic spin susceptibility calculations to identify the dominant nesting vectors that potentially give rise to interband pairing with nodal d- or s±-wave gap functions.

Spin Fluctuation, Orbital States and Non-conventional Superconductivity in Actinides Compounds

2012 ◽  
Vol 1444 ◽  
Author(s):  
S. Kambe ◽  
H. Sakai ◽  
Y. Tokunaga
Keyword(s):  
Spin Fluctuation ◽  
Pairing Symmetry ◽  
Unconventional Superconductivity ◽  
Superconducting Transition ◽  
Magnetic Fluctuations ◽  
Fermi Surfaces ◽  
Unconventional Superconductors ◽  
Wave Pairing ◽  
Superconducting Pairing ◽  
Orbital Character

ABSTRACTIn d-wave unconventional superconductors, superconducting Cooper pairs are believed to be formed via magnetic fluctuations. In fact, the superconducting transition temperature Tc roughly correlates with the antiferromagnetic spin fluctuation energy in d-wave unconventional superconductors including high Tc cuprates. In addition to this correlation, the superconducting pairing symmetry and the magnetic anisotropy of the normal state are found empirically to be strongly correlated in f-electron unconventional superconductors having crystallographic symmetry lower than cubic. In antiferromagnetic systems, unconventional superconductivity appears with singlet (d-wave) pairing for cases of XY anisotropy. In contrast, in ferromagnetic systems, unconventional superconductivity with triplet (e.g. p-wave) pairing appears for cases of Ising anisotropy. In this report, the d-wave case is addressed, the origin of XY anisotropy is discussed in terms of the orbital character; and the angular momentum character jz for each piece of Fermi surfaces is determined.

IMPACT OF THE ORDER PARAMETER SYMMETRIES ON THE VORTEX CORE STRUCTURE IN IRON-BASED SUPERCONDUCTORS

2012 ◽  
Vol 26 (21) ◽  
pp. 1230013
Author(s):  
POLINA BELOVA ◽  
IVAN ZAKHARCHUK ◽  
KONSTANTIN BORISOVICH TRAITO ◽  
ERKKI LÄHDERANTA
Keyword(s):  
Fermi Surface ◽  
Mixed State ◽  
Order Parameter ◽  
Spin Fluctuation ◽  
Pairing Symmetry ◽  
Gap Function ◽  
Spin Fluctuations ◽  
Field Range ◽  
Cutoff Parameter ◽  
Antiferromagnetic Spin

Effects of the order parameter symmetries on the cutoff parameter ξh (determining the magnetic field distribution) in the mixed state are investigated in the framework of quasiclassical Eilenberger theory for isotropic s±, s++ and anisotropic dx2-y2-wave superconducting pairings. These symmetries are proposed for the pairing state of the Fe -pnictides. In s± pairing symmetry, the gap function has opposite sign at the electron and hole pockets of the Fermi surface, it is connected with interband antiferromagnetic spin fluctuations. In s++ pairing symmetry, the gap function has the same sign at the Fermi surface, it is mediated by moderate electron–phonon interaction due to Fe -ion oscillation and the critical orbital fluctuation. The dx2-y2 pairing symmetry can rise from intraband antiferromagnetic spin fluctuation in strongly hole overdoped iron pnictide KFe 2 As 2 and ternary chalcogenides. The s± pairing symmetry results in different effects of intraband (Γ0) and interband (Γπ) impurity scattering on ξh. It is found that ξh/ξc2 value decreases with Γ0 leading to the values much less than those predicted by the analytical Ginzburg–Landau (AGL) theory for high Γ0. At very high Γ0, the interband scattering suppresses ξh/ξc2 considerably below one in the whole field range making it flat for both s± and s++ pairing symmetries. Scaling of the cutoff parameter with the electromagnetic coherence length shows the importance of the nonlocal effects in mixed state. The small values of ξh/ξc2 were observed in μSR measurements of Co -doped BaFe 2 As 2. If Γ0 and Γπ are small and equal than the ξh/ξc2(B/Bc2) dependence for s± symmetry behaves like that of the AGL model and shows a minimum with value much more than that obtained for s++ superconductors. With high Γπ, the ξh/ξc2(B/Bc2) dependence resides above the AGL curve for s± pairing symmetry, as observed in SANS measurements of stoichiometrical LiFeAs compound. In d-wave superconductors, ξh/ξc2 always increases with Γ similar to the s± symmetry case with Γ0 = Γπ.

scholarly journals The Superconducting Critical Temperature

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 911
Author(s):  
Mike Guidry ◽  
Yang Sun ◽  
Lian-Ao Wu
Keyword(s):  
Critical Temperature ◽  
Dynamical Symmetry ◽  
Many Body ◽  
Unconventional Superconductors ◽  
The Many ◽  
Pair Coupling ◽  
Intrinsic Strength ◽  
Superconducting Transitions

Two principles govern the critical temperature for superconducting transitions: (1) intrinsic strength of the pair coupling and (2) the effect of the many-body environments on the efficiency of that coupling. Most discussions take into account only the former, but we argue that the properties of unconventional superconductors are governed more often by the latter, through dynamical symmetry relating to normal and superconducting states. Differentiating these effects is essential to charting a path to the highest-temperature superconductors.

Extended Dynamic Spin-Fluctuation Theory with Application to Iron

2012 ◽  
Vol 190 ◽  
pp. 55-58 ◽  
Author(s):  
B.I. Reser ◽  
N.B. Melnikov ◽  
Vladimir I. Grebennikov
Keyword(s):  
Phase Transition ◽  
Magnetic Properties ◽  
Green Function ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Dynamic Spin ◽  
Discontinuous Phase ◽  
The Mean ◽  
Extended Dynamic

The problem of discontinuous phase transition in the dynamic spin-fluctuation theory is resolved by taking into account large anharmonic spin fluctuations and nonlocality of the mean Green function. The extended theory is applied to the calculation of magnetic properties of iron.

Break junction measurements on Bi2Sr2Ca1Cu2O8+x single crystals: analysis of the superconducting pairing symmetry

1997 ◽  
Vol 280 (1-2) ◽  
pp. 71-76 ◽  
Author(s):  
H. Hancotte ◽  
D.N. Danydov ◽  
R. Deltour ◽  
A.G.M. Jansen ◽  
P. Wyder
Keyword(s):  
Single Crystals ◽  
Pairing Symmetry ◽  
Break Junction ◽  
Superconducting Pairing

Spin Fluctuation Effect on Electrical Resistivity of La0.8Ca0.2MnO3 Manganite Nanoparticles

2015 ◽  
Vol 14 (04) ◽  
pp. 1550010 ◽  
Author(s):  
K. K. Choudhary
Keyword(s):  
Experimental Data ◽  
Electrical Resistivity ◽  
Temperature Regime ◽  
Spin Fluctuation ◽  
Metallic Phase ◽  
Spin Fluctuations ◽  
Electron Interaction ◽  
Manganite Nanoparticles ◽  
Wide Range ◽  
Insulating Phase

The electrical resistivity ρ(T) of La 0.8 C 0.2 MnO 3 manganite nanoparticles (particle size 18 nm and 70 nm) significantly depends on temperature and size of nanoparticles. ρ(T) of 70 nm La 0.8 C 0.2 MnO 3 manganite exhibits metallic phase in low temperature regime (T < 250 K ), develops a maxima near 250 K and decrease with T at high temperatures (250 K < T < 300 K ). However, the ρ(T) of 18 nm La 0.8 C 0.2 MnO 3 manganite shows insulating phase in overall temperature regime, where resistivity decrease with temperature. The resistivity in metallic phase is theoretically analyzed by considering the strong spin fluctuations effect which is modelled using Drude–Lorentz type function. In addition to the spin fluctuation-induced contribution the electron-phonon and electron-electron ρe-e(T) = BT2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons (ρac) as well as high frequency optical phonons (ρop) were estimated using Bloch–Gruneisen [BG] model of resistivity. It is observed that the resistivity contribution due to electron-electron interaction shows typical quadratic temperature dependence. Resistivity in Semiconducting/insulating phase is discussed with small polaron conduction (SPC) model. Finally the theoretically calculated resistivity compared with experimental data which found consistent in wide range of temperature.

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