scholarly journals Order parameter fluctuation and ordering competition in Ba1−xKxFe2As2

2017 ◽  
Vol 95 (2) ◽  
Author(s):  
Jing Wang ◽  
Guo-Zhu Liu ◽  
Dmitry V. Efremov ◽  
Jeroen van den Brink
Keyword(s):  
Order Parameter ◽  
Parameter Fluctuation

scholarly journals Instabilities of quantum critical metals in the limit $N_f\rightarrow0$

2021 ◽  
Vol 10 (3) ◽  
Author(s):  
Petter Säterskog
Keyword(s):  
Fermi Surface ◽  
Long Range ◽  
Charge Density Wave ◽  
Order Parameter ◽  
Finite Interval ◽  
Density Wave ◽  
Parameter Fluctuation ◽  
Critical Metals ◽  
Quantum Critical Points ◽  
Quantum Critical

We study a model in 2+1 dimensions composed of a Fermi surface of N_fNf flavors of fermions coupled to scalar fluctuations near quantum critical points (QCPs). The N_f\rightarrow0Nf→0 limit allows us to non-perturbatively calculate the long-range behavior of fermion correlation functions. We use this to calculate charge, spin and pair susceptibilities near different QCPs at zero and finite temperatures, with zero and finite order parameter gaps. While fluctuations smear out the fermionic quasiparticles, we find QCPs where the overall effect of fluctuations leads to enhanced pairing. We also find QCPs where the fluctuations induce spin and charge density wave instabilities for a finite interval of order parameter fluctuation gaps at T=0T=0. We restore a subset of the diagrams suppressed in the N_f\rightarrow0Nf→0 limit, all diagrams with internal fermion loops with at most 2 vertices, and find that this does not change the long-range behavior of correlators except right at the QCPs.

High Frequency Resistivity in YBa2Cu3O7-δ: Effects of Anisotropic Renormalized Fluctuations

1999 ◽  
Vol 13 (09n10) ◽  
pp. 1097-1100 ◽  
Author(s):  
D. Neri ◽  
R. Marcon ◽  
E. Silva ◽  
R. Fastampa ◽  
L. Iacobucci ◽  
...  
Keyword(s):  
High Frequency ◽  
Order Parameter ◽  
Parameter Fluctuation ◽  
Superconducting Transition ◽  
High Temperature Region ◽  
Linear Temperature ◽  
Microwave Frequencies ◽  
Fundamental Parameters ◽  
Microwave Resistivity ◽  
24 Ghz

We discuss the excess conductivity above Tc due to renormalized order-parameter fluctuation in YBCO at microwave frequencies. We show that a phenomenological cut-off in the fluctuative spectrum can extend the results of the anisotropic theory of renormalized fluctuations up to the high temperature region. Measurements of the real part of the microwave resistivity at 24 GHz are performed on two YBCO films. The onset of the superconducting transition and the deviation from the linear temperature behavior can be fully accounted for by the extended theory. Very consistent values of the fundamental parameters (critical temperature, coherence lenghts, penetration depth) of the superconducting state are obtained.

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