Abstract
At temperatures above the superconducting transition temperature, the pairfield susceptibility provides information on the nature of the pairfield fluctuations. Here, we study the d-wave pairfield susceptibility of a 2D Hubbard model for a doping which has a pseudogap (PG) and for a doping which does not. In both cases, there will be a region of Kosterlitz–Thouless fluctuations as the transition at TKT is approached. Above this region, we find evidence for pairfield-order parameter-phase fluctuations for dopings with a PG and BCS Cooper pair fluctuations for dopings without a PG.
Highlights
Tunneling experiments have been used to study pairfield fluctuations in both the underdoped and overdoped cuprates.[1,2]In these experiments, the tunneling current I versus voltage V between an optimally doped YBCO ðTcHigh $ 90 KÞ electrode and an underdoped or overdoped ðTcLow $ 50 KÞ electrode was measured
Similar phenomena are well known in the traditional low Tc superconductors[3] where the fluctuating pairfield is well described by Cooper pair fluctuations,[4] with parameters set by the lattice phonon spectrum and the Fermi liquid, out of which the superconducting state emerges
The measurements are limited to temperatures below the Tc of the higher transition temperature film and require the careful separation of the excess pair current from the quasi-particle background. Motivated by these experiments, we will carry out a numerical study of the dwave pairfield fluctuations for a 2D Hubbard model
Summary
Tunneling experiments have been used to study pairfield fluctuations in both the underdoped and overdoped cuprates.[1,2]. In these experiments, the tunneling current I versus voltage V between an optimally doped YBCO ðTcHigh $ 90 KÞ electrode and an underdoped or overdoped ðTcLow $ 50 KÞ electrode was measured. Various authors[5–7] have discussed the possibility of using pair tunneling as a probe to study the differences in the pairfield fluctuations between the PG and non-PG regions. After introducing the pairfield susceptibility and describing the type of experiment which motivated this study, we use the dynamic cluster approximation (DCA) with a continuous-time auxiliary-field quantum Monte-Carlo (QMC) solver to study the pairfield fluctuations for a 2D Hubbard model, with an on-site Coulomb interaction U/t = 7 and a next-nearest-neighbor hopping t′/t = −0.15 in units of the nearest-neighbor hopping amplitude t. In the ladder approximation[4,12] χ d ðω; T
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