Fermi surface dichotomy of the superconducting gap and pseudogap in underdoped pnictides

Abstract

High-temperature superconductivity in iron-arsenic materials (pnictides) near an antiferromagnetic phase raises the possibility of spin-fluctuation-mediated pairing. However, the interplay between antiferromagnetic fluctuations and superconductivity remains unclear in the underdoped regime, which is closer to the antiferromagnetic phase. Here we report that the superconducting gap of underdoped pnictides scales linearly with the transition temperature, and that a distinct pseudogap coexisting with the superconducting gap develops on underdoping. This pseudogap occurs on Fermi surface sheets connected by the antiferromagnetic wavevector, where the superconducting pairing is stronger as well, suggesting that antiferromagnetic fluctuations drive both the pseudogap and superconductivity. Interestingly, we found that the pseudogap and the spectral lineshape vary with the Fermi surface quasi-nesting conditions in a fashion that shares similarities with the nodal-antinodal dichotomous behaviour observed in underdoped copper oxide superconductors.

Unconventional superconductivity

“…Kwon et al [508] measured the optical reflectivity of Ba0.6K0.4Fe2As2, Tc=36 K (where TSDW has been suppressed below the superconducting dome), and make a strong case for pseudogap behavior starting below 100 K. These data and their interpretation are not inconsistent with the ARPES data of Xu et al [494] discussed above for Ba0.75K0.25Fe2As2, Tc=26 K and T*=120 K, considering (as discussed for the cuprates) that T* should fall with increasing doping. Kwon et al also discuss the preformed pairing model (proposed by Emery and Kivelson [509]) (see Rice, Yang, and Zhang [39] for a discussion) of the pseudogap to explain their data.…”

“…On underdoped Ba0.75K0.25Fe2As2, Tc=26 K, Xu et al [494] report ARPES data on the ,  and , Fermi surface sheets and show convincing data of a pseudogap that extends up to about 120 K. This is clearly above the SDW transition at this composition which, according to Johrendt and Pöttgen [495] is somewhere below 90 K. Xu et al discuss extensively the possible insights to be gained from their data, and conclude that both the superconducting gap and the pseudogap could have their origins from antiferromagnetic correlations (the s model). They further note the similarity between their underdoped data in Ba1-xKxFe2As2 and data in underdoped cuprates, and argue for a possible "unifying picture" of high temperature superconductivity based on antiferromagnetic fluctuations.…”

Structural and magnetic properties and superconductivity in Ba(Fe_1-xTM_x)₂As₂

“…Unfortunately, the K substitution was found to be nonuniform when a Sn flux is used, which makes the transition quite wide. Luo et al (2008) were able to synthesize single crystals of (Ba 1−x K x )Fe 2 As 2 using a self flux by prereacting the Ba and K to circumvent the volatility of the K. These samples are homogeneous -as determined by the narrow resistive superconducting transition -with T c ∼ 36 K. The crystal quality is excellent, and detailed photoemission studies have been done Xu et al (2011)). Unfortunately, the crystals are also small ( 1 mm 2 ), which limits their usefulness for many measurements, such as xray and neutron diffraction.…”

Nonlocal correlations induced by Hund's coupling: A cluster DMFT study

“…[34][35][36][37][38] It is an interesting future issue to study these materials by combining the present scheme with realistic band-structure calculations. Phys …”