Doping Dependence of Pseudogap in LaFeAsO_1-xF_x

Abstract

We have performed systematic ultrahigh-resolution photoemission spectroscopy on the ironbased superconductor LaFeAsO1−xFx (x = 0-14%) to elucidate the evolution of electronic states with doping. We found that the density of states (DOS) around the Fermi level of the superconducting sample is markedly smaller than that of the undoped sample in contrast to conventional phonon-mediated superconductors. We observed a pseudogap in the DOS above the superconducting transition temperature (Tc) which opens/closes at a temperature (T *) well above Tc. The energy scale of pseudogap and the T * value are gradually reduced upon fluorine substitution. The origin of pseudogap is discussed in terms of the partial nesting of Fermi surfaces due to the spin-density-wave formation or the short-range spin correlations.

Pseudogap formation above the superconducting dome in iron pnictides

“…Synchrotron-based ARPES thus show that SC gap in AsP122 is smaller than PG, consistent with laser-ARPES. PG with an energy scale higher than SC gap has been also reported for a variety of iron-based superconductors by several experimental probes [32,33,35,36,39,40].…”

Fermion dynamical symmetry and strongly-correlated electrons: A comprehensive model of high-temperature superconductivity

“…Whether a pseudogap exists for the iron-based compounds is not settled (positive evidence for one is given in Refs. [28][29][30][31][32]). The pseudogap state is not a "normal" normal state, and it is not well described by traditional Fermi liquid concepts.…”

“…The total energy of the SU(4) state may be found in coherent state approximation by evaluating the expectation value of the Hamiltonian (14). There are only two independent variational parameters in the coherent state variational equations because of the unitarity condition (31). They may be chosen as either v + and v − , or as α and β , using the definitions…”

Unusual Pseudogap Features Observed in Iron Oxypnictide Superconductors

“…Temperature-dependent angle-integrated PES studies by other groups have also shown evidence for pseudogaps in the iron-oxypnictide compounds. [13][14][15][16][17] Most of the re- * E-mail: ishida@spring8.or.jp ports showed a pseudogap having an energy scale of ∼20 meV, [13][14][15][16][17] indicating that this feature occurs commonly in the layered iron oxypnictides and is insensitive to T c or to doping. Through a wide-temperature-range study, Ou et al also showed T -dependent pseudogap features in SmFeAsO:F 15) similar to that in As26, 12) although there are rooms for speculation concerning its origin.…”

“…2(a) is a common feature observed in the iron oxypnictides. [13][14][15][16] We were able to detect this feature with He PES in spite of the large spot size of ∼5 mm in diameter compared to the small sample area exposed by soft scraping [right panel of Fig. 1(b)].…”