Quasiparticle relaxation dynamics in spin-density-wave and superconductingSmFeAsO1−xFxsingle crystals

Abstract

We investigate the quasiparticle (QP) relaxation and low-energy electronic structure in undoped SmFeAsO and near-optimally doped SmFeAsO0.8F0.2 single crystals-exhibiting spin-density wave (SDW) ordering and superconductivity, respectively-using pump-probe femtosecond spectroscopy. In the undoped single crystals a single relaxation process is observed, showing a remarkable critical slowing down of the QP relaxation dynamics at the SDW transition temperature TSDW125 K. In the superconducting (SC) crystals multiple relaxation processes are present with distinct SC-state quasiparticle recombination dynamics exhibiting a BCS-like T-dependent superconducting gap, and a pseudogap (PG)-like feature with an onset above 180 K indicating the existence of a pseudogap of magnitude 2ΔPG120 meV above Tc. From the pump-photon energy dependence we conclude that the SC state and PG relaxation channels are independent, implying the presence of two separate electronic subsystems. We discuss the data in terms of spatial inhomogeneity and multiband scenarios, finding that the latter is more consistent with the present data.

Fluence-dependent femtosecond quasiparticle and Eu2+ spin relaxation dynamics in EuFe2(As,P)Pogrebna1, Mertelj2, Cao3 et al. 2016Phys. Rev. BSelf Cite1100View full textAdd to dashboardCite

“…3 we show R/R transients at a few characteristic temperatures for both samples. Starting at T = 300 K we observe subpicosecond isotropic transients in both samples consistent with previous results in related iron-based pnictides [16][17][18]. With decreasing T the twofold anisotropy appears below ∼250 K in Eu-122 and ∼190 K in EuP-122.…”

Theory of photoexcited carrier relaxation across the energy gap of phase-ordered materials

“…Usually the anomalous T dependence of τ exp is observed in many gapped systems, for example, phaseordered systems showing an energy gap opening in the electron band below the transition temperature T c . It has been found that a wide variety of superconductors [1][2][3][4][5][6][7][8][9][10][11][12][13] and density-wave compounds [14][15][16][17][18][19] show diverging behavior of τ exp near T c , as confirmed by femtosecond time-resolved optical spectroscopy. 1,4,5,[7][8][9][10][11][12][13][14][15][16][17]19 The divergence of τ exp in these gapped systems is believed to result from a recursive energy transfer between electrons and phonons.…”

Electronic behavior of superconducting SmFeAsO0.75

“…Furthermore, the change of the band structure may be attributed to a change on the Fermi surface supported by the pseudogap which causes the partial gapping of the Fermi surface. The pseudogap has actually been found from NMR [34] and photoemission experiments [35]; recently the quasiparticle relaxation dynamics on single crystal SmFeAsO 1-x F x [36] reveals the pseudogap with an onset above 180 K.…”