engleski

Transient optical reflectivity in SDW iron-based pnictides: a supercontinuum-probe study

Employing a broadband ultrafast transient optical spectroscopy we investigate quasiparticle relaxation in normal and spin density wave (SDW) states of BaFe2As2, EuFe2As2 and SrFe2As2 iron-based-pnictide parent compounds in a 1.6-2.6 eV spectral region. With decreasing temperature all samples start to show a twofold inplane rotational symmetry already in the tetragonal phase, signifi cantly above the SDW/structural transition temperature, suggesting the presence of nematic fluctuations. In the SDW state the reflectivity transients across the full spectral range can be described by just two distinct relaxation components consistent with previous optical results at 1.55 eV probe energy. One of the components is absent at high temperature and shows a critical-like slowing down near the SDW transition temperature. Two diff erent possible assignments of this component related either to a single-particle relaxation bottleneck or the collective mode dynamics will be presented and discussed.

spin density wave; SDW; iron-based-pnictide; quasi-particle; broadband ultrafast transient optical spectroscopy

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