SOLID STATE & STRUCTURAL CHEMISTRY UNIT
INDIAN INSTITUTE OF SCIENCE
BANGALORE – 560 012
Professor Kalobaran Maiti
Tata Institute of Fundamental Research
Mumbai – 400 005
Orbital-dependent electron dynamics in Fe-pnictide superconductors
Date & Time : Tuesday 24th July, 2018 at 11:00 AM
Venue : SSCU Auditorium
It is realized that electron correlation plays the key role in deriving varied exotic properties of materials and in particular, in unconventional superconductivity. This is evidenced by the finding of Mott insulating phase in the parent compounds of cuprate superconductors. Exoticity in Fe-based systems is also believed to be driven by electron correlation and Hund’s coupling. One of the complicating factors in Fe-based compounds is that multiple bands (or orbitals) form the Fermi surface, which makes these systems more complex than cuprates, where the contribution to the Fermi surface comes only from the dx2-y2 orbital. De Medici et al. [Phys. Rev. Lett. 112, 177001 (2014)] proposed orbital selective Mottness as an explanation of unconventional properties of Fe-based superconductors, where each orbital shows single-band Mott behavior and the degree of electron correlation depends on the doping of the bands from half filling.
Here, we propose an orbital-selective experimental method allowing to study the relaxation dynamics of photo-excited electrons near the Fermi level, and use it as a powerful tool to gain a deep insight into electron localization in Fe-pnictides. We studied the quasiparticle dynamics in EuFe2As2, a parent compound of Fe-based superconductors employing time- and angle- resolved photoemission spectroscopy (trARPES). We exploited the polarization of the pump pulse to selectively excite electrons of different orbital character and studied the relaxation dynamics of the hot electrons and hot holes across the spin density wave transition. We observe two different relaxation time scales for photo-excited dxz/dyz and dxy electrons. While the itinerant dxz/dyz electrons relax faster through the electron-electron scattering channel, dxy electrons form a quasi-equilibrium state with the lattice due to their relatively stronger local character, and the state decays slowly. Our findings suggest that electron correlation in Fe-pnictides is an important property, which should be taken into careful account when describing the electronic properties of both parent and carrier-doped compounds.
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