Ultrafast electron dynamics in strontium iridate (Conference Presentation)

Since the discovery of high-Tc superconductors, understanding Mott insulating phases and their insulator to metal transitions has become increasingly important [1]. As opposed to the Mott-insulating ground state found in 3d-electron compounds, a metallic ground state is expected to be found in strontium iridates, due to the extended 5d electronic orbitals of the Ir ions. However Sr2IrO4, shows a non metallic behavior[2]. Its insulating ground state arises mainly from the cooperative action of the onsite Coulomb interaction and strong spin-orbit coupling, leading to a novel Jeff=1/2 Mott-insulating ground state [3].While the insulating ground state of Sr2IrO4 below TN = 240K is stabilized by a Mott-Slatter mecanism, the origin of the high temperature insulating ground state remains under controversy. The presence of magnetic fluctuations may also give rise to a possibly Mott-Slatter hybrid scenario in which pseudo-spins long range correlations may cooperate with spin-orbit and onsite Coulomb interaction[5-6]. A possible way to disentangle magnetic fluctuations effects from Mott physics signatures is realized by photo-exciting strontium iridate single crystals with femtosecond light pulses. Following this approach, earlier pump-probe studies [7,8] have pointed out strong similarities between iridates and cuprates electron dynamics such as a two-time scale dynamics along with the formation of in-gap states. In order to uncover short time (< 100fs) electron dynamics we present a combined super-continuum based time resolved reflectivity along with a HHG based time resolved photoemission study of Sr2IrO4 at room temperature. Our data reveal for the first time, crucial information about the time and energy resolved dynamics of the short lived in-gap states forming in the first 50fs after the photo-excitation. The origin of these in-gap states seems to be consistent with the framework of photo-doping of Mott insulators[9] in which a photo-induced Mott gap renormalization occur. [1] M. Imada, A. Fujimori et al., Rev. Mod. Phys., 70, 1039 (1998) [2] D. A. Zocco, J. J. Hamlin et al., J. Phys.: Condens. Matter, 26, 255603 (2014) [3] B. J. Kim, Hosub Jin et al., Phys. Rev. Lett., 101, 076402 (2008) [4] F. Ye, S. Chiet et al., Phys. Rev. B, 87, 140406R (2013) [5] D. Hsieh, F. Mahmood et al., Phys. Rev. B, 86, 035128 (2012) [6] R. Arita, J. Kuneš et al., JPS Conf. Proc., 3, 013023 (2014) [7] D. Hsieh, F. Mahmood et al., Phys. Rev. B, 86, 035128 (2012) [8] C. Piovera, V. Brouet, Phys. Rev. B, 93, 241114(R) (2016) [9] P. Werner and M. Eckstein, Struc. Dyn., 3, 023603 (2016)