Critical speeding up of nonequilibrium electronic relaxation near nematic phase transition in unstrained Ba( Fe1−xCox ) 2

Abstract

The origin of the anisotropic, paramagnetic phase associated with electronic nematicity in the iron pnictides is yet to be resolved. Furthermore, the detwinning technique used to study the nematic order in single crystals is known to introduce extra anisotropy into the sample, which can smear out the transition and even modify intrinsic characteristics associated with "spontaneous" Ising, Z2, symmetry breaking. Here we use a strain and stress free, twinned sample to show that there is a significant reduction in the energy relaxation times of the hot electrons following non-equilibrium femtosecond laser excitation on both the high and low temperature sides of the nematic phase transition. This femtosecond, critical speeding-up behavior provides an alternative way to study complex, electronically-driven nematicity, invoking neither external strain nor measuring a small anisotropy in twinned crystals. Particularly, a detailed analysis of the observed ultrafast decay time and the amplitude associated with an initial electronic relaxation provides compelling implications on the physical origin of nematicity in iron pnictides: (1) nematic fluctuations strongly influence the dynamics of electron cooling; and (2) spin fluctuations determine the part of amplitude arising from the nematicity. Finally, we discuss ultrafast coherent phonon generation which may contribute to the measured transition temperature in our ultrafast measurements.

Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherence in the Metal Halide Perovskite CH3NH3PbI3<

“…This provides compelling implications for "Rashba engineering," i.e., periodic brightening of the dark excitons via modulation of Rashba parameters, for probing and controlling charge transfer and collection in photovoltaic devices. Our results also inspire merging quantum control [35], ultrafast phononics, and spintronics [36][37][38][39] to explore multifunction perovskite devices.…”

Light quantum control of persisting Higgs modes in iron-based superconductors

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“…As illustrated in Fig. 1a, a dominant Coulomb coupling between the h-and e-like Fermi sea pockets, unlike in other SCs, is manifested by, e.g., s± pairing symmetry 1,2 , spin-density wave resonant peaks, and nesting wave vectors (black arrows) [3][4][5][6] . Despite the extensive studies, experimental evidence for Higgs amplitude coherent excitations in FeSCs has not been reported yet, despite recent progress in non-equilibrium superconductivity and collective modes [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] .…”

Lightwave terahertz quantum manipulation of nonequilibrium superconductor phases and their collective modes

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