Photoexcitation

About: Photoexcitation is a research topic. Over the lifetime, 5874 publications have been published within this topic receiving 134733 citations.

Photoinduced Melting of Antiferromagnetic Order in La0.5Sr1.5MnO4 Measured Using Ultrafast Resonant Soft X-Ray Diffraction

Abstract: We used ultrafast resonant soft x-ray diffraction to probe the picosecond dynamics of spin and orbital order in La0:5Sr1:5MnO4 after photoexcitation with a femtosecond pulse of 1.5 eV radiation. Complete melting of antiferromagnetic spin order is evidenced by the disappearance of a ð 1 ; 1 ; 1 Þ diffraction peak. On the other hand, the ð 1 ; 1 ; 0Þ diffraction peak, reflecting orbital order, is only partially reduced. We interpret the results as evidence of destabilization in the short-range exchange pattern with no significant relaxation of the long-range Jahn-Teller distortions. Cluster calculations are used to analyze different possible magnetically ordered states in the long-lived metastable phase. Nonthermal coupling between light and magnetism emerges as a primary aspect of photoinduced phase transitions in manganites.

Enhanced coherent terahertz emission from indium arsenide in the presence of a magnetic field

Abstract: We demonstrate enhancement of terahertz (THz) emission from indium arsenide at 170 K in magnetic fields (B) up to 8 T. An order of magnitude increase in visible to terahertz conversion efficiency was observed, with no suggestion of saturation of the TE polarization at higher magnetic fields. Free-space electro-optic sampling measurements confirmed the coherent nature of this radiation over the field range investigated, and gave an insight into the carrier motion subsequent to photoexcitation, which may be responsible for the observed THz power enhancement.

Selective Probing of Photoinduced Charge and Spin Dynamics in the Bulk and Surface of a Topological Insulator

Abstract: Topological insulators possess completely different spin-orbit coupled bulk and surface electronic spectra that are each predicted to exhibit exotic responses to light. Here we report time-resolved fundamental and second harmonic optical pump-probe measurements on the topological insulator Bi_2Se_3 to independently measure its photoinduced charge and spin dynamics with bulk and surface selectivity. Our results show that a transient net spin density can be optically induced in both the bulk and surface, which may drive spin transport in topological insulators. By utilizing a novel rotational anisotropy analysis we are able to separately resolve the spin depolarization, intraband cooling, and interband recombination processes following photoexcitation, which reveal that spin and charge degrees of freedom relax on very different time scales owing to strong spin-orbit coupling.

Localized Excited Charge Carriers Generate Ultrafast Inhomogeneous Strain in the Multiferroic BiFeO3

Abstract: We apply ultrafast x-ray diffraction with femtosecond temporal resolution to monitor the lattice dynamics in a thin film of multiferroic BiFeO3 after above-band-gap photoexcitation. The sound-velocity limited evolution of the observed lattice strains indicates a quasi-instantaneous photoinduced stress which decays on a nanosecond time scale. This stress exhibits an inhomogeneous spatial profile evidenced by the broadening of the Bragg peak. These new data require substantial modification of existing models of photogenerated stresses in BiFeO3: the relevant excited charge carriers must remain localized to be consistent with the data.

Shallow and deep traps in conjugated polymers of high intrachain order.

Abstract: We present measurements of thermally stimulated currents and photoinduced absorption (PIA) in a planarized form of poly(para-phenylene). Due to the high intrachain order of the samples and their narrow distribution of effective conjugation lengths the density of states shows a very steep onset at the band gap energy. This is the prerequisite for detecting distinct trap levels and to determine their concentration and depth. We show that charges trapped at depths of 0.1 and 0.4 eV govern the observed charge transport and change in the absorption upon photoexcitation and in particular that the temperature dependence of the PIA intensity in the millisecond range reflects thermal effects on transport processes. \textcopyright{} 1996 The American Physical Society.