Diffusion-Dominated Luminescence Dynamics of CsPbBr Studied Using Cathodoluminescence and Microphotoluminescence Spectroscopy.

Time-resolved or time-correlation measurements using cathodoluminescence (CL) reveal the electronic and optical properties of semiconductors, such as their carrier lifetimes, at the nanoscale. However, halide perovskites, which are promising optoelectronic materials, exhibit significantly different decay dynamics in their CL and photoluminescence (PL). We conducted time-correlation CL measurements of CsPbBr using Hanbury Brown-Twiss interferometry and compared them with time-resolved PL.

Attosecond-Resolved Coherent Control of Lattice Vibrations in Thermoelectric SnSe.

Manipulating lattice vibrations is the cornerstone to achieving ultralow thermal conductivity in thermoelectrics. Although spatial control by novel material designs has been recently reported, temporal manipulation, which can shape thermoelectric properties under nonequilibrium conditions, remains largely unexplored. Here, taking SnSe as a representative, we have demonstrated that in the ultrafast pump-pump-probe spectroscopy, electronic and lattice coherences inherited from optical excitations can be exploited independently to manipulate phonon oscillations in a highly selective manner.

Photoinduced Ultrafast Symmetry Switch in SnSe.

Layered tin selenide (SnSe) has recently emerged as a high-performance thermoelectric material with the current record for the figure of merit () observed in the high-temperature phase. So far, access to the phase has been mainly obtained via thermal equilibrium methods based on sample heating or application of external pressure, thus restricting the current understanding only to ground-state conditions. Here, we investigate the ultrafast carrier and phononic dynamics in SnSe.

Microstructural deformation process of shock-compressed polycrystalline aluminum.

Plastic deformation of polycrystalline materials under shock wave loading is a critical characteristic in material science and engineering. However, owing to the nanosecond time scale of the shock-induced deformation process, we currently have a poor mechanistic understanding of the structural changes from atomic scale to mesoscale. Here, we observed the dynamic grain refinement of polycrystalline aluminum foil under laser-driven shock wave loading using time-resolved X-ray diffraction.

Coherent control theory and experiment of optical phonons in diamond.

The coherent control of optical phonons has been experimentally demonstrated in various physical systems. While the transient dynamics for optical phonons can be explained by phenomenological models, the coherent control experiment cannot be explained due to the quantum interference. Here, we theoretically propose the generation and detection processes of the optical phonons and experimentally confirm our theoretical model using the diamond optical phonon by the doublepump-probe type experiment.

Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements.

The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored.

Ultrafast time-resolved electron diffraction revealing the nonthermal dynamics of near-UV photoexcitation-induced amorphization in Ge2Sb2Te5.

Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass material Ge2Sb2Te5 triggered by ultrashort optical pulses; however, a detailed understanding of the amorphization and damage mechanisms governed by nonthermal processes is still lacking.

Ultrafast zone-center coherent lattice dynamics in ferroelectric lithium tantalate.

Femtosecond time-resolved pump-probe experiments were carried out to study ultrafast lattice dynamics of ferroelectric lithium tantalate. Both the fully symmetric (A mode) and doubly degenerate (E mode) coherent phonons at the center of the Brillouin zone were excited via impulsive stimulated Raman scattering, as confirmed by the excitation intensity dependence.

Optical manipulation of coherent phonons in superconducting YBa2Cu3O7-delta thin films.

The coherent phonons of YBa2Cu3O7-delta are believed to be strongly coupled to its superconductivity. Controlling the phonons below its transition temperature, therefore, may serve as a promising scheme of the control of superconductivity. Here we demonstrate optical manipulation of the Ba-O and Cu-O vibrations in a thin-film YBa2Cu3O7-delta below its transition temperature using a pair of femtosecond laser pulses.

Pathway for the transformation from highly oriented pyrolytic graphite into amorphous diamond.

We report the discovery of a novel pathway for the transformation from highly oriented pyrolytic graphite foils into amorphous diamond platelets. This pathway consists of three stages of neutron irradiation, shock compression, and rapid quenching. We obtained transparent platelets which show photoluminescence but no diamond Raman peak, similar to the case of amorphous diamond synthesized from C60 fullerene.

Diagnostic system to measure spatial and temporal profiles of shock front using compact two-stage light-gas gun and line reflection method.

A diagnostic system has been developed to obtain spatial and temporal profiles of shock front. A two-stage light-gas gun is used to accelerate impactors in velocity range with 4-9 km/s. The system consists of the Faraday-type electromagnetic sensors to measure impactor velocity, optical system with high-speed streak camera to measure shock-wave velocities, and the delay trigger system with self-adjustable pre-event pulse generator.

Nanosecond rapid freezing of liquid benzene under shock compression studied by time-resolved coherent anti-Stokes Raman spectroscopy.

Nanosecond time-resolved coherent anti-Stokes Raman spectroscopy is used to investigate the shock-induced liquid-solid phase transition and crystallization of liquid benzene. Temporal evolution of the Raman shift of the ring-breathing and C-H stretching modes is investigated. A metastable supercompressed state and a liquid-solid phase transition are observed under shock compression.