Nonlinear Optical Properties in an Epitaxial YbFeO Film Probed by Second Harmonic and Terahertz Generation.

An epitaxial film of YbFeO, a candidate for oxide electronic ferroelectrics, was fabricated on yttrium-stabilized zirconia (YSZ) substrate by magnetron sputtering technique. For the film, second harmonic generation (SHG), and a terahertz radiation signal were observed at room temperature, confirming a polar structure of the film. The azimuth angle dependence of SHG shows four leaves-like profiles and is almost identical to that in a bulk single crystal.

Generation of sub-100 fs electron pulses for time-resolved electron diffraction using a direct synchronization method.

To investigate photoinduced phenomena in various materials and molecules, ultrashort pulsed x-ray and electron sources with high brightness and high repetition rates are required. The x-ray and electron's typical and de Broglie wavelengths are shorter than lattice constants of materials and molecules. Therefore, photoinduced structural dynamics on the femtosecond to picosecond timescales can be directly observed in a diffraction manner by using these pulses.

Separation between low-energy hole dynamics and spin dynamics in a frustrated magnet.

An angle-resolved photoemission spectroscopy (ARPES) study is reported on a Mott insulator NiGa2S4 in which Ni2+ (S=1) ions form a triangular lattice and the Ni spins do not order even in its ground state. The first ARPES study on the two-dimensional spin-disordered system shows that low-energy hole dynamics at high temperatures is characterized by wave vectors Q(E) which are different from wave vectors Q(M) dominating low-energy spin excitations at low temperatures. The unexpected difference between Q(E) and Q(M) is deeply related to charge fluctuation across the Mott gap in the frustrated lattice and is a key issue to understand the spin-disordered ground states in Mott insulators.