Masayoshi Tonouchi

The crystallographic anisotropy in electromagnetic terahertz radiation from multiferroic BiFeO3 (100), (110), and (111) films suggests the ultrafast depolarization of ferroelectric order as a new mechanism of terahertz emission. This implies that the spontaneous polarization in ferroelectric materials can be manipulated in time scale of picoseconds, thus paving the way to ultrafast data-storage devices based on nonvolatile ferroelectric memories.

We have observed ultrashort electromagnetic pulse radiation from YBa 2 Cu 3 O 7-δ thin-film dipole antennas. The supercurrent transient is created by the excitation of the supercarriers into quasiparticles with a femtosecond laser pulse, and freely propagated electromagnetic pulses are measured and characterized. A pulse with 0.5 ps full width at half-maximum was obtained, containing frequency components up to 2.0 THz. A femtosecond time-resolved characterization of the spectra revealed that the

We have developed a supercurrent distribution imaging system for high Tc superconductive thin films and demonstrated the visualization of the supercurrent distribution in the vortex-penetrated YBa2Cu3O7−δ thin film strips. The terahertz (THz) radiation and detection system with a scanning femtosecond laser was employed to visualize the distribution. The imaging system utilizes the principle that the femtosecond optical pulses excite THz radiation into the free space by optical supercurrent modul

NbN epitaxial growth on an ultrathin MgO/semiconductor system was carried out by reactive sputtering. It was revealed that (100)-oriented NbN epitaxy was achieved on a (100)-oriented Si substrate by introducing a MgO buffer layer as thin as 5 Å at the interface. An interrupt-sputtering technique was newly conducted to obtain the epitaxial films, which were intermittently deposited by rf sputtering. A metal-insulator-semiconductor tunneling Schottky diode with epitaxial NbN was prepared using thi

Abstract During the past two decades, terahertz (THz) science and technology have rapidly expanded in all fundamental and applied aspects of physical, chemical, and biological sciences. In physical sciences, these developments have been twofolds: i) the use of THz technology in understanding the complexities of materials and ii) the exploration of new THz functionalities of emerging materials for further advancement of THz technology. Here, the THz emission spectroscopy and the ultrafast functio

We discovered a new type of terahertz (THz) radiation from YBa 2 Cu 3 O 7-δ thin films. Ultrashort electromagnetic pulses, which are referred to as THz radiation, were emitted into free space by irradiating the superconductive films with femtosecond laser pulses. The THz radiation, with a spectrum extending from 0.1 to 3 THz, was excited in both the films applied with a magnetic field and the flux-trapped films. The results suggest that the screening current for the external magnetic field and c

We observed the temperature dependence of a femtosecond time-transient photoresponse in YBa 2 Cu 3 O 7-δ thin films by detecting terahertz (THz) emission. Ultrashort electromagnetic pulses which are referred to as THz emission were generated by ultrafast supercurrent modulation with femtosecond laser pulse irradiation. The transient response is discussed in relation to the quasiparticle dynamics of the nonequilibrium superconductor.