Faculty Profiles - KIWA Toshihiko

Partial and macroscopic phase coherences in an underdoped Bi<inf>2</inf>Sr<inf>2</inf>CaCu<inf>2</inf>O<inf>8+δ</inf> thin film

H. Murakami, T. Kiwa, N. Kida, M. Tonouchi, T. Uchiyama, I. Iguchi, Z. Wang

Europhysics Letters 60 ( 2 ) 288 - 294 2002.10

Language：English Publisher：E D P SCIENCES

A combined study using the time-resolved pump-probe technique and the time domain terahertz transmission spectroscopy has been carried out to investigate the normal-state anomalies in underdoped Bi2Sr2CaCu2O8+δ. It was observed that a superconducting gap and a pseudogap coexist in the superconducting state. The pseudogap locally evolves below T* ≃ 210 K simultaneously with the appearance of partial phase coherence with a short lifetime less than 1 ps. With decreasing temperature, the domains with a pseudogap developed and saturated at TS ∼ 95 K, and the frequency-dependent superconductivity fluctuation appeared as cooperative phenomena among the partial phase-coherent domains. These experimental data show that the development of the partial coherent local domains with a pseudogap has an important role to switch from the partial to the macroscopic phase-coherent state.

DOI： 10.1209/epl/i2002-00349-x

Resonant terahertz radiation from Tl<inf>2</inf>Ba<inf>2</inf>CaCu <inf>2</inf>O<inf>8+δ</inf> thin films by ultrafast optical pulse excitation

Yukihiro Tominari, Toshihiko Kiwa, Hironaru Murakami, Masayoshi Tonouchi, Hagen Wald, Paul Seidel, Henrik Schneidewind

Applied Physics Letters 80 ( 17 ) 3147 - 3149 2002.4

Language：English Publisher：AMER INST PHYSICS

We have observed the free-space radiation of the resonant terahertz wave from c-axis oriented Tl2Ba2CaCu2O 8+δ thin films by femtosecond optical pulse excitation under a radial magnetic field of about 100 Oe nearly parallel to the c axis of the thin film. The observed wave form showed clear oscillations up to 80 K. The frequency was shifted from ∼620GHz at 24 K to ∼300GHz at 80 K, corresponding to an increase in c-axis penetration depth, λc, from ∼26μm to ∼53μm, and disappeared above TC as expected for the Josephson plasma resonance. © 2002 American Institute of Physics. © 2002 American Institute of Physics.

DOI： 10.1063/1.1475770

Tetrahertz pulse radiation properties of a Bi<inf>2</inf>Sr<inf>2</inf>CaCu<inf>2</inf>O<inf>8+δ</inf> bowtie antenna by optical pulse illumination

Hironaru Murakami, Toshihiko Kiwa, Muku L. Misra, Masayoshi Tonouchi, Tetsuji Uchiyama, Ienari Iguchi, Zhen Wang

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 41 ( 4 ) 1992 - 1997 2002.4

Language：English Publisher：INST PURE APPLIED PHYSICS

We demonstrate, for the first time, terahertz (THz) pulse radiation properties from a current biased Bi2Sr2CaCu2O8+δ (BSCCO) bowtie antenna by femtosecond laser pulse illumination. The bias current, excitation laser power and temperature dependence of the radiated amplitude of THz pulse are basically in good agreement with those observed on YBa2Cu3O7-δ (YBCO). However, the detailed properties of the THz pulse from BSCCO are considerably different from those for YBCO. The observed amplitude of the terahertz (THz) radiation pulse was very strong due to the small index value of BSCCO thin film even for the small bias current, and the Fourier components of the pulse contains the frequencies lower than 0.4 THz with a central frequency around 0.1-0.16 THz reflecting its long relaxation time of photo-excited quasi-particle in BSCCO.

DOI： 10.1143/jjap.41.1992

25aYH-10 Optically excited Josephson plasma emission of THz-wave from Tl_2Ba_2CaCu_2O_<8+δ> thin films

Tominari Y., Kiwa T., Murakamic H., Tonouchi M., Wald H., Seidel P., Schneidewind H.

Meeting abstracts of the Physical Society of Japan 57 ( 1 ) 546 - 546 2002.3

24pYK-11 Ultrafast carrier dynanics in pseudgap state of BSCCO

Murakami H., Kiwa T., Tonouchi M., Uchiyama T., Iguchi I., Wang Z., Yasuda T.

Meeting abstracts of the Physical Society of Japan 57 ( 1 ) 506 - 506 2002.3

Preparation and picosecond optical response of Bi system high-T<inf>c</inf> superconductors

Yukihiro Tominari, Toshihiko Kiwa, Hironaru Murakami, Masayoshi Tonouchi, Takeshi Arai, Takafumi Aomine

Physica C: Superconductivity and its Applications 367 ( 1-4 ) 332 - 336 2002.2

Language：English Publisher：ELSEVIER SCIENCE BV

Bi2Sr2Ca1-xYxCu2 O8+δ single crystals were grown by traveling solvent floating zone method. The crystallinity and the superconducting property of the single crystals were characterized by X-ray diffraction and in-plane resistivity measurements. To investigate the ultrafast optical response, time-resolved pump-probe reflectivity measurements were carried out on the single crystals. As a result, fairly long relaxation times of about 20 and 6 ps of excited carriers were estimated for the crystals with x=0 and 0.2, respectively, as compared to 1.7 ps for YBa2Cu3O7-δ thin films in previous study. The relaxation time observed on the underdoped crystal with x=0.2 showed a good consistency with that of Bi2Sr2CaCu2O8+δ thin film in underdoped regime. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)01027-9

Time-domain terahertz spectroscopy of Bi<inf>2</inf>Sr<inf>2</inf>CaCu<inf>2</inf>O<inf>8+δ</inf> thin film

Hironaru Murakami, Toshihiko Kiwa, Masayoshi Tonouchil, Tetsuji Uchiyama, Ienari Iguchi, Zhen Wang

Physica C: Superconductivity and its Applications 367 ( 1-4 ) 322 - 326 2002.2

Language：English Publisher：ELSEVIER SCIENCE BV

Time-domain terahertz (THz) spectroscopy was carried out on a c-axis oriented Bi2Sr2CaCu2O8+δ (BSCCO) thin film. We extracted various optical parameters at frequencies from 0.3 to 1.0 THz and temperatures from 5 to room temperature by numerically solving the observed complex transmittance without Kramers-Kronig analysis. As a result, the frequency dependence of surface resistance RS showed different power laws of RS∝f (f<0.5 THz) and RS∝f1/2 (0.5 THz <f) in the superconducting state. Below the characteristic frequency, fC≃0.5 THz, rapid increase in the density of supercarrier, NS, was obtained. These obtained results well explained the electromagnetic-wave radiation property which had been observed on the same BSCCO thin film. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)01025-5