Faculty Profiles - TANIYAMA Tomoyasu

Selective Addressing of Single Electron Spins in a Semiconductor Double Quantum Dot Integrated with a Micro-Magnet Reviewed

Obata Toshiaki, Pioro-Ladriere Michel, Tokura Yasuhiro, Shin Yun-Sok, Kubo Toshihiro, Yoshida Katsuharu, Taniyama Tomoyasu, Tarucha Seigo

PHYSICS OF SEMICONDUCTORS Vol. 1199 page： 381-+ 2009

Dynamical polarization effect of nuclear spin bath dragged by electron spin resonance in double quantum dot integrated with micro-magnet Reviewed

Obata T., Pioro-Ladriere M., Tokura Y., Brunner R., Shin Y. -S., Kubo T., Yoshida K., Taniyama T., Tarucha S.

16TH INTERNATIONAL CONFERENCE ON ELECTRON DYNAMICS IN SEMICONDUCTORS, OPTOELECTRONICS AND NANOSTRUCTURES (EDISON 16) Vol. 193 2009

Synthesis and Magnetic Properties of Ba2Mn2Si2O9: the First Example of S=2 Spin-Dimer with Spin-Singlet Ground Reviewed International journal

Zhangzhen He, Myung-Hwan Wangbo, Yutaka Ueda, Yasuo Narumi, Koichi Kindo, Tomoyasu Taniyama, Mitsuru Itoh, Wendan Cheng

CHEMISTRY-AN ASIAN JOURNAL Vol. 4 ( 10 ) page： 1530 - 1535 2009

Low temperature magnetism of the S=1/2 quasi one-dimensional Ising-like anitiferromagnet BaCo2V2O8 Reviewed International journal

S. Kimura, T. Takeuchi, M. Hagiwara, K. Okunishi, Z. He, T. Taniyama, M. Itoh

25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4 Vol. 150 ( 4 ) page： 042090/1 - 4 2009

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We report the results of thermodynamic measurements on the quasi one-dimensional (1D) Ising-like antiferromagnet BaCo2V2O8 in the magnetic fields for H//c down to 200 mK. An appearance of a long range magnetic ordered phase is observed in the field induced region above H-c similar or equal to 3.9 T at temperature below 1.8 K. A peculiar incommensurate ordering, which reflects a quantum critical nature of S = 1/2 1D Ising-like antiferromagnet, realizes in this ordered phase.

DOI： 10.1088/1742-6596/150/4/042090

Tunneling magnetoresistance effect in a few-electron quantum-dot spin valve Reviewed International journal

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, S. Ishida, T. Taniyama, K. Hirakawa, Y. Arakawa, T. Machida

APPLIED PHYSICS LETTERS Vol. 93 ( 22 ) page： 222107/1 - 3 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

We demonstrate the tunneling magnetoresistance (TMR) effect through a semiconductor quantum dot (QD) with a few electrons in a lateral QD spin-valve device. At one-to-two electron transition, only inverse TMR effect is observed, where the TMR ratio is relatively large compared with the value based on the Julliere model. When the bias window reaches near the charging energy of the QD, the inverse TMR almost disappears. These features can be interpreted in terms of spin transport via the ground state of a two-electron QD.

DOI： 10.1063/1.3042098

Scopus

Longitudinal Spin Density Wave Order in a Quasi-1D Ising-like Quantum Antiferromagnet Reviewed International journal

S. Kimura, M. Matsuda, T. Masuda, S. Hondo, K. Kaneko, N. Metoki, M. Hagiwara, T. Takeuchi, K. Okunishi, Z. He, K. Kindo, T. Taniyama, M. Itoh

PHYSICAL REVIEW LETTERS Vol. 101 ( 20 ) page： 207201/1 - 4 2008.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

From neutron diffraction measurements on a quasi-1D Ising-like Co2+ spin compound BaCo2V2O8, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Neel-type ordering, which is expected for the classical system, and the peculiar spin structure is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.

DOI： 10.1103/PhysRevLett.101.207201

Scopus

Reply to Comment on "Origin of Giant Dielectric Response in Nonferroelectric CaCu3Ti4O12: Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy" Reviewed International journal

Desheng Fu, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Shin-ya Koshihara

CHEMISTRY OF MATERIALS Vol. 20 ( 19 ) page： 6286 - 6287 2008.10

Electrically driven single-electron spin resonance in a slanting Zeeman field Reviewed International journal

M. Pioro-Ladriere, T. Obata, Y. Tokura, Y. -S. Shin, T. Kubo, K. Yoshida, T. Taniyama, S. Tarucha

NATURE PHYSICS Vol. 4 ( 10 ) page： 776 - 779 2008.10

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

The rapid rise of spintronics and quantum information science has led to a strong interest in developing the ability to coherently manipulate electron spins(1). Electron spin resonance(2) is a powerful technique for manipulating spins that is commonly achieved by applying an oscillating magnetic field. However, the technique has proven very challenging when addressing individual spins(3-5). In contrast, by mixing the spin and charge degrees of freedom in a controlled way through engineered non-uniform magnetic fields, electron spin can be manipulated electrically without the need of high-frequency magnetic fields(6,7). Here we report experiments in which electrically driven addressable spin rotations on two individual electrons were realized by integrating a micrometre-size ferromagnet into a double-quantum-dot device. We find that it is the stray magnetic field of the micromagnet that enables the electrical control and spin selectivity. The results suggest that our approach can be tailored to multidot architecture and therefore could open an avenue towards manipulating electron spins electrically in a scalable way.

DOI： 10.1038/nphys1053

Scopus

Carrier induced magnetic anomalies in Mn-doped AgGaSe(2) magnetic semiconductor Reviewed International journal

Kenji Yoshino, Aya Kinoshita, Yasuhiro Shirahata, Tetuo Ikari, Tomoyasu Taniyama

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 7 ) page： 07D103/1 - 3 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Magnetic behaviors of the magnetic semiconductor Mn-doped AgGaSe(2) with no secondary phases are reported. Magnetization measurements show that Mn-doped AgGaSe(2) exhibits a superparamagnetic behavior while undoped AgGaSe(2) shows diamagnetism. Significant anomalies are also seen in the temperature dependent ac susceptibility and specific heat at 190 and 275 K. These results indicate that the substitution of Mn induces magnetism in AgGaSe(2). The origin of the magnetic behaviors is discussed on the basis of the combined results of susceptibility, specific heat, and photoluminescence.

DOI： 10.1063/1.2831500

Optically spin oriented electron transmission across fully epitaxial Fe(3)O(4)/GaAs(001) interfaces Reviewed International journal

T. Taniyama, T. Mori, K. Watanabe, E. Wada, M. Itoh, H. Yanagihara

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 7 ) page： 07D705/1 - 3 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

We demonstrate fully epitaxial growth of Fe(3)O(4)/GaAs(001) heterostructures using a reactive molecular beam epitaxy (MBE) method. The Fe(3)O(4) film was obtained by oxidizing an ultrathin Fe layer into an Fe(3)O(4) seed layer in an O(2) atmosphere at 260 degrees C, followed by the reactive MBE growth of Fe(3)O(4). The Fe(3)O(4) seed layer effectively works as a template for the successive growth of Fe(3)O(4). Also, a clear spin filtering effect of optically spin oriented electrons at the Fe(3)O(4)/GaAs(001) interface is shown at room temperature. The results clearly demonstrate that the spin filtering effect occurs at the Fe(3)O(4)/GaAs(001) interface and has its origin in the spin split density of states of the Fe(3)O(4) layer. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2832415

Crossover of electron transmission mechanism and spin filtering effect at Fe/GaAs(001) interfaces Reviewed International journal

E. Wada, M. Itoh, T. Taniyama

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 7 ) page： 07A702/1 - 3 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

A clear correlation between the spin filtering effect of optically pumped spin-polarized electrons at Fe/GaAs(001) Schottky interfaces and its electron transmission mechanism is reported. Current-voltage (I-V) characteristics of the Schottky diode demonstrate tunneling and thermionic emission transmission processes in the low and high bias voltage regions, respectively. A spin filtering current contribution, on the other hand, exhibits a significant peak at a particular bias voltage while spin selectivity shows a shoulder at the same bias voltage. The bias voltage where the features occur corresponds well to the crossover regime of the electron transmission mechanisms. The spin selectivity also shows a field dependence similar to the magnetization curve, assuring that the spin selectivity has its origin in the spin filtering effect. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2829904

Piezoelectric properties of lithium modified silver niobate perovskite single crystals Reviewed International journal

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Shin-ya Koshihara, Mitsuru Itoh

APPLIED PHYSICS LETTERS Vol. 92 ( 17 ) page： 172905/1 - 3 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1-xLixNbO3. It possesses a rhombohedral structure with high ferroelectric phase transition (T-c=548 K for x=0.086) and large spontaneous polarization (P-s similar to 40 mu C/cm(2) for x=0.062) along the < 111 >(c) direction of pseudocubic perovskite structure for x>0.05-0.06. High quasistatic d(33)similar to 210 pC/N and low dielectric constant have lead to a very large value of piezoelectric voltage constant g(33)similar to 53.9x10(-3) Vm/N for the < 001 >(c)-cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2918837

Size dependence of martensite transformation temperature in ferromagnetic shape memory alloy FePd Reviewed International journal

Kenta Seki, Hiroaki Kura, Tetsuya Sato, Tomoyasu Taniyama

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 6 ) page： 63910/1 - 9 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Martensite transformation temperature of ferromagnetic shape memory alloy FePd was studied in the shape of nanoparticle and the polycrystalline samples with grain size in micrometers based on the x- ray diffraction and magnetic measurement as a function of sample size. Both the forward transformation start temperature M(s) and reverse transformation finish temperature A(f) of polycrystalline sample monotonically decreased with decreasing grain size and were not observed in the nanoparticles. The size dependence of transformation temperature is explained based on the change in transformation mode, i. e., the decrease in sample size induces the change from the multivariant mode to single variant mode in which the strain energy is large. In the small sample, the strain energy becomes large, and thus the large driving force is required for the transformation. As a result, the large amount of undercooling occurs, which leads to the lowering of Ms. The measurement of heat capacity indicates that the strain energy is elastically stored without dispersion in the transformation process even in the small size because the volume change of FePd at the transformation is very small. The large elastic strain energy works as the driving force to reverse transformation, and then the lowering of Af is induced. Therefore, the lowering of transformation temperature in FePd is characterized by the lowering of thermodynamic equilibrium temperature. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2890143

Origin of giant dielectric response in nonferroelectric CaCu3Ti4O12: Inhomogeneous conduction nature probed by atomic force microscopy Reviewed International journal

Desheng Fu, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Shin-ya Koshihara

CHEMISTRY OF MATERIALS Vol. 20 ( 5 ) page： 1694 - 1698 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Local probing of conduction behaviors using atomic force microscopy clearly shows that the grain boundary of polycrystalline CaCu3Ti4O12 is Semiconducting. In contrast, the grain is a mixture of semiconductinc, and insulating regions. This inhomogeneous conductive feature leads to giant dielectric response in CaCu3Ti4O12. Theoretical analysis demonstrates that the dielectric response follows a typical Debye-type relaxation, and its unusual temperature dependence originates from the thermal activation behavior of free carries within the semiconducting regions in the grain. An effective way to control the electrical properties of CCTO is to control the defect density within a grain rather than the grain boundary.

DOI： 10.1021/cm0710507