RESEARCH

In the past, I have studied various novel materials which present useful "quantum functionalities" such as high-temperature superconductivity or efficient thermoelectricity. The edge of my research resides in the growths of world-best single crystals and top-notch transport measurements. Recently, I am most interested in topological insulators and topological superconductors.

Topological insulator (TI) is an emerging class of materials that host a new quantum-mechanical state of matter where an insulating bulk state supports an intrinsically metallic surface state that is "topologically protected"; namely, the quantum-mechanical wavefunction of the bulk insulating state of a TI bears a "Z₂ topological invariant" distinct from that of the vacuum, which makes a smooth transition from a TI to the vacuum impossible without closing the energy gap along the way, making the surface of a TI to be intrinsically conducting. Intriguingly, the resulting metallic surface state is expected to be "helically spin-polarized" (i.e., right- and left-moving electrons carry up and down spins, respectively) and consist of "Dirac fermions" (i.e., the energy of quasiparticles is linearly dependent on the momentum and hence they are "massless"). Those peculiar properties of the surface state open exciting new possibilities for novel quantum functionalities. However, the "real-life" topological insulator samples available today contain too much bulk carriers that hinder exploiting their surface properties in device forms. In this project, we develop techniques to prepare topological-insulator single crystals with sufficiently low bulk carrier density and fabricate devices to electrically detect the surface spin currents. At the same time, taking advantage of the top-notch single crystals, we explore novel quantum phenomena in TIs for its fundamental understanding.

EDUCATION

1987

Bachelor of Science (Physics), University of Tokyo

1989

Master of Science (Physics), University of Tokyo

1994

Ph.D. (Science), University of Tokyo

PROFESSIONAL EXPERIENCE

1989-1991

Associate Researcher, CRIEPI

1991-1994

Research Scientist, Superconductivity Research Laboratory, ISTEC

1994-1996

Postdoc / Visiting Scientist, Bell Laboratories

1996-2007

Senior Research Scientist, Central Research Institute of Electric Power Industry (CRIEPI)

(2004-2005

Head, Department of Materials Physics and Synthesis, CRIEPI)

(1997-2005

Visiting Associate Professor, Tokyo University of Science)

2007-Present

Professor, ISIR, Osaka University

HONORS AND AWARDS

2003

Superconductivity Science and Technology Award

2006

JSPS Prize

SELECTION OF PUBLICATIONS

Zero-doping state and electron-hole asymmetry in an ambipolar cuprate,
Kouji Segawa, M. Kofu, S-H. Lee, I. Tsukada, H. Hiraka, M. Fujita, S. Chang,
K. Yamada, and Yoichi Ando,
Nature Physics 6 (2010) 579-583.

Quantum oscillations in a topological insulator Bi_1-xSb_x,
A. A. Taskin and Yoichi Ando,
Phys. Rev. B 80 (2009) 085303-(1-6).

Transport and magnetic properties of GdBaCo₂O_5+x single crystals: A cobalt oxide with square-lattice CoO₂ planes over a wide range of electron and hole doping,
A. A. Taskin, A. N. Lavrov, and Yoichi Ando,
Phys. Rev. B 71 (2005) 134414-(1-28) (84 times cited).

Electrical resistivity anisotropy from self-organized one-dimensionality in high-temperature superconductors,
Yoichi Ando, Kouji Segawa, Seiki Komiya, and A. N. Lavrov,
Phys. Rev. Lett. 88 (2002) 137005 (137 times cited).

Mobility of the Doped Holes and the Antiferromagnetic Correlations in Underdoped High-T_c Cuprates,
Yoichi Ando, A. N. Lavrov, Seiki Komiya, Kouji Segawa, and X. F. Sun,
Phys. Rev. Lett. 87 (2001) 017001 (127 times cited).

Specific-heat evidence for strong electron correlations in the thermoelectric material (Na,Ca)Co₂O₄,
Yoichi Ando, N. Miyamoto, Kouji Segawa, T. Kawata, and I. Terasaki,
Phys. Rev. B 60 (1999) 10580 (137 times cited).

Insulator-to-metal crossover in the normal state of La_2-xSr_xCuO₄ at optimum doping,
G. S. Boebinger, Yoichi Ando, A. Passner, T. Kimura, M. Okuya, J. Shimoyama, K. Kishio, K. Tamasaku, N. Ichikawa, and S. Uchida,
Phys. Rev. Lett. 77 (1996) 5417 (341 times cited).

Logarithmic Divergence of both in-plane and out-of-plane normal-state resistivities of superconducting La_2-xSr_xCuO₄ in the zero-temperature limit,
Yoichi Ando, G.S. Boebinger, A. Passner, Tsuyoshi Kimura, and Kohji Kishio,
Phys. Rev. Lett. 75 (1995) 4662 (305 times cited).