多々良 源 氏（大阪大学大学院理学研究科）
"Persistent current and hall effedt driven by spin chirality"
Persistent current in metallic rings is an equilibrium current which can be induced when the time-reversal symmetry is broken, for instance, by magnetic flux, and in the presence of electron coherence. In this talk, we demonstrate theoretically the existence of a novel persistent current induced by three magnetic contacts attached to a normal ring, without magnetic flux through the ring[1]. Based on the perturbative treatment of the interaction with magentization, the current is shown to be proportional to the non-coplanarity (spin chirality) of the three magnetizations, S_1.(S_2 X S_3) (S_i's are magnetizations). The effect is due to the breaking of the time-reversal symmetry in the orbital motion as a consequence of non-commutativity of the SU(2) spin algebra, and is an SU(2) analog of Josephson effect in superconducting junctions. The persistent current here is shown to result in a Hall effect when external voltage is applied to the ring, and hence detection of such current by electric transport measurement would be possible. The Hall effect observed in some frustrated ferromagnets may be understood in terms of this persistent current[1,2,3]. The application of this chirality-driven persistent current to quantum computers is discussed[4].
[1] G. Tatara and H. Kohno, Phys. Rev. B67, 113316 (2003).
[2] G. Tatara and H. Kawamura, J. Phys. Soc. Jpn. 71, 2613 (2002).
[3] G. Tatara,M. Yamanaka and M. Onoda, preprint.
[4] G. Tatara and N. Garcia, Phys. Rev. Lett., 91, 076806 (2003).