Prof. Jun-ichiro Kishine (Natural and Environmental Science Program, open University of Japan)

"Quantum transport through topological spin texture in chiral helimagnet"

In a magnetic crystal belonging to chiral space group, competition of the relativistic spin-orbit Dzyaloshinskii-Moriya (DM) interaction and ferromagnetic exchange interaction causes a helical magnetic arrangement with definite vector chirality and a spatial period of several tens of nanometers. The most intriguing property of chiral helimagnet is that there appears a nonlinear regular lattice of spin magnetic moments under weak magnetic field applied perpendicular to the helical axis. This state, called chiral soliton lattice (CSL), is an extremely robust topological ground state, where magnetic topological charges condense into regular lattice. The spatial period of the CSL is controlled by magnetic field. When itinerant electrons coexist such as in the case of Cr1/3NbS2[1], the CSL acts on the itinerant electrons as magnetic superlattice potential. On the other hand, the itinerant electrons cause spin torque transfer into the CSL to cause collective translation of the CSL. Consequently, we anticipate that the CSL would exhibit a variety of interesting functions, including spin current induction[2], nontrivial soliton transport[3], new kind of elementary excitations[4], current-driven collective transport[5], anomalous magnetoresistance[6] and so on. These theoretical proposals are strongly supported by experimental demonstration that the CSL is formed in a single crystal of Cr1/3NbS2[1] and will open up new perspectives in the field of spintronics. In this talk, I will give an overview of our recent progress on this topics.

[1] Y.Togawa, T.Koyama, K.Takayanagi, S.Mori, Y.Kousaka, J.Akimitsu, S.Nishihara, K.Inoue, A.S.Ovchinnikov, and J.Kishine, Phys.Rev.Lett.108, 107202 (2012), selected as APS Spotlighting Exceptional Research on March 5, 2012.

[2] I.G.Bostrem, J.Kishine and A.S.Ovchinnikov, Phys.Rev.B78, 064425(2008).

[3] A.B.Borisov, J.Kishine, I.G.Bostrem, and A.S.Ovchinnikov, Phys.Rev.B79, 134436(2009).

[4] J.Kishine and A.S.Ovchinnikov, Phys.Rev.B79, 220405(R) (2009).

[5] J.Kishine, A.S.Ovchinnikov, and I.V.Proskurin, Phys.Rev.B82, 064407 (2010).

[6] J.Kishine, I.V.Proskurin and A.S.Ovchinnikov, Phys.Rev.Lett. 107, 017205 (2011).