Hikaru WATANABE
Kyoto University
The physics of multipole moment has been discussed in broad systems such as
strongly-correlated electron systems [1], multiferroic materials [2], and so on. Multipole
moments arise from the coupling between spin, orbital, sublattice degrees of freedom,
and lead to various phenomena in condensed matter: e.g. unconventional phases and
peculiar responses to external fields.
Furthermore, recent studies suggest that the uniform alignment of parityviolating
multipole moments, namely, odd-parity multipole order induces exotic
quantum phases and cross-correlated responses in metals [3]. An important feature of
odd-parity multipole ordered systems is unusual itinerant properties. In fact,
spontaneous emergence of spin-momentum coupling or asymmetric band structure is
closely related to intriguing quantum phenomenon.
In our work, we classified the even-/odd-parity multipole from the viewpoint of
point-group classification [4]. Our results systematically clarify the physical properties
of odd-parity multipole ordered systems and cross-correlated responses both in metals
and insulators, while previous studies have been limited to case studies [3]. We further
identified a novel transport phenomenon, magneto-piezoelectric effect, which is caused
by a coupling between elasticity and electricity in “conductors” [5]. This response may
suggest a topic in a recently developed field, antiferromagnetic spintronics [6], and will
promote functionalities of antiferromagnets.
Santini, S. Carretta, G. Amoretti, R. Caciuffo, N. Magnani, and G. H. Lander, Rev. Mod.
Phys. 81, 807 (2009).
[2] N. A. Spaldin, M. Fiebig, and M. Mostovoy, J. Phys. Condens. Matter 20, 434203
(2008).
[3] Y. Yanase, J. Phys. Soc. Japan 83 , 014703 ( 2014); S. Hayami, H. Kusunose, and Y.
Motome, Phys. Rev. B 90 , 024432 (2014); S. Sumita and Y. Yanase, Phys. Rev. B 93 ,
224507 (2016).
[4] H. Watanabe and Y. Yanase, Phys. Rev. B 98 , 2451 29 (201 8)
[5] H. Watanabe and Y. Yanase, Phys. Rev. B
96 , 0 64432 (2017) 2017); Y. Shiomi, H. Watanabe,
H. Masuda, H. Takahashi, Y. Yanase, and S. Ishiwata, Phys. Rev. Lett. 122 , 127207
(
[6] T. Jungwirth, X. Marti, P. Wadley, and J. Wunderlich, Nat. Nanotechnol. 11 , 231
( 2016); V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, and Y. Tserkovnyak, Rev.
Mod. Phys. 90 , 015005 (