[その他セミナー/研究会]
新物質セミナー：Dynamical Magnetoelectric ffects of Spin Waves in the Multiferroic Ba2CoGe2O7
新物質セミナー：Dynamical Magnetoelectric ffects of Spin Waves in the Multiferroic Ba2CoGe2O7
| 標題： | 新物質セミナー：Dynamical Magnetoelectric ffects of Spin Waves in the Multiferroic Ba2CoGe2O7 |
| 日時： | 2012年2月7日(火) 午後1:30～ |
| 場所： | 物性研究所本館6階 第4セミナー室（A614) |
| 講師： | Dr. Bordacs Sandor |
| 所属： | 東京大学大学院 量子相エレクトロニクス研究センター |
| 要旨： | Lack of inversion and time reversal symmetry leads to cross-coupling between oscillating magnetic and electric polarization, namely dynamical magnetoelectric response. Perhaps, the most exotic manifestation of this phenomena is the non-reciprocal directional dichroism, that is the difference of the light absorption for counter propagating light beams irrespective of their polarization. Despite the early prediction of this phenomenon [1] it has been found minimal in conventional materials and hence of little technological potential. We proposed that multiferroic compounds endowed with electrically-active magnetic excitations (electromagnons) may provided a key to produce large optical magnetoelectric effect for long wavelengths of light [2]. By exploiting the control of ferroelectric polarization and magnetization in a multiferroic oxide Ba2CoGe2O7 , we demonstrated the enhancement of the directional dichroism – as large as 50% – at terahertz frequencies in resonance with the electromagnon absorption [2, 3]. Due to the non-centrosymmetric crystal structure of Ba2CoGe2O7 chirality can be induced via a magnetic field [4]. As a direct proof of such a chiral phase, we found large optical activity for propagation along each crystallographic direction [5]. This is the first demonstration that optical rotation from spin-waves at terahertz frequencies can be a sensitive indicator of chirality. In this chiral phase, another type of directional dichroism, the magnetochiral effect, was observed. Our results imply that this hidden potential is present in a broad variety of multiferroic materials. [1] W.F. Brown, Jr.S. Shtrikman, and D. Treves, J. Appl. Phys. 34, 1233 (1963). [2] I. Kézsmárki et al. Phys. Rev. Lett. 106, 057403 (2011). [3] H. Murakawa et al. Phys. Rev. Lett. 105, 137202 (2010). [4] M. Saito et al. Phys. Rev. Lett. 101, 117402 (2008). [5] S. Bordács et al., arXiv:1109.1597. |
| 世話人： | 大串 研也 (内線：63250) e-mail: ohgushi :at: issp.u-tokyo.ac.jp |