114th CEMS Colloquium

Title

Ultrafast dynamics in correlated systems, toward petahertz control

Abstract

i) An electromagnetic oscillation of light cannot directly access space inversion symmetry breaking because of its symmetric nature on the time axis (i. e., the time average of the oscillation is zero). However, recent developments of ultrashort laser technologies enable us to control the direction of charge motion by carrier-envelope phase (CEP) control of a strong light field. Considering non-scattering light-induced current, we can expect petahertz control of the space inversion symmetry in solids. Here, in a layered organic superconductor (κ-(ET)₂Cu[N(CN)₂]Br), SHG is observed by using a single-cycle 6 femtosecond near infrared pulse, which is in contrast to the perturbation theory where even harmonics are forbidden in centrosymmetric systems. The SHG shows a CEP sensitive nature and an enhancement near the superconducting temperature. The result and its quantum many-body analysis indicate that a polarized current is induced by non-dissipative acceleration of charge, which is amplified by superconducting fluctuations [1-3].

ii) In a honeycomb-lattice spin-orbit assisted Mott insulator α-RuCl₃, an ultrafast magnetization is induced by circularly polarized excitation below the Mott gap. A helicity dependent light-induced polarization rotation in spin-liquid phase is 400 times (20 times) larger than that of a conventional paramagnet (antiferromagnet). Photo-carriers play an important role, which are generated by turning down the synergy of the on-site Coulomb interaction and the spin-orbit interaction realizing the insulator state. An ultrafast 6- fs measurement of photo-carrier dynamics and a quantum mechanical analysis clarify the mechanism, according to which the magnetization emerges from a coherent charge motion between different t_2g orbitals (d_yz-d_xz-d_xy) of Ru³⁺

Schematic illustrations of (a) SHG induced by a light-induced non　scattering current in an organic superconductor and (b) light-induced magnetization in a Kitaev-type spin-liquid system.

References
[1] Y. Kawakami, T. Amano, Y. Yoneyama, Y. Akamine, H. Itoh, G. Kawaguchi, H. M. Yamamoto, H. Kishida, K. Itoh, T. Sasaki, S. Ishihara,    Y. Tanaka, K. Yonemitsu, and S. Iwai, Nat. Photon. 12, 474 (2018).
[2] Y. Kawakami, T. Amano, H. Ohashi, H. Itoh, Y. Nakamura, H. Kishida, T. Sasaki, G. Kawaguchi, H. M. Yamamoto, K. Yamaomto, S. Ishihara, K. Yonemitsu and S. Iwai, Nat. Commun. 11, 4138 (2020).
[3] S. Iwai, Y. Kawakami, H. Itoh, and K. Yonemitsu, Faraday Discussions 237, 353 (2022).
[4] T. Amano, Y. Kawakami, H. Itoh, K. Konno, Y. Hasegawa, T. Aoyama, Y. Imai, K. Ohgushi, Y. Takeuchi, Y. Wakabayashi, K. Goto, Y. Nakamura, H. Kishida, K. Yonemitsu, and S. Iwai, Phys. Rev. Research 4, L032032 (2022).