Wydarzenia

Seminarium Oddziału Badań Magnetyków

Majorana excitations revealed by thermodynamic measurements in the Kitaev magnet alpha-RuCl3

prof. Yuta Mizukami

Uniwersytet Tohoku w Sendai w Japonii

The exactly-solvable Kitaev model [1] realizes a quantum spin liquid with the 1/2 spins fractionalized into Majorana fermions [2,3]. The low energy excitations of the quantum spin liquid are dominated by the gapless itinerant Majorana excitations at low temperatures with Dirac-type linear dispersion. In the presence of the magnetic field, it is theoretically proposed that the bulk excitation spectra exhibit an excitation gap with unique field dependence given by the product of each component of the magnetic field as hxhyhz.
The high-field paramagnetic phase of -RuCl3 is one of the promising candidates for the Kitaev quantum spin liquid state. Several signatures of the Majorana excitations have been reported including the quantized thermal Hall conductivity indicating the chiral edge mode of the Majorana fermions [4], whose origin is now under hot debate. On the other hand, the bulk state of the Majorana excitations and its relation to the edge mode are still elusive and need to be uncovered. Here, I present the observation of the Majorana gap in the bulk state of -RuCl3 from precise field-angle-dependent heat capacity measurements [5,6]. The field-angle dependence of the gap is in good agreement with the theoretical prediction, providing evidence for the bulk Majorana excitations. I also present the recent observation of the defect-induced Majorana excitations in the irradiated -RuCl3 [7].
In collaboration with O. Tanaka, R. Harasawa, K. Imamura, Y. Yoshida, K. Hashimoto, T. Shibauchi (University of Tokyo), S. Suetsugu, K. Ohtsuka, Y. Kasahara, Y. Matsuda (Kyoto University), R. Grasset, M. Konczykowski (Ecole Polytechnique), K. Hwang, P. Noh, E.-G. Moon (KAIST), N. Kurita, H. Tanaka (Tokyo Institute of Technology), M. G. Yamada, S. Fujimoto (Osaka University), J. Nasu (Tohoku University).

References

1. A. Kitaev, Ann. Phys. 321,2-111 (2006).
2. H. Takagi, T. Takayama, G. Jackeli, G. Khaliullin, and S. E. Nagler, Nat. Rev. Phys. 1, 264-349 (2019).
3. Y. Motome, and J. Nasu, J. Phys. Soc. Jpn. 89, 012002 (2020).
4. Y. Kasahara, T. Ohnishi, Y. Mizukami et al., Nature 559, 227 (2018).
5. O. Tanaka, Y. Mizukami et al., Nat. Phys. 18, 429-435 (2022).
6. K. Imamura, S. Suetsugu, Y. Mizukami et al., Sci. Adv. 10, eadk3539 (2024).
7. K. Imamura, Y. Mizukami et al., Phys. Rev. X 14, 011045 (2024).