講演題目: The Role of Valence-Skipping in the Recently Discovered Superconductor In-doped GeTe
講師: Markus Kriener 氏 (RIKEN Center for Emergent Matter Science (CEMS))
日時: 2022年8月25日（木） 14:00-15:00
場所: 北海道大学 理学部 2-211室
要旨:
A major target in the field of superconductivity is to identify and understand the mechanisms which control and increase the superconducting transition temperature Tc. About 30 years ago, Varma pointed out the possibility of enhanced superconducting interactions in systems containing valence-skipping elements [1]. One example is In: It skips its 2+ state and usually appears as In1+ or In3+. In GeTe, it replaces divalent Ge giving rise to such a valence instability. GeTe itself is a wellknown multifunctional system (cf., e.g., [2] and References therein). In spite of its semiconducting nature, it exhibits metallic resistivity and superconducts below critical temperatures Tc < 350 mK due to Ge vacancies [3]. When doping In, the superconductivity is quickly suppressed. Upon further increasing the In content, Ge1-xInxTe exhibits a critical doping concentration xc = 0.12 where various properties change concurrently, among them the crystal structure, the nature of the charge carriers, and a several orders-of-magnitude enhancement and subsequent suppression of the resistivity [4]. Most importantly, a new superconducting phase with monotonically increasing Tc emerges for x > xc. Simultaneously, a crossover of the In valence state from 3+ to 1+ is observed. This subtle correlation strongly suggests that the superconducting phase in Ge1-xInxTe is a direct consequence of the valence instability of the In dopant. In this talk, we will present a comprehensive discussion of the characteristic features of this solid solution and propose a model which accounts satisfactorily for all observations.
[1] C. Varma, Phys. Rev. Lett. 61, 2713 (1988).
[2] M. Kriener, T. Nakajima, Y. Kaneko, A. Kikkawa, X. Z. Yu, N. Endo, K. Kato, M. Takata, T.Arima, Y. Tokura, and Y. Taguchi, Sci. Rep. 6, 25748 (2016).
[3] R. Hein et al., Phys. Rev. Lett. 12, 320 (1964).
[4] M. Kriener, M. Sakano, M. Kamitani, M. S. Bahramy, R. Yukawa, K. Horiba, H. Kumigashira,K. Ishizaka, Y. Tokura, and Y. Taguchi, Phys. Rev. Lett. 124, 047002 (2020)
世話人：井原慶彦
（北海道大学大学院理学研究院物理学部門）