Valence-Skipping Indium and Its Role in the New Superconductor (Ge,In)Te

Date

Nov 2, 2021

Time

2:50 PM - 4:20 PM

Speaker

Markus Kriener

Affiliation

RIKEN Center for Emergent Matter Science, Wako, Japan

Language

en

Main Topic

Physik

Other Topics

Physik

Host

D. Peets

Description

Abstract:

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 due to charge fluctuations [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 well-known multifunctional system (cf., e.g., [2] and References therein). In spite of its semiconducting nature, it exhibits metallic resistivity and superconducts below critical temperature 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 discuss 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)

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Last modified: Nov 2, 2021, 12:10:20 AM