Effect of modifying with light elements on properties of a topological superconductor Fe(Se,Te)

抄録

When a topological insulator becomes a superconductor, Majorana particles, which are themselves antiparticles, appear on the surface or edges of the material. Since they are robust to environmental disturbances and can memorize the history of particle exchanges (non-commutative anyons), they have attracted much attention as a group of materials that can contribute to next-generation quantum computer devices. The candidate materials for topological superconductors (TSCs) include Cu_xBi₂Se₃ (chiral p-wave superconductor) [1] and Pb/TlBiSe₂ (s-wave superconductor/topological insulator junction) [2]. However, the superconducting transition temperature T_C of these materials is still low, below 3.8 K and 10 K, respectively. Meanwhile, Fe(Se,Te), which was demonstrated as a TSC by ARPES and STS in 2018, has the highest T_c among TSCs, reaching up to 14 K when the Se/Te ratio is adjusted [3].

Fe(Se,Te) is a van der Waals material, and it is thought that intercalation (IC) of foreign atoms and molecules between the layers is possible in addition to adsorption on the surface. Therefore, it is expected that both the carrier density and Debye frequency can be increased by IC with light elements such as hydrogen and alkali metals. In fact, in the sister system FeSe, the T_C increased from 8 K to 44 K by IC of hydrogen in a bulk sample using the solution IC method [4]. We have attempted to realize TSCs having even higher T_C by modifying Fe(Se,Te) with hydrogen and alkali metals.

First, the cleaved surface of bulk Fe(Se,Te) was irradiated with cracked hydrogen atoms under ultra-high vacuum (UHV) environment, and the temperature dependence of electrical resistance was measured using an in-situ independently driven four-probe electrical transport measurement system. As shown in Figure 1, the normal resistance of the sample exposed to 10⁵ Langmuir hydrogen decreases from 0.52 Ω/Sq. to 0.31 Ω/Sq. and the T_C increases from 10.2 K to 12.3 K. This is thought to be due to the increase in carrier density and/or in Debye frequency caused by hydrogen modification. In the presentation, we will discuss results based on more systematic data.

Reference: [1] Y. S. Hor et al., Phys. Rev. Lett. 104, 057001 (2010). [2] C. X. Trang et al., Nat. Commun. 11, 159 (2020). [3] M.H. Fang et al., Phys. Rev. B 78, 224503 (2008). [4] Y. Meng et al., Phys. Rev. B 105, 134506 (2022).