Molecular beam epitaxy of superconducting FeSe\(_{x}\)Te\(_{1-x}\) thin films interfaced with magnetic topological insulators

Abstract

Engineering heterostructures with various types of quantum materials can provide an intriguing playground for studying exotic physics induced by proximity effect. Here, we report the successful synthesis of iron-based superconductor FeSe\(_{x}\)Te\(_{1-x}\) (FST) thin films in the entire composition of \(0 \leq x \leq 1\) and its heterostructure with a magnetic topological insulator by using molecular beam epitaxy. Superconductivity is observed in the FST films with an optimal superconducting transition temperature \(T_c\) \(\sim\) 12 K at around x = 0.1. We found that superconductivity survives in the very Te-rich films (\(x \leq 0.05\)), showing stark contrast to bulk crystals with suppression of superconductivity due to an appearance of bicollinear antiferromagnetism accompanied by monoclinic structural transition. By examining thickness t dependence on electrical transport properties, we observed strong suppression of the structural transition in films below t \(\sim\) 100 nm, suggesting that substrate effects may stabilize superconducting phase near the interface. Furthermore, we fabricated all chalcogenide-based heterointerface between FST and magnetic topological insulator (Cr,Bi,Sb)\(_{2}\)Te\(_{3}\) for the first time, observing both superconductivity and large anomalous Hall conductivity. The anomalous Hall conductivity increases with decreasing temperature, approaching to the quantized value of \(e^2/h\) down to the measurable minimum temperature at \(T_c\). The result suggests coexistence of magnetic and superconducting gaps at low temperatures opening at the top and bottom surfaces, respectively. Our novel magnetic topological insulator/superconductor heterostructure could be an ideal platform to explore chiral Majorana edge mode.