Robust Excitonic‐Insulating States in Cu‐Substituted Ta2NiSe5

Abstract

Abstract Excitonic insulators exhibit intriguing quantum phases that further attract numerous interests in engineering the electrical and optical properties of Ta2NiSe5. However, tuning the electronic properties such as spin‐orbit coupling strength and orbital repulsion via pressure in Ta2NiSe5 are always accompanied with electron‐hole pair breaking, which is a bottleneck for further applications. Here, the robust excitonic‐insulating states invariant with electron‐doping concentrations in Ta2NiSe5 are demonstrated. The electron doping is conducted by substituting Cu into Ni site (Ta2Ni1‐xCuxSe5). The majority carrier of pristine sample is a hole‐type and is converted to electron‐type with a doping concentration over x = 0.01, whose carrier density can be controlled by varying the Cu concentration. The excitonic transition temperature (Tc) does not significantly alter with electron‐doping concentrations, which is stark contrast with the declining Tc as the hole‐type dopant of Fe or Co increases. The optical conductivity data also demonstrate the invariant excitonic‐insulating states in Cu‐doped Ta2NiSe5. The findings of invariant excitonic‐insulating states in n‐type Cu‐substituted Ta2NiSe5 can be utilized for further electronic device applications by using excitons.

Keywords

• charge doping
• electrical transport
• excitonic insulator
• optical conductivity
• semiconductor