Regensburg 2019 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 59: Complex Oxides Interfaces and Charge Order

TT 59.8: Vortrag

Donnerstag, 4. April 2019, 17:00–17:15, H22

Scanning tunneling microscopy on an excitonic insulator Ta₂NiSe₅ — Qingyu He¹, Xinglu Que¹, Alexander Yaresko¹, •Andreas Rost¹, Masahiko Isobe¹, Tomohiro Takayama¹, Lihui Zhou¹, and Hidenori Takagi^1,2 — ¹Max Planck Institute for solid state research, Stuttgart, Germany — ²University of Tokyo, Tokyo, Japan

Ta₂NiSe₅ is the strongest candidate for the long conjectured excitonic insulator state. It is a direct zero gap semiconductor at high temperature, and undergoes at T_c = 326 K a semiconductor-insulator transition simultaneous with an orthorhombic-monoclinic q = 0 structure transition. Our low temperature STM evidences its layered structure with rippling atomic chains. The local spectroscopy reveals the opening of the excitonic insulator gap and the spectral weight shift with decreasing temperature. High resolution STM topography shows a local distortion associated with the structure transition. This distortion may play an important role in the formation of the excitonic state, as also supported by our band structure calculations.