Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 42: Charge Order
TT 42.10: Vortrag
Dienstag, 13. März 2018, 12:45–13:00, HFT-FT 131
Nearfield Optical Probe of the Excitonic Insulator Transition in Ta2NiSe5 — •Amrit Raj Pokharel1,2, Heiko Linnenbank2, Tomohiro Takayama1,2, Hidenori Takagi1,2, and Stefan Kaiser1,2 — 1Max Planck Institute for Solid State Research, Stuttgart — 2University of Stuttgart
The Excitonic Insulator (EI) is an intriguing phase of condensed excitons that undergo Bose Einstein Condensation (BEC). A prominent solid-state candidate for an EI is Ta2NiSe5, which is a quasi-one-dimensional material that undergoes a semiconductor to excitonic insulator phase transition at Tc=328K [1]. Here we investigate the formation of the excitonic gap using Scattering-Scanning Nearfield Optical Microscope (s-SNOM). That allows us tracing the optical response with spatial resolution down to tens of nanometer when the system is driven across Tc by temperature.
Probing at different energy scales - in the gap, at the exciton peaks and close to strongly coupled phonons - reveals the nature of the EI transition. We will discuss a homogeneous gap and an inhomogeneous near field pattern on the exciton peak around Tc with respect to the second order nature of the phase transition.
Y.F.Lu, et al. Nat.Com. 8, 14408 (2017).