A combination of ARPES and Neutron Scattering studies of the Jahn-Teller physics in 1T- TiSe₂

We have conducted temperature-dependent Angle Resolved Photoemission Spectroscopy (ARPES) and Neutron Scattering (NS) studies of 1T- TiSe₂, a canonical commensurate Charge Density Wave (CDW) system. Our NS data provide evidences for Jahn-Teller (JT) distortions in 1T- TiSe₂ both below and above the CDW transition temperature (T_cdw). In this context, JT distortion has been proposed to be one of the possible mechanisms of the CDW order in 1T- TiSe₂. In one of the models relating the CDW order to JT distortion, proposed by Whangbo and Canadell (J. Am. Chem. Soc.,114, 9587-9600, 1992), the energy lowering in the CDW state occurs due to a downward movement of the Se 4p bands with decreasing temperature through T_cdw. Furthermore, there should be some shortening in Ti-Se bond-length in the observed displacement pattern at temperatures below T_cdw. These features are observed in our ARPES and Neutron Scattering studies. Being consistent with previous works, our ARPES data indeed show that both Ti 3d bands and Se 4p bands shift downward in energy as temperature of the material is reduced through T_cdw. However, the energy movement of Ti 3d bands is entirely due to the T-dependent change in chemical potential, while Se 4p bands do display nontrivial T-dependent motion.