Photoemission study on a special type of multiferroics: GaV4S8 & GeV4S8
Amol Singh1*, Jung-Han Li1,2, Yen-Fa Liao1, Hsiao-Yu Huang1, Yen-Yi Chu1, Jing Chang1, Ku-Ding Tsuei1, Lunyong Zhang3, Sang-Wook Cheong3,4, Michel van Veenendaal5,6, Di-Jing Huang1,2
1Naional Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan
2Department of Physics, National Tsing-Hua University, Hsinchu, 30013, Taiwan
3Laboratory for Pohang Emergent Materials and Max Plank POSTECH Center for Complex Phase Materials, Pohang University of Science and Technology, Pohang 790-784, Korea
4Rutgers Center for Emergent Materials and Department of Physics and Astronomy, 136 Frelinghuysen Road, Piscataway, New Jersey 08854, USA
5Department of Physics, Northern Illinois University, DeKalb, IL 60115, USA
6Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA
* Presenter:Amol Singh, email:rrcat.amol@gmail.com
The lacunar spinels (AV4S4) with A=Ga and Ge, consisting of tetrahedral (AS4)n- and weakly linked cubane (V4S4)n+ are unique in known skyrmions because of a sizable ferroelectric polarization of ~ 1 μC/cm2 and polar crystal structure. Their electronic properties depend on the special degrees of freedom of the basic electronic units of V4S4. These materials are classified as a special class of Mott insulators in which strong electron correlations arise from weak intercluster hybridization. From the viewpoint of ionic formula, average valency of V is 3.25+ in GaV4S8 and 3+ in GeV4S8, yet exact valency of V in these compounds is not known. We conducted hard X-ray photoemission to study the electronic structure of GaV4S8 & GeV4S8 single crystals and to investigate the valency of V in these compounds. The V 2p photoemission spectra are best explained with (V4S4)5+ and (V4S4)6+ for GaV4S8 and GeV4S8 respectively. Further S 2p XPS spectra shows results consistent with the scenario of dynamical Jahn-Teller distortion in the paraelectric phase.
Keywords: Stongly Correlated Electron Systems, Multiferroic, Magnetic Electrical Coupling