NJIT Physics Department Seminar

9/24/07, Monday

Direct imaging of nano-scale electronic phase separation in La_1-xCa_xMnO₃

Dr. Jing Tao, Brookhaven National Laboratory

(Condensed Matter Experiment, Host: Tyson)

*** Room: 202 ECE ***

(Note the room change)

Time: Noon-1 pm with 11:30 am tea time

Abstract

Manganites exhibit very complex phase diagrams and phase separation (PS) has been believed to be a key phenomenon to understand their rich physical properties, including the well known colossal magnetoresistance effect. Recently, charge ordered (CO) nano-clusters were found near the CMR temperature and suspected to have a possible role underlying the insulator-metal transition in manganites. However, the real space distribution and the nano-scale origin of the CO phase in manganites still remains elusive. This talk will present our in-situ electron microscopic study in La_1-xCa_xMnO₃ system over a wide doping range 0.3 < x < 0.8. Scanning electron nano-diffraction (SEND) and electron energy loss spectra (EELS), using an electron probe about 1 nm in size, were combined to investigate the structural and electronic information from individual nanoclusters. The real space evolution of the temperature-dependent CO phase at different doping levels will be discussed and correlated to the physical properties. Our results consistently show that the charge density associated with the CO structure inside the CO nano-clusters is different with the charge density in the bulk materials. This spontaneous electronic phase separation has great influence on the transport properties in the systems.