Electrical-field-induced insulator-to-metal transition in samarium monosulfides

Electrical-field-induced insulator-to-metal (I-to-M) transition of samarium monosulfides was investigated systematically. Experiment results demonstrate that Sm_0.9Ca_0.1S undergoes the I-to-M transition when in a small electric field of 250 V/cm at liquid-nitrogen temperatures. However, simultaneous measurement of I–V characteristics and strain did not detect the electrical-field-induced strain expected from the large volume contraction originating from the valence transition of Sm. Mid-infrared to visible region reflectivity spectroscopy in the field-induced transition revealed no spectral change other than the temperature change attributable to Joule heat. This lack of change contrasts to the large-scale spectrum changes, such as a sharp rise in reflectivity, which appear in the metallic phase induced by pressure or element substitution. The detailed analysis of the field-induced strain suggests that filamentary metallic paths are formed during the breakdown process, just as they are for strongly correlated insulators.