Nano-Resolved Current-Induced Insulator-Metal Transition in the Mott Insulator Ca2RuO4

• Published in: Physical review. X Vol. 9; no. 1
• Main Authors: Zhang, Jiawei, McLeod, Alexander S, Han, Qiang, Chen, Xinzhong, Bechtel, Hans A, Yao, Ziheng, Gilbert Corder, S N, Ciavatti, Thomas, Tao, Tiger H, Aronson, Meigan, Carr, G L, Martin, Michael C, Sow, Chanchal, Yonezawa, Shingo, Nakamura, Fumihiko, Terasaki, Ichiro, Basov, D N, Millis, Andrew J, Maeno, Yoshiteru, Liu, Mengkun
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 15.02.2019
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Conductors; Crystallography; Domain propagation; Electric currents; Electric fields; Electronic control; Infrared imaging; Insulators; Microscopy; Nucleation; Ohmic dissipation; Optical microscopy; Optical properties; Phase transitions; Phases; Quantum phenomena; Resistance heating; Single crystals; Steady flow
• ISSN: 2160-3308; 2160-3308
• DOI: 10.1103/PhysRevX.9.011032

The Mott insulatorCa2RuO4is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry out infrared nano-imaging and optical-microscopy measurements on bulk single crystalCa2RuO4under conditions of steady current flow to obtain insight into the current-driven insulator-to-metal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.