This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Metal-insulator transitions (MITs), in which a material changes from a metallic state with low resistivity to an insulating state because of a change in an external parameter, such as temperature, pressure or an electric field, are a central topic in fundamental physics research. In materials that undergo MITs, it has also been observed that in the insulating phase, but near the transition point, applying an electric field or current can sometimes trigger a sudden drop in resistance, known as resistive switching.
This volatile resistive switching holds promise for various applications, including resistive memory, optoelectronics and neuromorphic computing, which is key to artificial intelligence implementation. However, the fundamental mechanism behind this phenomenon remains poorly understood. Although Joule heating is known to play an important role, it has been difficult to determine how heat generation and dissipation couple with the MIT to stabilize a resistive-switched state.
A key reason is that this phenomenon has mainly been studied in inorganic thin films, where strong heat flow into the substrate and relatively broad MITs can obscure the nonlinear thermal response. In a new study, a research team led by Professor Tetsuaki Itou from the Department of Applied Physics at Tokyo University of Science (TUS) in Japan addressed this issue by investigating a resistive-switched state in a bulk organic conductor that exhibits an extremely sharp MIT and weak heat dissipation. "While resistive switching is actively studied from a device application perspective, what actually happens inside the material during this process is not always fully understood," Itou explains.
"In this study, we present an experimental elucidation of the volatile resistive-switched state, aiming to establish a microscopic basis for understanding the thermal self-organization that links phase coexistence, heat flow, and electrical transport." The team also included Riku Ishii and Assistant Professor Takayoshi Kouchi, both from TUS; Dr. Hiroshi Oike from the National Institute for Materials Science, Japan; Professor Fumitaka Kagawa from the Institute of Science Tokyo, Japan; and Dr. Reizo Kato from RIKEN, Cluster for Pioneering Research, Japan.
Their study was published in Physical Review Applied. The researchers investigated a needlelike crystal of the organic conductor (d7-DMe-DCNQI)2Cu, a deuterated derivative of N,N′‑dicyanoquinonediimine (DCNQI). This material exhibits a sharp MIT on heating and cooling around a transition temperature of 79 K.
Specifically, it exhibits a metallic phase above 79 K and an insulating phase below 78 K. For the experiments, the crystal was suspended inside a Teflon tube without contacting its walls, while two gold wires attached to its ends supplied electrical current. The entire setup was placed in a helium (He) gas atmosphere.
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