Researchers have devised a groundbreaking synthetic material design capable of precisely regulating the temperature at which a material transitions from an electrical insulator to a conductor, paving the way for highly efficient electronic switches surpassing traditional transistors.
In the realm of materials encountered in everyday life, one typically encounters electrical conductors like copper or aluminum, or electrical insulators such as plastic and paper. However, there exists a class of materials known as correlated electron materials, which undergo a transition from an insulating state to a metallic one. Yet, these transitions are temperature-dependent, limiting their utility in devices like electronic switches that operate at a consistent temperature, typically room temperature. Additionally, these transitions often occur at temperatures unsuitable for room temperature operation.
In a collaborative effort involving scientists from the Indian Institute of Science (IISc) and counterparts from Japan, Denmark, and the United States, a novel synthetic material design has been proposed to address this challenge. Led by Prof. Naga Phani and his team at the solid-state and structural chemistry unit of IISc Bangalore, researchers introduced a three-layer structure. This structure comprises an ‘active’ channel layer responsible for the metal-to-insulator transition, a charge reservoir layer capable of regulating the transition temperature by supplying electrons to the active layer, and a charge-regulating spacer layer situated between the active and reservoir layers to control the flow of electrons.
The precise fabrication of nanometer-thick, atomically smooth layers of these materials is crucial for the success of this endeavor. Such thin layers are prepared using pulsed laser deposition, a technique allowing precise atomic layer control akin to atom-by-atom spray painting. Researchers employed an atomic force microscope (AFM), funded by the DST-FIST program, to assess the quality of these layers. Extensive AFM studies were conducted to determine optimal conditions, including temperature, pressure, and growth rate, for developing this synthetic material stack.
In their research published in Nature Communications, scientists utilized vanadium oxide (VO2) to demonstrate the ability to introduce over a billion-trillion electrons per cubic centimeter (>10^21 electrons/cm3) into the VO2 layer. Typically, adding such a significant number of electrons to a material involves a process called ‘doping,’ which alters the material’s atomic arrangement and properties. However, the novel synthetic material design proposed in this study obviates the need for doping, preserving the crystal’s periodic arrangement and utility. Additionally, researchers devised an easily reproducible amorphous-layer design for the reservoir and spacer layers.
This breakthrough enables the exploration and manipulation of properties in exotic materials capable of exhibiting both insulating and conducting behaviors. Moreover, it sheds light on the stubborn nature of electronic ‘traffic jams’ leading to insulating behavior in correlated electron materials, challenging current understanding. Researchers anticipate extending this research to explore other exotic materials such as superconductors and investigating the potential for developing new devices harnessing phase transitions in synthetic structures. The electronic control of phase transitions proposed herein also opens avenues for studying quantum critical points and interfaces, with potential applications in classical and quantum computing.