NIMS Award 2021 Winners
This year, NIMS will present the honor to outstanding research achievements in the field of “research on quantum materials, such as materials and structures that exhibit quantum effects or research that leads to the innovative use of the materials.” Their efforts have led to a breakthrough in the development of next-generation quantum devices.
Condensed Matter Physics
Fundamental theoretical studies on quantum states of low-dimensional materials
(Honorary Professor, Emeritus Professor, Tokyo Institute of Technology /
Emeritus Professor, University of Tokyo)
Condensed Matter PhysicsPioneering work of new quantum physics by twistronics
Allan H. MacDonald
(Professor of Physics,
University of Texas at Austin)
(Cecil and Ida Green Professor of Physics, Massachusetts Institute of Technology)
Research Summary and Impact on the Academic and Industrial Sectors
At surfaces and interfaces of materials, or in nanometer-scale thin films, the movement of electrons is restricted and the energy of electrons is quantized. Since such quantization leads to a variety of interesting physical properties of the materials, it is expected to bring about innovations in various fields. For example, the precise control of quantum effects and electron-electron interactions is a fundamental technology that forms the basis of current electronics and optical technologies, and is directly related to the control of electrical conduction and light absorption and emission.
In addition, various research is being actively pursued to utilize quantum effects, such as the quantum Hall effect, ballistic electrical conduction, and single electron tunneling effect. This is expected to contribute greatly to the realization of a safe and secure society, including an ultra-low energy consumption society, advanced use of big data and AI, and information security.
Prof. Ando conducted pioneering research focused on the quantum effects in electron transport phenomena and the effects of multi-electron interactions, and provided many theoretical insights into interesting quantum phenomena such as ballistic electrical conduction, conductance fluctuations, quantum Hall effect, edge states, and quantum chaos. In particular, in his research on quantum effects in semiconducting two-dimensional electron systems, he clarified that carbon nanotubes and graphene are low-dimensional materials that have essentially the quantum electrical conductivity properties. This achievement has greatly contributed to the development of the research field of “nanocarbon” materials.
[Impact on the academic and industrial sectors]
Prof. Ando’s theoretical research on semiconducting two-dimensional electron systems is a pioneering study that provided the basis for electrical conduction in two-dimensional materials, and is used as a fundamental framework for understanding low-dimensional conduction. For example, Prof. Ando’s theory has been applied to the analysis of scattering factors that determine the electrical conduction of two-dimensional electrons, and has made a significant contribution to the characterization of silicon MOS transistors and GaAs heterostructure devices, which are widely used today. Also, based on the theory by Prof. Ando, a precise resistance standard utilizing the quantum Hall effect has been realized. Prof. Ando’s theoretical work on carbon nanotubes and graphene continues to lead low-dimensional condensed matter physics research and continues to influence a wide range of research fields including physics, materials science, and electronics.
Allan H. MacDonald・Pablo Jarillo-Herrero
Graphene is a sheet of carbon with a thickness of one atom. Since the establishment of the method for extracting high-quality graphene by Professor Andre Geim and Professor Konstantin Novoselov (Nobel Laureates in Physics 2010), numerous experimental studies have been conducted, and its unique electronic properties have attracted attention from basic science to applied research in a wide range of fields. However, in order to use graphene as an electronic material, it is essential to develop new material technologies, such as technologies to modify semi-metallic properties into semiconductor properties and technologies to control the quantum effects that appears on graphene.
Prof. MacDonald conducted a theoretical study on two-layer graphene stacked at slightly different angles (twisted bilayer graphene), and predicted that the electronic state of the graphene changes depending on the twist angle, and that a quantum-mechanically remarkable electronic state called flat band appears at certain twist angles (magic angles). Materials with a flat band, in which the electron-electron interaction effect is enhanced, are especially interesting and they are expected to exhibit useful properties unique to strongly correlated materials, such as magnetism and superconductivity. Prof. MacDonald’s theoretical study showed that strongly correlated phenomena appear in twisted bilayer graphene, a material composed entirely of carbon atoms. It was a remarkable, pioneering achievement.
Prof. Jarillo-Herrero developed a technique for creating twisted bilayer graphene, and experimentally proved that unique electronic states appear near the magic angle as predicted by Prof. MacDonald. He found two phases which are thought to be derived from electron correlation: an insulating phase and a superconducting phase near the insulating phase. The similarity of the phase diagram drawn by Prof. Jarillo-Herrero et al. to that of copper oxide high-temperature superconductors was also of great interest, and those achievements triggered an explosion of research on twisted bilayer graphene and related materials.
[Impact on the academic and industrial sectors]
The theoretical work of Prof. MacDonald in 2011 and the experimental work of Prof. Jarillo-Herrero et al. seven years later led to the development of a new material control technique called “twistronics.” Since then, it has been theoretically clarified that the electronic state of twisted bilayer graphene is very unique in that it is related not only to the strong correlation effect but also to the topology. As the control of physical properties through twistronics in three- or four-layer graphene and atomic-layer transition metal dichalcogenides has also been studied, it can be said that their research achievements have opened up a new field. In addition, their achievements in providing a new method for controlling physical properties, which are useful for the development of devices using atomic layer materials, have been highly evaluated worldwide in terms of opening up new avenues for applied research.
NIMS Award Ceremony and Lectures 2021 Online
November 17th, 2021