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ResearchNano-System Field

Nano-System Coordinator: Masakazu Aono

New Nano-Systems are Changing the World: From Artificial Intelligence to Energy and the Environment, Diagnosis and Medicine

This research field is searching for various nano-systems that will express novel functions by the interaction of nanostructures with unique characteristics, and is engaged in research to research to utilize those new nano-systems systematically. Concretely, based on basic research on nanoscale materials, such as atomic and molecular transport and chemical reaction processes, polarization and excitation of charge and spin and superconducting phenomena, we are conducting research on atomic switches, artificial synapses, molecular devices, new quantum bits, neural network-type network circuits, next-generation devices, high sensitivity integrated molecular sensors and other new applied technologies. Since the development of new nanoscale measurement methods is also a high priority, we are developing multi-probe scanning probe microscopes and other cutting-edge instruments. We also attach great importance to interdisciplinary fusion-type research with other research fields in MANA.

Driving innovation in research on artificial intelligence by new nano-systems

The “atomic switch,” which functions through nanoscale atomic and ionic transport, is an original and unique technology developed in Japan, mainly at MANA. We discovered that, like the synapses in the brain’s neural network, this atomic switch exhibits plasticity in response to input signals. Taking advantage of this characteristic, we are developing novel devices that mimic the functions of the human brain by constructing nano-systems consisting of large numbers of self-assembled atomic switches. Our aim is to create intelligent information-processing functions with a totally different architecture from today's semiconductor device-based von Neumann computation.

Development of neural network devices using atomic switches

Innovations in the science of superconductivity brought by new nano-systems

Nano-systems shed the light of innovation on the future research of superconductivity. Layer-structured FeSe is known as the simplest material among Fe-based superconductors with a superconducting transition temperature of Tc~8K. We have highly organized the fine structure of KFe2Se2, which has FeSe layers in its crystal structure, and elucidated that the appearance of superconductivity at Tc~31K or Tc ~44K depends on the morphology of the fine structures. This relationship between the fine structure and Tc will lead to better understanding a mechanism for increments of Tc. We have also created an indium atomic layer two-dimensional material on the surface of silicon, and have clarified for the first time ever that macroscopic supercurrents and Josephson quantum vortices exist in this atomic layer. Research activities at MANA involving the design and systemization of superconducting materials based on the concepts of nanoarchitectonics are accelerating progress in superconductivity science.

(Left) Fine structures of a KFe2Se2 superconductor, which has FeSe layers
(Right) STM image of Josephson vortices formed in a surface atomic layer superconductor

Theoretical search for the great potential of new nano-systems

Uncertainty due to fluctuations is unavoidable in the nano world, so new theoretical investigations are necessary to achieve novel functionalities by nano systems. For example, although quantum computation has power far superior to the capacity of computers used at present, quantum states are fragile and lose coherence easily. We are focusing on Majorana quasiparticle excitations of topological superconductivity, which appear at the edge of a topological superconductor containing an odd number of quantum vortices, while they disappear in the case of an even number. Utilizing this feature, we developed a method to manipulate quickly and stably the charge-neutral Majorana quasiparticles by applying local gate voltages at junctions between superconductors, and demonstrated theoretically that this could be used for quantum bit manipulation. MANA is also carrying out experimental research with the goal of realizing such a quantum device.

Schematics and computer-simulation results of a device for manipulating charge-neutral Majorana quasiparticles by local gate voltage

Pioneering new methods for precisely measuring novel nano-systems

In pioneering novel nano-systems, new instruments and methodologies are indispensable to cover a wide range of characterizations, from measurements of physical properties of individual nanomaterials to the evaluation of functionalities of nano-systems constructed at the micrometer and larger sizes through nanoarchitectonics. We were the first in the world to develop the multi-probe scanning tunneling microscope (MP-STM) and the quadruple-probe atomic force microscope (MP-AFM). These new instruments and techniques are essential in the development of innovative nano-systems because they provide nanoscale resolution in a local vicinity while measuring electrical properties at both nano- and macro-scales. We are now developing a precise measurement methodology for ultratrace substance detection using nanoplasmonics.

Schematic diagram of quadruple-probe atomic force microscope and its application to the characterization of a neuromorphic materials network