Mesoscopic horizons

"My research at Tokyo Tech," explains Ando, "focuses on the action of quantum effects and many-body effects on transport and optical phenomena in man-made, low-dimensional systems. My colleagues have achieved two-dimensional systems of superb quality in semiconductor heterostructures. And recent advances in lithography have allowed for fabricating quantum structures, such as quantum wires, dots, and antidots.

"Examples of the phenomena that we have been studying in mesoscopic systems include ballistic transport in quantum point contacts in the presence of a magnetic field, conductance fluctuations, quantum wires and their response to external fields, the quantum Hall effect and edge states, the dynamics of tunneling across mesoscopic junctions, quantum effects and chaos in anti-dot lattices, and the breakdown of Kohn's theorem in quantum cyclotron resonance. We are also looking carefully at the electronic properties of nanotubes."

A broad perspective

Ando, a theorist through and through, famously maintains a thoughtful perspective on the broader context of his work. "The history of physics," he observes, "is a tale of discoveries and novel concepts arising from the study of new and intriguing materials. That is especially true of material studies at the nanoscale. A researcher in our department, for example, has fabricated gold nanowires with the tip of a scanning tunneling microscope, and the nanowires exhibit a helical multishell structure that evokes multiples of the number seven. Another theorized that a metallic carbon nanotube would be a perfect, resistance-free conductor, even in the presence of scatterers, and our initial findings are bearing out that prediction."

His theoretical persuasion notwithstanding, Ando is alert to the practical implications of his work. "I've always been close to real-world applications. I've worked closely with semiconductor engineers, especially, over the years." And he is visibly enthusi-astic about the possible applications for his recent theoretical explorations.

"Mesoscopic systems," notes Ando, "occupy the realm between micro and nano. They are small enough to support useful quantum effects but big enough to negotiate with well-established technology. Mesoscopic systems vastly extend the scope of solid-state physics. They spawn a whole new portfolio of effects and phenomena. The systems offer a fresh vantage on the formation and characterization of quantum structures and suggest exciting new possibilities for quantum devices. The implications of mesoscopic systems will shape future electronic devices decisively. So we need to come to terms with those systems and determine what they mean for the direction of solid-state electronics."

The aesthetics of the discipline

A query about early encounters with physics brings a smile to Ando's face. He says that he found the experiments and problems in high school physics counterintuitive.

"I couldn't make heads or tails of the subject," rues the world-renowned physicist. "The subject only became really understandable for me when I got to college. And that's a shame. Physics should be a means of making the world easier to understand, not more difficult. It should be a matter of finding principles that provide simple explanations for apparently complicated phenomena."

Ando reports that he found mathematics more approachable than physics in high school. "I especially liked working my way through the proofs of geometry while referring to the figures. Physics finally came alive for me in university when I encountered analytical mechanics. I finally discovered the logical simplicity in physics that I had enjoyed in mathematics."