Investigating material properties in the nano-world, and finding applications for quantum dots

Описание: In Keio University's Faculty of Science and Technology, the Eto Group does research on materials science. This research on physical properties reveals diverse phenomena in many materials, including metals, semiconductors, magnetic materials, and superconductors.
In particular, the Group is focusing on new physical phenomena that emerge when semiconductor microfabrication is done on a nanometer scale.

The nanoworld is intermediate between the micro-world of atoms and molecules, at around 0.1 nm, and the macro-world of everyday life, at about 1 m. So, it's often called the mesoscopic realm.

Q. Meso means intermediate between micro and macro. In the micro world, quantum mechanics describes the properties of atoms and molecules, In the mesoscopic world, the quantum mechanical properties of electrons reveal themselves directly, through physical phenomena such as electrical conductivity.
The micro- and macro- worlds are already well-understood by the quantum mechanics, or Newtonian mechanics and electromagnetism, but theories to describe what happens in between those scales are not well-understood in many ways. In this frontier area, lots of experiments are now being done to show what happens. And in our research, we devise theories to explain the phenomena that occur.

The Eto Group's research mainly concerns quantum dots.
Quantum dots are nano-sized containers made of semiconductors, with electrons trapped inside. They enable the number of electrons to be controlled electrically. So, quantum dots are also called "artificial atoms."
In the periodic table of artificial atoms, the third one has been named after Professor Eto. Its symbol is Et.

Q. We've theoretically explained the electron states in artificial atoms, where we can vary the number of electrons one by one. In addition, in some experiments, leads are attached to quantum dots, to measure their electrical conductivity. Various new phenomena unique to quantum dots have now become clear. For example, in specialist terms, we've elucidated the Kondo effect, which is due to interaction between electrons, properties related to electron spin, and those induced by the spin-orbit interaction, which is a relativistic effect.

Controlling electron number and electron spin could enable single-electron transistors - the ultimate in energy-efficient devices -- and quantum computers. Other applications for quantum dots include highly efficient solar cells.
The Eto Group will be doing further R&D, from new perspectives utilizing semiconductor nanostructures.

Q. There are various fields of theoretical physics, but quite unique feature of our research is we formulate theories that are closely linked to experimental research. It's only recently become possible to make tiny systems by semiconductor microfabrication, and to investigate their properties. Right now, doing experiments is leading to the discovery of new physical phenomena. We devise theories to explain newly obtained experimental data, or in an opposite way, we suggest the experimental observation of new phenomena based on our theoretical study first.
Then the research progresses by verifying those phenomena experimentally. In that sense, our work involves a very close relationship between theory and experiment.