Today’s electronics are based on the progress of semiconductor devices. Modern nanotechnology pushes the minimum line width of semiconductor structures to less than 10 nm. These semiconductors are very important in engineering, but they also provide an ideal stage to study physics. A structural size smaller than or nearly equal to the electron wavelength results in prominent quantum effects and novel physical phenomena.
We are studying these semiconductor quantum structures with an emphasis on the concept of carrier interaction. We can utilize quantum transport phenomena in two-dimensional electron systems through the interplay between spin, orbital, and valley degrees of freedom. The quantum wire and quantum point contact are fundamental semiconductor nanostructures, and we are studying manipulation and detection of electron spin and nuclear spin features in these structures.
We have verified a strong interaction between electrons and nuclear spins in certain conditions. We have successfully applied this phenomenon to novel highly-sensitive resistively-detected NMR (Nuclear Magnetic Resonance). Such studies are connected to the study of electron spin features by using nuclear spin detector, and high-precision coherent control of nuclear spins in semiconductor nanodevice. We are leading the world in these topics. We are also interested in developing an interface between nuclear spins and photons via optical means in addition to electrical ones. NMR and MRI (Magnetic Resonance Image) have been widely used in chemical and medical analysis, and the extension of the powerful nature of nuclear-spin-based measurements to solid-state systems will establish a novel spintronics. We have also succeeded to extend high-sensitive resistively detected NMR to InSb two-dimensional system, typical narrow-gap quantum system.
In order to elucidate these physical properties, it is essential to understand them on a nanoscale, in addition to macroscopic measurements such as resistance. We are focusing on direct observation of the local properties of semiconductor quantum structures using nanoprobes operating at dilution refrigerator temperature. A semiconductor quantum structure version of MRI has been demonstrated recently.