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Low Dimensional Electron System

  • Hideki Yayama, Professor
Our group studies the following topics.
  1. Electrical properties of two-, one-, and zero-dimensional electron system on liquid helium.
  2. Novel cryogenic technologies.

1. Low Dimensional Electron System on Super-fluid Helium

Figure 1. One-Dimensional Electron System on Superfluid Helium

It is known that the electrons can exist on a surface of superfluid helium as a Tow-Dimensional Fermion System. We are interested in the system of lower dimensions than this: One- and Zero-dimensions. We have succeeded to create them by using “structured surface” of solid dielectrics as shown in Fig. 1. Superfluid helium goes up to the glass surface which has parallel grooves with micrometer size width. The helium surface has a sag in the center of the groove and the upward electric field is applied perpendicular to the surface. So that the electrons are pushed down to the center of the grooves, creating the one-dimensional Fermion system. All the impurities are frozen in this temperature range, this system is the cleanest system of all including solid-state devices. We are investigating the Luttinger liquid state by this system. By reducing the dimension further, we can get zero-dimensional system as well.

2. Novel cryogenic technologies

Figure 2. Cryogen-free Dilution Refrigerator in mK region

In order to investigate low temperature physics, cryogenic refrigerator is required. In the milli Kelvin region, a Dilution Refrigerator is conven-tionally used. We have developed the dilution refrigerator without using liquid helium as a cryogen. Only electricity and cooling water are required to run the fridge. The Fig. 2 shows the dilution refrigerator which we developed in our laboratory. Our interests are not only in the refrigerators but also some novel measurement technologies, e.g., heat capacity measurement, magnetic susceptibility measurement, electrical property measurement, etc.