Electron tunneling measurements in atomic scale gap filled with liquid 4He below 4.2K

We report the tunneling spectroscopy investigation in an atomic scale gap filled with liquid 4He using mechanically controllable break junction (MCBJ) technique. In order to assure the filling of liquid 4He into the gap, we construct a cryostat with an inner chamber for the tunneling spectroscopy inside the vacuum jacket of the liquid 4He bath. MCBJ apparatus is installed in the inner chamber with a flexible bellows. After filling inner chamber with liquid 4He below 4.2 K, Au electrical electrodes were stretched by the mechanical force generated by a piezo device. We observed the increase of the tunnel conductance through liquid 4He compared to that in the vacuum environment.