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.