Pseudogap in quasicrystals probed by tunneling spectroscopy

We present tunneling spectroscopy measurements at 4 K on three quasicrystal line phases i-AlPdMn, i-AlCuFe and i-AlPdRe. In the spectroscopic curves, d I/dU, we observe a structure centered about zero bias voltage and with a sq uare root voltage dependence from 300 mV down to at least 5 mV. This struct ure can be interpreted as the preopening of a correlation gap in the electr onic density of states (DOS), which is consistent with the proximity to a m etal-insulator transition in the three phases. (C) 1999 Elsevier Science B. V. All rights reserved.