Tunnelling and point contact spectroscopy of the density of states in quasicrystalline alloys

Point contact and tunnelling experiments performed at low temperatures were used to study the electronic behaviour of the icosahedral quasicrystalline alloys AlPdRe, AlCuFe, and AlPdMn. With samples of high quality we observe d at low temperatures a zero-bias anomaly that we related to the decrease o f the electronic density of states (DOS) due to the electron-electron inter action. This interaction tends to diminish the DOS at the Fermi level and c an be seen as the energy pseudogap of the alloy. Our experiments indicate t hat the DOS is strongly modified near EF and consists of a spiky feature in abroad pseudogap, with the width of the feature of the order of 100 meV or even larger for the AlPdRe, whereas it is as small as 20-22 meV for Al-Cu- Fe and 17-20 meV for Al-Pd-Mn. The broad pseudogap has widths larger than 4 00 meV for AlPdRe, whereas for AlCuFe it is about 80-90 meV and for AlPdMn it is of the order of 110-122 meV. The studies were performed on three samp les of the compositions Al70.5Pd21Re8.5, Al68.2Pd22.8Mn9.0, and Al63Cu25Fe1 2 The junctions were of the types alloy-Au(ln, Al) and alloy-insulator-Au(I n, Al), and were studied at different temperatures between that of liquid n itrogen and 2 K, and even to 400 mK for the AlCuFe alloy.