C. Gignoux

Resistivity, hall effect and thermopower in AIPdMn and AlCuFe quasicrystals

The long range ordered quasicrystals present anomalous electronic properties for metallic alloys. We present here for the first time a correlation between the temperature dependences of resistivity (p), Hall effect (RH) and thermoelectric power (S), in high structural, quality AlPdMn and AlCuFe quasicrystalline phases for various compositions. Strong composition effects are emphasized, for the high p values and the strong temperature dependences of the transport properties, as well as for sign reversals of both RH(T) and S(T). This is an indication for band structure effects in these phases. A simple two band model well accounts for these behaviours.

Pseudogap in quasicrystals probed by tunneling spectroscopy

We present tunneling spectroscopy measurements at 4 K on three quasicrystalline phases i-AlPdMn, i-AlCuFe and i-AlPdRe. In the spectroscopic curves, dI/dU, we observe a structure centered about zero bias voltage and with a square root voltage dependence from 300 mV down to at least 5 mV. This structure can be interpreted as the preopening of a correlation gap in the electronic density of states (DOS), which is consistent with the proximity to a metal–insulator transition in the three phases.

Low temperature transport properties in high resistivity (i)-AlPdRe

Abstract The transport properties of icosahedral Al 70.5 Pd 21 Re 8.5 have been measured. Samples were prepared either by arc melting or by melt-spinning with subsequent annealing in both cases. Measurements of the resistivity were performed between 40 mK and 300 K and of the magnetoresistance up to 12 T from 0.2 K to 4 K. The resistivity was found to become constant at different temperatures between 0.2 and 2 K, but both the temperature dependence of the resistivity and the magnetoresistance differ at low temperatures for the two kinds of samples. The differences between the samples are briefly discussed. Our results indicate that the conductivity in AlPdRe remains finite at low temperatures in the present samples, and a metal–insulator transition cannot thus be confirmed from these measurements.

Transition from weak to strong electronic localization in icosahedral AlPdRe

Abstract In this paper we investigate when the transition from weak to strong localization takes place in icosahedral AlPdRe. This was made by determining an upper limit of the residual resistance ratio, RRR = ϱ 4.2 K /ϱ 295 K , where theories of quantum interference effects (QIE) can account for the magnetoresistance in these materials. It was found that QIE can describe the magnetoresistance in samples with RRR up to about 10. For samples with higher RRR several observations strongly suggest that other transport mechanisms have to be considered.

Transition to a quasi-insulating state in quasi-crystalline AlPdRe

Abstract We present results about electronic properties of quasi-crystalline AlPdRe samples, assumed to be on each side of the metal–insulator transition. The structural quality and the chemical composition are investigated by X-ray diffraction, scanning electron microscopy and microprobe analysis. Conductivity is reported. The density of states (DOS) at the Fermi level is probed by specific heat and diamagnetic susceptibility measurements, and the energy dependence around the Fermi level by scanning tunneling spectroscopy. The DOS at the Fermi level and the preopening of a correlation gap confirm the proximity to the metal–insulator transition, as indicated by the conductivity. The transition towards an insulating state could be related to local compositional fluctuations.

Magnetoresistance in the region of the possible metal–insulator transition in icosahedral AlPdRe

The magnetoresistance, Δρ(B,T)/ρ(T), has been measured between 200 mK and 20 K, in magnetic fields up to 12 T for icosahedral AlPdRe quasicrystals of nominal composition Al70.5Pd21.5Re8. Samples of varying resistivities and residual resistance ratios, R [=ρ(4 K)/ρ(295 K)], were studied. An analysis of Δρ(B,T)/ρ(T) in terms of quantum interference effects (QIE) was made, taking into account the possibility of QIE contributions to Δρ(T) up to room temperature. The results show that the regime of diffusive metallic conduction in i-AlPdRe extends up to R in the range of 20, corresponding approximately to ρ(4 K) up to 105 μΩ cm, beyond which a description of Δρ(B,T)/ρ(T) in terms of QIE breaks down.

Tunneling spectroscopy in quasicrystals

We present tunneling spectroscopy measurements for icosahedral i-AlPdRe, i-AlCuFe and approximant α-AlMnSi phases. We show that for both oxidized and bare surfaces the density of states (DOS) close to the Fermi level exhibits specific features for quasicrystals and approximants as compared with the crystalline non approximant ω-AlCuFe phase. The Fermi energy lies in the middle of a narrow pseudo-gap of about 50 meV width. For higher energies, the DOS varies as the square root of energy, which is attributed to electron-electron interaction. The overall DOS differs from ab initio calculations and the possible roles of electron scattering and non homogeneous electronic structure close to the surface are discussed.

Breakdown of weak localization in icosahedral AlPdRe

The magnetoresistance of seven icosahedral AlPdRe samples with residual resistivity ratios (RRR) between 2 and 45 has been measured in the temperature range 0.23 K to 4.2 K in magnetic fields up to 12 T. The results indicate that weak localization breaks down when RRR exceeds values in the range 5 to 10.