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

Escudero, R.; Lasjaunias, J.C.; Calvayrac, Y.; Boudard, Michel

doi:10.1088/0953-8984/11/2/006

Cited by 71 publications

(89 citation statements)

References 54 publications

(87 reference statements)

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“…[17][18][19] At the time being, the very existence of such peaks remains controversial. [20][21][22] In any event, in order to make a meaningful comparison between experimental measurements and numerically calculated electronic structures, one should take into account possible phason, finite lifetime and temperature broadening effects. In so doing, it is observed that most finer details in the DOS are significantly smeared out and only the most conspicuous peaks remain in the vicinity of the Fermi level at room temperature.…”

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confidence: 99%

Do quasicrystals follow Wiedemann–Franz’s law?

Maciá

2002

Applied Physics Letters

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In this work we present a theoretical study on the thermal and electrical conductivities of quasicrystals. By considering a realistic model for the spectral conductivity we derive closed analytical expressions for the transport coefficients which allow us to study the temperature dependence of the Lorenz ratio L(T)ϭ e (T)/T (T) at different temperature regimes. We conclude that quasicrystals closely follow Wiedemann-Franz's law over a wide temperature range. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1488696͔ According to Wiedemann-Franz's law ͑WFL͒ in most materials thermal and electrical conductivities are mutually related, over certain temperature ranges, through the relationship e (T)/ (T)ϭL 0 T, where e (T) gives the contribution to the thermal conductivity due to the charge carriers, (T) is the electrical conductivity, T is the temperature, and L 0 ϭ(k B /e) 2 0 is the Lorenz number, where k B is the Boltzmann constant, e is the electron charge, and 0 is a constant whose value depends on the nature of the sample. Thus, for metallic systems 0 ϭ 2 /3, and we get the Sommerfeld's value L 0 ϭ2.44ϫ10 Ϫ8 W ⍀K Ϫ2 , while for semiconductors described by Maxwell-Boltzmann statistics we have 0 Ӎ2. 1 The WFL has a broad range of validity, and usually holds for arbitrary band structures provided that the change in energy during an electron collision is small compared with k B T. Then, elastic processes dominate the transport coefficients, and the carriers motion determines both the electrical and thermal currents. 2 Quasicrystals ͑QCs͒ are well-ordered metallic alloys exhibiting a broad collection of anomalous transport properties, 3-5 resembling more semiconductor-like than metallic character. 6 Thus, a proper classification of these materials, able to account for both their peculiar electronic structure and their related transport properties, remains elusive. 7 In addition, it has been reported that Ohm's law holds in high quality icosahedral QCs, 8 hence, opening the question regarding what other fundamental laws may also be followed by these materials. From a fundamental viewpoint it seems then quite pertinent to ascertain whether one may expect the WFL to hold in the case of QCs as well. Furthermore, the study of the WFL validity range is also crucial in order to test the working hypothesis usually made when estimating the phonons contribution to the thermal conductivity, ph (T), by substracting to the experimental data, mes (T), the electronic contribution according to the expression ph ϭ mes ϪL 0 T . In fact, were the WFL not valid for QCs, several conclusions about the phonon dynamics in these materials should be substantially revised, an important question which has been scarcely considered in the literature. 9 Unfortunately, the high electrical resistivity of QCs currently prevents an accurate experimental evaluation of the Lorenz number for these materials. 10,11 The main goal of this work is then to theoretically estimate the validity of WFL for QCs, providing some physical insight aimed to spur...

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confidence: 99%

Do quasicrystals follow Wiedemann–Franz’s law?

Maciá

2002

Applied Physics Letters

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“…In a point contact junction the relevant characteristics will be related to pure Andreev reflections as Blonder et al model specifies [24]. In this work the point contacts junctions were prepared as explained by Escudero et al [18].…”

Section: Methodsmentioning

confidence: 99%

Point contact tunneling spectroscopy of the density of states in Tb–Mg–Zn quasicrystals

Escudero

Morales

2016

Journal of Non-Crystalline Solids

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According to theoretical predictions the quasicrystalline (QC) electronic density of states (DOS) must have a rich and fine spiky structure which actually has resulted elusive. The problem with its absence may be related to poor structural characteristics of the studied specimens, and/or to the non-existence of this spike characteristic. Recent calculations have shown that the fine structure indeed exists, but only for two dimensional approximants phases. The aim of the present study is to show our recent experimental studies with point contacts tunnel junction spectroscopy performed in samples of very high quality. The studies were performed in icosahedral QC alloys with composition Tb 9 Mg 35 Zn 56 . We found the presence of a pseudogap feature at the Fermi level, small as compared to the pseudogap of other icosahedral materials. This study made in different spots on the QC shows quite different spectroscopic features, where the observed DOS was a fine non-spiky structure, distinct to theoretical predictions. In some regions of the specimens the spectroscopic features could be related to Kondo characteristics due to Tb magnetic atoms acting as impurities. Additionally, we observed that the spectroscopic features vanished under magnetic field.

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“…21 Quite interestingly the electronic structure of QCs fits in this framework in a natural way since their electronic structure is characterized by two main contributions: ͑1͒ a pronounced pseudogap at the Fermi level 2,22 and ͑2͒ several narrow spectral features in the DOS near the Fermi level. 23,24 …”

Section: Samplementioning

confidence: 99%

“…1͒ agrees well with the experimental results obtained from tunneling and point contact spectroscopy measurements, where the presence of a dip feature of small width ͑20-60 meV͒, superimposed onto a broad ͑0.5-1 eV͒ asymmetric pseudogap, has been reported. 23,[31][32][33] Thus, Eq. ͑2͒ satisfactorily describes the electronic structure of these alloys in terms of a wide Lorentzian peak ͑related to the Fermi surface-Brillouin zone interaction͒ plus a narrow Lorentzian peak ͑related to sp-d hybridization effects͒.…”

Section: ͑2͒mentioning

confidence: 99%

Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys

Maciá

2009

Phys. Rev. B

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In this work we analyze the potential role of quasicrystals and related alloys in thermoelectric material research. Relatively large figure of merit values are expected for those samples exhibiting two properly located narrow features in the density of states close to the Fermi level. It is expected that optimized quasicrystals will perform better at relatively low temperatures, whereas the ZT curve of complex metallic alloys reaches its maximum at high temperatures. Among state-of-the-art quasicrystals most promising samples for thermoelectric applications are found in the AlPd͑Mn,Re͒ system. Quasicrystalline and related approximants in the ScMgCuGa and CaAuIn systems, synthesized on the basis of pseudogap tuning concepts, appear as promising candidates as well.

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

Cited by 71 publications

References 54 publications

Do quasicrystals follow Wiedemann–Franz’s law?

Do quasicrystals follow Wiedemann–Franz’s law?

Point contact tunneling spectroscopy of the density of states in Tb–Mg–Zn quasicrystals

Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys

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