Fermi surface determination from wavevector quantization in LaSrCuO films

We have observed the wavevector quantization in LaSrCuO films thinner than 12 unit cells grown on SrTiO3 substrates. Low energy dispersions were determined in situ for different photon energies by angle resolved photoemission spectroscopy. From the wavevector quantization, we extract three dimensional dispersions within a tight-binding model and obtain the Fermi surface topology, without resorting to the nearly free-electron approximation. Such method can be extended to similar confined electron nanostructures.

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Claudia Cancellieri, Ping-Hui Lin, Davor Pavuna
2008
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https://infoscience.epfl.ch/record/161130?ln=fr

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Role of a higher-dimensional interaction in stabilizing charge density waves in quasi-one-dimensional NbSe3 revealed by angle-resolved photoemission spectroscopy

Helmuth Berger, Christophe Berthod

We revisit charge density wave (CDW) behavior in the archetypal quasi-one-dimensional (quasi-1D) material NbSe3 by high-resolution angle-resolved photoemission spectroscopy measurements utilizing a microfocused laser with a photon energy of 6.3 eV. We present a detailed view of the electronic structure of this complex multiband system and unambiguously resolve CDW gaps at the Fermi level (E-F). By employing a tight-binding model, we argue that these gaps are the result of interband coupling between electronic states that reside predominantly on distinct 1D chains within the material. Two such localized states are found to couple to an electronic state that extends across multiple 1D chains, highlighting the importance of a higher-dimensional interaction in stabilizing the CDW ordering in this material. In addition, the temperature evolution of intrachain gaps caused by the CDW periodicities far below E-F deviate from the behavior expected for a Peierls-type mechanism driven by nesting; the upper and lower bands of the renormalized CDW dispersions maintain a fixed peak-to-peak distance while the gaps are gradually removed at higher temperatures. This points toward a gradual loss of long-range phase coherence as the dominant effect in reducing the CDW order parameter, which may correspond to the loss of coherence between the coupled chains. Furthermore, one of the gaps is observed above the bulk and surface CDW transition temperatures, implying the persistence of short-range incoherent CDW order. The influence of such higher-dimensional interactions likely plays an important role in a range of low-dimensional systems.

2020

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Quantum interference effects of out-of-plane confinement on two-dimensional electron systems in oxides

Ji Dai, Emmanouil Frantzeskakis

It was recently discovered that a conductive, metallic state is formed on the surface of some insulating oxides. First observed on SrTiO3 (001), it was then found in other compounds as diverse as anatase TiO2, KTaO3, BaTiO3, ZnO, and also on different surfaces of SrTiO3 (or other oxides) with different symmetries. The spatial extension of the wave function of this electronic state is of only a few atomic layers. Experiments indicate its existence is related to the presence of oxygen vacancies induced at or near the surface of the oxide. We present a simplified model aimed at describing the effect of its small spatial extension on measurements of its threedimensional (3D) electronic structure by angular resolved photoemission spectroscopy. For the sake of clarity, we base our discussion on a simple tight-binding scheme plus a confining potential that is assumed to be induced by the oxygen vacancies. Our model parameters are, nevertheless, obtained from density functional calculations. With this methodology, we can explain, from a very simple concept of selective interference, the "wobbling," i.e., the photoemission intensity modulation and/or apparent dispersion of the Fermi surface and spectra along the out-of-plane (k(z)) direction, and the "mixed 2D/3D" characteristics observed in some experiments. We conclude that the critical model parameters for such an effect are the relative strength of the electronic hopping of each band and the height/width aspect ratio of the surface confining potential. By considering recent photoemission measurements, in light of our findings, we can get relevant information on the electronic wave functions and the nature of the confining potential.

2020

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Direct photoemission spectroscopy and electronic properties of in situ grown, strained high-T-c and related oxide films

Mike Abrecht, Dominique Cloëtta, Giorgio Margaritondo, Davor Pavuna, Dusan Vobornik

We have optimized laser ablation thin film deposition and transfer procedures within synchrotron vault, specifically to perform angle-integrated and angle-resolved photoemission spectroscopy (ARPES) on high-T-c and related films without cleaving the samples. However, the chain-containing phases like YBCO-123 easily loose surface oxygen and do not exhibit stable Fermi edge, hence are not suitable for ARPES studies. Direct in situ ARPES studies on strained LSCO-214 films show striking strain effects on the electronic structure. The Fermi surface (FS) of LSCO evolves with doping, yet changes even more significantly with strain. The strain changes the FS topology from hole-like to electron-like, and causes band dispersion along k(x) and the Fermi level crossing before the Brillouin zone boundary, in sharp contrast to the 'usual' flat band remaining approximate to 30 meV below E-F measured on unstrained samples. The associated reduction of the density of states does not diminish the superconductivity; T-c is enhanced in all our strained samples. Implications for the evolving high-T-c theory and studies of nano-engineered film heterostructures are briefly discussed. (C) 2004 Elsevier Ltd. All rights reserved.

2004

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La spectroscopie photoélectronique (photoelectron spectroscopy, PES) ou spectroscopie de photoémission (photoemission spectroscopy) est un ensemble de méthodes spectroscopiques basées sur la détect

Surface de Fermi

En mécanique quantique et en physique de la matière condensée, la surface de Fermi est une limite abstraite utile pour prédire les caractéristiques électriques, magnétiques, etc. de matériaux, en pa