D. Cloetta

Experimental electronic structure and Fermi-surface instability of the correlated 3d sulphide BaVS3: High-resolution angle-resolved photoemission spectroscopy

The correlated

Photoemission, correlation and superconductivity: New avenues

3d

Electronic properties of high temperature superconducting thin films grown by pulsed laser deposition

sulphide BaVS_3 exhibits an interesting coexistence of one-dimensional and three-dimensional properties. Our experiments determine the electronic band structure and shed new light on this puzzle. High-resolution angle-resolved photoemission measurements in a 4-eV wide range below the Fermi energy level uncover and investigate the coexistence of a_{; ; ; ; ; 1g}; ; ; ; ; wide-band and e_g narrow-band d-electrons that lead to the complicated electronic properties of this material. We explore the effects of strong correlations and the Fermi surface instability associated with the metal-insulator transition.The correlated 3d sulphide BaVS_3 is a most interesting compound because of the apparent coexistence of one-dimensional and three-dimensional properties. Our experiments explain this puzzle and shed new light on its electronic structure. High-resolution angle-resolved photoemission measurements in a 4eV wide range below the Fermi level explored the coexistence of weakly correlated a_1g wide-band and strongly correlated e_g narrow-band d-electrons that is responsible for the complicated behavior of this material. The most relevant result is the evidence for a_1g--e_g inter-band nesting condition.

Experimental electronic structure and Fermi-surface instability of the correlated 3d sulphide BaVS_3

We review some of the problems still affecting photoemission as a probe of high-temperature superconductivity, as well as important recent results concerning their solution. We show, in particular, some of the first important results on thin epitaxial films grown by laser ablation, which break the monopoly of cleaved BCSCO in this type of experiments. Such results, obtained on thin LSCO, may have general implications on the theory of high-temperature superconductivity.

Systematic studies of La 2-x Sr x CuO 4 in direct synchrotron light: on the role of compressive against tensile strain

We use a pulsed laser deposition (PLD) setup to grow ultra-thin films of high temperature superconductors (HTSC) and transfer them in-situ into a photoemission chamber. Photoemission measurements on such films allow us to study non-cleavable materials, but can also give insights into aspects never measured before, like the influence of strain on the low energy electronic structure. Systematic studies of many different materials grown as films showed that Bi2Sr2CaCu2O8+x, Bi2Sr2Cu1O6+x, Bi2Sr2Ca2Cu3O10+x and La2-xSrxCuO4 films exhibit a conductor-like Fermi edge, but materials containing chains (such as YBa2Cu3O7-x) are prone to very rapid surface degradation, possibly related to critical oxygen loss at the surface. Among HTSC materials, La2-xSrxCuO4 is extremely interesting because of its rather simple structure and the fact that its critical temperature Tc can be enhanced by epitaxial strain. Here we present our first high resolution angular resolved photoemission spectroscopy (ARPES) results on 8 unit-cell thin La2-xSrxCuO4 films on SrLaAlO4 [001] substrates. Due to the lattice mismatch, such films are compressed in the copper oxygen planes and expanded in the c-axis direction. Results show a surprisingly modified Fermi surface compared to the one of non-strained samples.

Experimental Electronic Structure and Interband Nesting in BaVS_3

The correlated

Direct Arpes and TC Enhancement in Compressively Strained LSCO-214 Films

3d

Strain and high temperature superconductivity: Unexpected results from direct electronic structure measurements in thin films

sulphide BaVS_3 exhibits an interesting coexistence of one-dimensional and three-dimensional properties. Our experiments determine the electronic band structure and shed new light on this puzzle. High-resolution angle-resolved photoemission measurements in a 4-eV wide range below the Fermi energy level uncover and investigate the coexistence of a_{; ; ; ; ; 1g}; ; ; ; ; wide-band and e_g narrow-band d-electrons that lead to the complicated electronic properties of this material. We explore the effects of strong correlations and the Fermi surface instability associated with the metal-insulator transition.The correlated 3d sulphide BaVS_3 is a most interesting compound because of the apparent coexistence of one-dimensional and three-dimensional properties. Our experiments explain this puzzle and shed new light on its electronic structure. High-resolution angle-resolved photoemission measurements in a 4eV wide range below the Fermi level explored the coexistence of weakly correlated a_1g wide-band and strongly correlated e_g narrow-band d-electrons that is responsible for the complicated behavior of this material. The most relevant result is the evidence for a_1g--e_g inter-band nesting condition.

Three-dimensional dispersion induced by extreme tensile strain in La_(2−x)Sr_xCuO_4 films

We systematically study the structural and electronic properties of very thin cuprate films. Our direct angle resolved photoemission spectroscopy (ARPES) measurements on the low binding energy electronic structure of La2-xSrxCuO4 (LSCO) films confirmed that the Fermi surface evolves with doping, but changes even more significantly with growth-induced compressive strain. For a given doping, the in-plane compressive strain enhances TCs and modifies the 2-dimensional hole-like Fermi surface as to appear more electron-like. In contrast, the in-plane tensile strain reduces TC (suppressing superconductivity for huge tensile strain) and shows 3-dimensional ARPES dispersion with a corresponding 3-dimensional Fermi surface. To account for these striking changes in electronic structure and superconductivity, the out-of-plane states should be taken into account, as well as some subtle changes in the associated atomic distances.

Direct angle resolved photoemission spectroscopy and superconductivity of strained high-T c films

The correlated