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Materials with Novel Electronic Properties
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Prof. Dirk van der Marel
Unige
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Prof. Dirk van der Marel (Project leader - Project 2)
Groupe van der Marel
Team spring 2004
Ilvdm
SmLa0.8Sr0.2CuO4 has an alternation of SmO and LaO tunneling barriers between the CuO2 planes along the c-direction. In addition to the c-axis Josephson plasmon, which has been observed in almost all cuprate materials, two other collective modes appear in the superconducting state. These correspond to the excitons in the superconducting state, which were predicted in 1966 by A.J. Leggett. SmLa1-xSrxCuO4 is the first superconductor in which this type of excitons has been observed.
Fundamental excitations of strongly correlated matter

The interest of the group is to explore materials with strongly correlated electrons, and to contribute to the understanding of their properties. We use spectroscopic tools, in particular optical techniques, to probe the excitations from the ground state.

Examples are the investigation and subsequent falsification of the inter-layer tunneling model of high Tc superconductivity, the study of the partial f-sum rule related to the kinetic energy of the valence electrons, the study of quantum critical behaviour, and the prediction and detection of a variety of novel collective modes.

Fourier transform infrared spectroscopy, infrared ellipsometry and ellipsometry in the visible domain are used. These spectrometers are equipped with cryostats of our own design, which is radically different from commercially avaible optical tail designs, and which allows a precise, stable and reproducible positioning of our samples in the temperature range from 4 to 400 Kelvin in a vacuum of 10-10 Torr. In addition user facilities in Trieste, at the Paul Scherrer Institute and in Grenoble are used to study the optical absorption in the X-ray region and to perform experiments under intense magnetic field conditions.

References:
D. Dulic et al., Phys. Rev. Lett. 86, 4144 (2001).
H. J. A. Molegraaf et al., Science 295, 2239 (2002).

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