Experimentelle Physik IV

    One-Dimensional Crystals with Precursor Fluctuations

    Quasi-one-dimensional systems are also realized in certain crystals, which by their nature form highly directional bonds. Due to strong electron-phonon coupling, CDW phase transitions do occur in these crystals as a function of temperature. In particular, the resulting superstructures can be incommensurable with the lattice and especially long-ranged. Here we study the underlying physics of such instabilities. As a prominent signature, precursor instabilities of the phase transition can occur, known as fluctuations. This is reflected in pseudo gaps in the electronic band structure. Our investigations by means of photoelectron spectroscopy on one-dimensional systems could prove for the first time in k-resolved manner that a pseudo gap exists far above the actual critical temperature.