Completed projects

The transition metal oxide Li0.9Mo6O17, the so-called "violet bronze", shows properties of a one-dimensional correlated electron gas, which is investigated by us with low-temperature scanning tunneling spectroscopy. The violet bronze has quasi-one-dimensional properties in volume due to its crystal structure and it has been suggested in the literature that the electrons could form a Luttinger liquid. This special electronic property was predicted theoretically in the 1960s, but has so far only been demonstrated experimentally in a handful of materials. With our measurements, in cooperation with Rongying Jin and Ward Plummer (Luisiana State University), J. He and David Mandrus (Oak Ridge National Laboratory) and M.A. Cazalilla (Donostia International Physics Center), we were able to confirm the power law in the density of states expected for a Luttinger liquid and rule out a zero-bias anomaly caused by disorder.

Hager, J; Matzdorf, R; He, J; Jin, R; Mandrus, D; Cazalilla, MA; Plummer, EW, Non-fermi-liquid behavior in quasi-one-dimensional Li0.9Mo6O17, Phys. Rev. Lett. 95, 186402, 2005

These two ruthenates are of great interest as the former exhibits unconventional superconductivity with p-wave symmetry and the latter has a magnetically driven quantum critical endpoint at about 8 Tesla. The particular interest in this class of materials can be seen from the fact that around 1400 papers have already been published on it since its discovery in 1994. The ruthenates show a zero-bias anomaly (ZBA) in dI/dV spectra, the origin of which has not yet been clarified. There have been only a few references to this observation in the literature and no detailed investigation of the behavior of the anomaly at the Fermi energy. In a collaboration with Jiandi Jhang (Luisiana State University) and Zhiqiang Mao (Tulane University), zero bias anomalies in Sr2RuO4, Sr3Ru2O7 and Sr4Ru3O10 were detected and studied in detail. In principle, ZBAs are caused by a reduction in the ability of the electron gas to shield the injected tunnel electron. On the one hand, this can be caused by reduced dimensionality, as observed in the Luttinger liquid, for example. On the other hand, disorder can lead to a ZBA. Since the material under investigation is a quasi-two-dimensional substance, we have used various theories of disorder in two-dimensional systems to describe the ZBA, but have not yet found any convincing agreement with one theory. Currently, measurements of the temperature dependence of the ZBA are being carried out in order to clarify the cause of the ZBA.

Ismail; Zhang, JD; Matzdorf, R; Kimura, T; Tokura, Y; Plummer, EW, Surface lattice dynamics of layered transition metal oxides: Sr2RuO4 and La0.5Sr1.5MnO4, PHYSICAL REVIEW B, 67, 035407, 2003

R. Matzdorf, Ismail, T. Kimura, Y. Tokura and E. W. Plummer, Surface structure analysis of the layered perovskite Sr2RuO4 by LEED I(V), Phys. Rev. B 65 (2002) 085404

R. Matzdorf, Z. Fang, Ismail, J. Zhang, T. Kimura, Y. Tokura, K. Terakura and E. W. Plummer, Ferromagnetism stabilized by lattice distortion at the surface of the p-wave superconductor Sr2RuO4, Science 289 (2000) 746

An unoccupied surface state was identified in this system, which was extremely easy to study in the spectra. The lifetime of this state could be determined from the width of the increase in the density of states at the lower band edge. In addition, the adsorbate system was prepared in such a way that self-organization produces quasi-one-dimensional stripes that are only a few atoms wide and can be over 100 nm long with an atomically constant width. The lifetime of the state was measured on these stripes as a function of the stripe width. A comparable state was also sought in the adsorbate system Ag(110)p(n'1)O (n=2,3,..,7), but was not found with STS.

Corriol, C; Hager, J; Matzdorf, R; Arnau, A, Surface electronic structure of O(2 x 1)/Cu(110): Role of the surface state at the zone boundary -point in STS, Surface Science, 600, 4310, 2006

Hager, J; Matzdorf, R, Surface state lifetime in quasi-one-dimensional oxygen stripes on Cu(110), Surface Science, 600, 2581, 2006

The adsorbate system with the structure Cu(100)-c(2x2)N forms small squares with a typical size of (5x5)nm² through self-organization. An unoccupied electron band was spectroscoped in the adsorbate-covered squares and the standing electron waves were mapped using dI/dV maps (see figure). LEED-IV measurements were also performed on this adsorbate system to determine the exact structure. In a collaboration with Dr. Jürgen Braun and Dr. A. Postnikov, band structure calculations and photoemission calculations within the framework of the one-step model were carried out using the structural data obtained.

Michalke, T; Matzdorf, R; Braun, J; Postnikov, A, The two-dimensional electronic structure of the adsorbate system N/Cu(100): Photoelectron spectroscopy and one-step model calculations. Phys. Rev. B 77, 165425, 2008

In collaboration with Prof. Dr. J. Burgdörfer and F. Libisch from the Institute of Theoretical Physics at TU Wien, I have started a project in which ultrashort quantum phenomena are investigated using a classical analog with sound waves. The propagation of attosecond pulses through a resonator leads to the interaction of different states of the resonator, whereby peaks in the transmission with Fano profile are observed. In this project, the propagation of the pulses is theoretically modeled by the Vienna group and simulated by us with sound pulses in an acoustic resonator. The attosecond time scale, which is only accessible with extremely high experimental effort, can be transformed to the easily accessible millisecond time scale by these experiments. In this way, the theoretical methods can be tested on comparatively easy-to-perform experiments in order to use them later for the description of phenomena on the attosecond time scale.