Berlin 2005 – wissenschaftliches Programm

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SYQL: Measurements at the Quantum Limit

SYQL 1: SYQL

SYQL 1.2: Hauptvortrag

Freitag, 4. März 2005, 11:00–11:20, TU HE101

Optical Characterization of Single Two-Level Systems in Disordered Solids — •Lothar Kador and Markus Bauer — University of Bayreuth, Institute of Physics and Bayreuther Institut für Makromolekülforschung (BIMF), 95440 Bayreuth, Germany

The properties of disordered solids at low temperatures are well described by the phenomenological tunneling model [1,2] which postulates the presence of localized low-energy excitations (two-level systems, TLSs). These are attributed to groups of atoms which can change between two nearly degenerate states. In the optical spectra of single dopant molecules [3], interactions with nearby TLSs manifest themselves as spectral jumps and/or splitting of the molecular lines.

Single-molecule spectroscopy was used to characterize single TLSs in the amorphous polymer poly(isobutylene) and the Shpol’skiĭ system n-hexadecane. Some of the tunneling systems were found to be affected by temperature changes or electric fields, which allowed us to determine all their physical parameters. The results of most of our experiments are in very good agreement with the quantum-mechanical tunneling model. Only in a few cases, clear deviations were observed, e. g., interactions between two TLSs.

[1] P. W. Anderson, B. I. Halperin, and C. M. Varma, Phil. Mag. 25, 1 (1972).

[2] W. A. Phillips, J. Low Temp. Phys. 7, 351 (1972).

[3] Th. Basché, W. E. Moerner, M. Orrit, and U. P. Wild (eds.), Single-Molecule Optical Detection, Imaging, and Spectroscopy (VCH, Weinheim, 1996).