Effects of disorder on the physical properties of organic superconductors

• Antragsteller: Professor Dr. Reinhold Oppermann
• Fachliche Zuordnung: Theoretische Physik der kondensierten Materie
• Förderung: Förderung von 2011 bis 2015
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 195285870

The current research project focuses on effects of non-magnetic randomness on the critical temperature and on different thermodynamic properties of organic superconductors. Our aim in this project is to develop a consistent theory for the organic superconductors starting from their structural and energetic peculiarities, which may allow us to explain main unusual experimental measurements. The organic superconductors are modelled as a quasi-1D or a quasi-2D system, consisting of parallel and regularly placed wires or layers with Josephson coupling between nearest-neighboring units in the superconducting (SC) phase. Anion substitutions or chaotic distribution of the anions, which are peculiar to the organic metals, can be characterized as a non-magnetic randomness in the Josephson coupling energy. Furthermore point-like defects in the SC layers or chains will be taken into account too. Disorder driven superconductor-normal metal phase transitions due to the competition of non-magnetic randomness and phase fluctuations in quasi-2D organic superconductors will be particularly studied in the project.Some experimental measurements can be explained provided that an unconventional pairing with nodal structure is realized. In order to understand such kind of experimental results we consider two type pairing, namely intra-layer (intra-chain) and inter-layer (inter-chain) pairings, which constitute wave vector-dependent (unconventional) order parameter. The total order parameter should be sensitive to the disorder. Although the inter-layer or inter-chain pairing stabilizes the transverse rigidity of the SC phase against the phase fluctuations, effects of disorder existing between the layers (or the chains) as well as in the layers (or the chains) on the transverse rigidity are not trivial and demand detailed investigations.Influence of the non-magnetic randomness on the off-diagonal-long range order (ODLRO) can be studied by taking two type randomness in the Hamiltonian, namely point-like impurities, distributed in the planes or in the chains, and the randomness in the inter-layer or inter-chain hopping integral.The pseudogap phenomenon is one of the basic and complex problems, which has been observed not only in the organic superconductors but also in the high-Tc cuprates, heavy-fermionic superconductors and in the recently discovered Fe-contained pnictide superconductors. A glassy phase in the disordered superconductors may cause a pseudogap state in the system. Our aim in the project is to map the Hamiltonian written for the organic superconductors onto a fermionic spin-glass Hamiltonian and investigate the glass phase in the dirty SC state.

• DFG-Verfahren: Sachbeihilfen