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Organic Metals

Superconductivity and Superfluidity
Superconducting Quantum Circuits and Nanomechanics
Magnetism and Spintronics
Organic Metals

SFB 631
TRR 80
SPP 1458
SPP 1538
SPP 1601

single crystals (jpeg, 20k)From the everyday experience one normally identifies organic materials as perfect insulators. However, in the last 30 years chemists managed to synthesize a number of crystalline organic compounds which exhibit metallic and even superconducting properties.

A common feature of these organic (or synthetic) metals is a huge electronic anisotropy originating from their anisotropic crystal structures. Ratios between electrical conductivities in different directions reach values of up to 1 million! Therefore, they are often considered as quasi-two-dimensional or quasi-one-dimensional conductors. The figure shows single crystals of the organic superconductor κ-(ET)2Cu[N(CN)2]Br growing in an electro-chemical cell (left) and a fragment of the crystal structure (right).

Another remarkable feature characteristic of many organic metals is strong electron-electron and electron-phonon interactions. This renders the normal metallic state unstable against numerous spin and charge ordering phenomena, causing very rich phase diagrams.

phase diagram 1 (jpeg, 20k)
phase diagram 2 (jpeg, 14k)
Examples of phase diagrams of organic conductors: κ-(ET)2Cu[N(CN)2]Cl and α-(ET)2KHg(SCN)4

magnetotransport oscillations (jpeg, 34k)The research at the Walther-Meissner-Institut is aimed to reveal the nature of different electronic states in organic metals and mechanisms responsible for them. We study conducting and magnetic properties of these materials, applying high pressures, strong magnetic fields, and low temperatures to drive a material through various states of the phase diagram.

An important issue for understanding the nature of different electronic instabilities is a detailed characterisation of the conducting system in the metallic state. At the Walther-Meissner-Institut, properties of charge carriers are studied using high magnetic fields. Besides conventional high-field effects, like de Haas–van Alphen or Shubnikov–de Haas oscillations, a number of new magnetotransport phenomena have been discovered in organic metals, providing quantitative information on the Fermi surface, effective masses, scattering processes, and other important electronic parameters. The figure gives an overview over various kinds of magnetotransport oscillations and the derived Fermi surface cross section of α-(ET)2KHg(SCN)4.