Ordering phenomena in quasi-one-dimensional organic conductors |
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Authors: | Martin Dressel |
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Institution: | 1.1. Physikalisches Institut,Universit?t Stuttgart,Stuttgart,Germany |
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Abstract: | Low-dimensional organic conductors could establish themselves as model systems for the investigation of the physics in reduced
dimensions. In the metallic state of a one-dimensional solid, Fermi liquid theory breaks down and spin and charge degrees
of freedom become separated. But the metallic phase is not stable in one dimension: as the temperature is reduced, the electronic
charge and spin tend to arrange themselves in an ordered fashion due to strong correlations. The competition of the different
interactions is responsible for which broken-symmetry ground state is eventually realized in a specific compound and which
drives the system toward an insulating state. Here, we review the various ordering phenomena and how they can be identified
by optic and magnetic measurements. While the final results might look very similar in the case of a charge density wave and
a charge-ordered metal, for instance, the physical cause is completely different. When density waves form, a gap opens in
the density of states at the Fermi energy due to nesting of the one-dimension Fermi surface sheets. When a one-dimensional
metal becomes a charge-ordered Mott insulator, on the other hand, the short-range Coulomb repulsion localizes the charge on
the lattice sites and even causes certain charge patterns. We try to point out the similarities and conceptional differences
of these phenomena and give an example for each of them. Particular emphasis will be put on collective phenomena that are
inherently present as soon as ordering breaks the symmetry of the system. |
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Keywords: | One-dimensional solids Organic conductors Density wave states Charge order Spin order Collective excitations |
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