Speaker: Serguei Brazovskii, Orsay, France
Date & Time: May 7, 2007 - 1:30pm
Location: Serin Physics 385
New Observations of Solitons in Quasi 1D Conductors
Physics and Astronomy
Serguei Brazovskii, Orsay, France
1:30pm, Serin Physics 385
We shall review recent progress in experiments and theory, elucidating the role of self-localized states in electronic systems with a symmetry breaking: orderings of charge and/or spins, or the superconductivity. Flexibility of these spontaneously formed states facilitates their local modifications, to which the ground state degeneracy gives a character of topological configurations – from macroscopic stripes as solitonic lattices to microscopic solitons as anomalous quasi-particles. These states accumulate electrons or holes embedded by doping, tunnelling, photoemission, optics, junctions. The effect is well established theoretically and experimentally in quasi-1D systems, where solitons emerge as elementary excitations, and instantons appear as transient processes for conversion of electrons, originating the pseudogap.
Recent interest to solitons in electronic processes rises from a discovery of the ferroelectric charge ordering in organic conductors1 and from nano-scale tunneling experiments2 in Charge Density Wave (CDW) materials. The charge ordering allows to observe several types of solitons in conductivity, and solitons' bound pairs in optics. The observed internal tunneling2a in CDWs goes through the channel of “amplitude solitons”, which correspond to the long sought quasi-particle - the spinon. The same experiment gives an access to the reversible reconstruction of the junction via spontaneous creation of a special lattice of embedded 2π solitons - a grid of dislocations 2b. Its formation shows up through the staircase structure of the subgap tunneling spectrum. Most of tunneling takes place in the cores of the solitonic grid. The resolved tunneling in the normally forbidden subgap region recovers collective quantum processes like coherent phase slips - 2π instantons 3.
On this solid basis we attempt to extend the theory of solitons in quasi-1D systems to arrive at a picture of combined topological excitations in general strongly correlated systems: from nearly antiferromagnetic oxides to high gap superconductors.
1 P.Monceau, F.Ya. Nad, S.Brazovskii, Phys. Rev. Lett., 86, 4080 (2001).
2 Yu.I. Latyshev, P. Monceau, S. Brazovski, et al, a : Phys. Rev. Lett., 95, 266402 (2005) ; b: Phys. Rev. Lett., 96, 116402 (2006).
3 S. I. Matveenko and S. Brazovskii, Phys. Rev. B 72, 085120 (2005), and refs therein.