Department of complex matter

Theory of complex systems

The discoveries of novel functional dynamics in new complex materials requires fundamentally new theroetical approach for reaching an understanding of the underlying physics. The dynamics of charged complex systems with correlated electrons, particularly high-Tc superconductors is investigated using a variety of phenomelogical and numerical methods.

Inhomogeneous phases my appear as a result of competition of short-range and long-range forces as well as a result of external perturbation like magnetic field.
In the first case mesoscopic phase separation appears as a consequence of the firs order phase transition and stabilized by the long range Coulomb forces. One example of this phase separation is ordering of Jahn-Teller polarons in oxides with doping (1). Another example of inhomogeneous state is the vortex lattice caused by external magnetic field. Combination of vortices and antivortices in the mesoscopic superconducting sample could be caused by the sample geometry (2). Another example of inhomogeneous phase id the vortex matter in charged Bose liquid (3). Vortex core is charged and superfluid density is larger then 1 outside of the vortex core to preserve global charge neutrality.

(1) Charged particles on a 2D plane subject to anisotropic Jahn-Teller interaction. MERTELJ T., KABANOV V.V., MIHAILOVIĆ D., PRL, 2005.

(2) Vortex-antivortex configurations and its stability in a mesoscopic superconducting square. MERTELJ T., KABANOV V.V., Phys.rev. B, 2003, 67, 135271.

(3) Vortex matter in the charged Bose liquid at absolute zero. KABANOV V.V., ALEXANDROV A.S. (to be published).

HTS theory of polaron ordering in copper oxide – superconductors

An intrinsic inhomogeneous phase in copper oxides appears naturally as a result of doping. Anisotropic lattice attractions and long-range Coulomb repulsion lead to the clustering of polarons and the formation of different patterns.

CLICK PICTURE FOR ANIMATION

Without the Coulomb interaction, global phase separation occurs when the temperature is lowered.

 

 

 

When the Coulomb interaction is present, microscopic phase separation is observed when the temperature is lowered.

 

 

 

Mesoscopic scale research

Another example of intrinsically inhomogeneous phases is magnetic field penetration in small superconducting sample. Combinations of vortices in anti-vortices are naturally created by the competition of symmetry induced by the external magnetic field and sample-geomerty symmetry.

 

 

 

 

Dynamics of superconductors and related systems

Nonequilibrium superconductivity is one of the most interesting subjects of contemporary solid state physics which covers a large variety of time scales from non-equilibrium vortex motion to recombination of hot quasiparticles. Our investigations are motivated by pump-probe experiments and related to the dynamics of quasiparticles and phonons.

 

Theory of complex system

Theory of complex systems