CM Seminar at ICTP Stasi Seminar Room Thursday 18 August at 11.30 - O. DERZHKO

[Condensed_Matter_Group]

CONDENSED MATTER SEMINAR
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Thursday, 18 August 2016 -   at  11.30 a.m.
Luigi Stasi Seminar Room, first floor, Leonardo Building



Oleg DERZHKO
Institute for Condensed Matter Physics,
National Academy of Sciences of Ukraine, L'viv, Ukraine


Title: “Strongly Correlated Systems with Nearly Flat Bands”


Abstract:
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There are plenty of lattices in one, two, and three dimensions  which
support a completely dispersionless (flat) one-particle energy band.  If
the flat band happens to be the lowest-energy one,  it is possible to
construct and completely characterize  a certain manifold of many-particle
ground states  even in the presence of strong interactions.  These states
determine the low-temperature properties  of strongly correlated systems 
in a specific range of external parameters [1].
In this talk I discuss the effect of slight dispersion of a previously
strictly flat band.  I focus on the high-field low-temperature properties 
of some quantum Heisenberg antiferromagnets [2] and on the
kinetic-energy-driven ground-state ferromagnetism  in the standard Hubbard
model at low electron densities [3].  I also discuss why these findings
are useful  in searching for experimental manifestation of flat-band
effects in strongly correlated systems.

[1] O. Derzhko, J. Richter, and M. Maksymenko,  Int. J. Mod. Phys. B 29,
1530007 (2015).
[2] O. Derzhko, J. Richter, O. Krupnitska, and T. Krokhmalskii,  Phys.
Rev. B 88, 094426 (2013);  Low Temp. Phys. 40, 513 (2014);  J. Richter, O.
Krupnitska, T. Krokhmalskii, and O. Derzhko,  J. Magn. Magn. Mater. 379,
39 (2015).