23 research outputs found
Interaction created effective flat bands in conducting polymers
For a general class of conducting polymers with arbitrary large unit cell and
different on-site Coulomb repulsion values on different type of sites, I
demonstrate in exact terms the emergence possibility of an upper, interaction
created "effective" flat band. This last appears as a consequence of a kinetic
energy quench accompanied by a strong interaction energy decrease, and leads to
a non-saturated ferromagnetic state. This ordered state clearly differs from
the known flat-band ferromagnetism. This is because it emerges in a system
without bare flat bands, requires inhomogeneous on-site Coulomb repulsions
values, and possesses non-zero lower interaction limits at the emergence of the
ordered phase.Comment: 22 pages, 3 figure
T>0 properties of the infinitely repulsive Hubbard model for arbitrary number of holes
Based on representations of the symmetric group , explicit and exact
Schr\"odinger equation is derived for Hubbard model in any
dimensions with arbitrary number of holes, which clearly shows that during the
movement of holes the spin background of electrons plays an important role.
Starting from it, at T=0 we have analyzed the behaviour of the system depending
on the dimensionality and number of holes. Based on the presented formalism
thermodynamic quantities have also been expressed using a loop summation
technique in which the partition function is given in terms of characters of
. In case of the studied finite systems, the loop summation have been
taken into account exactly up to the 14-th order in reciprocal temperature and
the results were corrected in higher order based on Monte Carlo simulations.
The obtained results suggest that the presented formalism increase the
efficiency of the Monte Carlo simulations as well, because the spin part
contribution of the background is automatically taken into account by the
characters of .Comment: 26 pages, 1 embedded ps figure; Phil. Mag. B (in press
Exact ground-state for the periodic Anderson model in D=2 dimensions at finite value of the interaction and absence of the direct hopping in the correlated f-band
We report for the first time exact ground-states deduced for the D=2
dimensional generic periodic Anderson model at finite , the Hamiltonian of
the model not containing direct hopping terms for -electrons .
The deduced itinerant phase presents non-Fermi liquid properties in the normal
phase, emerges for real hybridization matrix elements, and not requires
anisotropic unit cell. In order to deduce these results, the plaquette operator
procedure has been generalised to a block operator technique which uses blocks
higher than an unit cell and contains -operator contributions acting only on
a single central site of the block.Comment: 21 pages, 3 figure
Pentagon chain with spin orbit interactions: exact many-body ground states in the interacting case
Based on a positive semidefinite operator technique, exact ground states are
deduced for the non-integrable conducting polymers possessing pentagon type of
unit cell. The study is done in the presence of many-body spin-orbit
interaction (SOI), local and nearest neighbor Coulomb repulsion (NNCR) and
presence of external electric and magnetic fields, such that the
effects of on both orbital and spin degrees of freedom is considered. The
SOI, NNCR, and presented external field configurations presence in exact
conducting polymer ground states is a novelty, so the development of the
technique for the treatment possibility of such strongly correlated cases is
presented in details. The deduced ground states show a broad spectrum of
physical characteristics ranging from charge density waves, metal-insulator
transitions, to interesting external field driven effects as e.g. modification
possibility of a static charge distribution by a static external magnetic
field.Comment: 47 pages, 2 figure
Route to ferromagnetism in organic polymers
Employing a rigorous theoretical method for the construction of exact
many-electron ground states we prove that interactions can be employed to tune
a bare dispersive band structure such that it develops a flat band. Thereby we
show that pentagon chain polymers with electron densities above half filling
may be designed to become ferromagnetic or half metallic.Comment: 11 pages, 3 figure