Hole-polaron formation in the two-dimensional Holstein {ital t}-{ital J} model: A variational Lanczos study
- Physikalisches Institut, Universitaet Bayreuth, D-95440 Bayreuth (Germany)
- Research Centre of Crete, P.O. Box 1527, Heraklio 71110, Crete (Greece)
Polaronic features of dopant-induced charge carriers are manifest in recent experiments on La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4+{ital y}} and La{sub 2{minus}{ital x}}Ni{sub {ital x}}CuO{sub 4+{ital y}}. To study the formation of hole (bi)polarons in such systems exhibiting strong Coulomb interactions, the Holstein {ital t}-{ital J} model is examined by means of a variational diagonalization technqiue for a wide range of phonon frequencies and electron-phonon (EP) couplings on finite square lattices, up to 18 effective sites in size. Including static displacement field, polaron, and squeezing effects, our approach allows for the description of nearly free polarons in the weak-coupling limit as well as for adiabatic Holstein polarons and nonadiabatic Lang-Firsov polarons in the case of strong EP interactions. At low doping levels and low phonon frequencies we demonstrate that antiferromagnetic spin correlations and EP interactions reinforce each other to the effect of lowering the threshold for polaronic self-localization in a strongly distorted lattice. This is contrasted with the nonadiabatic regime, where we observe the formation of Lang-Firsov polarons with moderate polaronic mass enhancement in a nearly undistorted lattice. In the case of two doped holes, the hole binding energy is analyzed in detail and we find that hole binding is enhanced as a dynamical (static) effect of a rather weak (extremely strong) EP interaction for delocalized (self-trapped) polarons. At quarter-filling we notice, in the adiabatic regime, a sequence of transitions as the EP coupling increases from nearly free mobile polarons to a polaronic superlattice and finally to a charge-separated state. The ordering of polarons disappears at higher phonon frequencies.
- OSTI ID:
- 69473
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 51, Issue 23; Other Information: PBD: 15 Jun 1995
- Country of Publication:
- United States
- Language:
- English
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