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Self-trapping of particles from singular pockets in weakly doped AFM Mott insulator

Self-trapping of particles from singular pockets in weakly doped AFM Mott insulator. Alvaro ROJO-BRAVO LPTMS URM 8626, Université Paris-Sud, Orsay, France. Ecrys - August, 2008. N.P. Armitage et al , (2002). Experimental motivation. Weakly electronically doped cuprate materials: ARPES.

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Self-trapping of particles from singular pockets in weakly doped AFM Mott insulator

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  1. Self-trapping of particles from singular pockets in weakly doped AFM Mott insulator Alvaro ROJO-BRAVO LPTMS URM 8626, Université Paris-Sud, Orsay, France Ecrys - August, 2008

  2. N.P. Armitage et al, (2002) Experimental motivation Weakly electronically doped cuprate materials: ARPES Electrons first appear located near antinodal points (0, p) and (p,0) which are marked by the van Hoves (VH) singularity • Electrons pockets are very neat for weak doping. • These pockets exist even for high doping (~10%). • Note: For weakly hole doped systems • Holes are localized in nodal points (/2, /2) • AFM disappears at very weak hole doping

  3. S.R. Park, (2007) Experimental motivation Weakly electronically doped cuprate materials - optics Optical absorption shows the onset of the interband transition and indicates on existence of bound excitons The absorption peak is a signature of excited state which appears below the nominal insulating gap. Gap

  4. Experimental motivation - excitons Schematic band structure ARPES shows that spectra of electrons/holes above/below the AFM gap 2D=2Vππ are congruent, hence the e-h excitation is highly degenerate. It possesses the Van Hove singularity even when single electrons are perturbed and the hole is centered elsewhere, at (p/2,p/2). S.R. Park, (2007)

  5. Model Hamiltonian Spectrum of electrons/holes near the gap edges ±Δ, (anti-nodal points): ±Δ Spectrum of exciton: Quadratic terms, From corrugation of VH singularity Energy functional for electron near impurity with potential V(r):

  6. Model Amplitude breathing mode η Interaction of the electron / exciton with deformations η of the order parameter (fluctuations of ) : Energy functional for selftrapping :

  7. Results of simulations Localized state of one electron trapped by a point impurity Self-trapped state - polaron for one electron due to interaction with amplitude mode Amplitude is not constant, as it would be for free electrons This state is a collective state, which has an energy lower than the free electrons Neither of these bound states would exist for hole doped cases

  8. Results of simulations The exciton

  9. Results of simulations • Evolution of the self-trapped state and its gradual of suppression by increasing the corrugation of the van Hoves singularity Weakness of quadratic terms ~t’ is crucial for the existence of the polarons. For elevated values of t’ the polaron disappears.

  10. Conclusions • The VH singularity endorses the trapped and self-trapped states for added electrons and for optical excitons. • Quadratics terms (~ t’) corrugated VH and weaken self-trapped states. • The optical exciton is not affected by corrugations of VH singularity, it will be always strongly shifted inside the gap.

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