Quasidegenerate Self-Trapping in One-Dimensional Charge Transfer Exciton

Abstract

The self-trapping by the nondiagonal particle-phonon interaction between two quasi-degenerate energy levels of excitonic system, is studied. We propose this is realized in charge transfer exciton, where the directions of the polarization give the quasi-degeneracy. It is shown that this mechanism, unlike the conventional diagonal one, allows a coexistence and resonance of the free and self-trapped states even in one-dimensional systems and a quantitative theory for the optical properties (light absorption and time-resolved luminescence) of the resonating states is presented. This theory gives a consistent resolution for the long-standing puzzles in quasi-one-dimensional compound A-PMDA.PACS numbers: 71.38.+i, 78.66, 05.10.Ln The charge transfer (CT) exciton in one-dimension (1D) attracts great interests due to its peculiar features, e.g., strong interaction with the phonons, magnons, and large nonlinearity in the optical responses. However the theoretical understanding of it is rather limited compared with that of Wannier and Frenkel excitons, because of its intermediate radius and strong coupling nature. E.g., although the prototypical compound Anthracene-PMDA (A-PMDA), which shows unusual vibronic structure in the optical spectra, is thoroughly experimentally investigated from 70-th till nowdays [1][2][3][4][5][6][7][8], even qualitative theoretical understanding it's optical response is missing.The most dramatic phenomenon which occurs at intermediate or strong coupling with the phonons is the self-trapping where the free (F) state of polaron with small lattice deformation coexists and resonates with the state with strong lattice relaxation [9,10]. Although the latter state is Bloch invariant it is traditionally classified as being self-trapped (ST) to stress larger degree of ionic distortion around the quasiparticle. However, this self-trapping scenario was not considered yet since the F-ST resonance is prohibited by Rashba-Toyozawa theorem (RTT) in 1D systems [9,10]. Although the RTT is probably valid for one quasiparticle state in the relevant energy range, the neglect of it's domain of definition caused severe delusion in the physics of 1D systems because RTT was treated as the strict ban for F-ST coexistence in 1D. However, when there are two quasi-degenerate quasiparticle states, i.e. the conditions of the theorem are violated, one can consider the quasi-degenerate self-trapping (QDST) mechanism, when the F-ST resonance is driven by nondiagonal interaction with phonons with respect to quasiparticle levels. An example of QDST was observed in the mixed valence systems [11].In this paper we first demonstrate by exact diagrammatic Monte Carlo method [12] that QDST is general phenomenon pertinent for 1D lattice, study the optic properties of resonating QDST states, and resolve longstanding puzzle of the quasi-1D system A-PMDA [1][2][3][4][5][6][7][8]. The minimal model to demonstrate F-ST coexistence in 1D systems involves one optic phonon branch with frequency ω = 0.1, two quasiparticle branches with ener...

Electron-Phonon Coupling and a Polaron in thet−JModel: From the Weak to the Strong Coupling Regime

“…The key role of the vortex corrections for e-ph interaction in SCR can be demonstrated by numerically ex-act Diagrammatic Monte Carlo (DMC) method [21,22,23,24] where Feynman graphs for the Matsubara Green function of a hole in phonon bath are generated by Monte Carlo and summed up without systematic errors. In the framework of this technique one can compare results of complete summation of Feynman expansion with those of restricted summation where diagrams with inter-crossing of phonon propagators are neglected.…”

“…In this Letter we present a study of a single hole in t-J model interacting with dispersionless optical phonons (2) by DMC [21,22,23,24] method. We found that due to slowing down of the hole by spin flip cloud around it, the hole in t-J model is subject to the stronger eph coupling than the freely propagating hole and hence undergoes the crossover to SCR at smaller coupling.…”

“…We generate Feynman expansion of Matsubara Green function of a hole in momentum representation for the infinite system at zero temperature by DMC [22,23,24]. Then we obtain LSF by stochastic optimization method [22,26] which resolves equally well both sharp and broad features of the spectra.…”

Numerical study of the isotope effect in underdoped high-temperature superconductors: Calculation of the angle-resolved photoemission spectra

“…The frequency of the relevant phonon [4] is set to Ω/t = 0.2 and the isotope factor κ iso = 16/18 corresponds to substitution of O 18 isotope for O 16 . We use DMC method [18,19], which is the only available method for approximation-free study of excited states of problem (1-3) for the macroscopic system at strong EPI. Non-crossing approximation for phonon variables [20] is shown to be invalid approximation for strong EPI [9] while exact diagonalization studies of small clusters, although account for correct treatment of phonons, imply a discrete spectrum and, thus, tiny changes of the FCP lineshape for κ ≈ 1 are not reliable.…”

ARPES spectra of polaron in the t–J model

“…NCA is valid for the interaction of the hole with magnetic system because spin SZ1/2 can not flip more than one time and magnon cloud around the hole saturates. To the contrary, we demonstrate the key role of the vertex corrections for e-ph interaction by numerically exact Diagrammatic Monte Carlo (DMC) method [13][14][15][16] where Feynman graphs for a hole in phonon bath can be summed up …”