Excitonic resonances in the 2D extended Falicov-Kimball model

Phan, Van-Nham; Fehske, Holger; Becker, K. W.

doi:10.1209/0295-5075/95/17006

Cited by 34 publications

(31 citation statements)

References 30 publications

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“…Applying the unitary invariance of operator expressions under a trace, A(k, ω) is rewritten as (27) where the expectation value is now formed withH instead of with H. Correspondingly,b…”

Section: Influence Of Fluctuation Processesmentioning

confidence: 99%

Ground-state and spectral signatures of cavity exciton-polariton condensates

2016

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We propose a projector-based renormalization framework to study exciton-polariton Bose-Einstein condensation in a microcavity matter-light system. Treating Coulomb interaction and electronhole/photon coupling effects on an equal footing, we analyze the ground-state properties of the exciton-polariton model according to the detuning and the excitation density. We demonstrate that the condensate by its nature shows a crossover from an excitonic insulator (of Bose-Einstein, respectively, BCS type) to a polariton and finally photonic condensed state as the excitation density increases at large detuning. If the detuning is weak, polariton or photonic phases dominate. While in both cases a notable renormalization of the quasiparticle band structure occurs that strongly affects the coherent part of the excitonic luminescence, the incoherent wave-vector-resolved luminescence spectrum develops a flat bottom only for small detuning.

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“…Applying the unitary invariance of operator expressions under a trace, A(k, ω) is rewritten as (27) where the expectation value is now formed withH instead of with H. Correspondingly,b…”

Section: Influence Of Fluctuation Processesmentioning

confidence: 99%

Ground-state and spectral signatures of cavity exciton-polariton condensates

2016

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“…In particular, we examine the so-called halo phase around the EI, where excitons and excitonic resonances dominate the electron-hole excitation spectrum 2,17 . Figure 4 gives results for the SC region with U > U c (T ) and T > T EI (U ).…”

Section: Fig 2 (Color Online)mentioning

confidence: 99%

Electron-hole pair condensation at the semimetal-semiconductor transition: A BCS-BEC crossover scenario

et al. 2012

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We act on the suggestion that an excitonic insulator state might separate-at very low temperatures-a semimetal from a semiconductor and ask for the nature of these transitions. Based on the analysis of electron-hole pairing in the extended Falicov-Kimball model, we show that tuning the Coulomb attraction between both species, a continuous crossover between a BCS-like transition of Cooper-type pairs and a Bose-Einstein condensation of preformed tightly-bound excitons might be achieved in a solid-state system. The precursor of this crossover in the normal state might cause the transport anomalies observed in several strongly correlated mixed-valence compounds.PACS numbers: 71.30.+h, 71.35.Lk The challenging suggestion of electron-hole pair condensation in thermal equilibrium into the excitonic insulator (EI) phase at the semimetal (SM) to semiconductor (SC) transition 1 , where the SM-EI transition may be described in analogy with BCS theory of superconductivity and the SC-EI transition is discussed in terms of a BoseEinstein condensation (BEC) of preformed excitons 2-4 , is of topical interest. This is due to the growing amount of experimental data on materials which are candidates for the realization of the EI, where different situations with respect to the SM/SC-EI transition are given. For example, in the rare-earth chalcogenide TmSe 0.45 Te 0.55 , that is, an intermediate-valent SC, the pressure-induced resistivity anomaly at low temperatures was ascribed to exciton formation and a subsequent SC-EI transition 5-8 . An EI state in semiconducting Ta 2 NiSe 5 was recently probed by photoemission 9 . On the other hand, in the layered transition-metal dichalcogenide 1T -TiSe 2 , which is a SM, a BCS-like electron-hole pairing was considered as the driving force for the periodic lattice distortion 10 . Here evidence suggests electron-hole 'Cooper-pair' fluctuations above the SM-EI transition temperature. A BCSlike electron-hole pair condensation was also studied for graphene bilayers 11 . In this system a BCS-BEC crossover might be realized by a magnetic field that creates a gap and magneto-excitons which may condense. From a theoretical point of view, one of the main issues in this field is the better understanding and a detailed description of the normal phase above the SM/SC-EI transition, especially of the electron-hole pair fluctuations and of the BCS-BEC crossover scenario 12 that characterizes the EI instability and has not been observed in a solid so far.In this Rapid Communication we address this topic and the mechanisms behind in terms of a minimal two-band model, the so-called extended Falicov-Kimball model (EFKM) 3,13,14 which covers direct c-and f -band hopping and admits the pairing of c electrons with f holes via a strongly screened Coulomb interaction. Thereby we focus on the normal phase that surrounds the EI and look for precursor effects in the electron-hole pair susceptibility. In particular we analyze the nature of the electronhole bound states and determine their number and spectral weight....

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“…The existence of excitonic bound states in a SM is confirmed by a very recent EFKM study with the projector-based renormalization method. 30 The comparison of Figs. 8(b), 8(c), and 8(d) demonstrates that the energetic position of the continuum band decreases with increasing temperature and, as a result, the exciton binding energy is lowered.…”

Section: Excitonic Bound Statesmentioning

confidence: 99%

Slave-boson field fluctuation approach to the extended Falicov-Kimball model: Charge, orbital, and excitonic susceptibilities

et al. 2011

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Based on the SO(2)-invariant slave-boson scheme, the static charge, orbital, and excitonic susceptibilities in the extended Falicov-Kimball model are calculated. Analyzing the phase without long-range order, we find instabilities toward charge order, orbital order, and the excitonic insulator (EI) phase. The instability toward the EI is in agreement with the saddle-point phase diagram. We also evaluate the dynamic excitonic susceptibility, which allows the investigation of uncondensed excitons. We find qualitatively different features of the exciton dispersion at the semimetal-EI and at the semiconductor-EI transition supporting a crossover scenario between a BCS-type electron-hole condensation and a Bose-Einstein condensation of preformed bound electron-hole pairs.

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Excitonic resonances in the 2D extended Falicov-Kimball model

Cited by 34 publications

References 30 publications

Ground-state and spectral signatures of cavity exciton-polariton condensates

Ground-state and spectral signatures of cavity exciton-polariton condensates

Electron-hole pair condensation at the semimetal-semiconductor transition: A BCS-BEC crossover scenario

Slave-boson field fluctuation approach to the extended Falicov-Kimball model: Charge, orbital, and excitonic susceptibilities

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