Pump-driven normal-to-excitonic insulator transition: Josephson oscillations and signatures of BEC-BCS crossover in time-resolved ARPES

Perfetto, Enrico; Sangalli, Davide; Marini, Andrea; Stefanucci, Gianluca

doi:10.1103/physrevmaterials.3.124601

Cited by 49 publications

(58 citation statements)

References 76 publications

(108 reference statements)

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“…3(b)], i.e., the core-level broadening immediately follows the buildup of excited carriers n which includes contributions from both excitons [39] and QFCs in the CB. In contrast, the core-hole line shape renormalization governed by the quasiparticle screening n QFC ν 2 shows a clear delay in buildup compared to γ and n. This is consistent with the prediction that the pump energy tuned to the excitonic resonance should favor the creation of excitons [40] up to a critical density [41], and can be explained by means of an excitonic Mott transition-the initial stage of the dynamics is dominated by excitons which subsequently break into a QFC plasma due to increased screening as well as many-particle renormalizations [41]. An estimation of the excitation density per layer, n ¼ 7ð1.4Þ × 10 13 cm −2 [28], used in our experiment indeed significantly exceeds the predicted critical excitation density of approximately 3 × 10 12 cm −2 [2], and is close to the density of 1.1 × 10 14 cm −2 reported for experimental observation of excitonic Mott transition in single-layered WS 2 [42].…”

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confidence: 86%

Observation of an Excitonic Mott Transition Through Ultrafast Core- cum -Conduction Photoemission Spectroscopy

et al. 2020

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Time-resolved soft-x-ray photoemission spectroscopy is used to simultaneously measure the ultrafast dynamics of core-level spectral functions and excited states upon excitation of excitons in WSe 2. We present a many-body approximation for the Green's function, which excellently describes the transient core-hole spectral function. The relative dynamics of excited-state signal and core levels clearly show a delayed core-hole renormalization due to screening by excited quasifree carriers resulting from an excitonic Mott transition. These findings establish time-resolved core-level photoelectron spectroscopy as a sensitive probe of subtle electronic many-body interactions and ultrafast electronic phase transitions.

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confidence: 86%

Observation of an Excitonic Mott Transition Through Ultrafast Core- cum -Conduction Photoemission Spectroscopy

et al. 2020

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“…Henceforth we express all energies in units of ε g and choose U ¼ W=2 ¼ 1 [61,62]. The electronic system is coupled to a single (μ ¼ 1) phononic brancĥ…”

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confidence: 99%

Fast Green’s Function Method for Ultrafast Electron-Boson Dynamics

et al. 2021

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The interaction of electrons with quantized phonons and photons underlies the ultrafast dynamics of systems ranging from molecules to solids, and it gives rise to a plethora of physical phenomena experimentally accessible using time-resolved techniques. Green's function methods offer an invaluable interpretation tool since scattering mechanisms of growing complexity can be selectively incorporated in the theory. Currently, however, real-time Green's function simulations are either prohibitively expensive due to the cubic scaling with the propagation time or do neglect the feedback of electrons on the bosons, thus violating energy conservation. We put forward a computationally efficient Green's function scheme which overcomes both limitations. The numerical effort scales linearly with the propagation time while the simultaneous dressing of electrons and bosons guarantees the fulfillment of all fundamental conservation laws. We present a real-time study of the phonon-driven relaxation dynamics in an optically excited narrow band-gap insulator, highlighting the nonthermal behavior of the phononic degrees of freedom. Our formulation paves the way to first-principles simulations of electron-boson systems with unprecedented long propagation times.

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“…Similarly, the tr-ARPES signal is related to the transient spectral function [104,105] which in semiconductor or insulators can be evaluated using a steady-state approximation (provided that the carrier relaxation time is much longer than the probe pulse). In this context [106] the PSD diagrammatic construction may provide a powerful tool in the field of light-induced exciton fluids, whose incoherent plasma phase [105,107,108] and coherent condensed phase [96,[109][110][111][112][113][114] (B11)…”

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confidence: 99%

Dynamically screened vertex correction to GW

2020

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Diagrammatic perturbation theory is a powerful tool for the investigation of interacting many-body systems, the self-energy operator encoding all the variety of scattering processes. In the simplest scenario of correlated electrons described by the GW approximation for the electron self-energy, a particle transfers a part of its energy to neutral excitations. Higher-order (in screened Coulomb interaction W ) self-energy diagrams lead to improved electron spectral functions (SFs) by taking more complicated scattering channels into account and by adding corrections to lower order self-energy terms. However, they also may lead to unphysical negative spectral functions. The resolution of this difficulty has been demonstrated in our previous works. The main idea is to represent the self-energy operator in a Fermi golden rule form which leads to a manifestly positive definite SF and allows for a very efficient numerical algorithm. So far, the method has only been applied to the three-dimensional electron gas, which is a paradigmatic system, but a rather simple one. Here we systematically extend the method to two dimensions including realistic systems such as monolayer and bilayer graphene. We focus on one of the most important vertex function effects involving the exchange of two particles in the final state. We demonstrate that it should be evaluated with the proper screening and discuss its influence on the quasiparticle properties.

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Pump-driven normal-to-excitonic insulator transition: Josephson oscillations and signatures of BEC-BCS crossover in time-resolved ARPES

Cited by 49 publications

References 76 publications

Observation of an Excitonic Mott Transition Through Ultrafast Core- cum -Conduction Photoemission Spectroscopy

Observation of an Excitonic Mott Transition Through Ultrafast Core- cum -Conduction Photoemission Spectroscopy

Fast Green’s Function Method for Ultrafast Electron-Boson Dynamics

Dynamically screened vertex correction to GW

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