Efficient computation of the second-Born self-energy using tensor-contraction operations

Tuovinen, Riku; Covito, Fabio; Sentef, Michael A.

doi:10.1063/1.5121820

Cited by 12 publications

(9 citation statements)

References 85 publications

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“…The computational effort for the resolution of the out-of-equilibrium simulations is not to be underestimated. Due to the relatively large spin⊗particle-hole basis of the system studied here, the efficient construction of the many-body self-energies is important [73]. While the time-propagation via the GKBA approach considered here scales as the number of time steps squared (compared to the cubic scaling of the full Kadanoff-Baym equations), it may still render longer time evolutions fairly inaccessible.…”

Section: Discussionmentioning

confidence: 99%

Electron correlation effects in superconducting nanowires in and out of equilibrium

Tuovinen

2021

Preprint

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One-dimensional nanowires with strong spin-orbit coupling and proximity-induced superconductivity are predicted to exhibit topological superconductivity with condensed-matter analogues to Majorana fermions. Here, the nonequilibrium Green's function approach with the generalized Kadanoff-Baym ansatz is employed to study the electron-correlation effects and their role in the topological superconducting phase in and out of equilibrium. Electron-correlation effects are found to affect the transient signatures regarding the zero-energy Majorana states, when the superconducting nanowire is subjected to external perturbations such as magnetic-field quenching, laser-pulse excitation, and coupling to biased normal-metal leads.

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Section: Discussionmentioning

confidence: 99%

Electron correlation effects in superconducting nanowires in and out of equilibrium

Tuovinen

2021

Preprint

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“…For this purpose, we employ the second Born approximation, describing the non-equilibrium dynamics within the Keldysh formalism. This approach is non-perturbative in the strength of the electric field and properly describes electron-electron scattering, as well as the associated electron thermalization [50][51][52][53] .…”

Section: A Model and Methodsmentioning

confidence: 99%

Photo-induced phase transition and associated time scales in the excitonic insulator Ta$_2$NiSe$_5$

Saha,

Golez,

De Ninno

et al. 2021

Preprint

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We investigate the non-equilibrium electronic structure and characteristic time scales in a candidate excitonic insulator, Ta2NiSe5, using time-and angle-resolved photoemission spectroscopy with a temporal resolution of 50 fs. Following a strong photoexcitation, the band gap closes transiently within 100 fs, i.e., on a time scale faster than the typical lattice vibrational period. Furthermore, we find that the characteristic time associated with the rise of the photoemission intensity above the Fermi energy decreases with increasing excitation strength, while the relaxation time of the electron population towards equilibrium shows an opposite behaviour. We argue that these experimental observations can be consistently explained by an excitonic origin of the band gap in the material. The excitonic picture is supported by microscopic calculations based on the non-equilibrium Green's function formalism for an interacting two-band system. We interpret the speedup of the rise time with fluence in terms of an enhanced scattering probability between photo-excited electrons and excitons, leading to an initially faster decay of the order parameter. We show that the inclusion of electron-phonon coupling at a semi-classical level changes only the quantitative aspects of the proposed dynamics, while the qualitative features remain the same. The experimental observations and microscopic calculations allow us to develop a simple and intuitive phenomenological model that captures the main dynamics after photoexcitation in Ta2NiSe5.

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“…For efficient computation, we additionally use a recurrence relation for constructing Eq. (14) due to its group property [32,53], and we employ optimized matrix (tensor) operations for the construction of the 2B self-energy [92]. From now on, we refer to this approach as 2B@GKBA.…”

Section: B Time Propagation Of the Nonequilibrium Green's Functionsmentioning

confidence: 99%

Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

Tuovinen¹,

Golež²,

Eckstein³

et al. 2020

Phys. Rev. B

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We investigate out-of-equilibrium dynamics in an excitonic insulator (EI) with a finite-momentum pairing perturbed by a laser-pulse excitation and a sudden coupling to fermionic baths. The transient dynamics of the excitonic order parameter is resolved using the full nonequilibrium Green's function approach and the generalized Kadanoff-Baym ansatz (GKBA) within the second-order Born approximation. The comparison between the two approaches after a laser-pulse excitation shows a good agreement in the weak and the intermediate photodoping regime. In contrast, the laser-pulse dynamics resolved by the GKBA does not show a complete melting of the excitonic order after a strong excitation. Instead we observe persistent oscillations of the excitonic order parameter with a predominant frequency given by the renormalized equilibrium band gap. This anomalous behavior can be overcome within the GKBA formalism by coupling to an external bath, which leads to a transition of the EI system toward the normal state. We analyze the long-time evolution of the system and distinguish decay timescales related to dephasing and thermalization.

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Efficient computation of the second-Born self-energy using tensor-contraction operations

Cited by 12 publications

References 85 publications

Electron correlation effects in superconducting nanowires in and out of equilibrium

Electron correlation effects in superconducting nanowires in and out of equilibrium

Photo-induced phase transition and associated time scales in the excitonic insulator Ta$_2$NiSe$_5$

Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium

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