arXiv subjects

Tommaso Maria Mazzocchi

Publications and source records attributed to Tommaso Maria Mazzocchi.

8 recordsLinked to original sources

arXiv2026

Steady-state study of the nonequilibrium properties of SrVO$_3$

We present the mixed-configuration approximation (MCA) based on the auxiliary master equation approach impurity solver to study multiorbital correlated systems under equilibrium and nonequilibrium conditions within dynamical mean-field theory (DMFT). We benchmark the method for bulk and layered SrVO$_3$ in equilibrium and apply it to a prototypical nonequilibrium geometry in which a voltage bias is applied perpendicular to the layer via reservoirs held at different chemical potentials. For bulk SrVO$_3$, MCA reproduces the metallic state at moderate interaction strengths, but it overestimates the weight of the lower band relative to quantum Monte Carlo (QMC) and fork tensor product state (FTPS) solvers. With respect to QMC and FTPS, MCA yields an earlier metal-to-insulator transition as the electron-electron interaction is increased. In layered SrVO$_3$ at equilibrium, MCA partially captures the orbital polarization in favor of the in-plane $xy$ orbital, although not as strong as in the DMFT-converged results obtained with QMC. Finally, under applied bias, we observe a pronounced redistribution of orbital occupations, demonstrating that the method captures bias-driven orbital charge transfer in realistic materials in nonequilibrium conditions.

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arXiv2026

Extension of the iterated perturbation theory at arbitrary fillings to nonequilibrium steady states

We extend the Kajueter-Kotliar [Phys. Rev. Lett. 77, 131 (1996)] iterated perturbation theory (KK-IPT) away from half filling to nonequilibrium steady states. We benchmark the resulting nonequilibrium KK-IPT approach against the auxiliary master equation approach (AMEA), whose accuracy is controlled in and out of equilibrium. As expected, in equilibrium, KK-IPT reproduces the AMEA results for different fillings with high accuracy at the level of both spectral properties and electron densities. Out of equilibrium, we study quantum transport across a correlated impurity and compute the differential conductance and spectral functions. We find very good agreement between nonequilibrium KK-IPT and AMEA in the parameter regime where the latter is reliable, in particular at moderate temperatures and biases. Although a controlled benchmark is not available in the low-temperature, low-bias regime, where AMEA becomes less reliable, we show that this nonequilibrium KK-IPT impurity solver satisfies the exact spectral sum rules for the first and second moments to high accuracy throughout the entire parameter range studied. These results support nonequilibrium KK-IPT as an approximate description of nonequilibrium steady states away from half filling. At the same time, comparing against AMEA the double occupancy obtained from the nonequilibrium Galitskii-Migdal expression for the interaction energy shows that the deviation from AMEA remains small near half filling for moderate and large values of the bias, but grows markedly away from half filling, delineating the regime in which the method can be trusted quantitatively rather than merely qualitatively.

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arXiv2026

Mixed-configuration approximation for multiorbital systems out of equilibrium

We propose a mixed-configuration approximation based on single-band impurity solvers to efficiently study nonequilibrium multiorbital systems at moderate computational cost. In this work, we merge the approach with the so-called auxiliary master equation approach. As a benchmark, we first show that our approach reproduces the results of quantum Monte Carlo (QMC) for two-orbital impurity models at equilibrium with overall good accuracy, especially for non-degenerate orbitals. We then use our approach as an impurity solver for dynamical mean-field theory (DMFT) to address the case of a realistic two-orbital layered structure, recovering the strong crystal-field-driven charge polarization observed by solving the DMFT self-consistent cycle with QMC, albeit slightly reduced. Finally, we address a prototype nonequilibrium setup by sandwiching this layer between metallic contacts subject to a bias voltage described by different chemical potentials. This simplified model demonstrates our method's potential to access nonequilibrium steady-state behavior in realistic multi-orbital materials. These findings provide a first step toward theoretical studies of the nonequilibrium properties of multi-orbital compounds directly in the real-frequency domain.

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arXiv2026

Impact of disorder and phonons on the Hubbard bands of Mott insulators in strong electric fields

We characterize the current-carrying non-equilibrium steady-state (NESS) in a single-band Hubbard model confronted with a static electric field in the presence of quenched disorder. Beyond linear response regime, the electric field amplitude must be such to compensate for at least half of the band gap in order to have a non-negligible stationary current. As disorder is not expected to dissipate the extra energy injected by the field, optical phonons assisted by a fermionic heat bath serve as dissipation channels for the current-induced Joule heat generated by the accelerated electrons. The NESS of the system is addressed by means of the dynamical mean-field theory using the so-called auxiliary master equation approach as impurity solver. Disorder effects are treated locally via the coherent potential approximation (CPA) and the self-consistent Born (SCB) approach. In the regime in which the two schemes yield similar results, we employ the SCB as it is computationally cheaper than the CPA. We show that, in a purely electronic setup, the disorder-induced dephasing cannot contribute states within the gap but only smear out the edges of the Hubbard bands. When phonons are taken into account, the different nature of disorder-induced dephasing and phonon-related dissipation becomes clear. We show that although both disorder and electron-phonon interaction enhance the current at off-resonant fields, disorder effects play a marginal role since they cannot provide in-gap states which are instead brought about by phonons and represent the privileged relaxation pathway for excited electrons.

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arXiv2024

Photodriven Mott insulating heterostructures: A steady-state study of impact ionization processes

We investigate the photocurrent and spectral features in a simplified model of a Mott photovoltaic system consisting of a multilayered insulating heterostructure. The central correlated region is coupled to two metallic leads kept at different chemical potentials. A periodic drive applied to the correlated region produces excited doublons and holons across the Mott gap which are then separated by a potential gradient, which mimics the polarization-induced electric field present in oxyde heterostructures. The nonequilibrium Floquet steady-state is addressed by means of dynamical mean-field theory and its Floquet extension, while the so-called auxiliary master equation approach is employed as impurity solver. We find that impact ionization, identified by a kink in the photocurrent as function of the driving frequency, becomes significant and is generally favoured by weak, narrow-band hybridizations to the leads beyond a certain strength of the driving field. On the other hand, in the case of a direct coupling to metallic leads with a flat band, we observe a drastic reduction of impact ionization and of the photocurrent itself.

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arXiv2024

Iterated Perturbation Theory for Mott Insulators in a Static Electric Field with Optical Phonons

This manuscript aims to compare the so-called iterated perturbation theory (IPT) and auxiliary master equation approach (AMEA) impurity solvers for a Mott insulating system driven out of equilibrium by a static electric field. Electronic heat bath and optical phonons are employed as dissipation mechanism of the current-induced Joule heat that the excited electrons of the lattice experience as the result of the field's driving. Despite its simplicity, the IPT approach yields results which qualitatively are in good agreement with those obtained within the AMEA impurity solver, although fails to reproduce some correlation effects.

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arXiv2023

Correlated Mott insulators in a strong electric field: The effects of phonon renormalization

We characterize the response of a Mott insulating system to a static electric field in terms of its conducting and spectral properties. Dissipation is included by a coupling to fermionic baths and to either optical or acoustic phonons. This paper extends and completes the analysis made in a previous work by the authors [arXiv:2207.01921]. In the present work phonons are included diagrammatically within the Migdal approximation by also including self-consistency from the electronic feedback. The nonequilibrium steady-state is addressed by means of the dynamical mean-field theory based on the nonequilibrium Green's function approach, while the so-called auxiliary master equation approach is employed as impurity solver. With optical phonons the self-consistency suppresses the steady-state current at the onset of the metallic phase with respect to the nonself-consistent case. This is due to the interaction of phonons with the hot electrons of the lattice which increases their temperature, thus providing a less effective relaxation channel for the current-induced Joule heat. In addition, in the case of optical phonons the results are essentially independent of the temperature of the fermionic baths, as the latter is sensibly smaller than their characteristic frequency. On the other hand, with acoustic phonons the steady-state current is slightly suppressed by the self-consistent treatment only at field strengths close to half of the gap, away from the metallic phase, and especially at very small phonon frequency. Also, in this case the results seem to slightly depend on the temperature of the fermionic baths.

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arXiv2022

Impact ionization processes in a photodriven Mott insulator: influence of phononic dissipation

We study a model for photovoltaic energy collection consisting of a Mott insulating layer in presence of acoustic phonons, coupled to two wide-band fermion leads at different chemical potentials and driven into a nonequilibrium steady state by a periodic electric field. We treat electron correlations with nonequilibrium dynamical mean-field theory (DMFT) using the so-called auxiliary master equation approach as impurity solver and include dissipation by acoustic phonons via the Migdal approximation. For a small hybridization to the leads, we obtain a peak in the photocurrent as a function of the driving frequency which can be associated with impact ionization processes. For larger hybridizations the shallow peak suggests a suppression of impact ionization with respect to direct photovoltaic excitations. Acoustic phonons slightly enhance the photocurrent for small driving frequencies and suppress it at frequencies around the main peak at all considered hybridization strengths.

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