arXiv subjects

Giacomo Sesti

Publications and source records attributed to Giacomo Sesti.

3 recordsLinked to original sources

arXiv2026

A viable and accurate route to GW simulations of metals and doped semiconductors

In this work we present an efficient and fully ab-initio approach for the calculation of the screened Coulomb potential, specifically designed for two dimensional (2D) and three dimensional (3D) metals and suitable to evaluate $GW$ corrections. While quasiparticle renormalization effects are typically negligible in bulk metals, 2D metals may exhibit semiconductor-like features, such as sizeable renormalization of quasiparticle energies induced by Coulomb interaction, which follow from the suppression of screening due to the reduced dimensionality, Although this effect can in principle be described by the $GW$ method, apart from a few pioneering exceptions, such calculations have been hampered by sampling requirements exceeding feasibility. We demonstrate that the combination of interpolation and extrapolation schemes together with the accounting of dynamical effects is pivotal to the correct handling of the intraband polarizability in the long wavelength limit. As an application, we report the gap renormalization of selected doped 2D-semiconductors in excellent agreement with ARPES measurements.

cond-mat.mtrl-sci↗

arXiv2026

Binding and spontaneous condensation of excitons in narrow-gap carbon nanotubes

Ultraclean, undoped carbon nanotubes are observed to be always insulating, even when the gap predicted by band theory is zero: the residual band gap is then thought to have a many-body origin. Here we theoretically show that the correlated insulator is excitonic in $all stable$ narrow-gap tubes irrespective of their size, thus extending our previous claim, limited to gapless (armchair) tubes [D.~Varsano, S.~Sorella, D.~Sangalli, M.~Barborini, S.~Corni, E.~Molinari, M.~Rontani, Nature Communications $\mathbf{8}$, 1461 (2017)]. We derive the scaling law of the exciton binding energy with the tube radius and chirality, and compute self-consistently the fundamental transport gap of the excitonic insulator, by enhancing the two-band model with an accurate treatment of screening validated from first principles. Our findings point to the broader connection between the exciton length scale, dictated by structure, and the stability of the excitonic phase.

cond-mat.mes-hall↗

arXiv2022

Anomalous screening in narrow-gap carbon nanotubes

The screening of Coulomb interaction controls many-body physics in carbon nanotubes, as it tunes the range and strength of the force that acts on charge carriers and binds electron-hole pairs into excitons. In doped tubes, the effective Coulomb interaction drives the competition between Luttinger liquid and Wigner crystal, whereas in undoped narrow-gap tubes it dictates the Mott or excitonic nature of the correlated insulator observed at low temperature. Here, by computing the dielectric function of selected narrow- and zero-gap tubes from first principles, we show that the standard effective-mass model of screening systematically underestimates the interaction strength at long wavelength, hence missing the binding of low-energy excitons. The reason is that the model critically lacks the full three-dimensional topology of the tube, being adapted from graphene theory. As ab inito calculations are limited to small tubes, we develop a two-band model dielectric function based on the plane-wave expansion of Bloch states and the exact truncated Coulomb cutoff technique. We demonstrate that our -- computationally cheap -- approach provides the correct screening for narrow-gap tubes of any size and chirality. A striking result is that the screened interaction remains long-ranged even in gapless tubes, as an effect of the microscopic local fields generated by the electrons moving on the curved tube surface. As an application, we show that the effective electron-electron force that is felt at distances relevant to quantum transport experiments is super Coulombic.

cond-mat.mes-hall↗