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Dipartimento di Fisica - Politecnico di Milano

[26/10/2021 - 11:00]

Dr. Habib Rostami (Assistant Professor, Nordita, KTH Royal Institute of Technology and Stockholm University)

"Strong impact of multi-photon vertex renormalisation on the nonlinear response of 2D materials"


mar 26/10/2021 - 11:00 - Aula Castigliano (online at this link)



Because of the many-body interactions, the standard concepts of nonlinear response to electromagnetic fields break down in two dimensional Dirac materials, like graphene, in the quantum regime close to the Dirac point. In this talk, I will present how using a conserving Baym-Kadanoff approach, we can provide a fully compelling theory of nonlinear optical and transport response of a Dirac system to electric fields in the presence of disorder scattering. We show that the nonlinear terms are strikingly ruled by the appearance of a dominant two-photon vertex which is absent at the bare level and finite even in the weak-coupling limit. Such two-photon vertex self-generation highlights the crucial role of the frequency and field dependence of the scattering rates in the nonlinear regime. Moreover, we surprisingly predict four- and five-photon incoherent features in the third order optical response of the system. Our study reveals a novel many-body mechanism in the nonlinear response of Dirac materials whose effects are predicted to be observable in nonlinear dc transport, terahertz third-harmonic generation in graphene. If time allows, I can briefly discuss two other proceeding projects on nonlinear ellipsometry in single-layer WTe2 and acoustoelectric effect in graphene and Weyl semimetals.

H. Rostami and E. Cappelluti, npj 2D Materials and Applications 5, Article number: 50 (2021).
H. Rostami and E. Cappelluti, Phys. Rev. B 103, 125415 (2021).
P.O. Sukhachov and H. Rostami, Phys. Rev. Lett. 124 (12), 126602 (2020).

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