arXiv subjects

Angiolo Huamán

Publications and source records attributed to Angiolo Huamán.

3 recordsLinked to original sources

arXiv2026

Minimal d-Band Model for the Optical Susceptibility of Non-Centrosymmetric Monolayer Transition Metal Dichalcogenides

The optical response of two-dimensional materials has been customarily calculated {\it ab initio} using plane waves basis and the full Bloch wavefunction, without separating the most important orbital contributions. In the family of monolayer transition metal dichalcogenides lacking inversion symmetry, we take advantage of the mostly $d-$orbital content of the Bloch bands around the semiconductor gap to reduce the calculation of their linear and quadratic optical susceptibilities to a very minimal model that includes only three energy bands. As the Bloch wavefunction determines the microscopic response to external fields, this simple approach reproduces well first principles calculations up to roughly 2 eV above the band gap. This could be the starting point for the inclusion of many-body effects with only a few energy bands in a numerically inexpensive way.

cond-mat.mes-hall↗

arXiv2026

The Thomas-Reiche-Kuhn sum rule as a consequence of a non-singular optical susceptibility in semiconductors

The Thomas-Reiche-Kuhn optical (TRK) sum rules for bulk materials have customarily been obtained by combining the Kramers-Kronig relations with the high frequency limit of the optical susceptibility tensor $χ_{ij}$. Also, a non-singular expression for $χ_{ij}$ involve the reduction of some its parts to an effective mass tensor. In this paper we show that the latter procedure is intimately connected to the TRK sum rules, and in fact these sum rules can be obtained from it. In reaching this result, we present before a thorough description of the momentum matrix elements of Bloch eigenfunctions bypassing the so-called $\bf{k}-$representation.

cond-mat.other↗

arXiv2024

Insulating moiré homobilayers lack a threefold symmetric second harmonic generation

Atoms within moiré bilayers relax in-plane to minimize elastic energy [e.g., Cazeaux et al., J. Elast. 154, 443 (2023)]; such relaxation brings their space group symmetries down to P1. Here, the ab initio second harmonic generation (SHG) of twisted and atomistically optimized hBN bilayers was determined at four twist angles ($θ=38.21^{\circ}$, $60.00^{\circ}$, $73.17^{\circ}$, and $98.21^{\circ}$) and for three displacements $\boldsymbolτ$ measured away from the ground state $AA^{\prime}$ configuration. All moiré bilayers have a P1 space symmetry after structural optimization. This situation is quite different to monolayers with hexagonal lattices, which retain a three-fold symmetry. We point out that the actual symmetries of the SHG reported for hBN bilayers on two experimental works do not coincide with the sixfold symmetric theoretical profiles they provide [either $\sin^2(3ϕ)$ or $\cos^2(3ϕ)$], and show that the intrinsic low structural symmetry of (atomically optimized) hBN bilayer moirés can in fact be read out from experimental SHG intensity profiles--which are tunable by $θ$ and by the frequency of light $ω$: The SHG is most definitely not sixfold-symmetric because moirés do not retain a three-fold symmetry. Furthermore, an extrinsic twofold symmetry of the SHG emission is realized by tilting the pump by an angle $α$ away from the 2D material's normal, regardless of $θ$ and $ω$. The design of in-plane and ultrathin sources of SHG with low symmetry could be useful for the eventual creation of entanglement sources from 2D materials.

cond-mat.mtrl-sci↗