arXiv subjects

Javiera Cabezas-Escares

Publications and source records attributed to Javiera Cabezas-Escares.

5 recordsLinked to original sources

arXiv2026

Exact Mirror-Parity Selection Rule for Electron-Phonon Coupling in Two-Dimensional Crystals

The electron--phonon (e-ph) interaction underlies conventional superconductivity and plays a central role in transport and other many-body phenomena in solids. Here, we derive a symmetry selection rule for e-ph scattering in two-dimensional crystals possessing a horizontal mirror plane, $σ_h$. For electronic states of mirror parity $s_n(\mathbf{k})$ and $s_m(\mathbf{k}+\mathbf{q})$, and a phonon mode of parity $χ_ν(\mathbf{q})$, we show that the e-ph matrix element $g_{mn,ν}(\mathbf{k},\mathbf{q})$ vanishes identically unless $s_n(\mathbf{k})\,χ_ν(\mathbf{q})\, s_m(\mathbf{k}+\mathbf{q})=+1$. The rule follows from the covariance of the phonon-induced deformation potential under $σ_h$, constitutes the $C_s$ case of the general group-theoretical selection rule for matrix elements, and partitions the e-ph interaction throughout the Brillouin zone into symmetry-allowed and symmetry-forbidden scattering channels. Consequently, mirror-even phonons couple electronic states of the same mirror parity, either even--even or odd--odd, whereas mirror-odd phonons couple only states of opposite mirror parity, for both intra- and interband processes. We illustrate the selection rule through first-principles calculations for the two-dimensional superconductor $\mathrm{Sc_2BCH_4}$, where mirror parity is well defined throughout the entire Brillouin zone and symmetry-forbidden matrix elements vanish up to numerical precision. We then extend the analysis to bulk $\mathrm{MgB_2}$, where the rule applies exactly only on mirror-invariant planes of the three-dimensional Brillouin zone. Moving away from these planes removes the exact mirror constraint and activates scattering channels that are symmetry forbidden when the mirror eigenvalues are well defined. Our results establish horizontal mirror symmetry as an exact and practical filter of e-ph scattering processes.

cond-mat.supr-con↗

arXiv2026

Excitonic Charge Density Waves in Moire Ladders

An incommensurate charge density wave (CDW) is a periodic modulation of charge that breaks translational symmetry incongruently with the underlying lattice. Its low-energy excitations, the phason, are collective, gapless phase fluctuations. We study a half-filled, four-band ladder model where a shift $δ= p/q$ between the legs leads to a supercell of $q$ composite cells. The moiré potential narrows minibands near the Fermi level, resulting in additional peaks in the density of states, whose separation is controlled by $δ$. The inclusion of short-range Coulomb interactions leads to an excitonic incommensurate CDW state. We identify the oscillations in its amplitude with a gapped Higgs collective mode and a lowest-energy Goldstone mode, realized by long-lived neutral phasons whose propagation velocity is governed by the shift $δ$ and the inter-leg tunneling amplitude. Our results show that even the slightest interlayer mismatches can strongly modify both charge-ordering patterns and low-energy bosonic excitations in layered materials, and suggest that the enigmatic CDW phase in the quasi-one-dimensional compound $\rm HfTe_3 $ is excitonic in nature.

cond-mat.str-el↗

arXiv2026

Sliding phasons in Moiré Ladders

An incommensurate charge density wave is a periodic modulation of charge that breaks translational symmetry at a momentum that does not coincide with the primitive lattice vectors. Its Goldstone excitation, the phason, comprises collective gapless phase fluctuations. Aiming to unveil the mechanism behind the onset of incommensurate charge order in layered materials, we study a half-filled, four-band tight-binding model on a ladder with a relative shift $δ=p/q$ between the legs, induced by the dimerization of one of them. The shift results in a moiré supercell comprising $q$ composite cells and a modulated inter-leg tunneling. The moiré potential compresses the leg bands into flat minibands near the Fermi level, resulting in additional low-energy peaks in the density of states. Including Coulomb interactions, we find an incommensurate charge-density-wave phase in which the charge modulation is out of phase between the legs. The collective excitations of this state are long-lived neutral, acoustic phasons whose speed is controlled by the moiré parameter $δ$ and the inter-leg tunneling amplitude. This model sheds light on the role of interlayer incongruities in the formation of excitonic charge-ordered phases in van der Waals and heterostructured materials.

cond-mat.str-el↗

arXiv2025

Phonon-induced electronic degeneracy breaking: a SSAdNDP interpretation

This work explores how phonon perturbations can induce the breaking of electronic degeneracies near the Fermi level and how this response can be interpreted from a chemical perspective through the SSAdNDP method. We apply this approach to a family of structurally similar yet electronically distinct hexagonal materials-MgB2, graphene, and hBN-to analyze how a single phonon mode simultaneously modifies the electronic structure (band dispersion) and the nature of chemical bonding (natural occupations and nodal patterns) in real space. Our results show that band splitting becomes physically relevant only when it is accompanied by an electronic redistribution, reflected in changes of the occupation numbers or bonding topology. Thus, SSAdNDP provides a direct bridge between reciprocal- and real-space representations, translating phenomena such as electron-phonon coupling into chemically intuitive reorganizations of multicenter bonds, and offering a unified framework to interpret vibrationally driven electronic effects in solids.

cond-mat.mtrl-sci↗

arXiv2024

Manipulating the wavelength of single photons in insulating van der Waals heterostructures: theory and application to bilayer hexagonal boron nitride

Van der Waals heterostructures are promising for adding new functionalities to two-dimensional materials. In this study, we focus on single photon emitters hosted in one layer and adjacent to other insulating two-dimensional material. Specifically, we show how the emission energy is modified by such a heterostructure. We developed a general approach to elucidate the mechanisms affecting the emission energy and studied the particular case of carbon substitutions in the hexagonal boron nitride bilayer.

cond-mat.mtrl-sci↗