arXiv subjects

M. Nabil Y. Lhachemi

Publications and source records attributed to M. Nabil Y. Lhachemi.

5 recordsLinked to original sources

arXiv2026

Efficient prediction of topological superlattice bands with spin-orbit coupling

We develop a symmetry indicator framework to efficiently predict the topology of superlattice-induced minibands with spin-orbit coupling. Our algorithm requires input only from the parent material before the superlattice is applied. The simplification arises by assuming a perturbatively weak superlattice potential; however, our results extend beyond the perturbative regime as long as the superlattice-induced gaps remain open. We first consider a time-reversal- and inversion-symmetric system subject to a weak superlattice potential and derive a compact formula for the $\mathbb{Z}_2$ invariant of the lowest miniband. We then extend to time-reversal breaking systems and compute the Chern number. We apply our theory to selected transition metal dichalcogenides, HgTe/CdTe quantum wells, and thin films of three-dimensional topological insulators and Dirac semimetals. We find topological superlattice bands can arise even from non-topological materials, broadening the pool of candidates for realizing topological flat bands. Our theory predicts which geometry and periodicity of superlattice will yield topological bands for a given material, providing a clear guiding principle for designing topological superlattice heterostructures.

cond-mat.mes-hall↗

arXiv2026

A unifying framework for sum rules and bounds on optical, thermoelectric and thermal transport from quantum geometry

We present a geometric formulation of optical, thermoelectric, and thermal linear response in clean, zero temperature band insulators based on a single object: a generalized time-dependent quantum geometric tensor (g-tQGT) built from correlations of projected particle and heat polarization operators. Within this framework, the AC transport tensors admit compact expressions that make their geometric content explicit. The response splits into a Berry curvature contribution that remains finite in the DC limit and a frequency correction governed by the quantum metric, implying geometry driven effects even in topologically trivial insulators. At equal times, the g-tQGT recovers the usual integrated QGT and yields energy-weighted thermal analogs whose antisymmetric parts are fixed by orbital and heat magnetization. Importantly, in the thermal channel, a thermal quantum geometric tensor is obtained. Casting the theory in a Hilbert-Schmidt inner product form yields a bound on the trace of the thermal QGT, an uncertainty relation on the projected polarization operators and a purely geometric upper bound on the finite-time accumulated response. The latter is used in the optical channel to derive a geometric upper bound on the electric current. Finally, time derivatives of the g-tQGT are used to generate a hierarchy of generalized thermoelectric and thermal sum rules, and bounds on these sum rules are obtained. These bounds are used to find inequalities between different physical objects such as the optical mass, susceptibility functions and magnetizations.

cond-mat.mes-hall↗

arXiv2025

Optimizing superlattice bilayer graphene for a fractional Chern insulator

Bernal-stacked bilayer graphene modulated by a superlattice potential is a highly tunable system predicted to realize isolated topological flat bands. In this work we calculate the band structure and quantum geometry of bilayer graphene subject to both triangular and square superlattices, across a wide range of gate voltages. We identify the parameter regime that optimizes the "single-particle indicators" for the stability of a fractional Chern insulator (FCI) when a topological flat band is partially filled. Our results guide the experimental realization of an FCI in this platform.

cond-mat.mes-hall↗

arXiv2024

Phononic dynamical axion in magnetic Dirac insulators

In cosmology, the axion is a hypothetical particle that is currently considered as candidate for dark matter. In condensed matter, a counterpart of the axion (the "axion quasiparticle") has been predicted to emerge in magnetoelectric insulators with fluctuating magnetic order and in charge-ordered Weyl semimetals. To date, both the cosmological and condensed-matter axions remain experimentally elusive or unconfirmed. Here, we show theoretically that ordinary lattice vibrations can form an axion quasiparticle in Dirac insulators with broken time- and space-inversion symmetries, even in the absence of magnetic fluctuations. The physical manifestation of the phononic axion is a magnetic-field-induced phonon effective charge, which can be probed in optical spectroscopy. By replacing magnetic fluctuations with lattice vibrations, our theory widens the scope for the observability of the axion quasiparticle in condensed matter.

cond-mat.mes-hall↗

arXiv2020

Phonon magnetochiral effect of band-geometric origin in Weyl semimetals

The phonon magnetochiral effect consists of a nonreciprocity in the velocity or attenuation of acoustic waves when they propagate parallel and antiparallel to an external magnetic field. The first experimental observation of this effect has been reported recently in a chiral magnet and ascribed to the hybridization between acoustic phonons and chiral magnons. Here, we predict a potentially measurable phonon magnetochiral effect of electronic origin in chiral Weyl semimetals. Caused by the Berry curvature and the orbital magnetic moment, this effect is enhanced for longitudinal phonons by the chiral anomaly.

cond-mat.mes-hall↗