arXiv subjects

Ivan Pasqua

Publications and source records attributed to Ivan Pasqua.

7 recordsLinked to original sources

arXiv2026

Direct minimization versus iterative embedding in the ghost-Gutzwiller method: a comparative study of magnetism in Mott insulators

Accurately describing a hypothetical symmetry-invariant Mott insulator presents a long-standing ing challenge in iterative quantum embedding methods. We address this issue within the ghost- Gutzwiller method, which can be solved either through an iterative embedding scheme, analogous to dynamical mean-field theory, or by directly minimizing its variational energy functional. Across the Mott transition of the single-band Hubbard model, these formally equivalent approaches behave very differently: the iterative scheme is computationally efficient but fragile, necessitating ad-hoc recipes in the Mott phase that fail in a Zeeman field, leading to a discontinuous energy and a spurious fully-polarized insulator. Direct minimization avoids these artifacts, stabilizing a genuinely paramagnetic solution. Conversely, when symmetry breaking is allowed, as in an antiferromagnetic phase, the iterative scheme yields the correct solution, closely aligning with dynamical mean-field theory. Our findings delineate the conditions under which the iterative embedding can be trusted and when direct minimization is instead required.

cond-mat.str-el↗

arXiv2026

Fractionalized Fermi liquids with the ghost-Gutzwiller Ansatz

Fractionalized Fermi liquids ($\mathrm{FL}^{\!*}$), elusive metallic states characterized by fractionalized quasiparticles alongside conventional ones and defying Luttinger's theorem, are prime candidates for the pseudogap regime of underdoped cuprates. We show that a $\mathrm{FL}^{\!*}$ phase emerges in the single-band $t$-$J$ model through a simple ghost-Gutzwiller Ansatz, optimized at the cost of a mean-field calculation. The resulting temperature-doping phase diagram encompasses a low-doping $\mathrm{FL}^{\!*}$, a $d$-wave superconducting dome, and an overdoped conventional Fermi liquid, thereby reproducing key qualitative features of cuprate phenomenology.

cond-mat.str-el↗

arXiv2025

Band structure picture for topology in strongly correlated systems with the ghost Gutzwiller ansatz

Understanding the interplay between electronic correlations and band topology remains a central challenge in condensed matter physics, primarily hindered by a language mismatch problem. While band topology is naturally formulated within a single-particle band theory, strong correlations typically elude such an effective one-body description. In this work, we bridge this gap leveraging the ghost Gutzwiller (gGut) variational embedding framework, which introduces auxiliary quasiparticle degrees of freedom to recover an effective band structure description of strongly correlated systems. This approach enables an interpretable and computationally efficient treatment of correlated topological phases, resulting in energy- and momentum-resolved topological features that are directly comparable with experimental spectra. We exemplify the advantages of this framework through a detailed study of the interacting Bernevig-Hughes-Zhang model. Not only does the gGut description reproduce established results, but it also reveals previously inaccessible aspects: most notably, the emergence of topologically nontrivial Hubbard bands hosting their own edge states, as well as possible ways to manipulate these through a finite magnetization. These results position the gGut framework as a promising tool for the predictive modeling of correlated topological materials.

cond-mat.str-el↗

arXiv2025

How chiral vibrations drive molecular rotation

We analyze two simple model planar molecules: an ionic molecule with D3 symmetry and a covalent molecule with D6 symmetry. Both symmetries allow the existence of chiral molecular orbitals and normal modes that are coupled to each other in a Jahn-Teller manner, invariant under U (1) symmetry with generator a pseudo angular momentum. In the ionic molecule, the chiral mode possesses an electric dipole but lacks physical angular momentum, whereas, in the covalent molecule, the situation is reversed. In spite of that, we show that in both cases the chiral modes can be excited by a circularly polarized light and are subsequently able to induce rotational motion of the entire molecule.

cond-mat.mes-hall↗

arXiv2024

Fermi-liquid corrections to the intrinsic anomalous Hall conductivity of topological metals

We show that topological metals lacking time-reversal symmetry have an intrinsic non-quantized component of the anomalous Hall conductivity which is contributed not only by the Berry phase of quasiparticles on the Fermi surface, but also by Fermi-liquid corrections due to the residual interactions among quasiparticles, the Landau f-parametes. These corrections pair up with those that modify the optical mass with respect to the quasiparticle effective one, or the charge compressibility with respect to the quasiparticle density of states. Our result supports recent claims that the correct expressions for topological observables include vertex corrections besides the topological invariants built just upon the Green's functions. Furthermore, it demonstrates that such corrections are naturally accounted for by Landau's Fermi liquid theory, here extended to the case in which coherence effects between bands crossing the chemical potential and those that are instead away from it play a crucial role, as in the anomalous Hall conductivity, and have important implications when those metals are on the verge of a doping-driven Mott transition, as we discuss.

cond-mat.str-el↗

arXiv2024

Exciton condensation driven by bound states of Green's functions zeros

The interaction driven transition between quantum spin-Hall and Mott insulators in the Bernevig, Hughes and Zhang model is studied by dynamical cluster approximation, and found to be accompanied by the emergence of Green's function zeros already in the quantum spin-Hall regime. The non-trivial interplay between Green's function poles and zeros leads to an exotic quantum spin-Hall insulator exhibiting two chiral branches of edge Green's function poles and one of zeros. When symmetry breaking is allowed, a non-topological excitonic insulator is found to intrude between quantum spin-Hall and Mott insulators. We find evidence that excitons in the Mott insulator, which become soft at the transition to the excitonic insulator, are actually bound states between valence and conduction bands of Green's function zeros, rather than between lower and upper Hubbard bands.

cond-mat.str-el↗

arXiv2024

Luttinger surface dominance and Fermi liquid behaviour of topological Kondo insulators SmB$_6$ and YbB$_{12}$

Defying the traditional classification into metals and insulators, several materials simultaneously display metallic thermal properties and insulating electric behaviour, as if they hosted quasiparticles carrying entropy but not charge. Among them, some materials also possess quantum oscillations in magnetic fields as if they had well-defined Fermi surfaces despite the insulating gap. This remarkable dichotomy has been observed in the topological Kondo insulators SmB$_6$ and YbB$_{12}$. Prompted by the peculiar mixed-valence nature of these compounds, involving $f$ and $d$ electrons of the lanthanide, we propose an explanation of their intriguing properties drawing inspiration from the physics of the pseudogap phase in underdoped cuprates. We argue that the $f$ and $d$ subsystems, when considered separately, act, respectively, as electron- and hole-doped Mott insulators, featuring Fermi pockets coexisting with Luttinger surfaces responsible for the pseudogap. When the two are coupled to each other a hybridisation gap opens up, and the whole turns into a topological insulator endowed with genuine chiral edge states. However, the Luttinger surfaces persist and support neutral quasiparticles. This scenario, supported by numerical simulations within the dynamical cluster approximation, effectively resolves the paradoxical phenomenology of SmB$_6$ and YbB$_{12}$.

cond-mat.str-el↗