arXiv subjects

Francesca Paoletti

Publications and source records attributed to Francesca Paoletti.

4 recordsLinked to original sources

arXiv2026

Poles-zeros duality in semi-holographic Mott insulators

Inspired by the poles-zeros duality of Green's functions that appears in transitions into Mott-insulating phases in strongly correlated condensed matter systems, we propose a semi-holographic approach to Mott insulators. In this model, a fundamental fermion is coupled to a large-$N$, strongly interacting sector that generates a self-energy for the fundamental fermion's Green's function. This coupling amounts to a hybridization of the fundamental fermion with a strongly correlated fermionic composite. Within the holographic framework, at large $N$, the Green's function of the composite fermion naturally exhibits a poles-zeros duality. Zeros of the Green's function are caused by the poles of the self-energy that correspond to collective many-body excitations of the holographic strongly interacting sector. We calculate the spectral function of the fundamental fermion, from which we characterize the semi-holographic metallic and the Mott-insulating phases. In addition to the new physical interpretation of the zeros, our analysis yields a well-defined picture of the poles-zeros duality in terms of the freedom to choose between standard and alternative quantization in the strongly coupled sector.

hep-th↗

arXiv2025

Topologically enabled superconductivity: possible implications for rhombohedral graphene

We present a topological mechanism for superconductivity emerging from Chern-2 insulators. While, naively, time-reversal symmetry breaking is expected to prevent superconductivity, it turns out that the opposite is the case: An explicit model calculation for a generalized attractive-U Haldane-Hubbard model demonstrates that superconductivity is only stabilized near the quantum anomalous Hall state, but not near a trivial, time-reversal symmetric band insulator. As standard Bardeen-Cooper-Schrieffer-like mean-field theory fails to capture any superconducting state, we explain this using an effective fractionalized field theory involving fermionic chargeons, bosonic colorons and an emergent U(1) gauge field. When the chargeons form a gapped topological band structure, the proliferation of single monopoles of this gauge field is forbidden. However, long-ranged monopole-antimonopole correlations emerge, and we argue that those correspond to superconducting order. Using random phase approximation on top of extensive slave-rotor mean-field calculations we characterize coherence length and stiffness of the superconductor. Thereby, we deduce the phase diagram in parameter space and furthermore discuss the effect of doping, temperature and an external magnetic field. We complement the fractionalized theory with calculations using an effective spin model and Gutzwiller projected wavefunctions. While mostly based on a simple toy model, we argue that our findings contribute to a better understanding of superconductivity emerging out of spin- and valley polarized rhombohedral graphene multilayers in a parameter regime with nearby quantum anomalous Hall insulators.

cond-mat.str-el↗

arXiv2023

Topological Gap Opening without Symmetry Breaking from Dynamical Quantum Correlations

Topological phase transitions are typically associated with the formation of gapless states. Spontaneous symmetry breaking can lead to a gap opening thereby obliterating the topological nature of the system. Here we highlight a completely different destiny for a topological transition in presence of interaction. Solving a Bernevig-Hughes-Zhang model with local interaction, we show that dynamical quantum fluctuations can lead to the opening of a gap without any symmetry breaking. As we vary the interaction and the bare mass of the model, the continuous gapless topological transition turns into a first-order one, associated with the presence of massive Dirac fermion at the transition point showing a Gross-Neveu critical behaviour near the quantum critical endpoint. We identify the gap opening as a condensed matter analog of the Coleman-Weinberg mechanism of mass generation.

cond-mat.str-el↗

arXiv2023

Dynamical correlations and order in magic-angle twisted bilayer graphene

In magic angle twisted bilayer graphene, transport, thermodynamic and spectroscopic experiments pinpoint at a competition between distinct low-energy states with and without electronic order. We use Dynamical Mean Field Theory (DMFT) on the topological heavy Fermion (THF) model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We contrast moment formation, Kondo screening and ordering on a temperature basis and explain the nature of emergent correlated states based on three central phenomena: (i) the formation of local spin and valley isospin moments around 100K, (ii) the ordering of the local isospin moments around 10K preempting Kondo screening, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a "bad metal" above the ordering temperature, where scattering off the disordered local moments suppresses electronic coherence, and a "good metal" in the ordered states with coherence of quasiparticles facilitated by isospin order. This finding reveals coherence from order as the microscopic mechanism behind the Pomeranchuk effect observed experimentally. Upon doping, there is a periodic charge reshuffling between localized and delocalized electronic orbitals leading to cascades of doping-induced Lifshitz transitions, local spectral weight redistributions and periodic variations of the electronic compressibility. Our findings provide a unified understanding of the most puzzling aspects of scanning tunneling spectroscopy, transport, and compressibility experiments.

cond-mat.str-el↗