arXiv subjects

Pierre Lombardo

Publications and source records attributed to Pierre Lombardo.

5 recordsLinked to original sources

arXiv2025

Topological Hall Response from Canted Antiferromagnetic Order in $d$-Electron Kagome Systems

In a two-dimensional kagome monolayer, a nontrivial intrinsic Berry curvature may arise in the $d$-electron system from the interaction with a non-collinear spin order induced by an underlying antiferromagnetic exchange. This opens the route for a quantum anomalous Hall effect in the multi-orbital system, even without an external magnetic field, explicit spin-orbit coupling or relativistic effects. For spin orders with an out-of-plane component, the scalar spin chirality is finite, and the integration of the Berry curvature over the Brillouin zone may yield integer Hall conductivities in units of $e^2/h$. For a Fermi level within a nontrivial gap, the canted configuration offers, at least in principle, the possibility of a maximal Chern number, $C=\pm 5$. Candidate materials are considered in this paper. In existing materials, the electron hopping is generally highly anisotropic, leading to a quantum anomalous Hall effect with smaller Chern numbers. A topological phase transition between Hall plateaus of opposite $C$ can be driven by flipping the out-of-plane component of the spin order, alluding to the potential of this system to applications in quantum information.

cond-mat.mes-hall↗

arXiv2025

Quantum dot-based device for high-performance magnetic microscopy and spin filtering in the Kondo regime

We propose a nanoscale device consisting of a double quantum dot with a full exchange and pair hopping interaction. In this design, the current can only flow through the upper dot, but is sensitive to the spin state of the lower dot. The system is immersed in a highly inhomogeneous magnetic field, and only the bottom dot feels a substantial magnetic field, while the top dot experiences only a residual one. We show that our device exhibits very interesting magnetic field-dependent transport properties at low temperatures. The Kondo effect partially survives the presence of the magnetic field and allows to obtain conductances that differ by several orders of magnitude for the two spin types across the top dot. Interestingly, as a function of the magnetic field, our two-dot device changes from a spin singlet state to a spin triplet state, in which the amplitudes of the spin-dependent conductances are reversed. Our device is able to discriminate between positive and negative magnetic fields with a high sensitivity and is therefore particularly interesting for imaging the surface of anti-ferromagnetic (AF) insulating materials with alternated surface magnetic field, as well as for spin filtering applications.

cond-mat.mes-hall↗

arXiv2024

Quantum Anomalous Hall Effect in $d$-Electron Kagome Systems: Chern Insulating States from Transverse Spin-Orbit Coupling

The possibility of quantum anomalous Hall effect (QAHE) in two-dimensional kagome systems with $d$-orbital electrons is studied within a multi-orbital tight-binding model. We concentrate on the case of isotropic Slater-Koster integrals which is realized in a recently discovered class of metal-organic frameworks TM$_3$C$_6$O$_6$ with transition metals (TM) in the beginning of the 3$d$ series. Furthermore, in the absence of exchange-type spin-orbit coupling, only isotropic Slater-Koster integrals give a perfect flatband in addition to the two dispersive bands hosting relativistic (Dirac) and quadratic band crossing points at high symmetry spots in the Brillouin zone. A quantized topological invariant requires a flux-creating spin-orbit coupling, giving Chern number (per spin sector) $C=1$ not only from the familiar Dirac points at the six corners of the Brillouin zone, but also from the quadratic band crossing point at the center $\Gamma$. In the case of isotropic Slater-Koster integrals the on-site spin-orbit coupling (SOC) is ineffective to create the QAHE and it is only the transfer or exchange-type SOC which can lead to a QAHE. Surprisingly, this QAHE comes from the nontrivial effective flux induced by the \textit{transverse} part of the spin-orbit coupling, exhibited by electrons in the $d$-orbital state with $m_l=0$ ($d_{z^2}$ orbital), in stark contrast to the more familiar form of QAHE due to the $d$-orbitals with $m_l \neq 0$, driven by the Ising part of spin-orbit coupling. The $C=1$ Chern plateau (per spin sector) due to Dirac point extends over a smaller region of Fermi energy than that due to quadratic band crossing. Our result hints at the promising potential of kagome $d$-electron systems as a platform for dissipationless electronics by virtue of its unique QAHE.

cond-mat.str-el↗

arXiv2021

Kondo-assisted switching between three conduction states in capacitively coupled quantum dots

We propose a nanoscale device consisting of a double quantum dot with strong intra- and inter- dot Coulomb repulsions. In this design, the current can only flow through the lower dot, but is triggered by the gate-controlled occupancy of the upper dot. At low temperatures, our calculations predict the double dot to pass through a narrow Kondo regime, resulting in highly sensitive switching characteristics between three well-defined states : insulating, normal conduction and resonant conduction.

cond-mat.mes-hall↗

arXiv2000

Electronic properties of the degenerate Hubbard Model : A dynamical mean field approach

We have investigated electronic properties of the degenerate multi-orbital Hubbard model, in the limit of large spatial dimension. A new local model, including a doubly degenerate strongly correlated site has been introduced and solved in the framework of the non-crossing approximation (NCA). Mott-Hubbard transitions have been examined in details, including the calculation of Coulomb repulsion critical values and electronic densities of states for any regime of parameters.

cond-mat.str-el↗