arXiv subjects

J. Colbois

Publications and source records attributed to J. Colbois.

3 recordsLinked to original sources

arXiv2026

Excitation caging in a vertex-frustrated quasiperiodic Einstein artificial spin ice

Naturally occurring bulk quasicrystals are rare, and magnetic instances are rarer still, with chemical constraints typically permitting the synthesis of approximants rather than true quasicrystalline magnets. Here, we present an artificial spin ice based on a recently discovered Einstein lattice, the Hat tiling, which is built from the first known shape - the hat - that tiles the plane only aperiodically. The Einstein artificial spin ice has long-range structural order with no translational symmetry, and low-connectivity vertices with well-defined local ground states and excitations. Together, these properties provide a model two-dimensional quasicrystalline magnet, with magnetic correlations that we probe with magnetic force microscopy and parallel-tempered Monte Carlo simulations. We identify a two-stage partial ordering process, driven by the competition between two possible positions for magnetic excitations. This competition is resolved in the ground-state manifold, where exactly one magnetic excitation is caged on each antihat, yet the manifold remains macroscopically degenerate. This yields an unusual type of medium-range order, where the underlying quasiperiodic long-range order is randomly modulated by a strictly constrained disorder. Our findings establish the Einstein artificial spin ice as a blueprint for understanding quasicrystalline magnetism, demonstrating how quasiperiodic monotile geometries can be exploited to engineer unconventional magnetic phases with no direct equivalent in periodic systems.

cond-mat.mes-hall↗

arXiv2020

Probing the topology of the quantum analog of a classical skyrmion

In magnetism, skyrmions correspond to classical three-dimensional spin textures characterized by a topological invariant that keeps track of the winding of the magnetization in real space, a property that cannot be easily generalized to the quantum case since the orientation of a quantum spin is in general ill-defined. Moreover, as we show, the quantum skyrmion state cannot be directly observed in modern experiments that probe the local magnetization of the system. However, we show that this novel quantum state can still be identified and fully characterized by a special local three-spin correlation function defined on neighbouring lattice sites -- the scalar chirality -- which reduces to the classical topological invariant for large systems, and which is shown to be nearly constant in the quantum skyrmion phase.

cond-mat.str-el↗

arXiv2018

Quantum Nanoskyrmions

Skyrmions in condensed matter physics appear as classical topological spin structures. This nontrivial state can be obtained solving the corresponding micromagnetic model, where the magnetization is treated as a continuous classical vector field. Here, we introduce a new concept of quantum skyrmions of a nanoscale size. This distinct magnetic state can be formed in spin-1/2 low dimensional magnets characterized by a strong Dzyaloshinskii-Moriya interaction. This concept can also be applied to usual spin systems characterized by a nonzero exchange interaction if the quantum solution of the problem is accessible. To perform a complete characterization of such a quantum nanoskyrmion state, we analyze basis functions giving the largest contribution to the ground state at different values of external magnetic field and temperature. We observe that the quantum skyrmionic state is stabilized even when the corresponding classical skyrmionic solution has already undergone a phase transition towards the polarized ferromagnetic state.

cond-mat.str-el↗