arXiv subjects

M. B. Sturla

Publications and source records attributed to M. B. Sturla.

6 recordsLinked to original sources

arXiv2021

Anomalous Hall effect in the coplanar antiferromagnetic coloring-triangular lattice

We study the anomalous Hall effect on the antiferromagnetic coloring-triangular lattice with a coplanar magnetic configuration in presence of a spin-orbit interaction. The effect of the spin-orbit coupling is included at effective level as a rotation of the electronic spin as the electrons hop from site to site. Our result reveals that a finite Hall conductivity in the planar 120$^{\circ}$ structure takes place if a finite spin-orbit coupling is present. A quantized Hall conductivity occurs at global band gaps resulting from the topologically non-trivial band structure.

cond-mat.str-el↗

arXiv2020

Vortex lattice in two-dimensional chiral XY ferromagnets and the inverse Berezinskii-Kosterlitz-Thouless transition

In this Letter we will show that, in the presence of a properly modulated Dzyaloshinskii-Moriya (DM) interaction, a $U(1)$ vortex-antivortex lattice appears at low temperatures for a wide range of the DM interaction. Even more, in the region dominated by the exchange interaction, a standard BKT transition occurs. In the opposite regime, the one dominated by the DM interaction, a kind of inverse BKT transition (iBKT) takes place. As temperature rises, the vortex-antivortex lattice starts melting by annihilation of pairs of vortex-antivortex, in a sort of "inverse" BKT transition.

cond-mat.str-el↗

arXiv2019

From skyrmions to Z2 vortices in distorted chiral antiferromagnets

Swirling topological spin configurations, known as magnetic skyrmions, are known to be stabilised in chiral ferromagnets with Dzyaloshinskii-Moriya interaction (DMI). In particular, for appropriate values of the external magnetic field they appear in a topological crystalline phase, termed Skyrmion crystal phase (SkX). A similar phenomenon is present in the antiferromagnetic case, for the Heisenberg triangular antiferromagnet (HTAF) with DMI. Here, the most striking feature is that the emergent topological phase consists of three SkX interpenetrated sublattices. On the other hand, the pure HTAF, being described by an SO(3) order parameter, can host Z2 vortices. This rises the fundamental question on whether both non trivial structures are related. In this paper we unravel a hidden connection between both topological entities by studying the HTAF with anisotropic DMI. To this end, we combine an effective field theory description, the Luttinger-Tisza approximation and Monte Carlo simulations. We show that even a slight anisotropy in the DMI proves to be the key ingredient to deform the interpenetrated SkX structure and reveal a Z2-vortex crystal.

cond-mat.str-el↗

arXiv2018

Stability of skyrmions in perturbed ferromagnetic chiral magnets

Magnetic skyrmions, topological spin textures observed in chiral magnets, have attracted huge interest due to their applications in the field of spintronics. In this work we study the stability of circular isolated skyrmions in ferromagnetic chiral magnets under the influence of different perturbations and external fields. To this end we develop a general systematic procedure based in a harmonic expansion series of the skyrmion boundary which allows the identifycation of the breakdown of the skyrmion circular shape on each instability channel independently. We apply our approach to a few representative spin models with actual interest in order to obtain the zero temperature phase diagram, where isolated skyrmions emerge as metaestable states. The results presented in this paper are in agreement with properties of isolated skyrmions observed in recent experiments opening the possibility of extending the analysis to more complex situations.

cond-mat.str-el↗

arXiv2016

Composite Spin Crystal Phase in Antiferromagnetic Chiral Magnets

We study the classical antiferromagnetic Heisenberg model on the triangular lattice with Dzyaloshinskii-Moriya interactions in a magnetic field. We focus in particular in the emergence of a composite spin crystal phase, dubbed antiferromagnetic skyrmion lattice, that was recently observed in [Phys. Rev. B 92, 214439 (2015)] for intermediate fields. This complex phase can be made up from three inter-penetrated skyrmion lattices, one for each sub-lattice of the original triangular one. Following these recent numerical results, in this paper we explicitly construct the low-energy effective action that reproduces the correct phenomenology and could serve as a starting point to study the coupling to charge carriers, lattice vibrations, structural disorder and transport phenomena.

cond-mat.str-el↗

arXiv2013

Low energy electron-phonon effective action from symmetry analysis

Based on a detailed symmetry analysis, we state the general rules to build up the effective low energy field theory describing a system of electrons weakly interacting with the lattice degrees of freedom. The basic elements in our construction are what we call the "memory tensors", that keep track of the microscopic discrete symmetries into the coarse-grained action. The present approach can be applied to lattice systems in arbitrary dimensions and in a systematic way to any desired order in derivatives. We apply the method to the honeycomb lattice and re-obtain the by now well-known effective action of Dirac fermions coupled to fictitious gauge fields. As a second example, we derive the effective action for electrons in the kagomé lattice, where our approach allows to obtain in a simple way the low energy electron-phonon coupling terms.

cond-mat.str-el↗