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Register a new userMagnetic Skyrmionic Polarons
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Authors
Luis Brey
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We study a two-dimensional electron gas exchanged-coupled to a system of classical magnetic ions. For large Rashba spin-orbit coupling a single electron can become self-trapped in a skyrmion spin texture self-induced in the magnetic ions system. This new quasiparticle carries electrical and topological charge as well as a large spin, and we named it as magnetic skyrmionic polaron. We study the range of parameters; temperature, exchange coupling, Rashba coupling and magnetic field, for which the magnetic skyrmionic polaron is the fundamental state in the system. The dynamics of this quasiparticle is studied using the collective coordinate approximation, and we obtain that in presence of an electric field the new quasiparticle shows, because the chirality of the skyrmion, a Hall effect. Finally we argue that the magnetic skyrmionic polarons can be found in large Rashba spin-orbit coupling semiconductors as GeMnTe.
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Magnetic skyrmions have the potential to provide solutions for low-power, high-density data storage and processing. One of the major challenges in developing skyrmion-based devices is the skyrmions magnetic stability in confined helimagnetic nanostructures. Through a systematic study of equilibrium states, using a full three-dimensional micromagnetic model including demagnetisation effects, we demonstrate that skyrmionic textures are the lowest energy states in helimagnetic thin film nanostructures at zero external magnetic field and in absence of magnetocrystalline anisotropy. We also report the regions of metastability for non-ground state equilibrium configurations. We show that bistable skyrmionic textures undergo hysteretic behaviour between two energetically equivalent skyrmionic states with different core orientation, even in absence of both magnetocrystalline and demagnetisation-based shape anisotropies, suggesting the existence of Dzyaloshinskii-Moriya-based shape anisotropy. Finally, we show that the skyrmionic texture core reversal dynamics is facilitated by the Bloch point occurrence and propagation.
We report on the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite. We probe the time evolution of four distinct exciton resonances by means of time-resolved photoluminescence and transient absorption spectroscopies, and find that at 5,K a subset of excitons form on a $lesssim$ 1-ps timescale, and that these relax subsequently to lower-energy excitons on $sim$ 5--10,ps with a marked temperature dependence over $<$ 100,K. We implement a mode projection analysis that determines the relative contribution of all observed phonons with frequency $leq$50,cm$^{-1}$ to inter-exciton nonadiabatic coupling, which in turn determines the rate of exciton relaxation. This analysis ranks the relative contribution of the phonons that participate in polaronic lattice distortions to the exciton inter-conversion dynamics and thus establishes their role in the nonadiabatic mixing of exciton states, and this in the exciton relaxation rate.
We study bound magnetic polarons (BMP) in a very diluted magnetic semiconductor CdMnTe by means of site selective spectroscopy. In zero magnetic field we detect a broad and asymmetric band with a characteristic spectral width of about 5 meV. When external magnetic fields are applied a new line appears in the emission spectrum. Remarkably, the spectral width of this line is reduced greatly down to 0.24 meV. We attribute such unusual behavior to the formation of BMP, effected by sizable fluctuations of local magnetic moments. The modifications of the optical spectra have been simulated by the Monte-Carlo method and calculated within an approach considering the nearest Mn ion. A quantitative agreement with the experiment is achieved without use of fitting parameters. It is demonstrated that the low-energy part of the emission spectra originates from the energetic relaxation of a complex consisting of a hole and its nearest Mn ion. It is also shown that the contribution to the narrow line arises from the remote Mn ions.
Fractons are a type of emergent quasiparticle which cannot move freely in isolation, but can easily move in bound pairs. Similar phenomenology is found in boson-affected hopping models, encountered in the study of polaron systems and hole-doped Ising antiferromagnets, in which motion of a particle requires the creation or absorption of bosonic excitations. We show that boson-affected hopping models can provide a natural realization of fractons, either approximately or exactly, depending on the details of the system. We first consider a generic one-dimensional boson-affected hopping model, in which we show that single particles move only at sixth order in perturbation theory, while motion of bound states occurs at second order, allowing for a broad parameter regime exhibiting approximate fracton phenomenology. We explicitly map the model onto a fracton Hamiltonian featuring conservation of dipole moment via integrating out the mediating bosons. We then consider a special type of boson-affected hopping models with mutual hard-core repulsion between particles and bosons, accessible in hole-doped mixed-dimensional Ising antiferromagnets, in which the hole motion is one dimensional in an otherwise two-dimensional antiferromagnetic background. We show that this system, which is within the current reach of ultracold-atom experiments, exhibits perfect fracton behavior to all orders in perturbation theory, thereby enabling the experimental study of dipole-conserving field theories. We further discuss diagnostic signatures of fractonic behavior in these systems. In studying these models, we also identify simple effective one-dimensional microscopic Hamiltonians featuring perfect fractonic behavior, paving the way to future studies on fracton physics in lower dimensions.
Magnetic solitons are twisted spin configurations, which are characterized by a topological integer (textit{Q}) and helicity ($gamma$). Due to their quasi-particle properties, relatively smaller size, and the potential to set themselves into motion with smaller critical current densities than domain walls, they hold promising aspects as bits of information in future magnetic logic and memory devices. System having Dzyaloshinskii-Moriya Interaction (DMI) prefers a particular rotational sense, which determines a single value of Q and $gamma$. However, the case of frustrated ferromagnet is of particular interest since solitons with different $Q$ and $gamma$ can be stabilized. Recently, higher order skyrmion($Q>2$) and coexistence of skyrmion and antiskyrmion in frustrated ferromagnets has been predicted using $J_1$--$J_2$--$J_3$ classical Heisenberg model. cite{zxcv} In this work, we modelled a synthetic antiferromagnet (SAF) system to co-exist both skyrmion and antiskyrmion, but without considering frustrated exchange interaction. The bottom layer of the SAF has isotropic DMI and the top layer has anisotropic DMI. The presence of antiskyrmion and skyrmion in the two different layers may induce magnetic frustration in the SAF. Here we have varied the strength of Ruderman--Kittel--Kasuya--Yosida (RKKY) coupling as a perturbation and observed 6 novel elliptical skyrmionic states. We have observed that skyrmionic states have a 3 fold degeneracy and another two fold degeneracy. We also report a novel elliptical Q = 0 state.
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