arXiv subjects

Alvaro S. Nunez

Publications and source records attributed to Alvaro S. Nunez.

At least 19 recordsLinked to original sources

arXiv2026

Altermagnetic memcapacitors

We propose a spintronic memcapacitance effect based upon altermagnetic multiferroic materials. We identify the rare-earth vanadates RVO$_3$ as a concrete platform, with all key parameters tied to measured properties. Under an oscillating electric field, the resulting charge and spin currents trace pinched hysteresis loops that close tangentially at zero field -- the hallmark of memcapacitive, type-2 memdevice behavior -- with charge current densities exceeding, by a factor of about 3.6, the lowest deterministic switching current density reported for optimized spin-transfer-torque magnetic tunnel junctions. We model the system theoretically as a dimerized two-orbital $d$-wave altermagnetic lattice via a Su--Schrieffer--Heeger-type bond modulation, in the spirit of the spin-dependent Rice--Mele model, thereby coupling the altermagnetic order to field-switchable charge and spin polarizations. The associated polarization loops close tangentially at zero field and yield a sign-changing, history-dependent ``butterfly'' differential capacitance, identifying the device as a genuine memcapacitor. Both responses are protected by the same inversion symmetry, so charge and spin channels switch simultaneously with no separate control needed. These results establish altermagnetic multiferroics, realized concretely in RVO$_3$, as an efficient, non-volatile platform for combined electric and spintronic memory.

cond-mat.mes-hall↗

arXiv2026

Electrically Switchable Spintronics in a Multiferroic Altermagnet

We introduce a minimal model of a two-dimensional lattice that, upon spontaneous symmetry breaking, simultaneously develops altermagnetic order, a finite electric polarization, and a spin-polarized transport response, all of which are controlled by an external electric field. By coupling a dimerized altermagnet to an external electric field, we show that the three order parameters are not merely compatible but dynamically entangled, so that switching one (for instance, reversing the polarization with an electric field) necessarily reconfigures the other two. We show that this model offers a clear physical blueprint for designing next-generation spintronic logic and pure spin current memdevices that merge the ultrafast, stray-field-free advantages of compensated magnets with the low-power switching architectures of ferroelectrics.

cond-mat.mes-hall↗

arXiv2026

Moving Analogue Horizons in Stationary Ferroelectrics

We show that a traveling modulation of the polarization-gradient stiffness in a ferroelectric material induces an effective flow in its collective polarization dynamics. Within a controlled local approximation, small polarization fluctuations, or ferrons, obey a massive Klein-Gordon equation with flow. Unlike conventional analogue-gravity platforms, the effective flow originates from the modulation of the material parameters rather than from the physical transport of the medium. This mechanism enables mobile analogue horizons separating sub-ferronic and super-ferronic regions, the latter supporting negative-norm antiferron modes. Their coupling to positive-norm ferrons gives rise to superradiant-like amplification, while the effective mass gap can be tuned independently through an external electric field. Ferroelectric systems therefore provide a novel and experimentally controllable platform for analogue gravity with massive scalar excitations.

cond-mat.mes-hall↗

arXiv2026

Antiferromagnetic Pure Spin Current Memdevices

Spin currents can be generated through various mechanisms, including the piezospintronic effect, which arises when strain or lattice distortions induce a change in the dipolar spin moment, causing a pure spin current without necessarily being accompanied by net charge transport. This opens new possibilities for low-power information processing and novel device architectures. In this work, we propose a novel effect, the spintronic-magneto-impedictive effect, as the theoretical basis for a pure spin-current memory-like device based on antiferromagnetic components. We focus on materials that can be modeled by the so-called spin-Rice-Mele Hamiltonian, incorporating a magnetic field gradient that explicitly breaks inversion symmetry. Our results shed light on how spin currents are generated and controlled, providing new insights into the potential of these materials for next-generation spintronic technologies.

cond-mat.mes-hall↗

arXiv2026

Scattering theory of spin waves by lattice dislocation defects

We investigate spin-wave propagation in magnetic insulators in the presence of lattice dislocations. Within a continuum magnetoelastic framework, we show that the strain fields generated by dislocations induce equilibrium magnetic textures. The morphology of these textures depends sensitively on the dislocation type and acts as a localized scattering potential for spin-wave excitations. As a result, the scattering response exhibits pronounced asymmetries and interference effects governed by the magnetoelastic coupling and the dislocation type. By combining numerical simulations with analytical scattering theory, we compute differential cross sections and frequency-dependent transmission coefficients. Furthermore, analysis of the effective potential landscape reveals that the defect forms a barrier that modulates spin-wave transport and, crucially, breaks the intrinsic reflectionless nature of magnetic domain walls. Our findings identify lattice dislocations as tunable scattering centers, opening new avenues for defect engineering in magnonic devices.

cond-mat.mes-hall↗

arXiv2025

Magnetic topological textures in nonorientable surfaces

Topological magnetic textures confined to two-dimensional (2D) non-orientable manifolds exhibit behaviors absent in planar systems. We investigate bimerons on Möbius surfaces and show that the lack of global orientation alters conservation laws, yielding geometry-dependent topology and dynamics. Micromagnetic simulations reveal that the helical twist and non-orientable geometry reshape the effective topological charge and stabilize chiral configurations imposed by the surface. Under spin-polarized currents, bimerons display unconventional transport: the transverse response is locally reversed or globally suppressed due to charge inversion along the manifold. Moreover, we establish an Aharonov-Bohm effect associated with the magnonic modes of the texture; in particular, the translational Goldstone mode implies that a bimeron on a Möbius strip should exhibit path-dependent quantum interference. These results identify a geometry-driven regime of magnetization dynamics and provide a route to curvature-engineered spintronic functionalities.

cond-mat.mes-hall↗

arXiv2025

Topological magnonic dislocations modes

Spin fluctuations in two-dimensional (2D) ferromagnets in the presence of crystalline lattice dislocations are investigated. We show the existence of topologically protected non-propagative modes that localize at dislocations. These in-gap states, coined as {\it magnonic dislocation modes}, are characterized by the $Z_2$ topological invariant that derives from parity symmetry broken induced by sublattice magnetic anisotropy. We uncover that bulk topology existing in the perfect crystal is robust under the influence of lattice defects, which is monitored by the real-space Bott index. It is also revealed that the topology of {magnonic dislocation modes} remains unaffected when bulk topology becomes trivial and is remarkably resilient against magnetic disorder. Our findings point to the intriguing relationship between topological lattice defects and the spectrum of topological spin excitations.

cond-mat.mes-hall↗

arXiv2025

Antiferron Modes in Ferroelectric Materials

We introduce the concept of antiferron modes in ferroelectric materials as dynamically stabilized collective excitations over inverted polarization states that decrease the system energy. While ferrons represent quantized oscillations around the stable polarization minimum, antiferrons require dynamic stabilization via high-frequency driving. Using a generalized Landau-Ginzburg-Devonshire framework, we derive the effective curvature corrections from external driving, demonstrate the conditions for stabilizing metastable wells, and present the quantized Hamiltonian. Antiferrons could be a promising candidate for developing electrical sensing devices, offering tunable, dynamically controllable excitations with high sensitivity to external electric fields.

cond-mat.mtrl-sci↗

arXiv2025

Elastic Dislocation-based Skyrmion Traps: Fundamentals and Applications

Topologically secure spin configurations, such as skyrmions and bimerons, offer a compelling alternative to conventional magnetic domains, potentially enabling high-density, low-power spintronic devices. These pseudo-particles, characterized by their swirling spin textures and nontrivial topological charges, are prevalent and notably influence their electronic, magnetic, and mechanical traits. This paper provides an in-depth overview of the interaction between a screw dislocation within a distorted magnetic lattice, exploring possible coupling mechanisms and establishing a promising link between two disparate topics in materials science: topological magnetism and topological elasticity. We first provide a classical analysis of skyrmion motion that reveals the dislocations as shallow traps on the magnetic texture. Afterwards, we provide an analysis of the quantized motion of the skyrmion and identify its quantum states. We conclude by illustrating how the ideas in our paper can be implemented in simple yet compelling devices based on the shallow traps from an array of dislocations acting as frets in a race-track, controlling the motion with a low current activation mechanism.

cond-mat.mes-hall↗

arXiv2025

Electric-Field Control of Josephson Oscillations in Dipolar Bose-Einstein Condensates

We study the dynamic behavior of a Bose-Einstein condensate (BEC) with dipolar interactions when the influence of external electric fields affects the coherent tunneling properties. Here, we propose a tunable platform based on BECs where Josephson oscillations can be engineered and modulated through external electric fields. We develop a theoretical and numerical frame-work that reveals how electric fields affect intercondensate tunneling, phase dynamics, and collective excitations. By employing a coupled set of Gross-Pitaevskii equations with adiabatic elimination of excited states, we demonstrate field-induced tuning of Josephson frequencies and a transition from contact to dipole-dominated regimes. These findings corroborate theoretical predictions about the sensitivity of dipolar BECs to external fields and deepen our understanding of quantum coherence and tunneling in long-range interacting quantum systems.

cond-mat.quant-gas↗

arXiv2025

Quantized Piezospintronic Effect in Moiré Systems

This paper presents a novel approach for generating and controlling spin currents in an antiferromagnetic twisted honeycomb bilayer in response to an elastic deformation. Utilizing a continuum model, closely based upon the seminal Bistritzer-MacDonald model, that captures the essential physics of low-energy moiré bands, we calculate the spin current response to the deformation in terms of the familiar Berry phase formalism. The resulting moiré superlattice potential modulates the electronic band structure, leading to emergent topological phases and novel transport properties such as quantized piezo responses both for spin and charge transport. This approach allows us to tune the system across different topological regimes and to explore the piezo-spintronic responses as a function of the band topology. When inversion symmetry is broken either by a sublattice potential $V$, alignment with an hBN substrate, uniaxial strain, or structural asymmetry present in the moiré superlattice, the system acquires a finite Berry curvature that is opposite in the $K$ and $K'$ valleys (protected by valley time reversal symmetry). In contrast, for strain, the valley-contrasting nature of the pseudo-gauge field ensures that the quantized response is robust and proportional to the sum of the valley Chern numbers. These notable physical properties make these systems promising candidates for groundbreaking spintronic and valleytronic devices.

cond-mat.mes-hall↗

arXiv2025

Magnetic Worms: Oscillatory Bimeron Pairing And Collective Transport In Patterned Stripes

Magnetic bimerons in a domain wall provide a practical route for current driven transport in patterned magnetic stripes. However, coupling between bimerons and pinning by defects complicate reliable motion. Here we show that a periodic array of edge defects both stabilizes transport of multiple bimerons and gives rise to a distinctive collective state, the magnetic worm. A single bimeron travels at constant speed; defects lower this speed while preserving an approximately linear relation between velocity $v$ and current density $J$. With two bimerons, the center of mass advances nearly uniformly while their separation exhibits a bounded oscillation whose frequency increases and amplitude decreases with current. For larger trains, these oscillations lose synchrony, producing segmented, worm like motion. The center of mass speed grows with current but decreases as the number of bimerons increases. Notably, eight bimerons cannot be sustained in a smooth stripe but can be stabilized by the periodic defects

cond-mat.mes-hall↗

arXiv2025

Antiferromagnetic Hall-Memristors

Spin-memristors are a class of materials that can store memories through the control of spins, potentially leading to novel technologies that address the constraints of standard silicon electronics, thereby facilitating the advancement of more intelligent and energy-efficient computing systems. In this work, we present a spin-memristor based on antiferromagnetic materials that exhibit Hall-memresistance. Moreover, the nonlinear Edelstein effect acts as both a writer and eraser of memory registers. We provide a generic symmetry-based analysis that supports the viability of the effect. To achieve a concrete realization of these ideas, we focus on CuMnAs, which has been shown to have a controllable nonlinear Hall effect. Our results extend the two-terminal spin-memristor setting, which is customarily the standard type of device in this context, to a four-terminal device.

cond-mat.mtrl-sci↗

arXiv2025

Static and Dynamics of Twisted Skyrmion Tubes in Frustrated Magnets

Stable three-dimensional topological skyrmion structures in frustrated magnets are investigated. The texture exhibits a helicoid pattern along the vertical direction, described by a position-dependent helicity, which interpolates between Neel- and hedgehog-like two-dimensional skyrmions, characterized by the Hopf index, and is referred to as "twisted skyrmion tubes" (TSkTs). The stability and topology of TSkTs are achieved by competing next-nearest-neighbor exchange interactions, the thickness of the magnet, and the applied magnetic field. The dynamical behavior of a twisted structure in frustrated magnets is determined. Specifically, we derive that the helicity dynamics of the TSkT can be driven by an electric current resulting from spin-orbit torque interaction. Furthermore, we address the study of the electronic scattering problem using a spin-orbit-torque-driven TSKT, which offers promising applications for low-power storage nanodevices and nanobatteries with enhanced control.

cond-mat.mes-hall↗

arXiv2025

Electrical Control of the Exchange Bias Effect at Model Ferromagnet-Altermagnet Junctions

This work analyzes the behavior of the interface between a ferromagnetic material and an alter-magnet. We use a well-established line of arguments based on electronic mean-field calculations to show that new surface phenomena that lead to altermagnetic materials induce an exchange bias effect on the nearby ferromagnet. We reveal the physical mechanisms behind this phenomenon that lead to quantitative control over its strength. Interestingly, we predict exotic electric-field-induced phenomena. This is an analogy to the relationship between exchange bias and the injection of spin currents in spin-transfer-dominated scenarios, which has been reported earlier in the traditional antiferromagnetic/ferromagnetic junction.

cond-mat.mtrl-sci↗

arXiv2024

Elementary theory of Magnetoferrons: bringing magnons and ferrons together in multiferroic systems

The collective excitations of a multiferroic material are analyzed. We show that these excitations also exhibit magnetoelectric behavior, leading to the hybridization of magnons ,oscillations of the magnetization field, and ferrons, which are oscillations of the electric dipolar density field. We term these emergent entities 'magnetoferrons', study their main properties, and discuss their potential applications. Additionally, we provide a phenomenological framework for these systems, which will be invaluable for describing the dynamics of the multiferromagnetic state.

cond-mat.mes-hall↗

arXiv2024

Quantized Toroidal Waves on Ferrotoroidal Magnets

Magnetic-ferroic ordering and magnetic-toroidal moments are essential concepts in molecular electronics and magnetics. The magnetic toroidal moment is critical in understanding new electronic states and their possible uses. This paper discusses the notion of toroidicity waves. In particular, we present a one-dimensional model of interconnected toroidicity leading to an organization principle around an emergent quantum particle, a carrier of toroidicity waves, dubbed the toroidon. We illustrate some functionalities that could be achieved once control over the toroidon is acquired. We show that a 1D dimerized and antiferromagnetic-like spin chain can display ferrotoroidicity and propose its description in terms of an effective quasi-1D spin chain, marking a crucial step towards further research on the phenomena and potential applications of ferrotoroids.

cond-mat.mes-hall↗

arXiv2024

Magnonics along the wall in Bimeron Chain Domain Walls

We demonstrate that domain walls built from bimeron chains (bc-DW) in two-dimensional systems constitute a spontaneously assembled medium that holds magnonic excitations along its direction. We prove that such magnons are topological, leading to protected edge states. We also verify the stability of the domain walls and its edge modes' resilience against disorder. Analytical calculations and micromagnetic simulations support our findings. The robustness of these edge modes holds promise for potential applications in the design of nanoscale magnonic devices for information storage and transport.

cond-mat.mes-hall↗