arXiv subjects

Mohsen Yarmohammadi

Publications and source records attributed to Mohsen Yarmohammadi.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry-selective nonrelativistic spin splitting in antiferromagnets driven by coherent phonons

Nonrelativistic spin splitting (NRSS) in antiferromagnets (AFMs) enables magnetization-free spin polarization for ultrafast spintronics. Here, we demonstrate that coherent phonons can dynamically induce and control NRSS in collinear AFMs. Excitation of $Γ$-point infrared-active phonons lifts the spin degeneracy of the ground state, while the residual sublattice-connecting symmetries determine the momentum-space form of the induced splitting. Because the relevant infrared modes couple to orthogonal in-plane light polarizations, distinct spin-split phases can be selectively activated by the polarization of the driving field. Using first-principles calculations for MnPS$_3$, we show that a mode that breaks all sublattice-connecting symmetries induces an $s$-wave spin-split state with $Δ(Γ)\neq0$, whereas a symmetry-distinct mode that preserves a sublattice-connecting mirror symmetry generates a $d$-wave altermagnetic state with $Δ(Γ)=0$. In both cases, the spin splitting grows linearly with the phonon amplitude and reverses the induced spin polarization when the displacement is reversed. Our results establish coherent lattice driving as a direct, polarization- and mode-selective route to dynamically induce distinct NRSS phases in AFMs.

cond-mat.mtrl-sci↗

arXiv2026

Efficient two-color Floquet control of the RKKY interaction in altermagnets

Magnetic impurities in real materials can mask the intrinsic spin-dependent properties of hosts. They interact indirectly through the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism, which limits the use of isolated impurity spins in applications such as qubits and spintronics. By suppressing the RKKY interaction, an effective control scheme should therefore enable access to the host's unperturbed behavior while simultaneously isolating the impurity spins for functional use. Although beyond static approaches, single-color laser driving can suppress the RKKY interaction, it typically requires strong fields that may be impractical or destabilizing. To overcome these limitations, we show that two-color laser driving provides efficient and tunable control over all components of the RKKY interaction using two weak laser fields. Focusing on two-dimensional Rashba altermagnets, we show that interference between one- and two-photon processes produces altermagnet-specific Floquet corrections. These include additional AC Stark shifts, magnetizations, spin-orbit renormalization, and emergent in-plane Zeeman fields, which are absent under single-color driving and in non-altermagnetic systems. Notably, two-color driving induces a finite $z$-component of the Dzyaloshinskii-Moriya (DM) interaction, stabilizing in-plane chiral magnetism and related textures in Rashba altermagnets. These effects enable tunable, near-complete on-off switching of the Heisenberg, Ising, and DM interactions through a Lifshitz-like modulation of the Fermi surface. We also show that the tuning process is highly sensitive to the chirality of both beams. We further map out phase diagrams for ferromagnetic and antiferromagnetic alignment of impurities with clockwise and counterclockwise canting as a function of Rashba coupling and altermagnetic order. Finally, we discuss candidate material platforms and experimental feasibility.

cond-mat.mes-hall↗

arXiv2026

Anomalous dynamical energy flows via nonlinear phononics in spin-Peierls chains

We investigate the nonequilibrium spin-phonon dynamics and energy cascades in a strongly dimerized spin-Peierls chain using a multi-tiered nonlinear phononics architecture. To bypass linear selection rules prohibiting the direct excitation of the Raman-active dimerization mode, a terahertz laser drives an infrared mode that nonlinearly couples to the Raman lattice displacement, subsequently modulating the magnetic exchange. Employing a bond-operator formalism with a second-order cumulant expansion of the Lindblad master equation, we show that maximum energy transfer into the magnetic sector is governed by a dynamical impedance-matching condition rather than the unperturbed triplon density of states. We find that the sustained energy input of continuous-wave driving builds high excitation densities that severely back-act on the lattice, overdamping the primary phonon and smearing magnetic features via power broadening. Conversely, the small time-integrated energy of a pulse keeps the response perturbative, terminating before back-action accumulates and preserving sharp Fano-like quantum interferences. These insights establish limits for controlling dynamic magnetic states without quenching the driving lattice modes.

cond-mat.str-el↗

arXiv2026

Interplay of nonrelativistic and relativistic spin splittings in altermagnets

Despite their compensated magnetic moments, altermagnets (AMs) exhibit nonrelativistic spin splitting (NRSS) that offers routes to spintronic functionality without relying on relativistic spin-orbit coupling. However, how NRSS influences relativistic phenomena remains largely unexplored. Here we show that NRSS plays a crucial role in reshaping the Rashba effect in AMs with broken inversion symmetry. Using a tight-binding model, we demonstrate that Rashba spin splitting, whose magnitude is typically limited by the strength of spin-orbit coupling, is governed by NRSS energy scales. The resulting Rashba bands combined with NRSS generate anomalously large charge-to-spin conversion with a Néel-vector-tunable spin polarization. First-principles calculations for the noncentrosymmetric AM GdAlSi corroborate the emergence of these effects in a real system. Our results reveal the interplay between nonrelativistic and relativistic effects in AMs and identify them as fertile platforms for spin-orbitronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Parity-selective spin splitting in coplanar antiferromagnets via bichromatic driving

Parity is a central characteristic of momentum-dependent spin splitting in antiferromagnets (AFMs). Yet, intrinsic crystal symmetries typically restrict the splitting to either even or odd parity, preventing flexible spin control. Using a coplanar AFM, we demonstrate that bichromatic ($ω$--$nω$) Floquet driving offers a natural way to bypass this constraint. This mechanism generates asymmetric spin textures unattainable in static AFMs or under monochromatic driving. For the specific AFM considered here, we reveal an elegant relation between spin-splitting parity and harmonic hierarchy: $ω$--$2ω$ fields generate highly tunable odd- and mixed-parity spin splittings, whereas higher-order harmonics ($n \ge 3$) exclusively produce even-parity states. The macroscopic magnetization can also be toggled via the specific driving protocol and harmonic $n$. These distinct spin splitting states manifest in qualitatively different macroscopic spin currents generated after an optical quench---a definitive transport signature complementing direct visualization via spin- and angle-resolved photoemission spectroscopy.

cond-mat.mtrl-sci↗

arXiv2026

Chirped Floquet linear drives activate forbidden charge-to-spin conversions in Rashba two-dimensional electron gases

In Rashba two-dimensional electron gases (2DEGs), charge-to-spin conversion via the Edelstein effect is conventionally limited to the transverse plane. Accessing longitudinal or out-of-plane pathways typically requires static magnetic fields or interface engineering, which cause stray fields and lack tunability. While dynamic circular or elliptical Floquet drives can also unlock these forbidden pathways, a simple Floquet linear drive cannot. Here, we propose an alternative approach: a \textit{chirped} Floquet linear drive. The chirp induces in-plane Floquet-Zeeman fields and an odd-parity momentum drift, which simultaneously break rotational and time-reversal symmetries. This mechanism activates the forbidden Edelstein charge-to-spin conversions in Rashba 2DEGs. Experimentally accessible via programmable spatial light modulators or optical delay lines, this tunable chirped linear drive offers a broadly applicable route to spin-orbit torque switching and high-efficiency spintronics.

cond-mat.str-el↗

arXiv2026

Giant perpendicular Edelstein polarization in 2D compensated magnets via bichromatic Floquet driving

While unconventional $p$-wave magnets can generate nonrelativistic Edelstein polarizations, spin-group symmetries strictly forbid these responses in unconventional magnets with higher-order harmonics, such as $d$-wave altermagnets. Here, we demonstrate that combining Rashba spin-orbit coupling with bichromatic Floquet driving activates giant perpendicular Edelstein polarizations (PEPs) across 2D altermagnets and broader classes of unconventional spin-polarized magnets -- a feat monochromatic driving cannot achieve. By dynamically breaking two-fold rotational symmetry, the two-frequency drive (including bilinear, bicircular, and circular-linear configurations) induces a stray-field-free in-plane Zeeman-like field that generates orbitally dominated PEPs (0.5--1.5 $μ_{\rm B}$). This massive response is governed by universal selection rules tied to the system's magnetic parity and the second beam's harmonics. These emergent PEPs provide a powerful mechanism for perpendicular memory writing.

cond-mat.mtrl-sci↗

arXiv2026

Floquet-induced anisotropic magnetoresistance and anomalous Hall effect in 2D $d$-wave altermagnets with Rashba spin-orbit coupling

Altermagnets (AMs) combine momentum-dependent spin splitting with zero net magnetization, making them promising for spintronics. Periodic driving enables dynamic symmetry engineering beyond static, material-specific control. We show that Floquet engineering in 2D $d$-wave AMs with out-of-plane Néel order and Rashba spin-orbit coupling unlocks equilibrium-forbidden transport responses. Monochromatic driving produces purely out-of-plane magnetization, yielding longitudinal anisotropic magnetoresistance (AMR) and an anomalous Hall effect, whereas bichromatic driving generates both in-plane and out-of-plane magnetizations and additionally activates transverse AMR via the second harmonic of the secondary beam. Comparable static magnetic fields would require hundreds of tesla, avoided in Floquet driving. These effects persist across linear, circular, and mixed light polarizations and are tunable via light parameters. Our results establish multi-color Floquet engineering for controlling magnetization and symmetry-protected transport in AMs.

cond-mat.mtrl-sci↗

arXiv2026

Robust qubit interactions mediated by photonic topological edge states

We investigate the coupling of two spatially separated qubits via topologically protected edge states in a two-dimensional Hofstadter lattice. In this hybrid platform, the qubits are coupled to distinct edge sites of the lattice, enabling long-range interactions mediated by topological edge modes. We solve the full system Hamiltonian and analyze the resulting eigenstate structure to uncover the conditions under which coherent qubit interactions emerge. Our analysis reveals that the effective coupling is highly sensitive to the qubit placement, energy detuning, and the topological character of the edge spectrum. We obtain an analytical solution that goes beyond the perturbative regime, capturing the full interplay between the qubits and edge modes. These results provide a foundation for exploring information transport and many-body effects in engineered quantum systems where interactions are mediated by topological edge modes.

quant-ph↗

arXiv2026

Slow-phonon control of spin Edelstein effect in Rashba $d$-wave altermagnets

Altermagnets have zero net magnetization yet feature spin-split bands. Here, we investigate how slow lattice vibrations (phonons) influence both the intrinsic and externally induced spin polarizations in two-dimensional $d$-wave altermagnets. For the induced spin polarization, we employ a Rashba continuum model with electron-phonon coupling (EPC) treated at the static Holstein level and analyze the spin Edelstein effect using the Kubo linear-response formalism to probe EPC-induced contributions. We find that, under a specific symmetry-lowering pattern such as a piezomagnetically active strain that explicitly breaks the inherent $C_4 \mathcal{T}$ symmetry, moderate-to-strong EPC progressively suppresses the induced polarization via both intraband and interband channels, with a threshold coupling marking the onset of complete spin Edelstein depolarization. The depolarization arises from a phonon-induced energy renormalization that leads to a complete collapse of the Fermi surface. While depolarization can occur even in the Rashba non-altermagnetic phase, it remains isotropic. The presence of altermagnetism makes it anisotropic and breaks the conventional antisymmetry between spin susceptibilities that occurs with pure spin-orbit coupling, rendering the effect highly relevant for spintronic applications. We further investigate how the phonon coupling to the altermagnetic order, Rashba spin-orbit strength, and carrier doping collectively tune the depolarization. Our findings demonstrate that static phononic effects offer a powerful means for on-demand control of spin polarization, enabling reversible switching between spin-polarized and depolarized states--a key functionality for advancing spin logic architectures and optimizing next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Cavity-induced coherent magnetization and polaritons in altermagnets

Altermagnets feature antiparallel spin sublattices with $d$-, $g$-, or $i$-wave spin order, yielding nonrelativistic spin splitting without net magnetization. We show that embedding a two-dimensional $d$-wave altermagnet in a driven optical cavity induces a finite, tunable magnetization. Coherent photon driving couples selectively to electronic sublattices, and the resulting altermagnets' symmetry-broken spin texture yields a pronounced steady-state spin imbalance -- coherent magnetization -- absent in conventional antiferromagnets for the same lattice configuration. A mean-field Lindblad analysis reveals the dominance of quadratic over linear couplings. In the strong-coupling regime, distinct polariton signatures emerge in the steady state of induced magnetization. This work demonstrates cavity control of altermagnets for spintronic applications.

cond-mat.str-el↗

arXiv2025

Spin polarization engineering in $d$-wave altermagnets

Altermagnets host unconventional spin-polarized bands despite zero net magnetization, but controlling their spin structure remains challenging. We propose a multi-field approach to engineer spin polarization in $d$-wave altermagnets using gating, optical driving, and in-plane electric fields, which enable tunable and switchable polarizations along multiple directions. Optical driving induces out-of-plane ($z$) polarization, while gating and in-plane fields generate $x$- and $y$-polarizations via the Edelstein effect, all of which are experimentally detectable. We further find that spin- and band-selective doping induces chiral optical activity, a feature unique to altermagnets. Our approach provides a versatile route for full control of spin polarization in altermagnets.

cond-mat.mtrl-sci↗

arXiv2025

Dynamical phase transition in a strongly hybridized phonon-triplon chain

We study a dimerized spin-1/2 chain, such as CuGeO$_3$, hosting triplon excitations coupled to optical phonons under weak terahertz laser driving. Both phonons and triplons weakly lose energy into the surrounding baths, forming a non-equilibrium steady state. In the strong phonon-triplon coupling regime, phonons near the two-triplon continuum hybridize strongly with triplons. Using mean-field Lindblad dynamics, we show that this strong hybridization induces sharp first-order phase transitions -- either single or simultaneous double -- in the emission spectrum, mainly due to dissipation-induced nonlinearities. Using mean-field Floquet analysis of harmonic modes in both sectors, we analytically confirm the existence of these phase transitions. Furthermore, we map the complete steady-state phase diagram by varying key control parameters and provide experimentally relevant parameters for observing these transitions in laser-driven CuGeO$_3$.

cond-mat.str-el↗

arXiv2025

Cavity-assisted magnetization switching in a quantum spin-phonon chain

We propose a Néel magnetization switching mechanism in a hybrid magnon-phonon optical cavity system. A terahertz-pumped single-mode cavity photon couples to a spin-phonon chain, while the system dissipates energy via different baths. Our mean-field analysis reveals that the photon induces magnetization switching by generating strongly entangled magnon pairs with opposite momenta -- a feature weakly present in the cavity-free system. This switching occurs only at specific drive frequencies, namely at low magnon energies and near the upper edge (perpendicular modes) of the two-magnon band. Our results underscore the roles of laser fluence, damping, and photon loss in modulating the switching process, offering a promising route for cavity-assisted magnetization control in opto-spintronics.

cond-mat.str-el↗

arXiv2025

Anisotropic light-tailored RKKY interaction in two-dimensional $d$-wave altermagnets

Altermagnets are known in spintronics for their intrinsic spin-splitting and unconventional magnetic responses, particularly to magnetic impurities. However, effectively controlling the magnetic exchange interactions in altermagnets is challenging for practical applications. Here, we propose using circularly polarized light to tune the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in two-dimensional $d$-wave altermagnets. Using the real-space retarded Green's functions approach, our results show that while the Heisenberg and Ising exchanges dominate, a notable Dzyaloshinskii-Moriya (DM) interaction also plays a key role. Furthermore, the inherent strength of altermagnetism imprints chirp-like signatures into the magnetic responses, which can be dynamically tuned via light. We mainly demonstrate that gate-induced Rashba spin-orbit coupling is essential in response to light -- light selectively and anisotropically adjusts the DM interaction without affecting the other exchanges. Our findings further indicate that rotating the altermagnet by $45^\circ$ relative to the light's polarization direction generates a Dirac-like dispersion and different DM interactions. We finally extract critical thresholds where light reverses DM interactions along one axis or balances both in-plane components. The anisotropic light-driven control of RKKY interactions in 2D altermagnets not only highlights their unique properties but also opens new avenues for engineering tailored magnetic characteristics in spintronic applications.

cond-mat.mes-hall↗

arXiv2024

Topological anomalous Floquet photon pump

There is a close theoretical connection between topological Floquet physics and cavity QED, yet this connection has not been realized experimentally due to complicated cavity QED models that often arise. We propose a simple, experimentally viable protocol to realize non-adiabatic topological photon pumping mediated by a single qubit, which we dub the anomalous Floquet photon pump. For both quantized photons and external drive, the system exhibits a non-trivial topological phase across a broad range of parameter space. Transitions out of the topological phase result from frequency-space delocalization. Finally, we argue that the protocol can be implemented in existing experiments via driven qubit non-linearities, with topological pumping witnessed in measurements of the cavity Wigner distribution functions.

cond-mat.mes-hall↗

arXiv2024

Probing topological phases in a perturbed Kane-Mele model via RKKY interaction: Application to monolayer jacutingaite Pt$_2$HgSe$_3$

Quantum spin Hall insulators (QSHIs) are promising for spintronics, leveraging strong spin-orbit coupling for efficient spin manipulation via electrical and optical methods, with potential applications in memory storage, quantum computing, and spin-based logic. While the Kane-Mele model effectively captures the low-energy physics of these materials, the impact of perturbations driving phase transitions is less well understood. Developing approaches to describe these phases is crucial. Here, we study the noncollinear Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities in a \textit{perturbed} Kane-Mele model with strong spin-orbit coupling, relevant to monolayer jacutingaite Pt$_2$HgSe$_3$ as a prominent QSHI. By analyzing RKKY interactions, we reveal distinct, relative (rather than absolute) signatures of the different phase transitions induced by static and dynamic perturbations based on their impact on magnetic impurities. We then employ these perturbations to switch between ferromagnetic and antiferromagnetic or clockwise and counterclockwise magnetic interactions for control processes. Our results offer a practical way to track topological phases via magnetic properties.

cond-mat.mes-hall↗

arXiv2024

Terahertz high-harmonic generation in gapped antiferromagnetic chains

The nonlinear dynamics of magnetization in antiferromagnets, resulting in high-frequency spin waves (high-order harmonics) as signal carriers, enable fast magnetic state switching in spintronic devices. More harmonic orders potentially allow more information to be conveyed by the spins. Developing theoretical models to describe these waves in antiferromagnets is essential for predicting their properties and guiding experimental efforts. Here, we consider the role of linear and quadratic spin-phonon couplings (SPCs) in achieving high-order harmonics in the THz magnetization of a gapped antiferromagnetic spin chain. A THz steady laser's electric field indirectly drives spins via phonons. Using spin-wave theory, mean-field theory, and the Lindblad formalism, we analyze the resulting nonlinear dynamics. We highlight the distinct mechanisms for harmonic generation when a phonon is coupled to the easy-plane and easy-axis of spins. Moreover, we observe that quadratic SPC blocks odd harmonics due to invariant inversion symmetry, while linear SPC generates both odd and even harmonics. We also investigate the effects of drive frequency, drive amplitude, phonon damping, and spin damping on the number of harmonics. Our findings offer an alternative pathway for developing nonlinear magnonics.

cond-mat.str-el↗