Minimal Models and Transport Properties of Unconventional p-Wave Magnets.

New unconventional compensated magnets with a p-wave spin polarization protected by a composite time-reversal translation symmetry have been proposed in the wake of altermagnets. To facilitate the experimental discovery and applications of these unconventional magnets, we construct an effective analytical model. The effective model is based on a minimal tight-binding model for unconventional p-wave magnets that clarifies the relation to other magnets with p-wave spin-polarized bands.

Efficient ultrafast field-driven spin current generation for spintronic terahertz frequency conversion.

Efficient generation and control of spin currents launched by terahertz (THz) radiation with subsequent ultrafast spin-to-charge conversion is the current challenge for the next generation of high-speed communication and data processing units. Here, we demonstrate that THz light can efficiently drive coherent angular momentum transfer in nanometer-thick ferromagnet/heavy-metal heterostructures. This process is non-resonant and does neither require external magnetic fields nor cryogenics.

dc Josephson Effect in Altermagnets.

The ability of magnetic materials to modify superconductors is an active research area for possible applications in thermoelectricity, quantum sensing, and spintronics. We consider the fundamental properties of the Josephson effect in a class of magnetic materials that recently have attracted much attention: altermagnets. We show that despite having no net magnetization and a band structure qualitatively different from ferromagnets and from conventional antiferromagnets without spin-split bands, altermagnets induce 0-π oscillations.

Superconducting Proximity Effect and Long-Ranged Triplets in Dirty Metallic Antiferromagnets.

Antiferromagnets have no net spin splitting on the scale of the superconducting coherence length. Despite this, antiferromagnets have been observed to suppress superconductivity in a similar way as ferromagnets, a phenomenon that still lacks a clear understanding. We find that this effect can be explained by the role of impurities in antiferromagnets.

Detection of Topological Spin Textures via Nonlinear Magnetic Responses.

Topologically nontrivial spin textures, such as skyrmions and dislocations, display emergent electrodynamics and can be moved by spin currents over macroscopic distances. These unique properties and their nanoscale size make them excellent candidates for the development of next-generation race-track memory and unconventional computing. A major challenge for these applications and the investigation of nanoscale magnetic structures in general is the realization of suitable detection schemes.

Magnon Spin Current Induced by Triplet Cooper Pair Supercurrents.

At the interface between a ferromagnetic insulator and a superconductor there is a coupling between the spins of the two materials. We show that when a supercurrent carried by triplet Cooper pairs flows through the superconductor, the coupling induces a magnon spin current in the adjacent ferromagnetic insulator. The effect is dominated by Cooper pairs polarized in the same direction as the ferromagnetic insulator, so that charge and spin supercurrents produce similar results.

Electrically Controlled Crossed Andreev Reflection in Two-Dimensional Antiferromagnets.

We report generic and tunable crossed Andreev reflection (CAR) in a superconductor sandwiched between two antiferromagnetic layers. We consider recent examples of two-dimensional magnets with hexagonal lattices, where gate voltages control the carrier type and density, and predict a robust signature of perfect CAR in the nonlocal differential conductance with one electron-doped and one hole-doped antiferromagnetic lead. The magnetic field-free and spin-degenerate CAR signal is electrically controlled and visible over a large voltage range, showing promise for solid-state quantum entanglement applications.

Fingerprints of Universal Spin-Stiffness Jump in Two-Dimensional Ferromagnets.

Motivated by recent progress on synthesizing two-dimensional magnetic van der Waals systems, we propose a setup for detecting the topological Berezinskii-Kosterlitz-Thouless phase transition in spin-transport experiments on such structures. We demonstrate that the spatial correlations of injected spin currents into a pair of metallic leads can be used to measure the predicted universal jump of 2/π in the ferromagnet spin stiffness as well as its predicted universal square root dependence on temperature as the transition is approached from below. Our setup provides a simple route to measuring this topological phase transition in two-dimensional magnetic systems, something which up to now has proven elusive.

Observation of Magnon Polarons in a Uniaxial Antiferromagnetic Insulator.

Magnon polarons, a type of hybridized excitations between magnons and phonons, were first reported in yttrium iron garnet as anomalies in the spin Seebeck effect responses. Here, we report an observation of antiferromagnetic (AFM) magnon polarons in a uniaxial AFM insulator Cr_{2}O_{3}. Despite the relatively higher energy of magnon than that of the acoustic phonons, near the spin-flop transition of ∼6  T, the left-handed magnon spectrum shifts downward to hybridize with the acoustic phonons to form AFM magnon polarons, which can also be probed by the spin Seebeck effect.

Bosonic Bott Index and Disorder-Induced Topological Transitions of Magnons.

We investigate the role of disorder on the various topological magnonic phases present in deformed honeycomb ferromagnets. To this end, we introduce a bosonic Bott index to characterize the topology of magnon spectra in finite, disordered systems. The consistency between the Bott index and Chern number is numerically established in the clean limit.

Subterahertz spin pumping from an insulating antiferromagnet.

Spin-transfer torque and spin Hall effects combined with their reciprocal phenomena, spin pumping and inverse spin Hall effects (ISHEs), enable the reading and control of magnetic moments in spintronics. The direct observation of these effects remains elusive in antiferromagnetic-based devices. We report subterahertz spin pumping at the interface of the uniaxial insulating antiferromagnet manganese difluoride and platinum.

Propagation Length of Antiferromagnetic Magnons Governed by Domain Configurations.

The compensated magnetic order and characteristic terahertz frequencies of antiferromagnetic materials make them promising candidates to develop a new class of robust, ultrafast spintronic devices. The manipulation of antiferromagnetic spin-waves in thin films is anticipated to lead to new exotic phenomena such as spin-superfluidity, requiring an efficient propagation of spin-waves in thin films. However, the reported decay length in thin films has so far been limited to a few nanometers.

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators.

Electrons and holes residing on the opposing sides of an insulating barrier and experiencing an attractive Coulomb interaction can spontaneously form a coherent state known as an indirect exciton condensate. We study a trilayer system where the barrier is an antiferromagnetic insulator. The electrons and holes here additionally interact via interfacial coupling to the antiferromagnetic magnons.

Current Control of Magnetism in Two-Dimensional Fe_{3}GeTe_{2}.

The recent discovery of magnetism in two-dimensional van der Waals systems opens the door to discovering exciting physics. We investigate how a current can control the ferromagnetic properties of such materials. Using symmetry arguments, we identify a recently realized system in which the current-induced spin torque is particularly simple and powerful.

Anisotropic and Controllable Gilbert-Bloch Dissipation in Spin Valves.

Spin valves form a key building block in a wide range of spintronic concepts and devices from magnetoresistive read heads to spin-transfer-torque oscillators. We elucidate the dependence of the magnetic damping in the free layer on the angle its equilibrium magnetization makes with that in the fixed layer. The spin pumping-mediated damping is anisotropic and tensorial, with Gilbert- and Bloch-like terms.

Universal Scaling Theory of the Boundary Geometric Tensor in Disordered Metals.

We investigate the finite-size scaling of the boundary quantum geometric tensor (QGT) numerically close to the Anderson localization transition in the presence of small external magnetic fields. The QGT exhibits universal scaling and reveals the crossover between the orthogonal and unitary critical states in weak random magnetic fields. The flow of the QGT near the critical points determines the critical exponents.

Chiral Phonon Transport Induced by Topological Magnons.

The plethora of recent discoveries in the field of topological electronic insulators has inspired a search for boson systems with similar properties. There are predictions that ferromagnets on a two-dimensional honeycomb lattice may host chiral edge magnons. In such systems, we theoretically study how magnons and phonons couple.

Nonlocal Coupling between Antiferromagnets and Ferromagnets in Cavities.

Microwaves couple to magnetic moments in both ferromagnets and antiferromagnets. Although the magnons in ferromagnets and antiferromagnets radically differ, they can become entangled via strong coupling to the same microwave mode in a cavity. The equilibrium configuration of the magnetic moments crucially governs the coupling between the different magnons, because the antiferromagnetic and ferromagnetic magnons have opposite spins when their dispersion relations cross.

Theory of the Interfacial Dzyaloshinskii-Moriya Interaction in Rashba Antiferromagnets.

In antiferromagnetic (AFM) thin films, broken inversion symmetry or coupling to adjacent heavy metals can induce Dzyaloshinskii-Moriya (DM) interactions. Knowledge of the DM parameters is essential for understanding and designing exotic spin structures, such as hedgehog Skyrmions and chiral Néel walls, which are attractive for use in novel information storage technologies. We introduce a framework for computing the DM interaction in two-dimensional Rashba antiferromagnets.

Optical conversion of pure spin currents in hybrid molecular devices.

Carbon-based molecules offer unparalleled potential for THz and optical devices controlled by pure spin currents: a low-dissipation flow of electronic spins with no net charge displacement. However, the research so far has been focused on the electrical conversion of the spin imbalance, where molecular materials are used to mimic their crystalline counterparts. Here, we use spin currents to access the molecular dynamics and optical properties of a fullerene layer.

Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet.

We investigate spin transport by thermally excited spin waves in an antiferromagnetic insulator. Starting from a stochastic Landau-Lifshitz-Gilbert phenomenology, we obtain the out-of-equilibrium spin-wave properties. In linear response to spin biasing and a temperature gradient, we compute the spin transport through a normal-metal-antiferromagnet-normal-metal heterostructure.

Spin Superfluidity in Biaxial Antiferromagnetic Insulators.

Antiferromagnets may exhibit spin superfluidity since the dipole interaction is weak. We seek to establish that this phenomenon occurs in insulators such as NiO, which is a good spin conductor according to previous studies. We investigate nonlocal spin transport in a planar antiferromagnetic insulator with a weak uniaxial anisotropy.

Terahertz Antiferromagnetic Spin Hall Nano-Oscillator.

We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation.

Spin Superfluidity and Long-Range Transport in Thin-Film Ferromagnets.

In ferromagnets, magnons may condense into a single quantum state. Analogous to superconductors, this quantum state may support transport without dissipation. Recent works suggest that longitudinal spin transport through a thin-film ferromagnet is an example of spin superfluidity.