arXiv subjects

Hans Gløckner Giil

Publications and source records attributed to Hans Gløckner Giil.

10 recordsLinked to original sources

arXiv2026

Phenomenology of reactive and dissipative nutation in antiferromagnets

We formulate equations of motion for uniform magnetization dynamics in multisublattice magnets, with emphasis on a recently proposed inertial damping torque. We include intra- and intersublattice contributions to Gilbert damping, reactive inertia, and inertial damping. For a two-sublattice uniaxial antiferromagnet in an easy-axis static magnetic field, we derive the dynamical magnetic susceptibilities and approximate eigenfrequencies across all field-dependent equilibrium phases. In particular, we show how inertial damping affects the relaxation of the nutational modes and propose an experimental protocol to determine the dynamical coefficients.

cond-mat.mes-hall↗

arXiv2026

Nutational Spin Pumping and Dissipation

At terahertz drive frequencies, magnetization dynamics enter an inertial regime beyond the scope of standard Landau-Lifshitz-Gilbert (LLG) theory. We reveal a nutational damping torque comprising a bulk term and an interfacial contribution that describes spin emission into adjacent metals. The interfacial term generates nutational spin pumping: a dc spin current that scales quadratically with the drive frequency. Using a scattering approach, we relate this effect to microscopic material parameters and predict pronounced enhancements in ultrathin films and low-Fermi-energy conductors. Nutational spin pumping can be detected directly via the inverse spin Hall effect or indirectly via thickness-dependent renormalization of nutational damping.

cond-mat.mes-hall↗

arXiv2026

Unidirectional magnetoresistance driven by nonequilibrium antiferromagnetic magnons

Magnetoresistive effects are typically symmetric under magnetization reversal. However, nonlinear spin transport can give rise to unidirectional magnetoresistance in systems with strong spin-orbit interaction and broken inversion symmetry. Here, we demonstrate that the nonequilibrium magnon accumulation characterized by a finite magnon chemical potential can lead to a large and robust magnonic unidirectional spin Hall magnetoresistance (USMR) in the weakly coupled van der Waals antiferromagnet CrPS4 in contact with Pt. Unlike conventional magnonic USMR driven by magnetization fluctuations, this effect persists under strong magnetic fields and low temperatures, with a pronounced peak near the spin-flip transition. The magnitude of magnonic USMR in CrPS4/Pt exceeds that of YIG/Pt by more than two orders of magnitude and surpasses the electrical USMR in metallic Ta/Co bilayers by a factor of two. The observed field and temperature dependence indicates that spin transport is dominated by magnon chemical potential gradients rather than thermal- or fluctuation-driven magnon generation. These findings establish a new mechanism for nonlinear magnetoresistance in antiferromagnetic van der Waals heterostructures and open a route to magnon-based antiferromagnetic spintronic functionalities in two-terminal device geometries.

cond-mat.mtrl-sci↗

arXiv2025

Coexistence of $p$-wave magnetism and superconductivity

The symmetry requirements for realizing unconventional compensated magnets with spin-polarized bands such as altermagnets have recently been uncovered. The most recent addition to this family of magnets is parity-odd or $p$-wave magnets. We demonstrate that $p$-wave magnets are perfectly compatible with superconductivity due to the spin polarization of their electron bands and that they induce unexpected spin transport phenomena. We first show that $p$-wave magnetism can coexist with conventional superconductivity regardless of the magnitude of the spin splitting. We then predict that $p$-wave magnets induce a charge-to-spin conversion, which can be strongly enhanced by the presence of superconductivity providing a way to probe the coexistence in experiments. Our results open an avenue for material combinations with a synergetic relation between spintronics and superconductivity.

cond-mat.supr-con↗

arXiv2024

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. One of the most prominent advantages of our analytical model is the possibility to employ various analytical approaches while capturing essential features of $p$-wave magnets. We illustrate the effective model by evaluating the tunneling conductance in junctions with $p$-wave magnets, revealing a large magnetoresistance, spin filtering, and anisotropic bulk spin conductivity beyond linear response despite the absence of a net magnetization. These results show that unconventional $p$-wave magnets offer several useful functionalities, broadening the material selection for spintronics devices.

cond-mat.mes-hall↗

arXiv2024

Spin Seebeck in the weak exchange coupled van der Waals antiferromagnet

Spin Seebeck effect (SSE) refers to the creation of spin currents due to a temperature gradient in the magnetic materials or across magnet-normal metal interfaces, which can be electrically detected through the inverse spin Hall effect (ISHE) when in contact with heavy metals. It offers fundamental insights into the magnetic properties of materials, including the magnetic phase transition, static magnetic order, and magnon excitations. However, the SSE in van der Waals antiferromagnet is still elusive, especially across the spin-flip transition. Here, we demonstrate the SSE in the weak exchange coupled van der Waals antiferromagnet CrPS$_4$. The SSE increases as the magnetic field increases before the spin-flip transition due to the enhancement of the thermal spin current as a function of the applied field. A peak of SSE is observed at the spin-flip field, which is related to the magnon mode edges across the spin-flip field. Our results extend SSE research to van der Waals antiferromagnets and demonstrate an enhancement of SSE at the spin-flip transition.

physics.app-ph↗

arXiv2024

Quasiclassical theory of superconducting spin-splitter effects and spin-filtering via altermagnets

Conducting altermagnets have recently emerged as intriguing materials supporting strongly spin-polarized currents without magnetic stray fields. We demonstrate that altermagnets enable three key functionalities, merging superconductivity and spintronics. The first prediction is a controllable supercurrent-induced edge magnetization, which acts like a dissipationless spin-splitter effect. The second and third predictions are a Cooper pair spin-splitter and a filtering effect, respectively. These effects allow for spatial separation of triplet pairs with opposite spin-polarizations and spin-selective tunneling of Cooper pairs. We derive a quasiclassical theory with associated boundary conditions that describe these phenomena and explain how they can be experimentally verified. Our results open a new path for spatial control of spin signals via triplet Cooper pairs using hybrid superconductor-altermagnet devices.

cond-mat.supr-con↗

arXiv2024

Quantum Theory of Spin-Transfer and Spin-Pumping in Collinear Antiferromagnets and Ferrimagnets

Antiferromagnets are promising candidates as active components in spintronic applications. They share features with ferrimagnets in that opposing spin orientations exist in two or more sublattices. Spin transfer torque and spin pumping are essential ingredients in antiferromagnetic and ferrimagnet spintronics. This paper develops an out-of-equilibrium quantum theory of the spin dynamics of collinear magnets containing many spins coupled to normal metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the easy axis. The theory, therefore, covers collinear antiferromagnets and ferrimagnets. We focus on the resulting semi-classical spin dynamics. The dissipation in the spin dynamics is enhanced due to spin-pumping. Spin accumulations in the normal metals induce deterministic spin-transfer torques on the magnet. Additionally, each electron's discrete spin angular momentum causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We derive these fluctuating torques. The fluctuation-dissipation theorem holds at high temperatures, including the effects of spin-pumping. At low temperatures, we derive shot noise contributions to the fluctuations.

cond-mat.mes-hall↗

arXiv2024

Superconductor-altermagnet memory functionality without stray fields

A novel class of antiferromagnets, dubbed altermagnets, exhibit a non-relativistically spin-split band structure reminiscent of $d$-wave superconductors, despite the absence of net magnetization. This unique characteristic enables utilization in cryogenic stray-field-free memory devices, offering the possibility of achieving high storage densities. In this Letter, we determine how a proximate altermagnet influences the critical temperature $T_c$ of a conventional $s$-wave singlet superconductor. Considering both a bilayer and trilayer, we show that such hybrid structures may serve as stray-field free memory devices where the critical temperature is controlled by rotating the Néel vector of one altermagnet, providing infinite magnetoresistance. Furthermore, our study reveals that altermagnetism can coexist with superconductivity up to a critical strength of the altermagnetic order as well as robustness of the altermagnetic influence on the conduction electrons against non-magnetic impurities, ensuring the persistence of the proximity effect under realistic experimental conditions.

cond-mat.supr-con↗

arXiv2022

Effective quasiclassical models for odd-frequency superconductivity: energy-symmetry, preserved spectral weight, and Meissner response

The odd-frequency superconducting state appears generally in hybrid structures consisting of conventional superconductors and other materials, and features electrons that form temporally non-local Cooper pairs. The quasiclassical theory of superconductivity has been extensively used to model such systems, finding in many cases excellent agreement with experimental measurements. Therefore, it is of interest to study effective models of odd-frequency superconductivity to predict new phenomena associated with this form of unconventional pairing. We establish necessary criteria that the quasiclassical Green functions in odd-frequency superconducting systems in the dirty limit must satisfy in order to be physically reasonable, including conservation of spectral weight. We show that it is possible to write down effective models which satisfy all the abovementioned criteria, but which still predict different behavior when it comes to the density of states and the magnetic response of the superconductor. For instance, an effective model for the odd-frequency anomalous Green function that gives a conserved spectral weight can yield either a peaked or gapped density of states at the Fermi energy, and exhibit conventional, zero, or unconventional Meissner response. This finding demonstrates the importance of carefully considering the properties of effective models describing odd-frequency superconductivity in order to obtain physically reasonable results.

cond-mat.supr-con↗