Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling
Christoph W. Zollitsch, Safe Khan, Vu Thanh Trung Nam, Ivan A. Verzhbitskiy, Dimitrios Sagkovits, James O'Sullivan, Oscar W. Kennedy, Mara Strungaru, Elton J. G… 展开作者
Christoph W. Zollitsch, Safe Khan, Vu Thanh Trung Nam, Ivan A. Verzhbitskiy, Dimitrios Sagkovits, James O'Sullivan, Oscar W. Kennedy, Mara Strungaru, Elton J. G. Santos, John J. L. Morton, Goki Eda, Hidekazu Kurebayashi
Layered van der Waals (vdW) magnets can maintain a magnetic order even down to the single-layer regime and hold promise for integrated spintronic devices. While the magnetic ground state of vdW magnets was extensively studied, key parameters of spin dynamics, like the Gilbert damping, crucial for designing ultra-fast spintronic devices, remains largely unexplored. Despite recent studies by optical excitation and detection, achieving spin wave control with microwaves is highly desirable, as modern integrated information technologies predominantly are operated with these. The intrinsically small numbers of spins, however, poses a major challenge to this.
Here, we present a hybrid approach to detect spin dynamics mediated by photon-magnon coupling between high-Q superconducting resonators and ultra-thin flakes of Cr$_2$Ge$_2$Te$_6$ (CGT) as thin as 11\,nm. We test and benchmark our technique with 23 individual CGT flakes and extract an upper limit for the Gilbert damping parameter. These results are crucial in designing on-chip integrated circuits using vdW magnets and offer prospects for probing spin dynamics of monolayer vdW magnets.
In this article, we calculate the magnon spectrum of Kitaev-Heisenberg magnets. This model has been recently proposed as a spin Hamiltonian to model $\text{CrI}_3$ and other two-dimensional magnets. It is a minimal spin Hamiltonian that includes a contribution stemming from a Heisenberg, isotropic exchange, and a contribution arising from a Kitaev interaction, anisotropic and frustrated exchange. Our calculations reveal the topological nature of the magnons and a gap that opens at the $K$ and $K^\prime$ points. These topological properties give rise to effects such as thermal Hall effect. In a…
The recent emergence of 2D van der Waals magnets down to atomic layer thickness provides an exciting platform for exploring quantum magnetism and spintronics applications. The van der Waals nature stabilizes the long-range ferromagnetic order as a result of magnetic anisotropy. Furthermore, giant tunneling magnetoresistance and electrical control of magnetism have been reported. However, the potential of 2D van der Waals magnets for magnonics, magnon-based spintronics, has not been explored yet. Here, we report the experimental observation of long-distance magnon transport in quasi-twodimensio…
The recent isolation of two-dimensional (2D) magnets offers tantalizing opportunities for spintronics and magnonics at the limit of miniaturization. One of the key advantages of atomically-thin materials is their outstanding deformation capacity, which provides an exciting avenue to control their properties by strain engineering. Herein, we investigate the magnetic properties, magnon dispersion and spin dynamics of the air-stable 2D magnetic semiconductor CrSBr ($T_C$ = 146 K) under mechanical strain using first-principles calculations. Our results provide a deep microscopic analysis of the co…
Van der Waals magnets have emerged as a fertile ground for the exploration of highly tunable spin physics and spin-related technology. Two-dimensional (2D) magnons in van der Waals magnets are collective excitation of spins under strong confinement. Although considerable progress has been made in understanding 2D magnons, a crucial magnon device called the van der Waals magnon valve, in which the magnon signal can be completely and repeatedly turned on and off electrically, has yet to be realized. Here we demonstrate such magnon valves based on van der Waals antiferromagnetic insulator MnPS3. …
Using bilayer CrI$_3$ as an example, we demonstrate that stacking domain walls in van der Waals magnets can host one dimensional (1D) magnon channels, which have lower energies than bulk magnons. Interestingly, some magnon channels are hidden in magnetically homogeneous background and can only be inferred with the knowledge of stacking domain walls. Compared to 1D magnons confined in magnetic domain walls, 1D magnons in stacking domain walls are more stable against external perturbations. We show that the relaxed moiré superlattices of small-angle twisted bilayer CrI$_3$ is a natural realizati…
Van der Waals magnets are uniquely positioned at the intersection between two-dimensional materials, antiferromagnetic spintronics, and magnonics. The interlayer exchange interaction in these materials enables antiferromagnetic resonances to be accessed at GHz frequencies. Consequently, these layered antiferromagnets are intriguing materials out of which quantum hybrid magnonic devices can be fashioned. Here, we use both a modified macrospin model and micromagnetic simulations to demonstrate a comprehensive antiferromagnetic resonance spectra in van der Waals magnets near the ultrathin (monola…
We investigate the performance of niobium nitride superconducting coplanar waveguide resonators towards hybrid quantum devices with magnon-photon coupling. We find internal quality factors ~ 20000 at 20 mK base temperature, in zero magnetic field. We find that by reducing film thickness below 100 nm internal quality factor greater than 1000 can be maintained up to parallel magnetic field of ~ 1 T and perpendicular magnetic field of ~ 100 mT. We further demonstrate strong coupling of microwave photons in these resonators, with magnons in chromium trichloride, a van der Waals antiferromagnet, wh…
Emergent cooperative motions of individual degrees of freedom, i.e. collective excitations, govern the low-energy response of system ground states under external stimulations and play essential roles for understanding many-body phenomena in low-dimensional materials. The hybridization of distinct collective modes provides a route towards coherent manipulation of coupled degrees of freedom and quantum phases. In magnets, strong coupling between collective spin and lattice excitations, i.e., magnons and phonons, can lead to coherent quasi-particle magnon polarons. Here, we report the direct obse…
The bosonic analogues of topological insulators have been proposed in numerous theoretical works, but their experimental realization is still very rare, especially for spin systems. Recently, two-dimensional (2D) honeycomb van der Waals (vdW) ferromagnets have emerged as a new platform for topological spin excitations. Here, via a comprehensive inelastic neutron scattering study and theoretical analysis of the spin-wave excitations, we report the realization of topological magnon insulators in CrXTe$_3$ (X=Si, Ge) compounds. The nontrivial nature and intrinsic tunability of the gap opening at …
The hybridization of magnons (spin waves) with phonons, if sufficiently strong and comprising long wavelength excitations, may offer a new playground when manipulating the magnetically ordered systems with light. Applying a magnetic field to a quasi-2D antiferromagnet, FePS3, we tune the magnon-gap excitation towards coincidence with the initially lower-in-energy phonon modes. Hybrid magnon-phonon modes, the magnon polarons are unveiled with demonstration of a pronounced avoided crossing between the otherwise bare magnon and phonon excitations. The magnon polarons in FePS3 are primary traced w…
We theoretically study spin pumping from a layered van der Waals antiferromagnet in its canted ground state into an adjacent normal metal. We find that the resulting dc spin pumping current bears contributions along all spin directions. Our analysis allows for detecting intra- and cross-sublattice spin-mixing conductances via measuring the two in-plane spin current components. We further show that sublattice symmetry-breaking Gilbert damping can be realized via interface engineering and induces a dissipative coupling between the optical and acoustic magnon modes. This realizes magnon level att…
Unidirectional magnetoresistance driven by nonequilibrium antiferromagnetic magnons
South China University of Technology（华南理工大学）；Norwegian University of Science and Technology（挪威科技大学）；Peking University（北京大学）；Nanyang Technological University（南洋理工大学）
Spin and photonic systems are at the heart of modern information devices and emerging quantum technologies. An interplay between electron-hole pairs (excitons) in semiconductors and collective spin excitations (magnons) in magnetic crystals would bridge these heterogeneous systems, leveraging their individual assets in novel interconnected devices. Here, we report the magnon-exciton coupling at the interface between a magnetic thin film and an atomically-thin semiconductor. Our approach allies the long-lived magnons hosted in a film of yttrium iron garnet (YIG) to strongly-bound excitons in a …
Stacking-Controlled Altermagnetism and Topological Magnons in Bilayer CrI$_3$
Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices, State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Neutron Science and Technology, School of Physics, Sun Yat-Sen University（中山大学物理学院中子科学与技术研究所光电材料与技术国家重点实验室磁电物理与器件广东省重点实验室）
Two-dimensional (2D) van der Waals (vdW) magnets have been a fertile playground for the discovery and exploration of physical phenomena and new physics. In this Letter, we report the observation of an anomalous thermal Hall effect (THE) with \k{appa}_xy ~ 1x10^(-2) W K^(-1) m^(-1) in an insulating van der Waals ferromagnet VI3. The thermal Hall signal persists in the absence of an external magnetic field and flips sign upon the switching of the magnetization. In combination with theoretical calculations, we show that VI3 exhibits a dual nature of the THE, i.e., dominated by topological magnons…
Driving a two-dimensional Mott insulator with circularly polarized light breaks time-reversal and inversion symmetry, which induces an optically-tunable synthetic scalar spin chirality interaction in the effective low-energy spin Hamiltonian. Here, we show that this mechanism can stabilize topological magnon excitations in honeycomb ferromagnets and in optical lattices. We find that the irradiated quantum magnet is described by a Haldane model for magnons that hosts topologically-protected edge modes. We study the evolution of the magnon spectrum in the Floquet regime and via time propagation …
Using a combination of density functional theory (DFT) and spin-wave theory methods, we investigate the magnetic interactions and spin excitations in semiconducting VI$_3$. Exchange parameters of monolayer, bilayer, and bulk forms are evaluated by mapping the magnetic energies of various spin configurations, calculated using DFT+$U$, onto the Heisenberg model. The intralayer couplings remain largely unchanged in three forms of VI$_3$, while the interlayer couplings show stronger dependence on the dimensionality of the materials. We calculate the spin-wave spectra within a linear spin-wave theo…
Tunable Ultrastrong Magnon-Magnon Coupling and Squeezed States in a Triaxial Van der Waals Antiferromagnet
National Key Laboratory of Spintronics and School of Physics, Nanjing University（南京大学自旋电子学国家重点实验室和物理学院）；School of Science, Nanjing University of Posts and Telecommunications（南京邮电大学理学院）；Laboratory of Solid State Microstructures, Nanjing University（南京大学固体微结构实验室）；State Key Laboratory of Spintronics, Nanjing University（南京大学自旋电子学国家重点实验室）
Magnomechanical Coupling in Suspended 2D van der Waals Ferromagnets
Kavli Institute of Nanoscience, Delft University of Technology（代尔夫特理工大学卡弗里纳米科学研究所）；Department of Precision and Microsystems Engineering, Delft University of Technology（代尔夫特理工大学精密与微系统工程系）
We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT calculations to shed light on the magnetic and lattice properties of VI3. The structural transition at TS1 = 79 K is accompanied by a large splitting of polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed. The variations of phonon frequencies at 55 K induced by magnetoelastic coupling enhanced by spin-orbit interaction indicate the proximity of long-range ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and show dramatic softening in the narrow interval around the t…
Thermal transport is a pivotal probe for studying low-energy, charge-neutral quasi-particles in insulating magnets. In this Letter, we report an observation of large magneto-thermal conductivity and thermal Hall effect (THE) in a van der Waals antiferromagnet FeCl2. The magneto-thermal conductivity reaches over ~700%, indicating strong magnon-phonon coupling. Furthermore, we find an appreciable thermal Hall signal which changes sign concurrently with the spin-flip transition from the antiferromagnetic state to the polarized ferromagnetic state. Our theoretical calculations suggest that, in add…
Optical pump-probe experiments carried out in the time domain reveal both the intrinsic low energy dynamics and its connections to higher energy excitations in correlated electron systems. In this work, we propose two microscopic mechanisms for the optical generation of coherent magnetic modes in van der Waals magnets, and derive the corresponding effective light-spin interactions: either through pumping atomic orbital excitations resonantly or via a light-induced Floquet spin Hamiltonian, the ground state of the system is driven out of equilibrium. The subsequent long-time relaxational dynami…
Spin-waves have been studied for data storage, communication and logic circuits in the field of spintronics based on their potential to substitute electrons. Recent discovery of magnetism in two-dimensional (2D) systems such as monolayer CrI$_3$ and Cr$_2$Ge$_2$Te$_6$ has led to a renewed interest in such applications of magnetism in the 2D limit. Here we present direct evidence of standing spin-waves along with the uniform precessional resonance modes in van der Waals magnetic material, CrCl$_3$. Our experiment is the first direct observation of standing spin-wave modes, set up across a thick…
Hybrid magnonic systems host a variety of characteristic quantum phenomena such as the magnetically-induced transparency (MIT) and Purcell effect, which are considered useful for future coherent quantum information processing. In this work, we experimentally demonstrate a tunable MIT effect in the Y3Fe5O12(YIG)/Permalloy(Py) magnon-magnon coupled system via changing the magnetic field orientations. By probing the magneto-optic effects of Py and YIG, we identify clear features of MIT spectra induced by the mode hybridization between the uniform mode of Py and the perpendicular standing spin-wav…
Magnetic van der Waals materials provide an ideal playground for exploring the fundamentals of low-dimensional magnetism and open new opportunities for ultrathin spin processing devices. The Mermin-Wagner theorem dictates that as in reduced dimensions isotropic spin interactions cannot retain long-range correlations; the order is stabilized by magnetic anisotropy. Here, using ultrashort pulses of light, we demonstrate all-optical control of magnetic anisotropy in the two-dimensional van der Waals antiferromagnet NiPS$_3$. Tuning the photon energy in resonance with an orbital transition between…
Field-driven triggering of self-induced Floquet magnons in a magnetic vortex
Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Saclay（纳米科学与工程中心，法国国家科学研究中心，巴黎萨克雷大学）；International Iberian Nanotechnology Laboratory（伊比利亚纳米技术国际实验室）
The quasi-two-dimensional antiferromagnet Ni$_2$P$_2$S$_6$ belongs to the family of magnetic van der Waals compounds that provides a rich material base for the realization of fundamental models of quantum magnetism in low dimensions. Here, we report high-frequency/high-magnetic field electron spin resonance measurements on single crystals of Ni$_2$P$_2$S$_6$. The results enable one to reliably determine the positive, "easy"-plane type of the single ion anisotropy of the Ni$^{2+}$ ions with the upper limit of its magnitude $\lesssim 0.7$ meV. The resonance response reveals strongly anisotropic …
