Dawn of Cavity Spintronics

Merging the progress of spintronics with the advancement in cavity quantum electrodynamics and cavity polaritons, a new field of Cavity Spintronics is forming, which connects some of the most exciting modern physics, such as quantum information and quantum optics, with one of the oldest science on the earth, the magnetism.Comment: 6 pages, 1 figur

Electrical Detection of Magnetization Dynamics via Spin Rectification Effects

The purpose of this article is to review the current status of a frontier in dynamic spintronics and contemporary magnetism, in which much progress has been made in the past decade, based on the creation of a variety of micro- and nano-structured devices that enable electrical detection of magnetization dynamics. The primary focus is on the physics of spin rectification effects, which are well suited for studying magnetization dynamics and spin transport in a variety of magnetic materials and spintronic devices. Intended to be intelligible to a broad audience, the paper begins with a pedagogical introduction, comparing the methods of electrical detection of charge and spin dynamics in semiconductors and magnetic materials respectively. After that it provides a comprehensive account of the theoretical study of both the angular dependence and line shape of electrically detected ferromagnetic resonance (FMR), which is summarized in a handbook formate easy to be used for analyzing experimental data. We then review and examine the similarity and differences of various spin rectification effects found in ferromagnetic films, magnetic bilayers and magnetic tunnel junctions, including a discussion of how to properly distinguish spin rectification from the spin pumping/inverse spin Hall effect generated voltage. After this we review the broad applications of rectification effects for studying spin waves, nonlinear dynamics, domain wall dynamics, spin current, and microwave imaging. We also discuss spin rectification in ferromagnetic semiconductors. The paper concludes with both historical and future perspectives, by summarizing and comparing three generations of FMR spectroscopy which have been developed for studying magnetization dynamics.Comment: Review article submitted to Physics Reports. 75 pages, 37 figure

Cavity Spintronics: An Early Review of Recent Progress in the Study of Magnon-Photon Level Repulsion

Light-matter interactions lie at the heart of condensed matter physics, providing physical insight into material behaviour while enabling the design of new devices. Perhaps this is most evident in the push to develop quantum information and spintronic technologies. On the side of quantum information, engineered light-matter interactions offer a powerful means to access and control quantum states, while at the same time new insights into spin-photon manipulation will benefit the development of spintronic technologies. In this context the recent discovery of hybridization between ferromagnets and cavity photons has ushered in a new era of light-matter exploration at the crossroads of quantum information and spintronics. The key player in this rapidly developing field of cavity spintronics is a quasiparticle, the cavity-magnon-polariton. In this early review of recent work, the fundamental behaviour of the cavity-magnon-polariton is summarized and related to the development of new spintronic applications. In the last few years a comprehensive theoretical framework of spin-photon hybridization has been developed. On an intuitive level many features can be described by a model of coupled oscillators, however the origin of hybridization is only revealed by considering a comprehensive electrodynamic framework. Here both approaches are summarized and a quantum description using the input-output formalism is outlined. Based on this foundation, in depth experimental investigations of the coupled spin-photon system have been performed. For example, the influence of hybridization on spin current generation has been revealed and several in-situ coupling control mechanisms have been developed. The many recent developments within this field represent only the first steps in what appears to be a bright future for cavity spintronics.Comment: Preprint version of a book chapter in Solid State Physics Volume 6

Study of the cavity-magnon-polariton transmission line shape

We experimentally and theoretically investigate the microwave transmission line shape of the cavity-magnon-polariton (CMP) created by inserting a low damping magnetic insulator into a high quality 3D microwave cavity. While fixed field measurements are found to have the expected Lorentzian characteristic, at fixed frequencies the field swept line shape is in general asymmetric. Such fixed frequency measurements demonstrate that microwave transmission can be used to access magnetic characteristics of the CMP, such as the field line width $\Delta H$. By developing an effective oscillator model of the microwave transmission we show that these line shape features are general characteristics of harmonic coupling. At the same time, at the classical level the underlying physical mechanism of the CMP is electrodynamic phase correlation and a second model based on this principle also accurately reproduces the experimental line shape features. In order to understand the microscopic origin of the effective coupled oscillator model and to allow for future studies of CMP phenomena to extend into the quantum regime, we develop a third, microscopic description, based on a Green's function formalism. Using this method we calculate the transmission spectra and find good agreement with the experimental results.Comment: 12 pages, 6 figure

Linking Magnon-Cavity Strong Coupling to Magnon-Polaritons through Effective Permeability

Strong coupling in cavity-magnon systems has shown great potential for use in spintronics and information processing technologies due to the low damping rates and long coherence times. Although such systems are conceptually similar to those coupled by magnon-polaritons (MPs), the link between magnon-cavity coupling and MPs has not been explicitly defined. In this work we establish such a connection by studying the frequency-wavevector dispersion of a strongly coupled magnon-cavity system, using a height-adjustable microwave cavity, and by modelling the observed behaviour through the system's effective permeability. A polariton gap between the upper and lower coupled modes of the magnon-cavity system is defined, and is seen to be dependent on the system's effective filling factor. This gap is equal to the MP polariton gap in the limit where filling factor = 1, corresponding to the removal of the microwave cavity. Thus, our work clarifies the connection between magnon-cavity and MP coupling, improving our understanding of magnon-photon interactions in coupled systems

Spin dynamical phase and anti-resonance in a strongly coupled magnon-photon system

We experimentally studied a strongly coupled magnon-photon system via microwave transmission measurements. An anti-resonance, i.e. the suppression of the microwave transmission, is observed, indicating a relative phase change between the magnon response and the driving microwave field. We show that this anti-resonance feature can be used to interpret the phase evolution of the coupled magnon-microwave system and apply this technique to reveal the phase evolution of magnon dark modes. Our work provides a standard procedure for the phase analysis of strongly coupled systems, enabling the phase characterization of each subsystem, and can be generally applied to other strongly coupled systems.Comment: 6 pages, 3 figure

Indirect Coupling between Two Cavity Photon Systems via Ferromagnetic Resonance

We experimentally realize indirect coupling between two cavity modes via strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG). We find that some indirectly coupled modes of our system can have a higher microwave transmission than the individual uncoupled modes. Using a coupled harmonic oscillator model, the influence of the oscillation phase difference between the two cavity modes on the nature of the indirect coupling is revealed. These indirectly coupled microwave modes can be controlled using an external magnetic field or by tuning the cavity height. This work has potential for use in controllable optical devices and information processing technologies

Transient spin current under a thermal switch

In this work, we explore the possibility of enhancing a spin current under a thermal switch, i.e., connecting the central transport region to two leads in individual thermal equilibrium abruptly. Using the nonequilibrium Green's function method for the transient spin current, we obtain a closed-form solution, which is applicable in the whole nonlinear quantum transport regime with a significant reduction of computational complexity. Furthermore, we perform a model calculation on a single-level quantum dot with Lorentzian linewidth. It shows that the transient spin current may vary spatially, causing spin accumulation or depletion in the central region. Moreover, general enhancement of the spin current in the transient regime is observed. In particular, the in-plane components of the transient spin current may increase by 2-3 orders of magnitude compared to the steady-state thermoelectric spin current under a temperature difference of 30 K. Our research demonstrates that ultrafast enhancement of spin currents can be effectively achieved by thermal switches.Comment: Submitted to J. Phys. D: Appl. Phys. (http://iopscience.iop.org/article/10.1088/1361-6463/aac7ca/meta

Ultrafast Manipulation of a Double Quantum Dot via Lyapunov Control Method

For a double quantum dot (DQD) system, here we propose alternative ultrafast manipulate approach: Lyapunov control method, to transfer the state from R to L on the picosecond scale, orders of magnitude faster and transfer probability higher than the previously measured electrically controlled charge- or spin-based quits. The control laws are composed of two-direction components, one is used to eliminate the dissipation in the system, another is used to transfer the state. The control theory's stability ensures the system can be transferred to the target state in high probability, and the coefficients in control laws leads very fast convergence. The role of eliminating the dissipation plays the suppression of decoherence effect. Numerical simulation results show that under the realistic implementation conditions, the transfer probability and fidelity can be increased up to 98.79% and 98.97%, respectively. This is the first result directly applicable to a DQD system's state transferring using the Lyapunov control method. We also give specific experimental realization scheme.Comment: 8 pages, 4 figure

Cavity mediated manipulation of distant spin currents using cavity-magnon-polariton

Using electrical detection of a strongly coupled spin-photon system comprised of a microwave cavity mode and two magnetic samples, we demonstrate the long distance manipulation of spin currents. This distant control is not limited by the spin diffusion length, instead depending on the interplay between the local and global properties of the coupled system, enabling systematic spin current control over large distance scales (several centimeters in this work). This flexibility opens the door to improved spin current generation and manipulation for cavity spintronic devices.Comment: 5 pages, 3 figure