Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3

Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed

Parity-controlled spin-wave excitations in synthetic antiferromagnets

We report in this study the current-induced-torque excitation of acoustic and optical modes in Ta/NiFe/Ru/NiFe/Ta synthetic antiferromagnet stacks grown on SiO2/Si substrates. The two Ta layers serve as spin torque sources with the opposite polarisations both in spin currents and Oersted fields acting on their adjacent NiFe layers. This can create the odd symmetry of spatial spin torque distribution across the growth direction, allowing us to observe different spin-wave excitation efficiency from synthetic antiferromagnets excited by homogeneous torques. We analyse the torque symmetry by in-plane angular dependence of symmetric and anti-symmetric lineshape amplitudes for their resonance and confirm that the parallel (perpendicular) pumping nature for the acoustic (optical) modes in our devices, which is in stark difference from the modes excited by spatially homogeneous torques. We also present our macrospin model for this particular spin-torque excitation geometry, which excellently supports our experimental observation. Our results offer capability of controlling spin-wave excitations by local spin-torque sources and we can explore further spin-wave control schemes based on this concept.Comment: 31 pages, 12 figure

Coupling microwave photons to topological spin textures in Cu2OSeO3

Topologically protected nanoscale spin textures, known as magnetic skyrmions, possess particlelike properties and feature emergent magnetism effects. In bulk cubic helimagnets, distinct skyrmion resonant modes are already identified using a technique such as ferromagnetic resonance in spintronics. However, direct light-matter coupling between microwave photons and skyrmion resonance modes still needs to be demonstrated. Utilizing two distinct cavity systems, we observe a direct interaction between the cavity resonant mode and two resonant skyrmion modes, the counterclockwise gyration and breathing modes, in bulk Cu 2 OSeO 3 . For both resonant modes, we find the largest coupling strength at 57 K indicated by an enhancement of the cavity linewidth at the degeneracy point. We study the effective coupling strength as a function of temperature within the expected skyrmion phase. We attribute the maximum in effective coupling strength to the presence of a large number of skyrmions, and correspondingly to a completely stable skyrmion lattice. Our experimental findings indicate that the coupling between photons and resonant modes of magnetic skyrmions depends on the relative density of these topological particles instead of the pure spin number in the system

Quantum spin pumping mediated by magnon

We theoretically propose quantum spin pumping mediated by magnons, under a time-dependent transverse magnetic field, at the interface between a ferromagnetic insulator and a non-magnetic metal. The generation of a spin current under a thermal equilibrium condition is discussed by calculating the spin transfer torque, which breaks the spin conservation law for conduction electrons and operates the coherent magnon state. Localized spins lose spin angular momentum by emitting magnons and conduction electrons flip from down to up by absorbing the momentum. The spin transfer torque has a resonance structure as a function of the angular frequency of the applied transverse field. This fact is useful to enhance the spin pumping effect induced by quantum fluctuations. We also discuss the distinction between our quantum spin pumping theory and the one proposed by Tserkovnyak et al.Comment: 27 pages, 2 figures. v2; the detail of the calculation has been added in Appendix. The distinction from the spin pumping theory proposed by Tserkovnyak et al. has been clarified in section 5. v3; typos correcte

Task-adaptive physical reservoir computing

Reservoir computing is a neuromorphic architecture that may offer viable solutions to the growing energy costs of machine learning. In software-based machine learning, computing performance can be readily reconfigured to suit different computational tasks by tuning hyperparameters. This critical functionality is missing in 'physical' reservoir computing schemes that exploit nonlinear and history-dependent responses of physical systems for data processing. Here we overcome this issue with a 'task-adaptive' approach to physical reservoir computing. By leveraging a thermodynamical phase space to reconfigure key reservoir properties, we optimize computational performance across a diverse task set. We use the spin-wave spectra of the chiral magnet Cu2OSeO3 that hosts skyrmion, conical and helical magnetic phases, providing on-demand access to different computational reservoir responses. The task-adaptive approach is applicable to a wide variety of physical systems, which we show in other chiral magnets via above (and near) room-temperature demonstrations in Co8.5Zn8.5Mn3 (and FeGe)

Causes of Abnormal Ca2+ Transients in Guinea Pig Pathophysiological Ventricular Muscle Revealed by Ca2+ and Action Potential Imaging at Cellular Level

BACKGROUND: Abnormal Ca(2+) transients are often observed in heart muscles under a variety of pathophysiological conditions including ventricular tachycardia. To clarify whether these abnormal Ca(2+) transients can be attributed to abnormal action potential generation or abnormal Ca(2+) handling/excitation-contraction (EC) coupling, we developed a procedure to determine Ca(2+) and action potential signals at the cellular level in isolated heart tissues. METHODOLOGY/PRINCIPAL FINDINGS: After loading ventricular papillary muscle with rhod-2 and di-4-ANEPPS, mono-wavelength fluorescence images from rhod-2 and ratiometric images of two wavelengths of emission from di-4-ANEPPS were sequentially obtained. To mimic the ventricular tachycardia, the ventricular muscles were field-stimulated in non-flowing Krebs solution which elicited abnormal Ca(2+) transients. For the failed and alternating Ca(2+) transient generation, there were two types of causes, i.e., failed or abnormal action potential generation and abnormal EC coupling. In cells showing delayed initiation of Ca(2+) transients with field stimulation, action potential onset was delayed and the rate of rise was slower than in healthy cells. Similar delayed onset was also observed in the presence of heptanol, an inhibitor of gap junction channels but having a non-specific channel blocking effect. A Na(+) channel blocker, on the other hand, reduced the rate of rise of the action potentials but did not result in desynchronization of the action potentials. The delayed onset of action potentials can be explained primarily by impaired gap junctions and partly by Na(+) channel inactivation. CONCLUSIONS/SIGNIFICANCE: Our results indicate that there are multiple patterns for the causes of abnormal Ca(2+) signals and that our methods are useful for investigating the physiology and pathophysiology of heart muscle

Vascular endothelial growth factor-C expression and its relationship to pelvic lymph node status in invasive cervical cancer

Vascular endothelial growth factor-C (VEGF-C) has been implicated in lymphangiogenesis, the process of new lymphatics formation. The present study investigated VEGF-C mRNA expression in invasive cervical cancer tissue. Additionally, the association of VEGF-C mRNA with clinicopathological features was examined. VEGF-C mRNA expression was assessed by reverse transcription-polymerase chain reaction using β-action as an internal control. 75 patients presenting with invasive cervical cancer were included in the trial. VEGF-C mRNA expression was markedly higher in tumours in which pelvic lymph node metastasis was diagnosed by magnetic resonance (MR) imaging (P = 0.002). 53 patients displaying stage Ib–IIb cervical cancer underwent radical hysterectomy and pelvic lymphadenectomy. VEGF-C expression was significantly higher in tumours exhibiting deep stromal invasion, pelvic lymph node metastasis and lymph-vascular space involvement (P = 0.016, P = 0.006 and P = 0.036, respectively). Multivariate analysis revealed VEGF-C mRNA expression to be the sole independent factor influencing pelvic lymph node metastasis. Subjects demonstrating VEGF-C mRNA expression displayed significantly poorer prognoses than those lacking VEGF-C mRNA expression (P = 0.049). These findings provide evidence supporting the involvement of VEGF-C expression in the promotion of lymph node metastasis in cervical cancer. Furthermore, examination of VEGF-C expression in biopsy specimens may be beneficial in the prediction of pelvic lymph node metastasis. © 2001 Cancer Research Campaign http://www.bjcancer.co

Polaron spin current transport in organic semiconductors

In spintronics, pure spin currents play a key role in transmitting, processing and storing information. A pure spin current is a flow of electron spin angular momentum without a simultaneous flow of charge current. It can be carried by conduction electrons or magnons and has been studied in many inorganic metals, semiconductors and insulators, but not yet in organic semiconductors. Charge carriers in π-conjugated organic materials are localized spin-1/2 polarons which move by hopping, but the mechanisms of their spin transport and relaxation are not well understood. Here we use ferromagnetic resonance spin pumping in a ferromagnet/conjugated polymer/nonmagnetic spin-sink trilayer to demonstrate the ability of polarons to carry pure spin currents over hundreds of nanometres with long spin relaxation times of up to a millisecond and to exhibit Hanle precession. By systematically comparing charge and spin transport on the same trilayer we show that spin-orbit coupling mediates spin relaxation at room temperature.This work was supported by the Cabinet Office, Government of Japan through its “Funding Program for Next Generation World-Leading Researchers”, PRESTO-JST “Innovative nano-electronics through interdisciplinary collaboration among material, device and system layers”, the Asahi Glass Foundation and the Engineering and Physical Sciences Research Council (EPSRC).This is the accepted version of the article. The final version was published in Nature Physics and is available at http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2901.html. Nature Publishing Group's licence and reuse policy is available at http://www.nature.com/authors/policies/license.html