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The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction that stabilizes spin chirality. One scientific and technological challenge is understanding and controlling the interaction between spin chirality and electric field. In this study, we investigate an unconventional electric field effect on interfacial DMI, skyrmion helicity, and skyrmion dynamics in a system with broken inversion symmetry. We design heterostructures with a 3d-5d atomic orbital interface to demonstrate the gate bias control of the DMI energy and thus transform the DMI between opposite chiralities. Furthermore, we use this voltage-controlled DMI (VCDMI) to manipulate the skyrmion spin texture. As a result, a type of intermediate skyrmion with a unique helicity is created, and its motion can be controlled and made to go straight. Our work shows the effective control of spin chirality, skyrmion helicity, and skyrmion dynamics by VCDMI. It promotes the emerging field of voltage-controlled chiral interactions and voltage-controlled skyrmionics.

Quantum anomalous Hall phases arising from the inverted band topology in magnetically-doped topological insulators have emerged as an important subject of research for quantization at zero magnetic fields. Though necessary for practical implementation, sophisticated electrical control of molecular beam epitaxy grown quantum anomalous Hall matter have been stymied by growth and fabrication challenges. Here we demonstrate a novel procedure, employing a combination of thin film deposition and two-dimensional material stacking techniques, to create dualgated devices of the molecular beam epitaxy grown quantum anomalous Hall insulator, Cr-doped (Bi,Sb)

Electric-field control of spin dynamics is significant for spintronic device applications. Thus far, effectively electric-field control of magnetic order, magnetic damping factor and spin–orbit torque (SOT) has been studied in magnetic materials, but the electric field control of spin relaxation still remains unexplored. Here, we use ionic liquid gating to control spin-related property in the ultra-thin (4 nm) heavy metal (HM) platinum (Pt) and ferromagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, YIG) heterostructure. It is found that the anomalous Hall effect (AHE), spin relaxation time and spin diffusion length can be effectively controlled by the electric field. The anomalous Hall resistance is almost twice as large as at 0 voltage after applying a small voltage of 5.5 V. The spin relaxation time can vary by more than 50 percent with the electric field, from 41.6 to 64.5 fs. In addition, spin relaxation time at different gate voltage follows the reciprocal law of the electron momentum scattering time, which indicates that the D’yakonov–Perel’ mechanism is dominant in the Pt/YIG system. Furthermore, the spin diffusion length can be effectively controlled by an ionic gate, which can be well explained by voltage-modulated interfacial spin scattering. These results help us to improve the interface spin transport properties in magnetic materials, with great contributions to the exploration of new physical mechanisms and spintronics device.

The quantum anomalous Hall (QAH) effect has been demonstrated in two-dimensional topological insulator systems incorporated with ferromagnetism. However, a comprehensive understanding of mesoscopic transport in sub-micron QAH devices has yet been established. Here we fabricated miniaturized QAH devices with channel widths down to 600 nm, where the QAH features are still preserved. A back-scattering channel is formed in narrow QAH devices through percolative hopping between 2D compressible puddles. Large resistance fluctuations are observed in narrow devices near the coercive field, which is associated with collective interference between intersecting paths along domain walls when the device geometry is smaller than the phase coherence length $L_\phi$. Through measurement of size-dependent breakdown current, we confirmed that the chiral edge states are confined at the physical boundary with its width on the order of Fermi wavelength., Comment: 7 pages, 5 figures

Integer quantum Hall effect allows to gauge the resistance standard up to more than one part in a billion. Combining it with the speed of light, one obtains the fine-structure constant α [Formula: see text] 1/137, a dimensionless reference number that can be extracted from a physical experiment. Most exact notion of this value and especially its possible variation on the cosmological time scales is of enormous relevance for fundamental science. In an optical experiment, the fine-structure constant can be directly obtained as purely geometrical angle by measuring the quantized rotation of light polarization in two-dimensional quantum wells. In realistic conditions, high external magnetic fields have to be applied, which strongly affects possible attainable accuracy. An elegant solution of this problem is provided by quantum anomalous Hall effect where a universal quantized value can be obtained in zero magnetic field. Here, we measure the fine-structure constant in a direct optical experiment that requires no material adjustments or technical calibrations. By investigating the Faraday rotation at the interference maxima of the dielectric substrate, the angle close to one α is obtained at liquid helium temperatures without using a dilution refrigerator. Such calibration and parameter-free experiment provides a system-of-unit-independent access to universal quantum of rotation.

Ideally, quantum anomalous Hall systems should display zero longitudinal resistance. Yet in experimental quantum anomalous Hall systems elevated temperature can make the longitudinal resistance finite, indicating dissipative flow of electrons. Here, we show that the measured potentials at multiple locations within a device at elevated temperature are well-described by solution of Laplace's equation, assuming spatially-uniform conductivity, suggesting non-equilibrium current flows through the two-dimensional bulk. Extrapolation suggests that at even lower temperatures current may still flow primarily through the bulk rather than, as had been assumed, through edge modes. An argument for bulk current flow previously applied to quantum Hall systems supports this picture., Comment: 6 pages, 4 figures, plus supplemental materials

In transport, the topological Hall effect (THE) presents itself as nonmonotonic features (or humps and dips) in the Hall signal and is widely interpreted as a sign of chiral spin textures, like magnetic skyrmions. However, when the anomalous Hall effect (AHE) is also present, the coexistence of two AHEs could give rise to similar artifacts, making it difficult to distinguish between genuine THE with AHE and two-component AHE. Here, we confirm genuine THE with AHE by means of transport and magneto-optical Kerr effect (MOKE) microscopy, in which magnetic skyrmions are directly observed, and find that genuine THE occurs in the transition region of the AHE. In sharp contrast, the artifact "THE" or two-component AHE occurs well beyond the saturation of the "AHE component" (under the false assumption of THE + AHE). Furthermore, we distinguish artifact "THE" from genuine THE by three methods: (1) minor loops, (2) temperature dependence, and (3) gate dependence. Minor loops of genuine THE with AHE are always within the full loop, while minor loops of the artifact "THE" may reveal a single loop that cannot fit into the "AHE component". In addition, the temperature or gate dependence of the artifact "THE" may also be accompanied by a polarity change of the "AHE component", as the nonmonotonic features vanish, while the temperature dependence of genuine THE with AHE reveals no such change. Our work may help future researchers to exercise caution and use these methods for careful examination in order to ascertain the genuine THE.

Presently, porous materials have become essential to many technological applications. In this account, 3-dimensional skeleton composite materials consisting of a core-shell amorphous porous carbon/multilayer graphene are synthesized by chemical vapor deposition on Ni foam using a facile one-step growth method. The data suggest that these composites have not only outstanding electrical and mechanical properties of the multilayer graphene but also the mesoporous characteristics of the amorphous carbon. Moreover, the composited carbon materials perfectly inherit the macroporous structure of Ni foam, and the amorphous carbon core in the skeleton serves as a cushion to buffer the volume variation after the removal of Ni. The carbon composites reveal ultralow density (4.45 mg cm-3) and high conductivity (45 S cm-1), essentially issued from the perfectly preserved structural integrity of graphene. The novel carbon composites can be used as anodes for lithium ion batteries. After these carbon composites are incorporated with NaBiO3, superior electrochemical activities above 2 V can be achieved with a discharge capacity of ∼300 mAh g-1.

Smith–Purcell radiation (SPR) is electromagnetic radiation generated by free electrons passing over a periodic grating. Here, having the electron beam pass through 30 nm wide slots in an Al grating greatly shortens the SPR wavelength, and a directional, ultra-broadband, tunable light source spanning λ0≈230–1100 nm is demonstrated. By adjusting the electron energy, backward SPR can be tuned over λ0=251–340 nm. This work greatly extends the wavelength of SPR from the previously reported 320 nm to 230 nm, and provides a means of realizing an integrated free-electron broadband light source covering the deep ultraviolet.