Topological effect on fluorescence emission of tetraphenylethylene-based metallacages

Herein,we describe the selective formation of a barrel-shaped or a ball-shaped fluorescent metallacage by controlling the shape and stoichiometry of the building blocks.Specifically,the tetraphenylethylene-based donor and two acceptors with different numbers of Pt(Ⅱ)centers were combined via coordination-driven self-assembly.Owing to the differences in the shapes of the assemblies,the resultant ball-shaped metallacage displayed stronger and blue-shifted fluorescence compared to the barrel-shaped one in dilute solutions,while a reversal of fluorescence intensities was observed in the aggregation process.Overall,this work demonstrates that the photophysical properties of supramolecular coordination complexes can be affected by subtle geometrical factors,which can be controlled precisely at the molecular level.

Giant topological Hall effect of ferromagnetic kagome metal Fe3Sn2

We present the experiment observation of a giant topological Hall effect(THE)in a frustrated kagome bilayer magnet Fe3Sn2.The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K.Its maximum absolute value reaches^2.01μΩ·cm at 300 K and 0.76 T.The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration,possibly related to the magnetic frustration interaction in Fe3Sn2.

Random-Gate-Voltage Induced Al'tshuler–Aronov–Spivak Effect in Topological Edge States

Helical edge states are the hallmark of the quantum spin Hall insulator. Recently, several experiments have observed transport signatures contributed by trivial edge states, making it difficult to distinguish between the topologically trivial and nontrivial phases. Here, we show that helical edge states can be identified by the randomgate-voltage induced Φ_(0)/2-period oscillation of the averaged electron return probability in the interferometer constructed by the edge states. The random gate voltage can highlight the Φ_(0)/2-period Al'tshuler–Aronov–Spivak oscillation proportional to sin^(2)(2πΦ/Φ_(0)) by quenching the Φ_(0)-period Aharonov–Bohm oscillation. It is found that the helical spin texture induced π Berry phase is key to such weak antilocalization behavior with zero return probability at Φ = 0. In contrast, the oscillation for the trivial edge states may exhibit either weak localization or antilocalization depending on the strength of the spin-orbit coupling, which has finite return probability at Φ = 0. Our results provide an effective way for the identification of the helical edge states. The predicted signature is stabilized by the time-reversal symmetry so that it is robust against disorder and does not require any fine adjustment of system.

Magnetic Proximity Effect in an Antiferromagnetic Insulator/Topological Insulator Heterostructure with Sharp Interface

We report an experimental study of electron transport properties of MnSe/(Bi,Sb)_2Te_3 heterostructures,in which MnSe is an antiferromagnetic insulator,and(Bi,Sb)_2Te_3 is a three-dimensional topological insulator(TI).Strong magnetic proximity effect is manifested in the measurements of the Hall effect and longitudinal resistances.Our analysis shows that the gate voltage can substantially modify the anomalous Hall conductance,which exceeds 0.1 e^(2)/h at temperature T=1.6 K and magnetic field μ_0H=5 T,even though only the top TI surface is in proximity to MnSe.This work suggests that heterostructures based on antiferromagnetic insulators provide a promising platform for investigating a wide range of topological spintronic phenomena.

Topological phase transition in cavity optomechanical system with periodical modulation

We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation.By calculating the steady-state equations of the system,the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated.It is found that the cavity optomechanical system can be modulated to different topological Su–Schrieffer–Heeger(SSH)phases via designing the optomechanical couplings legitimately.Meanwhile,combining the effective optomechanical couplings and the probability distributions of gap states,we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields.Moreover,we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.

Progress on 2D topological insulators and potential applications in electronic devices

Two-dimensional topological insulators(2DTIs)have attracted increasing attention during the past few years.New 2DTIs with increasing larger spin-orbit coupling(SOC)gaps have been predicted by theoretical calculations and some of them have been synthesized experimentally.In this review,the 2DTIs,ranging from single element graphene-like materials to bi-elemental transition metal chalcogenides(TMDs)and to multi-elemental materials,with different thicknesses,structures,and phases,have been summarized and discussed.The topological properties(especially the quantum spin Hall effect and Dirac fermion feature)and potential applications have been summarized.This review also points out the challenge and opportunities for future 2DTI study,especially on the device applications based on the topological properties.

Experimental observation of topological Hall effects in compensated ferrimagnet-heavy metal layered structures

The topological Hall effect(THE) as a powerful probe for the experimental observation of topological spin textures, such as magnetic skyrmions, has been observed in a wide variety of distinct material systems. However, limited experimental observations have been reported for antiferromagnetic(AFM) materials. Here, the THE signals in the AFM state were observed in compensated ferrimagnetic thin films interfaced with heavy metals at the magnetization compensation temperature(TM).Ferrimagnetic CoTb thin films grown on Pt thin films were used in the experiments. The Co Tb films exhibited a magnetization compensation point at which the moments of Co and Tb sublattices canceled each other, giving rise to the AFM state. The temperature(T)-dependent Hall measurements showed anomalous Hall effect(AHE) and THE responses at T≠T_(M) but pure THE responses at T=T_(M). Control measurements and analyses suggest that the THE responses are associated with interfacial Dzyaloshinskii-Moriya interaction(DMI) rather than the overlapping of different AHE signals in the structure. This work presents the first-ever observation of interfacial DMI-induced THE in AFM metal trilayered systems and demonstrates a new approach for electrical reading of chiral spin textures in AFM thin film-based heterostructures.

Broadband photovoltaic effect of n-type topological insulator Bi2Te3 films on p-type Si substrates

We report the photovoltaic effects of n-type topological insulator （TI） Bi2Te3 films grown on p-type Si substrates by chemical vapor deposition （CVD）. The films containing large nanoplates with a smooth surface formed on p-Si exhibit good p-n diode characteristics under dark and light illumination conditions and display a good photovoltaic effect under the broadband range from ultraviolet （UV） to near infrared （N1R） wavelengths. Under the light illumination with a wavelength of 1,000 nm, a short circuit current （Isc） of 19.2 μA and an open circuit voltage （Voc） of 235 mV are achieved. The maximum fill factor （FF） increases with a decrease in the wavelength or light density, achieving a value of 35.6% under 600 nm illumination. The photoresponse of the n-Bi2TeB/p-Si device can be effectively switched between the on and off modes in millisecond time scale. These findings are important for both the fundamental understanding and solar cell device avDlications of TI materials.

Silicene spintronics——A concise review

Spintronics involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. The fascinating spin-resolved properties of graphene motivate numerous researchers to study spintronics in graphene and other two-dimensional(2D) materials. Silicene, the silicon analog of graphene, is considered to be a promising material for spintronics. Here, we present a review of theoretical advances with regard to spin-dependent properties, including the electric field- and exchange field-tunable topological properties of silicene and the corresponding spintronic device simulations.

Synthesis and magnetotransport properties of Bi2Se3 nanowires

Bi2Se3, as a three-dimensional topological insulator, has attracted worldwide attention for its unique surface states which are protected by time-reversal symmetry. Here we report the synthesis and characterization of high-quality singlecrystalline Bi2Se3 nanowires. Bi2Se3 nanowires were synthesized by chemical vapor deposition（CVD） method via goldcatalyzed vapor-liquid-solid（VLS） mechanism. The structure and morphology were characterized by scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, x-ray photoelectron spectroscopy（XPS）, and Raman spectroscopy. In magnetotransport measurements, the Aharonov–Bohm（AB） effect was observed in a nanowire-based nanodevice, suggesting the existence of surface states in Bi2Se3 nanowires.

Visualization of ferromagnetic domains in vanadium-doped topological insulator thin films and heterostructures

Magnetically doped topological insulator(TI) thin films and related heterostructures have been extensively studied for years due to their exotic quantum transport properties and potential applications in low-dissipation electronic devices and quantum computation.The selection of magnetic dopants is crucial to realize a high-quality magnetic TI with a robust ferromagnetic ordering and a preserved topological band structure.In this paper,we briefly review the recent magnetic domain imaging works in vanadium-doped magnetic topological insulator thin films and heterostructures.Using cryogenic magnetic force microscopy and in situ transport measurements,a ferromagnetic domain behavior has been demonstrated in V-doped Sb2Te3(ST) and Cr,V co-doped(Bi,Sb)2Te3(BST) thin films.The direct visualization of long-range ferromagnetic ordering in a quantum anomalous Hall(QAH) system sheds light on enhancing the QAH temperature by improving the ferromagnetism.Taking advantage of the different coercivity of Cr-and V-doped BST films,an axion insulating state has been observed in Cr-doped BST/BST/V-doped BST sandwich heterostructures.The antiparallel magnetization alignment,which is the key ingredient for realization of axion insulating state,has been directly visualized via magnetic imaging at various magnetic fields.The V-doped ST/ST heterostructures also provide a platform for Berry phase engineering in momentum space.By suppressing the anomalous Hall effect in such heterostructures,an intrinsic topological Hall effect can be revealed,which resolved the long-term puzzle of the origin of THE in the ultrathin ferromagnetic thin films and two-dimensional ferromagnets.The review of magnetic domain imaging in vanadium-doped topological insulators and heterostructures inspires further exploration of quantum transport properties in magnetic topological insulators and deepens the understanding of the interplay between the magnetic ordering and topological electronic band structures in magnetic TIs and beyond.

Realization of quantum anomalous hall effect at tens of kelvin by n-p codoping of topological insulators

With the support by the National Natural Science Foundation of China,the research teams led by Prof.Xu Xiaohong（许小红）at the School of Chemistry and Materials Science,Shanxi Normal University and Prof.Zhang Zhenyu at ICQD,University of Science and Technology of China used vanadium-iodine（Ⅴ-Ⅰ）codoped Sb2Te3 to realize high-temperature quantum anomalous Hall effect（QAHE）,which was

Observation of unconventional anomalous Hall effect in epitaxial CrTe thin films

We have studied the magnetic and electrical transport properties of epitaxial NiAs-type CrTe thin films grown on SrTiO3（111） substrates. Unlike rectangle hysteresis loops obtained from magnetic measurements, we have identified intriguing extra bump/dip features from anomalous Hall experiments on the films with thicknesses less than 12 nm. This observed Hall anomaly is phenomenologically consistent with the occurrence of a topological Hall effect （THE） in chiral magnets with a skyrmion phase. Furthermore, the THE contribution can be tuned by the film thickness, showing the key contribution of asymmetric interfaces in stabilizing N6el-type skyrmions. Our work demonstrates that a CrTe thin film on SrTiO3（111） substrates is a good material candidate for studying real-space topological transport.

Strain and carrier-induced coexistence of topologically insulating and superconducting phase in iodized Si（111） films

The importance of silicon in modem electronic devices has led to considerable interest in exploring the unconventional electronic properties of Si-based materials for future applications in spintronics and quantum computing. Here, using density functional theory, we present the results of a systematic study of the effect of strain on Si（lll） thin films whose surfaces are functionalized with iodine. Films with an odd number of layers under biaxial strain are found to undergo a phase transition from a normal insulator to a topological insulator and ultimately to a metal. The spin-orbit coupling-induced topologically nontrivial band gap at the F point is found to be as large as 0.50 eV, which not only surpasses that of other Si-based topological materials, it is also large enough for practical realization of quantum spin Hall states at room temperature. No such nontrivial states are found in films for such a strain-induced transition with an even number of layers. Mechanisms are illustrated by a tight-binding model composed of s, px, and py orbitals. Equally important, we predict that iodized silicene, when stretched and hole-doped, would be a phonon-mediated super- conductor with a critical temperature of 9.2 K. This coexistence of a topological insulator and a superconducting phase in a single material is unusual; it has the potential for applications in electronic circuits and for the realization of Majorana fermions in quantum computations.

Pressure-tuning domain-wall chirality in noncentrosymmetric magnetic Weyl semimetal CeAlGe

Topological magnetic Weyl semimetals have been proposed to host controllable chiral domain walls which bear a great prospect in device applications. To exploit them in applications, it is important to have a proper way to tune and manipulate these domain walls. One possible means is through magnetoelastic coupling. The involvement of rare earth in the lately proposed RAl X(R =rare earth, X = Si and Ge) family magnetic Weyl semimetals may provide such a platform. Here we present the transport and thermodynamic properties of Ce Al Ge under hydrostatic pressure. We find that pressure enhances the antiferromagnetic exchange in Ce Al Ge but essentially retains its magnetic structure. A large topological Hall effect with a pronounced loop shape is observed within the magnetically ordered state, and it splits into two regions under pressure. Such an unusual electromagnetic response is inferred to be a consequence of chiral magnetic domain walls. The unprecedented concomitance of its evolution under pressure and the reentrance of antiferromagnetic order strongly suggest the capability of switching on/off this electromagnetic response in noncentrosymmetric magnetic Weyl semimetals via magnetoelastic coupling.