Unravelling the anisotropic light-matter interaction in strainengineered trihalide MoCl_(3)

Layered trihalides exhibit distinctive band structures and physical properties due to the sixfold coordinated 3d or 4d transition metal site and partially occupied d orbitals,holding great potential in condensed matter physics and advanced electronic applications.Prior research focused on trihalides with highly symmetric honeycomb-like structures,such as CrI3 andα-RuCl_(3),while the role of crystal anisotropy in trihalides remains elusive.In particular,the trihalide MoCl_(3) manifests strong in-plane crystal anisotropy with the largest difference in Mo–Mo interatomic distances.Research on such material is imperative to address the lack of investigations on the effect of anisotropy on the properties of trihalides.Herein,we demonstrated the anisotropy of MoCl_(3) through polarized Raman spectroscopy and further tuned the phonon frequency via strain engineering.We showed the Raman intensity exhibits twofold symmetry under parallel configuration and fourfold symmetry under perpendicular configuration with changing the polarization angle of incident light.Furthermore,we found that the phonon frequencies of MoCl_(3) decrease gradually and linearly with applying uniaxial tensile strain along the axis of symmetry in the MoCl_(3) crystal,while those frequencies increase with uniaxial tensile strain applied perpendicularly.Our results shed light on the manipulation of anisotropic light-matter interactions via strain engineering,and lay a foundation for further exploration of the anisotropy of trihalides and the modulation of their electronic,optical,and magnetic properties.

Gate-tunable Berry curvature in van der Waals itinerant ferromagnetic Cr_(7)Te_(8)

The anomalous Hall effect(AHE)that associated with the Berry curvature of occupied electronic states in momentum-space is one of the intriguing aspects in condensed matter physics,and provides an alternative for potential applications in topological electronics.Previous experiments reported the tunable Berry curvature and the resulting magnetization switching process in the AHE based on strain engineering or chemical doping.However,the AHE modulation by these strategies are usually irreversible,making it difficult to realize switchable control of the AHE and the resultant spintronic applications.Here,we demonstrated the switchable control of the Berry-curvature-related AHE by electrical gating in itinerant ferromagnetic Cr_(7)Te_(8)with excellent ambient stability.The gate-tunable sign reversal of the AHE can be attributed to the redistribution of the Berry curvature in the band structure of Cr_(7)Te_(8)due to the intercalation-induced change in the Fermi level.Our work facilitates the applications of magnetic switchable devices based on gate-tunable Berry curvature.

Selective substitution induced anomalous phonon stiffening within quasi-one-dimensional P–P chains in SiP2

Light-matter interactions in low-dimensional quantum-confined structures can dominate the optical properties of the materials and lead to optoelectronic applications.In anisotropic layered silicon diphosphide(SiP2)crystal,the embedded quasi-onedimensional(1D)phosphorus–phosphorus(P–P)chains directly result in an unconventional quasi-1D excitonic state,and a special phonon mode vibrating along the P–P chains,establishing a unique 1D quantum-confined system.Alloying SiP2 with the homologous element serves as an effective way to study the properties of these excitons and phonons associated with the quasi-1D P–P chains,as well as the strong interaction between these quasiparticles.However,the experimental observation and the related optical spectral understanding of SiP2 with isoelectronic dopants remain elusive.Herein,with the photoluminescence and Raman spectroscopy measurements,we demonstrate the redshift of the confined excitonic peak and the stiffening of the phonon vibration mode■of a series of Si(P1−xAsx)2 alloys with increasing arsenic(As)compositions.This anomalous stiffening of■is attributed to the selective substitution of As atoms for P atoms within the P–P chains,which is confirmed via our scanning transmission electron microscopy investigation.Such optical spectra evolutions with selective substitution pave a new way to understand the 1D quantum confinement in semiconductors,offering opportunities to explore quasi-1D characteristics in SiP2 and the resulting photonic device application.

Gate-tunable spin valve effect in Fe_(3)GeTe_(2)-based van der Waals heterostructures

Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MTJ devices has been proposed in two directions:improving device performance by utilizing advanced two-dimensional(2D)ferromagnetic materials or extending device functionalities by exploring the gate-tunable magnetic properties of ferromagnets.Based on the recent development of 2D magnets with the ease of external stimuli,such as electric field,due to their reduced dimensions,reliable prospects for gate-tunable MTJ devices can be achieved,shedding light on the great potential of next-generation MTJs with multiple functionalities for various application environments.While the electrical gate-tunable MTJ device is highly desirable for practical spintronic devices,it has not yet been demonstrated.Here,we demonstrate the experimental realization of a spin valve device by combining a vertical Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ with an electrolyte gate.The magnetoresistance ratio(MR ratio)of 36%for the intrinsic MTJ confirms the good performance of the device.By electrolyte gating,the tunneling MR ratio of Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ can be elevated 2.5 times,from 26%to 65%.Importantly,the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating,providing a promising method to control the magnetization configuration of the MTJ.Our work demonstrates a gate-tunable MTJ device toward the possibility for gate-controlled spintronic devices,paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.

Gate Tunable Labyrinth Domain Structures in a van der Waals Itinerant Ferromagnet Cr_(7)Te_(8)

Manipulating magnetic domain structure plays a key role in advanced spintronics devices.Theoretical rationale is that the labyrinthine domain structure,normally appearing in ferromagnetic thin films with strong magnetic anisotropy,shows a great potential to increase data storage density for designing magnetic nonvolatile memory and logic devices.However,an electrical control of labyrinthine domain structure remains elusive.Here,we demonstrate the gate-driven evolution of labyrinthine domain structures in an itinerant ferromagnet Cr_(7)Te_(8).By combining electric transport measurements and micromagnetic finite difference simulations,we find that the hysteresis loop of anomalous Hall effect in Cr_(7)Te_(8)samples shows distinct features corresponding to the generation of labyrinthine domain structures.The labyrinthine domain structures are found to be electrically tunable via Li-electrolyte gating,and such gate-driven evolution in Cr_(7)Te_(8)originates from the reduction of the magnetic anisotropic energy with gating,revealed by our micromagnetic simulations.Our results on the gate control of anomalous Hall effect in an itinerant magnetic material provide an opportunity to understand the formation and evolution of labyrinthine domain structures,paving a new route towards electric-field driven spintronics.

Thickness-dependent patterning of MoS2 sheets with well-oriented triangular pits by heating in air

Patterning ultrathin MoS2 layers with regular edges or controllable shapes is appealing since the properties of MoS2 sheets are sensitive to the edge structures. In this work, we have introduced a simple, effective and well-controlled technique to etch layered MoS2 sheets with well-oriented equilateral triangular pits by simply heating the samples in air. The anisotropic oxidative etching is greatly affected by the surrounding temperature and the number of MoS2 layers, whereby the pit sizes increase with the increase of surrounding temperature and the number of MoS2 layers. First-principles computations have been performed to explain the formation mechanism of the triangular pits. This technique offers an alternative avenue to engineering the structure of MoS2 sheets.

Strain engineering of anisotropic light-matter interactions in onedimensional P-P chain of SiP_(2)

Strain engineering can serve as a powerful technique for modulating the exotic properties arising from the atomic structure of materials.Examples have been demonstrated that one-dimensional(1D)structure can serve as a great platform for modulating electronic band structure and phonon dispersion via strain control.Particularly,in a van der Waals material silicon diphosphide(SiP_(2)),quasi-1D zigzag phosphorus–phosphorus(P–P)chains are embedded inside the crystal structure,and can show unique phonon vibration modes and realize quasi-1D excitons.Manipulating those optical properties by the atom displacements via strain engineering is of great interest in understanding underlying mechanism of such P–P chains,however,which remains elusive.Herein,we demonstrate the strain engineering of Raman and photoluminescence(PL)spectra in quasi-1D P–P chains and resulting in anisotropic manipulation in SiP_(2).We find that the phonon frequencies of SiP_(2)in Raman spectra linearly evolve with a uniaxial strain along/perpendicular to the quasi-1D P–P chain directions.Interestingly,by applying tensile strain along the P–P chains,the band gap energy of strained SiP_(2)can significantly decrease with a tunable value of~55 meV.Based on arsenic(As)element doping into SiP_(2),the strain-induced redshifts of phonon frequencies decrease,indicating the stiffening of the phonon vibration with the increased arsenic doping level.Such results provide an opportunity for strain engineering of the light–matter interactions in the quasi-1D P–P chains of SiP_(2)crystal for potential optical applications.

Electrical field tuning of magneto-Raman scattering in monolayer graphene

In this work, we report the electrical field tuning of magneto-phonon resonance in monolayer graphene under magnetic fields up to 9 T. It is found that the carrier concentration can drastically affect the G （E2g） phonon response to a varying magnetic field through a pronounced magneto-phonon resonance （MPR）. In charge neutral or slightly doped monolayer graphene, both the energy and the line width of the E2g phonon show clear variation with magnetic fields. This is attributed to magneto-phonon resonance between magnetoexcitations and the E2g phonons. In contrast, when the Fermi level of the monolayer graphene is far away from the Dirac point, the G band shows weak magnetic dependence and exhibits a symmetric line-shape. This suggests that the magneto-phonon coupling around 4 T has been switched off due to the Pauli blocking of the inter-Landau level excitations. Moreover, the G band asymmetry caused by Fano resonance between excitonic many-body states and the E2g phonons is observed. This work offers a way to study the magnetoexcitation phonon interaction of materials through magneto-Raman spectroscopy with an external electrical field.