Exploiting the valley degree of freedom introduces a novel paradigm for advancing quantum information technology. Currently, the investigation on spontaneous valley polarization mainly focuses on two major types of systems. One type magnetic systems by breaking the time-reversal symmetry, the other is ferroelectric materials through breaking the inversion symmetry. Might there be additional scenarios? Here, we propose to realize spontaneous valley polarization by breaking the mirror symmetry in the altermagnets, named type III valley polarization. Through symmetry analysis and first-principles calculations, we confirm that this mechanism is feasible in Non-Janus Fe2WS2Se2. Monolayer Non-Janus and Janus Fe2WS2Se2 are stable Neel-type antiferromagnetic state with the direct band gap semiconductor. More interestingly, their magnetic anisotropy energy exhibits the rare biaxial anisotropy and a four-leaf clover shape in the xy plane, while the xz and yz planes show the common uniaxial anisotropy. This originated from the fourth-order single ion interactions. More importantly, the valley splitting is spontaneously generated in the Non-Janus Fe2WS2Se2 due to the Mxy symmetry breaking, without requiring the SOC effect. Both the Non-Janus and Janus Fe2WS2Se2 exhibit diverse valley polarization and anomalous valley Hall effect properties. In addition, the magnitude and direction of valley polarization can be effectively tuned by the biaxial strain and magnetic field. Our findings not only expand the realization system of spontaneous valley polarization, but also provide a theoretical basis for the high-density storage of valley degrees of freedom.

Compared to the ferromagnetic materials that realize the anomalous valley Hall effect by breaking time-reversal symmetry and spin-orbit coupling, the antiferromagnetic materials with the joint spatial inversion and time-reversal (PT) symmetry are rarely reported that achieve the anomalous valley Hall effect. Here, we predict that the antiferromagnetic monolayer MnBr possesses spontaneous valley polarization. The valley splitting of valence band maximum is 21.55 meV at K and K' points, which is originated from Mn-dx2-y2 orbital by analyzing the effective Hamiltonian. Importantly, monolayer MnBr has zero Berry curvature in the entire momentum space but non-zero spin-layer locked Berry curvature, which offers the condition for the anomalous valley Hall effect. In addition, the magnitude of valley splitting can be signally tuned by the onsite correlation, strain, magnetization rotation, electric field, and built-in electric field. The electric field and built-in electric field induce spin splitting due to breaking the P symmetry. Therefore, the spin-layer locked anomalous valley Hall effect can be observed in MnBr. More remarkably, the ferroelectric substrate Sc2CO2 can tune monolayer MnBr to realize the transition from metal to valley polarization semiconductor. Our findings not only extend the implementation of the anomalous valley Hall effect, but also provides a platform for designing low-power and non-volatile valleytronics devices.

In order to promote the development of the next generation of nano-spintronic devices, it is of great significance to tune the freedom of valley in two-dimensional (2D) materials. Here, we propose a mechanism for manipulating the valley and nonlinear Hall effect by the 2D ferroelectric substrate. The monolayer Mn2P2S3Se3 is a robust antiferromagnetic valley polarized semiconductor. Importantly, the valley polarized metal-semiconductor phase transition of Mn2P2S3Se3 can be effectively tuned by switching the ferroelectric polarization of Sc2CO2. We reveal the microscopic mechanism of phase transition, which origins from the charge transfer and band alignment. Additionally, we find that transformed polarization direction of Sc2CO2 flexibly manipulate the Berry curvature dipole. Based on this discovery, we present the detection valley polarized metal-semiconductor transition by the nonlinear Hall effect devices. These findings not only offer a scheme to tune the valley degree of freedom, but also provide promising platform to design the nonlinear Hall effect devices.

This paper investigates optical bistability in a dual-cavity optomechanical system for optical switching applications. The hybrid configuration integrates an optical cavity with Kerr media and a mechanical resonator embedding semiconductor double quantum dot molecules. By solving steady-state Heisenberg-Langevin equations, we derive photon number expressions revealing bistable behavior. Numerical simulations demonstrate that bistability thresholds and hysteresis width can be tuned via external parameters (magnetic field intensity, probe frequency) and internal parameters (inter-cavity coupling strength, Kerr coefficient, quantum dot tunneling). The system's absorption response to the probe field shows dual-control mechanisms: external fields modulate medium interactions, while internal parameters adjust energy exchange dynamics. A novel optical switch design is proposed based on this controllable bistability. These findings highlight the system's potential for developing sensitive optical switches, optical memory devices, and photonic logic circuits.

The best carrier for quantum information transmission is light signal, which has a fast propagation speed and can carry a large amount of information. However, during the propagation of light, dispersion effect and diffraction effect can cause quantum information to be distorted to a certain extent. On the contrary, optical solitons are formed due to the balance between the system’s dispersion (diffraction) effect and nonlinear effect, and they exhibit very high stability and fidelity. Therefore, they have received widespread attention in electromagnetically induced transparency (EIT) media with ultracold atoms. However, cold atomic gas media require extremely low operating temperatures, and the performances of the materials are difficult to control precisely. These factors are unfavorable for the miniaturization and integration of future information devices, thus significantly limiting their practical applications. Semiconductor quantum dot media, on the other hand, possess advantages such as discrete energy level structures and spectral properties similar to those of cold atomic gases, longer decoherence times, larger electric dipole moments, more significant nonlinear optical effects, and easy integration, making them an ideal alternative to cold atomic media. In this work, semiconductor quantum dots are coupled with optical fibers, the most common carrier in optical communication, to explore the formation, storage, and retrieval of temporal optical solitons in the coupled system. The results show that due to the tunneling-induced transparency effect between dots in semiconductor quantum dot molecules, light absorption in the system is greatly suppressed. At the same time, the transverse confinement of the nanofiber can enhance the interaction between light and the system, and the enhanced nonlinear response of the system can balance the dispersion effect, resulting in stable temporal optical solitons. Further research indicates that by turning on and off the inter-dot tunneling coupling, the high-efficiency and high-fidelity storage and retrieval of optical solitons can be realized in the system. These findings have certain guiding significance and potential application value for the processing all-optical information in solid quantum materials.

Two-dimensional (2D) multiferroic materials have widespread application prospects in facilitating the integration and miniaturization of nanodevices. However, the magnetic, ferroelectric, and ferrovalley properties in one 2D material are rarely coupled. Here, we propose a mechanism for manipulating magnetism, ferroelectric, and valley polarization by interlayer sliding in a 2D bilayer material. Monolayer GdI2 is a ferromagnetic semiconductor with a valley polarization of up to 155.5 meV. More interestingly, the magnetism and valley polarization of bilayer GdI2 can be strongly coupled by sliding ferroelectricity, making these tunable and reversible. In addition, we uncover the microscopic mechanism of the magnetic phase transition by a spin Hamiltonian and electron hopping between layers. Our findings offer a new direction for investigating 2D multiferroic devices with implications for next-generation electronic, valleytronic, and spintronic devices.

Hourglass loop in two-dimensional (2D) systems is typically vulnerable against spin–orbit coupling (SOC). Here, we explore 2D systems with a type of spin-polarized nodal loop that is robust under SOC and characteristic of an hourglass-type dispersion. Through first-principles calculations, we identify the monolayer VCl2 materials as a realistic material platform to realize an hourglass loop. There exist three phases, all of which are dynamically stable. For the γ-structure, as a new single spin hourglass loop material. It shows semiconducting and gapless properties in spin down and spin up channels, respectively. Moreover, it always exhibits an hourglass loop property in the absence and presence of SOC. It indicates that the hourglass has strong against SOC. Our work suggests a realistic material platform for investigating the novel physics associated with band crossings in 2D systems.

In this study, we analyzed the storage and retrieval of vector optical fields in semiconductor double quantum dots with interdot tunneling coupling. Our findings indicate that temporal vector optical solitons (TVOS) can be effectively stored and retrieved through this coupling. Furthermore, we conducted numerical simulations to investigate the interaction between TVOS. Our results suggest that the interaction between in-phase solitons is attractive, while the interaction between anti-phase solitons is repulsive. Additionally, we found that TVOS remain stable even after a collision, which is significant for the processing of optical information in solid quantum materials. Overall, our study sheds light on the potential of interdot tunneling coupling for storing and retrieving vector optical fields in semiconductor double quantum dots. Additionally, our findings regarding the interaction between TVOS can inform future research in the field of optical information processing.

The electron’s charge and spin degrees of freedom are at the core of modern electronic devices. With the in-depth investigation of two-dimensional materials, another degree of freedom, valley, has also attracted tremendous research interest. The intrinsic spontaneous valley polarization in two-dimensional magnetic systems, ferrovalley material, provides convenience for detecting and modulating the valley. In this review, we first introduce the development of valleytronics. Then, the valley polarization forms by the p-, d-, and f-orbit that are discussed. Following, we discuss the investigation progress of modulating the valley polarization of two-dimensional ferrovalley materials by multiple physical fields, such as electric, stacking mode, strain, and interface. Finally, we look forward to the future developments of valleytronics.

The quantum anomalous Hall effect is an intriguing quantum state that exhibits chiral edge states in the absence of a magnetic field. The chiral edge states are topologically protected and robust against electron scattering, which possesses great potential applications in designing low energy consumption and dissipation less spintronic devices. The experimental conditions are required to be very high, such as extremely low temperature (< 100 mK) due to the small band gap and the greatly accurate control of the extrinsic impurities. These greatly hinder their devices from being put into applications further. Hence, it would be meaningful to search for a new Chern insulator with a large band gap and high Curie temperature. According to the first-principles calculations, we predict the room temperature quantum anomalous Hall effect in the monolayer BaPb. The nontrivial topology of this new type of ferroelectric semi-metal material derives from fully spin-polarized quadratic non-Dirac bands. The quantum anomalous Hall effect can be realized in the monolayer BaPb with fully spin-polarized quadratic px,y non-Dirac bands with the nonzero Chern number (C = 1). Because of the trigonal symmetry of monolayer BaPb material, these bands composed of px,y orbitals are at the \begin{document}$ \varGamma $\end{document} point, which is different from the Dirac state formed by the pz orbital reported previously. In addition, it can still retain its original topological properties even if strongly hybridized with the substrate. The calculated phonon spectrum shows no imaginary frequency in the entire Brillouin zone, indicating that the monolayer BaPb system is dynamically stable. By using Monte Carlo simulation, we determine the Curie temperature of BaPb monolayer toreach up to 378 K. We also calculate the magnetic anisotropy energy of the BaPb cell, defined as \begin{document}$ \Delta E={E_{100}}-{E_{001}} $\end{document}. Here, we consider two magnetization easy-axis directions, [100] and [001]. To our surprise, the MAE of monolayer BaPb is as high as 52.01 meV/cell by considering the spin-orbit coupling effect. Furthermore, the nontrivial band gap is opened with a magnitude of 177.39 meV when the spin-orbit coupling effect is included. The calculations of Berry curvature and edge states further prove that the monolayer BaPb system can realize the quantum anomalous Hall state. This discovery indicates that the monolayer BaPb materials can be used as a candidate for quantum anomalous Hall effect materials, thereby promoting the development of spintronics.

考虑半导体量子点间隧穿耦合效应,研究非对称半导体三量子点分子中的弱探测光的传播特性.线性情况下,由于点间隧穿耦合和外部控制光的协同调控,探测光的吸收特性将出现共振吸收、隧穿诱导透明单窗口、隧穿诱导透明双窗口及隧穿诱导透明三窗口的转变.此外,从反常色散到正常色散的开关效应可通过改变隧穿强度及光学控制场强度来实现.对于非线性情况,发现孤子的振幅随着点间隧穿耦合系数增大呈先增大再减小随即再次增大并减小的波动变化趋势且出现最大振幅及其对应的点间隧穿耦合强度随着外部控制光场的增大而减小.此外,发现孤子的群速度随着耦合强度的增加呈逐渐减小的趋势.

Recently, the discovery of two-dimensional transition-metal materials with non-trivial magnetic and electronic properties has spurred huge interest in investigating their applications in nanotechnology. Here, we report that the monolayer of CoBr3 possesses a quantum anomalous Hall insulating phase generated on the basis of first-principles calculations. We find that the CoBr3 monolayer is an intrinsic two-dimensional ferromagnetic material with a Curie temperature T-c = 264 K predicted from Monte Carlo simulations. The phonon spectra analysis indicates that the CoBr3 monolayer is dynamically stable. Taking into account spin-orbit coupling, this makes the electronic structure of the CoBr3 monolayer topologically non-trivial with a global band gap of 8.7 meV. The anomalous Hall conductivity calculation shows a Chern number C = 2, meaning the presence of a two edge state in nanoribbons of finite width. These findings not only add an experimentally feasible member to the quantum anomalous Hall insulator family, but also pave the way for highly promising application potentials in nanoelectronics and spintronics.

利用一束弱线性 π偏振探测光在与其平行的磁场作用下所形成的两偏振分量,在半导体单量子点中考虑声子辅助跃迁去构建环形四能级电磁感应透明介质模型.利用多重尺度法,解析研究发现:仅考虑系统的线性效应,随着耦合光强度的增加,介质对探测光的吸收迅速减少,形成透明窗口,并且透明窗口的宽度随之增大;进一步地,在相同的外加磁场下探测光的非线性法拉第偏转方向与线性法拉第偏转相反,且偏转角更大.随着声子辅助跃迁强度的增加,线性和非线性法拉第偏转角都会逐渐变小,并且非线性法拉第偏转角减小的更多.这说明系统中的声子辅助跃迁能有效地调制探测光的法拉第偏转.我们的研究可能对于弱光条件下的光信息处理和传输具有潜在的应用价值.

Based on density functional theory, we investigate the electronic and magnetic properties of semi-hydrogenated, fully hydrogenated monolayer and bilayer MoN2. We find that the AB stacking bilayer MoN2 exhibits ferromagnetic coupling of intralayer and antiferromagnetic coupling of interlayer, however, the ground states of the semi-hydrogenated, fully hydrogenated monolayer and AA stcaking bilayer MoN2 are nonmagnetic. The fully hydrogenated system has a quasidirect band-gap of 2.5 eV, which has potential applications in light-emitting diode and photovoltaics. The AB stacking bilayer MoN2 shows the Dirac cone at K point in BZ around Fermi energy. Furthermore, the interlayer of the AB stacking bilayer MoN2 is subjected to a weak van der Waals force, while the interlayer of the AA stacking forms N-N covalent bond.

Ferroelectric (FE) materials have been extensively applied to the multifunctional electronic devices, particularly the FE memories due to their excellent physical properties. The FE memory is a kind of nonvolatile memory device, and it could overcome the shortcomings of the traditional memory. But the development of the FE memory is very slow due to the FE failure problem. However, with the continuous decrease of the thickness of FE thin film, when it reaches microns or nanometers in magnitude, the leakage current is the main cause of the FE failure of FE thin film The leakage current of FE thin film is directly related to whether the FE memory is applicable, and it has been the hot spot of scientific researches. There are still a lot of factors influencing the FE memory leakage current except for the thickness of the film, such as interface, processing temperature, defect, domain wall, etc. Of these factors, the defect and domain wall are the most common and the most probable. In this paper, the first-principle calculation method through combining the density function theory with the nonequilibrium Green's function is used to systematically study the influence of oxygen vacancy defect on the leakage current of the FE thin film The doping with four kinds of Cu, Al, V, and Fe cations is used to regulate and control the leakage current of the FE thin PbTiO3 film caused by the oxygen vacancy defects. We investigate the leakage current induced by oxygen vacancies in PbTiO3 films, and the doped PbTiO3 thin FE films having oxygen vacancies. It is found that Fe and Al doping will increase the leakage current of oxygen vacancy defects of FE thin films, while the Cu and V doping significantly reduce the leakage current of oxygen vacancy defects of FE thin films. This is because the Cu and V doping have obvious pinning effect on oxygen vacancy defect. In addition, we find that the oxygen vacancies are pinned by Cu and V atoms due to the fact that the formation energy of oxygen vacancies can be remarkably reduced. So Cu and V doping in PbTiO3 not only induce the leakage current but also improve the fatigue resistance of the FE thin film induced by oxygen vacancies. Moreover, since the ionic radius of V is closer to the ionic radius of Ti than the ionic radius of Cu, V is easier to implement doping to suppress the leakage current caused by the oxygen vacancy defects. These conclusions are of important theoretical significance and application value for improving the performance of FE thin films and their FE memories.

Accumulating evidence suggests that expression of aromatase, the enzyme responsible for the conversion of androgens to estrogens, is transiently upregulated in rat stroke models. It was further suggested that increased aromatase expression is linked to neuroinflammation and that it is neuroprotective in females. Our goal was to investigate aromatase upregulation in male rats subjected to experimental stroke in relationship to neuroinflammation, infarct and response to treatment with different putative neuroprotective agents. Intact male rats were subjected to transient (90 min) middle cerebral artery occlusion (MCAO) and administered selfotel (N-methyl-d-aspartic acid (NMDA) receptor competitive antagonist), TPEN (a zinc chelator), a combination of the two drugs or vehicle, injected immediately after reperfusion. Animals were killed 14 days after MCAO and consecutive brain sections used to measure aromatase expression, cerebral infarct volume and neuroinflammation. Quantitative immunohistochemistry (IHC) demonstrated increased brain aromatase expression in the peri-infarct area relative to contralesional area, which was partially abrogated by neuroprotective agents. There was no correlation between aromatase expression in the peri-infarct zone and infarct volume, which was reduced by neuroprotective agents. Microglial activation, measured by quantitative autoradiography, was positively correlated with infarct and inversely correlated with aromatase expression in the peri-infarct zone. Our findings indicate that focal ischemia upregulates brain aromatase in the male rat brain at 14 days post surgery, which is within the time frame documented in females. However, the lack of negative correlation between aromatase expression and infarct volume and lack of positive correlation between microgliosis and aromatase do not support a major role for aromatase as a mediator of neuroprotection or a causal relationship between microglial activation and increased aromatase expression in male focal ischemia.

Magnetic resonance (MR) scanning has become an important diagnostic and management tool in cryptococcal meningitis (CM). However, there are only isolated case reports documenting neuroradiological findings in human immunodeficiency virus (HIV)-negative patients with CM and none has clearly addressed the relationship between cerebral lesions on magnetic resonance imaging (MRI) and prognosis. The MR brain images available from 114 HIV-negative patients with CM were retrospectively analysed. Patients were divided into Group I with one or more CM-related lesions and Group II without CM-related lesions. Initial clinical and biochemical markers and prognosis were collected and compared between the two groups. In the present study, the most common pattern of CM-related lesions by MRI was radiological meningitis, following by Virchow–Robin (VR) dilatation, hydrocephalus, intracerebral nodules and pseudocysts, which was different from previous studies reporting that the main MR findings of cerebral cryptococcosis in HIV-infected patients include dilated VR spaces, masses and pseudocysts. Compared to the patients without CM-related lesions, patients with CM-related lesions presented with a higher percentage of male patients, a higher frequency of altered mental status, a higher positive rate of Cryptococcus culture in cerebrospinal fluid (CSF) and a lower ratio of CSF glucose/blood glucose. Poor outcomes were more frequent in patients with presence of CM-related lesions compared to patients without CM-related lesions. In conclusion, the main pattern of cryptococcosis-related lesions on MR scanning differ between non-HIV- and HIV-positive patients with CM. The presence of CM-related lesions was significantly associated with predictors for poor outcome. Neuroimaging on MR scanning is a useful tool to evaluate the initial severity and prognosis of CM without HIV infection.