Based on the Gross–Pitaevskii equation, we theoretically investigate exciton Bose–Einstein condensation (BEC) in transition metal dichalcogenide monolayers (TMDC-MLs) under in-plane magnetic fields. We observe that the in-plane magnetic fields exert a strong influence on the exciton BEC wave functions in TMDC-MLs because of the mixing of the bright and dark exciton states via Zeeman effect. This leads to the brightening of the dark exciton BEC states. The competition between the dipole–dipole interactions caused by the long-range Coulomb interaction and the Zeeman effect induced by the in-plane magnetic fields can effectively regulate dark exciton BEC states. Our findings emphasize the utility of TMD-MLs as platforms for investigating collective phenomenon involving excited states.

Recently, high temperature ($T_{\rm c}\approx 80$ K) superconductivity (SC) has been discovered in La$_3$Ni$_2$O$_7$ (LNO) under pressure. This raises the question of whether the superconducting transition temperature $T_{\rm c}$ could be further enhanced under suitable conditions. One possible route for achieving higher $T_{\rm c}$ is element substitution. Similar SC could appear in the $Fmmm$ phase of rare-earth (RE) R$_3$Ni$_2$O$_7$ (RNO, R = RE element) material series under suitable pressure. The electronic properties in the RNO materials are dominated by the Ni $3d$ orbitals in the bilayer NiO$_2$ plane. In the strong coupling limit, the SC could be fully characterized by a bilayer single $3d_{x^2-y^2}$-orbital $t$–$J_{\parallel}$–$J_{\perp}$ model. With RE element substitution from La to other RE element, the lattice constant of the $Fmmm$ RNO material decreases, and the resultant electronic hopping integral increases, leading to stronger superexchanges between the $3d_{x^2-y^2}$ orbitals. Based on the slave-boson mean-field theory, we explore the pairing nature and the evolution of $T_{\rm c}$ in RNO materials under pressure. Consequently, it is found that the element substitution does not alter the pairing nature, i.e., the inter-layer s-wave pairing is always favored in the superconducting RNO under pressure. However, the $T_{\rm c}$ increases from La to Sm, and a nearly doubled $T_{\rm c}$ could be realized in SmNO under pressure. This work provides evidence for possible higher $T_{\rm c}$ R$_3$Ni$_2$O$_7$ materials, which may be realized in further experiments.

High-temperature superconductivity (HTSC) remains one of the most challenging and fascinating mysteries in condensed matter physics. Recently, superconductivity with transition temperature exceeding liquid-nitrogen temperature is discovered in La$_{3}$Ni$_{2}$O$_{7}$ at high pressure, which provides a new platform to explore the unconventional HTSC. In this work, using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structures of La$_{3}$Ni$_{2}$O$_{7}$ at ambient pressure. Our experiments are in nice agreement with ab initio calculations after considering an orbital-dependent band renormalization effect. The strong electron correlation effect pushes a flat band of $d_{z^{2}}$ orbital component below the Fermi level ($E_{\rm F}$), which is predicted to locate right at $E_{\rm F}$ under high pressure. Moreover, the $d_{x^{2}-y^{2}}$ band shows pseudogap-like behavior with suppressed spectral weight and diminished quasiparticle peak near $E_{\rm F}$. Our findings provide important insights into the electronic structure of La$_{3}$Ni$_{2}$O$_{7}$, which will shed light on understanding of the unconventional superconductivity in nickelates.

The discovery of ferroelectricity in HfO$_{2}$-based materials with high dielectric constant has inspired tremendous research interest for next-generation electronic devices. Importantly, films structure and strain are key factors in exploration of ferroelectricity in fluorite-type oxide HfO$_{2}$ films. Here we investigate the structures and strain-induced ferroelectric transition in different phases of few-layer HfO$_{2}$ films (layer number $N=1$–5). It is found that HfO$_{2}$ films for all phases are more stable with increasing films thickness. Among them, the $Pmn2_{1}$ (110)-oriented film is most stable, and the films of $N=4$, 5 occur with a $P2_{1}$ ferroelectric transition under tensile strain, resulting in polarization about 11.8 µC/cm$^{2}$ along in-plane $a$-axis. The ferroelectric transition is caused by the strain, which induces the displacement of Hf and O atoms on the surface to non-centrosymmetric positions away from the original paraelectric positions, accompanied by the change of surface Hf–O bond lengths. More importantly, three new stable HfO$_{2}$ 2D structures are discovered, together with analyses of computed electronic structures, mechanical, and dielectric properties. This work provides guidance for theoretical and experimental study of the new structures and strain-tuned ferroelectricity in freestanding HfO$_{2}$ films.

Detecting tiny deformations or vibrations, particularly those associated with strains below 1%, is essential in various technological applications. Traditional intrinsic materials, including metals and semiconductors, face challenges in simultaneously achieving initial metallic state and strain-induced insulating state, hindering the development of highly sensitive mechanical sensors. Here we report an ultrasensitive mechanical sensor based on a strain-induced tunable ordered array of metallic and insulating states in the single-crystal bronze-phase vanadium dioxide [VO$_{2}$(B)] quantum material. It is shown that the initial metallic state in the VO$_{2}$(B) flake can be tuned to the insulating state by applying a weak uniaxial tensile strain. Such a unique property gives rise to a record-high gauge factor of above 607970, surpassing previous values by an order of magnitude, with excellent linearity and mechanical resilience as well as durability. As a proof-of-concept application, we use our proposed mechanical sensor to demonstrate precise sensing of the micro piece, gentle airflows and water droplets. We attribute the superior performance of the sensor to the strain-induced continuous metal-insulator transition in the single-crystal VO$_{2}$(B) flake, evidenced by experimental and simulation results. Our findings highlight the potential of exploiting correlated quantum materials for next-generation ultrasensitive flexible mechanical sensors, addressing critical limitations in traditional materials.

Band convergence is considered to be a strategy with clear benefits for thermoelectric performance, generally favoring the co-optimization of conductivity and Seebeck coefficients, and the conventional means include elemental filling to regulate the band. However, the influence of the most electronegative fluorine on the CoSb$_{3}$ band remains unclear. We carry out density-functional-theory calculations and show that the valence band maximum gradually shifts downward with the increase of fluorine filling, lastly the valence band maximum converges to the highly degenerated secondary valence bands in fluorine-filled skutterudites. The effective degeneracy near the secondary valence band promotes more valleys to participate in electric transport, leading to a carrier mobility of more than the threefold and nearly twofold effective mass for F$_{0.1}$Co$_{4}$Sb$_{12}$ compared to Co$_{4}$Sb$_{12}$. This work provides a new and promising route to boost the thermoelectric properties of p-type skutterudites.

While density functional theory (DFT) serves as a prevalent computational approach in electronic structure calculations, its computational demands and scalability limitations persist. Recently, leveraging neural networks to parameterize the Kohn–Sham DFT Hamiltonian has emerged as a promising avenue for accelerating electronic structure computations. Despite advancements, challenges such as the necessity for computing extensive DFT training data to explore each new system and the complexity of establishing accurate machine learning models for multi-elemental materials still exist. Addressing these hurdles, this study introduces a universal electronic Hamiltonian model trained on Hamiltonian matrices obtained from first-principles DFT calculations of nearly all crystal structures on the Materials Project. We demonstrate its generality in predicting electronic structures across the whole periodic table, including complex multi-elemental systems, solid-state electrolytes, Moiré twisted bilayer heterostructure, and metal-organic frameworks. Moreover, we utilize the universal model to conduct high-throughput calculations of electronic structures for crystals in GNoME datasets, identifying 3940 crystals with direct band gaps and 5109 crystals with flat bands. By offering a reliable efficient framework for computing electronic properties, this universal Hamiltonian model lays the groundwork for advancements in diverse fields, such as easily providing a huge data set of electronic structures and also making the materials design across the whole periodic table possible.

The reliance on spin-orbit coupling or strong magnetic fields has always posed significant challenges for the mass production and even laboratory realization of most topological materials. Valley-based topological zero-line modes have attracted widespread attention due to their substantial advantage of being initially realizable with just an external electric field. However, the uncontrollable nature of electrode alignment and precise fabrication has greatly hindered the advancement in this field. By utilizing minimally twisted bilayer graphene and introducing exchange fields from magnetic substrates, we successfully realize a spin-resolved, electrode-free topological zero-line mode. Further integration of electrodes that do not require alignment considerations significantly enhances the tunability of the system's band structure. Our approach offers a promising new support for the dazzling potential of topological zero-line mode in the realm of low-energy-consumption electronics.

We present a study on inelastic thermoelectric devices, wherein charge currents and electronic and phononic heat currents are intricately interconnected. The employment of double quantum dots in conjunction with a phonon reservoir positions them as promising candidates for quantum thermoelectric diodes and transistors. We illustrate that quantum coherence yields significant charge and Seebeck rectification effects. It is worth noting that, while the thermal transistor effect is observable in the linear response regime, especially when phonon-assisted inelastic processes dominate the transport, quantum coherence does not enhance thermal amplification. Our work may provide valuable insights for the optimization of inelastic thermoelectric devices.

We systematically investigate in-plane transport properties of ternary chalcogenide Bi$_{2}$Rh$_{3}$Se$_{2}$. Upon rotating the magnetic field within the plane of the sample, one can distinctly detect the presence of both planar Hall resistance and anisotropic longitudinal resistance, and the phenomena appeared are precisely described by the theoretical formulation of the planar Hall effect (PHE). In addition, anisotropic orbital magnetoresistance rather than topologically nontrivial chiral anomalies dominates the PHE in Bi$_{2}$Rh$_{3}$Se$_{2}$. The finding not only provides another platform for understanding the mechanism of PHE, but could also be beneficial for future planar Hall sensors based on two-dimensional materials.

The rattling mode, an anharmonic vibrational phonon, is widely recognized as a critical factor in the emergence of superconductivity in caged materials. Here, we present a counterexample in a filled-skutterudite superconductor Ba$_{x}$Ir$_{4}$Sb$_{12}$ ($x = 0.8$, 0.9, 1.0), synthesized via a high-pressure route. Transport measurements down to liquid $^{3}$He temperatures reveal a transition temperature ($T_{\rm c}$) of 1.2 K and an upper critical field ($H_{\rm c2}$) of 1.3 T. Unlike other superconductors with caged structures, the Ba$_{x}$Ir$_{4}X_{12}$ ($X = {\rm P}$, As, Sb) family exhibits a monotonic decreasing $T_{\rm c}$ with the enhancement of the rattling mode, as indicated by fitting the Bloch–Grüneisen formula. Theoretical analysis suggests that electron doping from Ba transforms the direct bandgap IrSb$_{3}$ into a metal, with the Fermi surface dominated by the hybridization of Ir 5$d$ and Sb 5$p$ orbitals. Our findings of decoupled rattling modes and superconductivity distinguish the Ba$_{x}$Ir$_{4}$Sb$_{12}$ family from other caged superconductors, warranting further exploration into the underlying mechanism.

This review provides a comprehensive overview of current research on the structural, electronic, and magnetic characteristics of the recently discovered high-temperature superconductor La$_3$Ni$_2$O$_7$ under high pressures. We present the experimental results for synthesizing and characterizing this material, derived from measurements of transport, thermodynamics, and various spectroscopic techniques, and discuss their physical implications. We also explore theoretical models proposed to describe the electronic structures and superconducting pairing symmetry in La$_3$Ni$_2$O$_7$, highlighting the intricate interplay between electronic correlations and magnetic interactions. Despite these advances, challenges remain in growing high-quality samples free of extrinsic phases and oxygen deficiencies and in developing reliable measurement tools for determining diamagnetism and other physical quantities under high pressures. Further investigations in these areas are essential to deepening our understanding of the physical properties of La$_3$Ni$_2$O$_7$ and unlocking its superconducting pairing mechanism.

The 0.98(K$_{0.5}$Na$_{0.5})$NbO$_{3}$-0.02Ba(Nb$_{0.5}$Co$_{0.5})$O$_{3-\delta}$ ceramics with doped Ba$^{2+}$ and Co$^{2+}$ ions are fabricated, and the impacts of the thermal process are studied. Compared with the rapidly cooled (RC) sample, the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties, and an 11 K higher ferroelectric-paraelectric phase transition temperature, which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy. Heat treatment can reversibly modulate the content of the oxygen vacancies, and in turn the ferroelectric hysteresis loops of the samples. Finally, robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.

Two-dimensional (2D) topological materials have recently garnered significant interest due to their profound physical properties and promising applications for future quantum nanoelectronics. Achieving various topological states within one type of materials is, however, seldom reported. Based on first-principles calculations and tight-binding models, we investigate topological electronic states in a novel family of 2D halogenated tetragonal stanene (T-SnX, X = F, Cl, Br, I). All the four monolayers are found to be unusual topological nodal-line semimetals (NLSs), protected by a glide mirror symmetry. When spin-orbit coupling (SOC) is turned on, T-SnF and T-SnCl are still ascertained as topological NLSs due to the remaining band inversion, primarily composed of Sn $p_{xy}$ orbitals, while T-SnBr and T-SnI become quantum spin Hall insulators. The phase transition is ascribed to moving up in energy of Sn $s$ orbitals and increasing of SOC strengths. The topology origin in the materials is uniformly rationalized through elementary band representations. The robust and diverse topological states found in the 2D T-SnX monolayers position them as an excellent material platform for development of innovative topological electronics.

Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-$T_{\rm c}$ superconductors. In iron-based superconductors, spin excitations at low energy range, especially the spin-resonance mode at $E_{\rm R} \sim5k_{\rm B}T_{\rm c}$, are important for understanding the superconductivity. Here, we use inelastic neutron scattering (INS) to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned FeSe. The low-energy spin excitations ($E < 10$ meV) appear mainly at ${\boldsymbol Q} = (\pm 1,\, 0)$ in the superconducting state ($T\lesssim9$ K) and the nematic state ($T\lesssim90$ K), confirming the constant $C_2$ rotational symmetry and ruling out the $C_4$ mode at $E\approx3$ meV reported in a prior INS study. Moreover, our results reveal an isotropic spin resonance in the superconducting state, which is consistent with the $s^{\pm}$ wave pairing symmetry. At slightly higher energy, low-energy spin excitations become highly anisotropic. The full width at half maximum of spin excitations is elongated along the transverse direction. The $Q$-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from $d_{yz}$ intra-orbital selective Fermi surface nesting between the hole pocket around $\varGamma$ point and the electron pockets centered at $M_{\rm X}$ point.

Controlling the size and distribution of potential barriers within a medium of interacting particles can unveil unique collective behaviors and innovative functionalities. We introduce a unique superconducting hybrid device using a novel artificial spin ice structure composed of asymmetric nanomagnets. This structure forms a distinctive superconducting pinning potential that steers unconventional motion of superconducting vortices, thereby inducing a magnetic nonreciprocal effect, in contrast to the electric nonreciprocal effect commonly observed in superconducting diodes. Furthermore, the polarity of the magnetic nonreciprocity is in situ reversible through the tunable magnetic patterns of artificial spin ice. Our findings demonstrate that artificial spin ice not only precisely modulates superconducting characteristics but also opens the door to novel functionalities, offering a groundbreaking paradigm for superconducting electronics.

Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years. Among them is the Cr$_{x}$Te$_{y}$ family, the magnetism of which can persist above room temperature, thus providing an ideal system for potential spintronic applications. Here we report the synthesis of a new compound, Cr$_{0.82}$Te, which demonstrates a record-high topological Hall effect at room temperature in this family. Cr$_{0.82}$Te displays soft ferromagnetism below the Curie temperature of 340 K. The magnetic measurement shows an obvious magneto-crystalline anisotropy with the easy axis located in the $ab$ plane. The anomalous Hall effect can be well explained by a dominating skew scattering mechanism. Intriguing, after removing the normal Hall effect and anomalous Hall effect, a topological Hall effect can be observed up to 300 K and reaches up to 1.14 $µ\Omega\cdot$cm at 10 K, which is superior to most topological magnetic structural materials. This giant topological Hall effect possibly originates from the noncoplanar spin configuration during the spin flop process. Our work extends a new Cr$_{x}$Te$_{y}$ system with topological non-trivial magnetic structure and broad prospects for spintronics applications in the future.

Graphene (Gr) with widely acclaimed characteristics, such as exceptionally long spin diffusion length at room temperature, provides an outstanding platform for spintronics. However, its inherent weak spin–orbit coupling (SOC) has limited its efficiency for generating the spin currents in order to control the magnetization switching process for applications in spintronics memories. Following the theoretical prediction on the enhancement of SOC in Gr by heavy atoms adsorption, here we experimentally observe a sizeable spin–orbit torques (SOTs) in Gr by the decoration of its surface with Pt adatoms in Gr/Pt($t_{\rm Pt} $)/FeNi trilayers with the optimal damping-like SOT efficiency around 0.55 by 0.6-nm-thick Pt layer adsorption. The value is nearly four times larger than that of the Pt/FeNi sample without Gr and nearly twice the value of the Gr/FeNi sample without Pt adsorption. The efficiency of the enhanced SOT in Gr by Pt adatoms is also demonstrated by the field-free SOT magnetization switching process with a relatively low critical current density around 5.4 MA/cm$^2$ in Gr/Pt/FeNi trilayers with the in-plane magnetic anisotropy. These findings pave the way for Gr spintronics applications, offering solutions for future low power consumption memories.

The discovery of ferromagnetic two-dimensional (2D) van der Waals (vdWs) materials provides an opportunity to explore intriguing physics and to develop innovative spin electronic devices. However, the main challenge for practical applications of vdWs ferromagnetic crystals lies in the weak intrinsic ferromagnetism and small perpendicular magnetic anisotropy (PMA) above room temperature. Here, we report the intrinsic vdWs ferromagnetic crystal Fe$_{3}$GaTe$_{2}$, synthesized by the self-flux method, exhibiting a Curie temperature ($T_{\rm C}$) of 370 K, a high saturation magnetization of 33.47 emu/g, and a large PMA energy density of approximately $4.17 \times 10^{5}$ J/m$^{3}$. Furthermore, the magneto-optical effect is systematically investigated in Fe$_{3}$GaTe$_{2}$. The doubly degenerate $E_{\rm 2g} (\varGamma)$ mode reverses the helicity of incident photons, indicating the existence of pseudoangular-momentum (PAM) and chirality. Meanwhile, the non-degenerate non-chiral $A_{\rm 1g}(\varGamma)$ phonon exhibits a significant magneto-Raman effect under an external out-of-plane magnetic field. These results lay the groundwork for studying phonon chirality and magneto-optical phenomena in 2D magnetic materials, providing the feasibility for further fundamental research and applications in spintronic devices.

As a sister compound of PbTe, SnTe possesses the environmentally friendly elements. However, the pristine SnTe compounds suffer from the high carrier concentration, the large valence band offset between the $L$ and $\varSigma $ positions and high thermal conductivity. Using high-pressure and high-temperature technology, we synthesized the pristine SnTe samples at different pressures and systemically investigated their thermoelectric properties. High pressure induces rich microstructures, including the high-density dislocations and lattice distortions, which serve as the strong phonon scattering centers, thereby reducing the lattice thermal conductivity. For the electrical properties, pressure reduces the harmful high carrier concentration, due to the depression of Sn vacancies. Moreover, pressure induces the valence band convergence, reducing the energy separation between the $L$ and $\varSigma $ positions. The band convergence and suppressed carrier concentration increase the Seebeck coefficient. Thus, the power factors of pressure-sintered compounds do not deteriorate significantly under the condition of decreasing electrical conductivity. Ultimately, for a pristine SnTe compound synthesized at 5 GPa, a higher $ZT$ value of 0.51 is achieved at 750 K, representing a 140% improvement compared to the value of 0.21 obtained using SPS. Therefore, the high-pressure and high-temperature technology is demonstrated as an effectively approach to optimize thermoelectric performance.

Recently, giant intrinsic anomalous Hall effect (AHE) has been observed in the materials with kagome lattice. Here, we systematically investigate the influence of high pressure on the AHE in the ferromagnet LiMn$_{6}$Sn$_{6}$ with clean Mn kagome lattice. Our in situ high-pressure Raman spectroscopy indicates that the crystal structure of LiMn$_{6}$Sn$_{6}$ maintains a hexagonal phase under high pressures up to 8.51 GPa. The anomalous Hall conductivity (AHC) $\sigma_{xy}^{\rm A}$ remains around 150 $\Omega^{{-1}}\cdot$cm$^{{-1}}$, dominated by the intrinsic mechanism. Combined with theoretical calculations, our results indicate that the stable AHE under pressure in LiMn$_{6}$Sn$_{6}$ originates from the robust electronic and magnetic structure.

Quantum anomalous Hall (QAH) insulators have highly potential applications in spintronic device. However, available candidates with tunable Chern numbers and high working temperature are quite rare. Here, we predict a 1T-PrN$_2$ monolayer as a stable QAH insulator with high magnetic transition temperature of above 600 K and tunable high Chern numbers of $C = \pm3$ from first-principles calculations. Without spin-orbit coupling (SOC), the 1T-PrN$_2$ monolayer is predicted to be a p-state Dirac half metal with high Fermi velocity. Rich topological phases depending on magnetization directions can be found when the SOC is considered. The QAH effect with periodical changes of Chern number ($\pm1$) can be produced when the magnetic moment breaks all twofold rotational symmetries in the $xy$ plane. The critical state can be identified as Weyl half semimetals. When the magnetization direction is parallel to the $z$-axis, the system exhibits high Chern number QAH effect with $C = \pm3$. Our work provides a new material for exploring novel QAH effect and developing high-performance topological devices.

Based on first-principles calculations, we systematically study the stacking energy and interlayer magnetic interaction of the heterobilayer composed of CrI$_3$ and CrSe$_2$ monolayers. It is found that the stacking order plays a crucial role in the interlayer magnetic coupling. Among all possible stacking structures, the AA-stacking is the most stable heterostructure, exhibiting interlayer antiferromagnetic interactions. Interestingly, the interlayer magnetic interaction can be effectively tuned by biaxial strain. A 4.3% compressive strain would result in a ferromagnetic interlayer interaction in all stacking orders. These results reveal the magnetic properties of CrI$_3$/CrSe$_2$ heterostructure, which is expected to be applied to spintronic devices.

Understanding the doping evolution from a Mott insulator to a superconductor probably holds the key to resolve the mystery of unconventional superconductivity in copper oxides. To elucidate the evolution of the electronic state starting from the Mott insulator, we dose the surface of the parent phase Ca$_{2}$CuO$_{2}$Cl$_{2}$ by depositing Rb atoms, which are supposed to donate electrons to the CuO$_{2}$ planes underneath. We successfully achieved the Rb sub-monolayer thin films in forming the square lattice. The scanning tunneling microscopy or spectroscopy measurements on the surface show that the Fermi energy is pinned within the Mott gap but close to the edge of the charge transfer band. In addition, an in-gap state appears at the bottom of the upper Hubbard band (UHB), and the Mott gap will be significantly diminished. Combined with the Cl defect and the Rb adatom/cluster results, the electron doping is likely to increase the spectra weight of the UHB for the double occupancy. Our results provide information to understand the electron doping to the parent compound of cuprates.

The recent discovery of possible high temperature superconductivity in single crystals of La$_3$Ni$_2$O$_7$ under pressure renews the interest in research on nickelates. The density functional theory calculations reveal that both $d_{z^2}$ and $d_{x^2-y^2}$ orbitals are active, which suggests a minimal two-orbital model to capture the low-energy physics of this system. In this work, we study a bilayer two-orbital $t$–$J$ model within multiband Gutzwiller approximation, and discuss the magnetism as well as the superconductivity over a wide range of the hole doping. Owing to the inter-orbital super-exchange process between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals, the induced ferromagnetic coupling within layers competes with the conventional antiferromagnetic coupling, and leads to complicated hole doping dependence for the magnetic properties in the system. With increasing hole doping, the system transfers to A-type antiferromagnetic state from the starting G-type antiferromagnetic (G-AFM) state. We also find the inter-layer superconducting pairing of $d_{x^2-y^2}$ orbitals dominates due to the large hopping parameter of $d_{z^2}$ along the vertical inter-layer bonds and significant Hund's coupling between $d_{z^2}$ and $d_{x^2-y^2}$ orbitals. Meanwhile, the G-AFM state and superconductivity state can coexist in the low hole doping regime. To take account of the pressure, we also analyze the impacts of inter-layer hopping amplitude on the system properties.

Electrical control of magnetism in van der Waals semiconductors is a promising step towards development of two-dimensional spintronic devices with ultralow power consumption for processing and storing information. Here, we propose a design for two-dimensional van der Waals heterostructures (vdWHs) that can host ferroelectricity and ferromagnetism simultaneously under hole doping. By contacting an InSe monolayer and forming an InSe/In$_{2}$Se$_{3}$ vdWH, the switchable built-in electric field from the reversible out-of-plane polarization enables robust control of the band alignment. Furthermore, switching between the two ferroelectric states ($P_\uparrow$ and $P_\downarrow$) of hole-doped In$_{2}$Se$_{3}$ with an external electric field can interchange the ON and OFF states of the nonvolatile magnetism. More interestingly, doping concentration and strain can effectively tune the magnetic moment and polarization energy. Therefore, this provides a platform for realizing multiferroics in ferroelectric heterostructures, showing great potential for use in nonvolatile memories and ferroelectric field-effect transistors.

Magnetic domain wall (DW), as one of the promising information carriers in spintronic devices, have been widely investigated owing to its nonlinear dynamics and tunable properties. Here, we theoretically and numerically demonstrate the DW dynamics driven by the synergistic interaction between current-induced spin-transfer torque (STT) and voltage-controlled strain gradient (VCSG) in multiferroic heterostructures. Through electromechanical and micromagnetic simulations, we show that a desirable strain gradient can be created and it further modulates the equilibrium position and velocity of the current-driven DW motion. Meanwhile, an analytical Thiele's model is developed to describe the steady motion of DW and the analytical results are quite consistent with the simulation data. Finally, we find that this combination effect can be leveraged to design DW-based biological neurons where the synergistic interaction between STT and VCSG-driven DW motion as integrating and leaking motivates mimicking leaky-integrate-and-fire (LIF) and self-reset function. Importantly, the firing response of the LIF neuron can be efficiently modulated, facilitating the exploration of tunable activation function generators, which can further help improve the computational capability of the neuromorphic system.

Rare-earth-free Mn-based binary alloy ${\rm L1_{0}}$-MnAl with bulk perpendicular magnetic anisotropy (PMA) holds promise for high-performance magnetic random access memory (MRAM) devices driven by spin-orbit torque (SOT). However, the lattice-mismatch issue makes it challenging to place conventional spin current sources, such as heavy metals, between ${\rm L1_{0}}$-MnAl layers and substrates. In this work, we propose a solution by using the B2-CoGa alloy as the spin current source. The lattice-matching enables high-quality epitaxial growth of 2-nm-thick ${\rm L1_{0}}$-MnAl on B2-CoGa, and the ${\rm L1_{0}}$-MnAl exhibits a large PMA constant of $1.04\times 10^{6}$ J/m$^{3}$. Subsequently, the considerable spin Hall effect in B2-CoGa enables the achievement of SOT-induced deterministic magnetization switching. Moreover, we quantitatively determine the SOT efficiency in the bilayer. Furthermore, we design an ${\rm L1_{0}}$-MnAl/B2-CoGa/Co$_{2}$MnGa structure to achieve field-free magnetic switching. Our results provide valuable insights for achieving high-performance SOT-MRAM devices based on ${\rm L1_{0}}$-MnAl alloy.

Controlling collective electronic states hold great promise for development of innovative devices. Here, we experimentally detect the modification of the charge density wave (CDW) phase transition within a 1T-TaS$_{{2}}$ layer in a WS$_{{2}}$/1T-TaS$_{{2}}$ heterostructure using time-resolved ultrafast spectroscopy. Laser-induced charge transfer doping strongly suppresses the commensurate CDW phase, which results in a significant decrease in both the phase transition temperature ($T_{\rm c}$) and phase transition stiffness. We interpret the phenomenon that photo-induced hole doping, when surpassing a critical threshold value of $\sim$ $10^{18}$ cm$^{-3}$, sharply decreases the phase transition energy barrier. Our results provide new insights into controlling the CDW phase transition, paving the way for optical-controlled novel devices based on CDW materials.

A Moiré system is formed when two periodic structures have a slightly mismatched period, resulting in unusual strongly correlated states in the presence of particle-particle interactions. The periodic structures can arise from the intrinsic crystalline order and periodic external field. We investigate a one-dimensional Hubbard model with periodic on-site potential of period $n_{0}$, which is commensurate to the lattice constant. For large $n_{0}$, the exact solution demonstrates that there is a midgap flat band with zero energy in the absence of Hubbard interaction. Each Moiré unit cell contributes two zero energy levels to the flat band. In the presence of Hubbard interaction, the midgap physics is demonstrated to be well described by a uniform Hubbard chain in which the effective hopping and on-site interaction strength can be controlled by the amplitude and period of the external field. Numerical simulations are performed to demonstrate the correlated behaviors in the finite-sized Moiré Hubbard system, including the existence of an $\eta $-pairing state and bound pair oscillation. This finding provides a method to enhance the correlated effect by a spatially periodic external field.