The reversal of perpendicular magnetization (PM) by electric control is crucial for high-density integration of low-power magnetic random-access memory. Although the spin-transfer torque and spin-orbit torque technologies have been used to switch the magnetization of a free layer with perpendicular magnetic anisotropy, the former has limited endurance because of the high current density directly through the junction, while the latter requires an external magnetic field or unconventional configuration to break the symmetry. Here we propose and realize the orbit-transfer torque (OTT), that is, exerting torque on the magnetization using the orbital magnetic moments, and thus demonstrate a new strategy for current-driven PM reversal without external magnetic field. The perpendicular polarization of orbital magnetic moments is generated by a direct current in a few-layer WTe$_{2}$ due to the existence of nonzero Berry curvature dipole, and the polarization direction can be switched by changing the current polarity. Guided by this principle, we construct the WTe$_{2}$/Fe$_{3}$GeTe$_{2}$ heterostructures to achieve the OTT driven field-free deterministic switching of PM.

High-energy-density rechargeable lithium batteries are being pursued by researchers because of their revolutionary potential nature. Current advanced practical lithium-ion batteries have an energy density of around 300 W$\cdot$h$\cdot$kg$^{-1}$. Continuing to increase the energy density of batteries to a higher level could lead to a major explosion development in some fields, such as electric aviation. Here, we have manufactured practical pouch-type rechargeable lithium batteries with both a gravimetric energy density of 711.3 W$\cdot$h$\cdot$kg$^{-1}$ and a volumetric energy density of 1653.65 W$\cdot$h$\cdot$L$^{-1}$. This is achieved through the use of high-performance battery materials including high-capacity lithium-rich manganese-based cathode and thin lithium metal anode with high specific energy, combined with extremely advanced process technologies such as high-loading electrode preparation and lean electrolyte injection. In this battery material system, the structural stability of cathode material in a widened charge/discharge voltage range and the deposition/dissolution behavior of interfacial modified thin lithium electrode are studied.

A magnetic tunnel junction (MTJ) is the core component in memory technologies, such as the magnetic random-access memory, magnetic sensors and programmable logic devices. In particular, MTJs based on two-dimensional van der Waals (vdW) heterostructures offer unprecedented opportunities for low power consumption and miniaturization of spintronic devices. However, their operation at room temperature remains a challenge. Here, we report a large tunnel magnetoresistance (TMR) of up to 85% at room temperature ($T = 300$ K) in vdW MTJs based on a thin ($ < 10$ nm) semiconductor spacer WSe$_{2}$ layer embedded between two Fe$_{3}$GaTe$_{2}$ electrodes with intrinsic above-room-temperature ferromagnetism. The TMR in the MTJ increases with decreasing temperature up to 164% at $T = 10$ K. The demonstration of TMR in ultra-thin MTJs at room temperature opens a realistic and promising route for next-generation spintronic applications beyond the current state of the art.

The CsV$_{3}$Sb$_{5}$ kagome lattice holds the promise for manifesting electron correlation, topology and superconductivity. However, by far only three CsV$_{3}$Sb$_{5}$-like kagome materials have been experimentally spotted. We enlarge this family of materials to 1386 compounds via element species substitution, and the further screening process suggests that 28 promising candidates have superior thermodynamic stability, hence they are highly likely to be synthesizable. Moreover, these compounds possess several unique electronic structures, and can be categorized into five non-magnetic and three magnetic groups accordingly. It is our hope that this work can greatly expand the viable phase space of the CsV$_{3}$Sb$_{5}$-like materials for investigating or tuning the novel quantum phenomena in kagome lattice.

Enabling lithium-ion batteries (LIBs) to operate in a wider temperature range, e.g., as low or high as possible or capable of both, is an urgent need and shared goal. Here we report, for the first time, a low-temperature electrolyte consisting of traditional ethylene carbonate, methyl acetate, butyronitrile solvents, and 1 M LiPF$_{6}$ salt, attributed to its very low freezing point ($T_{\rm f} = -126.3\,^{\circ}\!$C) and high ion conductivity at extremely low temperatures (0.21 mS/cm at $-100\,^{\circ}\!$C), successfully extends the service temperature of a practical 9.6 Ah LIB down to $-100\,^{\circ}\!$C (49.6% capacity retention compared to that at room temperature), which is the lowest temperature reported for practical cells so far as we know, and is lower than the lowest natural temperature ($-89.2\,^{\circ}\!$C) recorded on earth. Meanwhile, the high-temperature performance of lithium-ion batteries is not affected. The capacity retention is 88.2% and 83.4% after 800 cycles at 25$\,^{\circ}\!$C and 45$\,^{\circ}\!$C, respectively. The progress also makes LIB a proper power supplier for space vehicles in astronautic explorations.

Non-Hermitian materials can exhibit not only exotic energy band structures but also an anomalous velocity induced by non-Hermitian anomalous Berry connection as predicted by the semiclassical equations of motion for Bloch electrons. However, it is unclear how the modified semiclassical dynamics modifies transport phenomena. Here, we theoretically demonstrate the emergence of anomalous oscillations driven by either an external dc or ac electric field, which arise from non-Hermitian anomalous Berry connection. Moreover, it is a well-known fact that geometric structures of electric wave functions can only affect the Hall conductivity. However, we are surprised to find a non-Hermitian anomalous Berry connection induced anomalous linear longitudinal conductivity independent of the scattering time. We also show the emergence of a second-order nonlinear longitudinal conductivity induced by non-Hermitian anomalous Berry connection, violating a well-known fact of its absence in a Hermitian system with symmetric energy spectra. These anomalous phenomena are illustrated in a pseudo-Hermitian system with large non-Hermitian anomalous Berry connection. Finally, we propose a practical scheme to realize the anomalous oscillations in an optical system.

It is known that $\alpha$-RuCl$_3$ has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid (QSL) phase and the possibility of approaching it by tuning the competing interactions. Here we present the first polarized inelastic neutron scattering study on $\alpha$-RuCl$_3$ single crystals to explore the scattering continuum around the $\varGamma$ point at the Brillouin zone center, which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence. With polarization analyses, we find that, while the spin-wave excitations around the $M$ point vanish above the transition temperature $T_{\rm N}$, the pure magnetic continuous excitations around the $\varGamma$ point are robust against temperature. Furthermore, by calculating the dynamical spin-spin correlation function using the cluster perturbation theory, we derive magnetic dispersion spectra based on the $K$–$\varGamma$ model, which involves with a ferromagnetic Kitaev interaction of $-7.2$ meV and an off-diagonal interaction of $5.6$ meV. We find this model can reproduce not only the spin-wave excitation spectra around the $M$ point, but also the non-spin-wave continuous magnetic excitations around the $\varGamma$ point. These results provide evidence for the existence of fractional excitations around the $\varGamma$ point originating from the Kitaev QSL state, and further support the validity of the $K$–$\varGamma$ model as the effective minimal spin model to describe $\alpha$-RuCl$_3$.

Motivated by the recent discovery of high-temperature superconductivity in bilayer La$_3$Ni$_2$O$_7$ under pressure, we study its electronic properties and superconductivity due to strong electron correlation. Using the inversion symmetry, we decouple the low-energy electronic structure into block-diagonal symmetric and antisymmetric sectors. It is found that the antisymmetric sector can be reduced to a one-band system near half filling, while the symmetric bands occupied by about two electrons are heavily overdoped individually. Using the strong coupling mean field theory, we obtain strong superconducting pairing with $B_{\rm 1g}$ symmetry in the antisymmetric sector. We propose that due to the spin-orbital exchange coupling between the two sectors, $B_{\rm 1g}$ pairing is induced in the symmetric bands, which in turn boosts the pairing gap in the antisymmetric band and enhances the high-temperature superconductivity with a congruent d-wave symmetry in pressurized La$_3$Ni$_2$O$_7$.

The discovery of magnetic skyrmions provides a promising pathway for developing functional spintronic memory and logic devices. Towards the future high-density memory application, nanoscale skyrmions with miniaturized diameters, ideally down to 20 nm are required. Using x-ray magnetic circular dichroism transmission microscopy, nanoscale skyrmions are observed in the [Pt/Co/Ir]$_{15}$ multilayer at room temperature. In particular, small skyrmions with minimum diameters approaching 20 nm could be generated by the current-induced spin-orbit torques. Through implementing material specific parameters, the dynamic process of skyrmion generation is further investigated by performing micromagnetic simulations. According to the simulation results, we find that both the tube-like Néel-type skyrmions and the bobber-like Néel-type skyrmions can be electrically generated. In particular, the size of the bobber-like Néel-type skyrmions can be effectively reduced by the spin-orbit torques, which leads to the formation of 20 nm Néel-type skyrmions. Our findings could be important for understanding the formation dynamics of nanoscale Néel-type spin textures, skyrmions and bobber in particular, which could also be useful for promoting nanoscale skyrmionic memories and logic devices.

The development of high-fidelity two-qubit quantum gates is essential for digital quantum computing. Here, we propose and realize an all-microwave parametric controlled-Z (CZ) gates by coupling strength modulation in a superconducting Transmon qubit system with tunable couplers. After optimizing the design of the tunable coupler together with the control pulse numerically, we experimentally realized a 100 ns CZ gate with high fidelity of 99.38%$ \pm 0.34$% and the control error being 0.1%. We note that our CZ gates are not affected by pulse distortion and do not need pulse correction, providing a solution for the real-time pulse generation in a dynamic quantum feedback circuit. With the expectation of utilizing our all-microwave control scheme to reduce the number of control lines through frequency multiplexing in the future, our scheme draws a blueprint for the high-integrable quantum hardware design.

Non-Abelian anyons are exotic quasiparticle excitations hosted by certain topological phases of matter. They break the fermion-boson dichotomy and obey non-Abelian braiding statistics: their interchanges yield unitary operations, rather than merely a phase factor, in a space spanned by topologically degenerate wavefunctions. They are the building blocks of topological quantum computing. However, experimental observation of non-Abelian anyons and their characterizing braiding statistics is notoriously challenging and has remained elusive hitherto, in spite of various theoretical proposals. Here, we report an experimental quantum digital simulation of projective non-Abelian anyons and their braiding statistics with up to 68 programmable superconducting qubits arranged on a two-dimensional lattice. By implementing the ground states of the toric-code model with twists through quantum circuits, we demonstrate that twists exchange electric and magnetic charges and behave as a particular type of non-Abelian anyons, i.e., the Ising anyons. In particular, we show experimentally that these twists follow the fusion rules and non-Abelian braiding statistics of the Ising type, and can be explored to encode topological logical qubits. Furthermore, we demonstrate how to implement both single- and two-qubit logic gates through applying a sequence of elementary Pauli gates on the underlying physical qubits. Our results demonstrate a versatile quantum digital approach for simulating non-Abelian anyons, offering a new lens into the study of such peculiar quasiparticles.

Within the extended vector meson dominance model, we investigate the $e^+ e^- \to \varLambda^+_c \bar{\varLambda}^-_c$ reaction and the electromagnetic form factors of the charmed baryon $\varLambda_c^+$. The model parameters are determined by fitting them to the cross sections of the process $e^+e^-\rightarrow \varLambda_c^+ \bar{\varLambda}_c^-$ and the magnetic form factor $|G_{\scriptscriptstyle{\rm M}}|$ of $\varLambda^+_c$. By considering four charmonium-like states, called $\psi(4500)$, $\psi(4660)$, $\psi(4790)$, and $\psi(4900)$, we can well describe the current data on the $e^+ e^- \to \varLambda^+_c \bar{\varLambda}^-_c$ reaction from the reaction threshold up to $4.96$ GeV. In addition to the total cross sections and $|G_{\scriptscriptstyle{\rm M}}|$, the ratio $|G_{\scriptscriptstyle{\rm E}}/G_{\scriptscriptstyle{\rm M}}|$ and the effective form factor $|G_{\mathrm{eff}}|$ for $\varLambda^+_c$ are also calculated, and found that these calculations are consistent with the experimental data. Within the fitted model parameters, we have also estimated the charge radius of the charmed $\varLambda_c^+$ baryon.

Twisted bilayer graphene (TBG), which has drawn much attention in recent years, arises from van der Waals materials gathering each component together via van der Waals force. It is composed of two sheets of graphene rotated relatively to each other. Moiré potential, resulting from misorientation between layers, plays an essential role in determining the band structure of TBG, which directly relies on the twist angle. Once the twist angle approaches a certain critical value, flat bands will show up, indicating the suppression of kinetic energy, which significantly enhances the importance of Coulomb interaction between electrons. As a result, correlated states like correlated insulators emerge from TBG. Surprisingly, superconductivity in TBG is also reported in many experiments, which drags researchers into thinking about the underlying mechanism. Recently, the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG. In addition, twisted multilayer graphene receives more and more attention, as they could likely outperform TBG although they are more difficult to handle experimentally. In this review, we mainly introduce theoretical and experimental progress on TBG. Besides the basic knowledge of TBG, we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations. The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG. In addition, we cover the recent hot topic, twisted multilayer graphene. While the bilayer situation can be relatively easy to resolve, multilayer situations can be really complicated, which could foster more unique and novel properties. Therefore, in the end of the review, we look forward to future development of twisted multilayer graphene.

High-temperature phases of solids are often dynamically stable only. First-principles study of point defects in such solids at 0 K is prohibited by their static instability, which results in random structures of the defect-containing supercell so that the total energy of the supercell is randomly affected by structural distortions far away from the defect. Taking cubic perovskite $\alpha$-CsPbI$_3$ as an example, we first present the problem incurred by the static instability and then propose an approach based on molecular dynamics to carry out ensemble average for tackling the problem. Within affordable simulation time, we obtain converged defect ionization energies, which are unattainable by a standard approach and allow us to evaluate its defect tolerance property. Our work paves the way for studying defects in statically unstable solids.

Two-dimensional electron gas (2DEG) with high electron mobility is highly desired to study the emergent properties and to enhance future device performance. Here we report the formation of 2DEG with high mobility at the interface between rock-salt BaO and perovskite SrTiO$_{3}$. The interface consists of the ionically compensated BaO$_{1-\delta}$ layer and the electronically compensated TiO$_{2}$ layer, which is demonstrated as a perfect interface without lattice mismatch. The so-formed interface features metallic conductivity with ultralow square resistance of $7.3 \times 10^{-4}\,\Omega /\square$ at 2 K and high residual resistance ratios $R_{\rm 300\,K}/R_{\rm 2\,K}$ up to 4200. The electron mobility reaches 69000 cm$^{2}$$\cdot$V$^{-1}$$\cdot$s$^{-1}$ at 2 K, leading to Shubnikov–de Haas oscillations of resistance. Density functional theory calculations reveal that the effective charge transfers from BaO to the Ti 3$d_{xy}$ orbital occur at the interface, leading to the conducting TiO$_{2}$ layer. Our work unravels that BaO can adapt itself by removing oxygen to minimize the lattice mismatch and to provide substantial carriers to SrTiO$_{3}$, which is the key to forming 2DEGs with high mobility at the interfaces.

Hermitian systems possess unitary scattering. However, the Hermiticity is unnecessary for a unitary scattering although the scattering under the influence of non-Hermiticity is mostly non-unitary. Here we prove that the unitary scattering is protected by certain type of pseudo-Hermiticity and unaffected by the degree of non-Hermiticity. The energy conservation is violated in the scattering process and recovers after scattering. The subsystem of the pseudo-Hermitian scattering center including only the connection sites is Hermitian. These findings provide fundamental insights on the unitary scattering, pseudo-Hermiticity, and energy conservation, and are promising for light propagation, mesoscopic electron transport, and quantum interference in non-Hermitian systems.

Neon (Ne) can reveal the evolution of planets, and nitrogen (N) is the most abundant element in the Earth's atmosphere. Considering the inertness of neon, whether nitrogen and neon can react has aroused great interest in condensed matter physics and space science. Here, we identify three new Ne–N compounds (i.e., NeN$_6$, NeN$_{10}$, and NeN$_{22}$) under pressure by first-principles calculations. We find that inserting Ne into N$_2$ substantially decreases the polymeric pressure of the nitrogen and promotes the formation of abundant polynitrogen structures. Especially, NeN$_{22}$ acquires a duplex host-guest structure, in which guest atoms (Ne and N$_2$ dimers) are trapped inside the crystalline host N$_{20}$ cages. Importantly, both NeN$_{10}$ and NeN$_{22}$ not only are dynamically and mechanically stable but also have a high thermal stability up to 500 K under ambient pressure. Moreover, ultra-high energy densities are obtained in NeN$_{10}$ (11.1 kJ/g), NeN$_{22}$ (11.5 kJ/g), tetragonal t-N$_{22}$ (11.6 kJ/g), and t-N$_{20}$ (12.0 kJ/g) produced from NeN$_{22}$, which are more than twice the value of trinitrotoluene (TNT). Meanwhile, their explosive performance is superior to that of TNT. Therefore, NeN$_{10}$, NeN$_{22}$, t-N$_{22}$, and t-N$_{20}$ are promising green high-energy-density materials. This work promotes the study of neon-nitrogen compounds with superior properties and potential applications.

Perfect vector beams are a class of special vector beams with invariant radius and intensity profiles under changing topological charges. However, with the limitation of current devices, the generation of these vector beams is limited in the visible and infrared wavebands. Herein, we generate perfect vector beams in the ultraviolet region assisted by nonlinear frequency conversion. Experimental and simulation results show that the radius of the generated ultraviolet perfect vector beams remains invariant and is thus independent of the topological charge. Furthermore, we measure the power of the generated ultraviolet perfect vector beams with the change of their topological charges. This study provides an alternative approach to generating perfect vector beams for ultraviolet wavebands and may promote their application to optical trapping and optical communication.

In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral “Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden $SU(2)$ symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb$_{3}$S$_{6}$. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions. Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb$_{3}$S$_{6}$, paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.

Owing to the nonequilibrium nature, the energy state of metallic glasses (MGs) can vary a lot and has a critical influence on the physical properties. Exploring new methods to modulate the energy state of glasses and studying its relationship with properties have attracted great interests. Herein, we systematically investigate the energy state, mixing entropy and physical properties of Zr–Ti–Cu–Ni–Be multicomponent high entropy MGs by experiments and simulations. We find that the energy state increases along with the increase of mixing entropy. The yield strength and thermal stability of MGs are also enhanced by high mixing entropy. These results may open a new door on regulation of energy states and thus physical properties of MGs.

We propose an extended BCS–Hubbard model and investigate its ground state phase diagram in an external magnetic field. By mapping the model onto a model of spinless fermions coupled with conserving $Z_2$ variables which are mimicked by pseudospins, the model is shown to be exactly solvable along the symmetric lines for an arbitrary on-site Hubbard interaction on the bipartite lattice. In the zero field limit, the ground states exhibit an antiferromagnetic order of pseudospins. In the large field limit, on the other hand, the pseudospins are fully polarized ordered. With the increase of the applied field, a first-order phase transition occurs between these kinds of phases when the on-site Coulomb interaction is less than a critical value $U_{\rm c}$. Above this critical $U_{\rm c}$, a novel intermediate phase emerges between the fully polarized and antiferromagnetic phases. The ground states in this phase are macroscopically degenerate, like in a spin ice, and the corresponding entropy scales linearly with the lattice size at zero temperature.

Polymeric nitrogen as a new class of high energy density materials has promising applications. We develop a new scheme of crystal structure searching in a confined space using external confining potentials fitted from first-principles calculations. As a showcase, this method is employed to systematically explore novel polymeric nitrogen structures confined in single-walled carbon nanotubes. Several quasi-one-dimensional (1D) single-bonded polymeric nitrogen structures are realized, two of them are composed of nanotubes instead of chains. These new polymeric nitrogen phases are mechanically stable at ambient pressure and temperature according to phonon calculations and ab initio molecular dynamics simulations. It is revealed that the stabilization of zigzag and armchair chains confined in carbon nanotubes (CNTs) are mostly attributed to the charge transfer from carbon to nitrogen. However, for the novel nitrogen nanotube systems, electrons overlapping in the middle space provide strong Coulomb repulsive forces, which not only induce charge transfer from the middle to the sides but also stabilize the polymeric nitrogen. Our work provides a new strategy for designing novel high-energy-density polymeric nitrogen materials, as well as other new materials with the help of confined space inside porous systems, such as nanotubes, covalent organic frameworks, and zeolites.

Random numbers are one of the key foundations of cryptography. This work implements a discrete quantum random number generator (QRNG) based on the tunneling effect of electrons in an avalanche photo diode. Without any post-processing and conditioning, this QRNG can output raw sequences at a rate of 100 Mbps. Remarkably, the statistical min-entropy of the 8,000,000 bits sequence reaches 0.9944 bits/bit, and the min-entropy validated by NIST SP 800-90B reaches 0.9872 bits/bit. This metric is currently the highest value we have investigated for QRNG raw sequences. Moreover, this QRNG can continuously and stably output raw sequences with high randomness over extended periods. The system produced a continuous output of 1,174 Gbits raw sequence for a duration of 11,744 s, with every 8 Mbits forming a unit to obtain a statistical min-entropy distribution with an average value of 0.9892 bits/bit. The statistical min-entropy of all data (1,174 Gbits) achieves the value of 0.9951 bits/bit. This QRNG can produce high-quality raw sequences with good randomness and stability. It has the potential to meet the high demand in cryptography for random numbers with high quality.

As a prototypical half-metallic ferromagnet, La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) has been extensively studied due to its versatile physical properties and great potential in spintronic applications. However, the weak perpendicular magnetic anisotropy (PMA) limits the controllability and detection of magnetism in LSMO, thus hindering the realization of oxide-based spintronic devices with low energy consumption and high integration level. Motivated by this challenge, we develop an experimental approach to enhance the PMA of LSMO epitaxial films. By cooperatively introducing 4$d$ Ru doping and a moderate compressive strain, the maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach $3.0 \times 10^{5}$ J/m$^{3}$ at 10 K. Furthermore, we find a significant anisotropic magnetoresistance effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our findings offer an effective pathway to harness and detect the orientations of magnetic moments in LSMO films, thus promoting the feasibility of oxide-based spintronic devices, such as spin valves and magnetic tunnel junctions.

The new dimensional deformation approach is proposed to generate higher-dimensional analogues of integrable systems. An arbitrary ($K$+1)-dimensional integrable Korteweg–de Vries (KdV) system, as an example, exhibiting symmetry, is illustrated to arise from a reconstructed deformation procedure, starting with a general symmetry integrable (1+1)-dimensional dark KdV system and its conservation laws. Physically, the dark equation systems may be related to dark matter physics. To describe nonlinear physics, both linear and nonlinear dispersions should be considered. In the original lower-dimensional integrable systems, only liner or nonlinear dispersion is included. The deformation algorithm naturally makes the model also include the linear dispersion and nonlinear dispersion.

High-resolution angle-resolved photoemission measurements were taken on FeSe$_{1-x}$S$_x$ ($x$ = 0, 0.04, and 0.08) superconductors. With an ultrahigh energy resolution of 0.4 meV, unusual two hole bands near the Brillouin-zone center, which was possibly a result of additional symmetry breaking, were identified in all the sulfur-substituted samples. In addition, in both of the hole bands highly anisotropic superconducting gaps with resolution limited nodes were evidenced. We find that the larger superconducting gap on the outer hole band is reduced linearly to the nematic transition temperature while the gap on the inner hole is nearly S-substitution independent. Our observations strongly suggest that the superconducting gap increases with enhanced nematicity although the superconducting transition temperature is not only governed by the pairing strength, demonstrating strong constraints on theories in the FeSe family.

We performed high-pressure transport studies on the flat-band Kagome compounds, Pd$_3$P$_2$(S$_{1-x}$Se$_x$)$_8$ ($x=0$, 0.25), with a diamond anvil cell. For both compounds, the resistivity exhibits an insulating behavior with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is observed at high temperatures in Pd$_3$P$_2$S$_8$, and superconductivity emerges at low temperatures. The onset temperature of superconducting transition $T_{\rm C}$ rises monotonically from 2 K to 4.8 K and does not saturate with pressure up to 43 GPa. For the Se-doped compound Pd$_3$P$_2$(S$_{0.75}$Se$_{0.25}$)$_8$, the $T_{\rm C}$ is about 1.5 K higher than that of the undoped one over the whole pressure range, and reaches 6.4 K at 43 GPa. The upper critical field with field applied along the $c$ axis at typical pressures is about 50$\%$ of the Pauli limit, suggesting a 3D superconductivity. The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K, which suggests either a multi-band electronic structure or an electron correlation effect in the system.

Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation, but also is helpful for further understanding the heavy fermion superconductivity. Here we report a low-temperature and vector-magnetic-field scanning tunneling microscopy and spectroscopy study on a superconducting compound (4Hb-TaS$_{2})$ with alternate stacking of 1T-TaS$_{2}$ and 1H-TaS$_{2}$ layers. We observe the quasi-two-dimensional superconductivity in the 1H-TaS$_{2}$ layer with anisotropic response to the in-plane and out-of-plane magnetic fields. In the 1T-TaS$_{2}$ layer, we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters. We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level, and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS$_{2}$ surface. Our results not only are important for fully understanding the electronic properties of 4Hb-TaS$_{2}$, but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.

The physical concept of synthetic dimensions has recently been introduced into optics. The fundamental physics and applications are not yet fully understood, and this report explores an approach to optical neural networks using synthetic dimension in time domain, by theoretically proposing to utilize a single resonator network, where the arrival times of optical pulses are interconnected to construct a temporal synthetic dimension. The set of pulses in each roundtrip therefore provides the sites in each layer in the optical neural network, and can be linearly transformed with splitters and delay lines, including the phase modulators, when pulses circulate inside the network. Such linear transformation can be arbitrarily controlled by applied modulation phases, which serve as the building block of the neural network together with a nonlinear component for pulses. We validate the functionality of the proposed optical neural network for the deep learning purpose with examples handwritten digit recognition and optical pulse train distribution classification problems. This proof of principle computational work explores the new concept of developing a photonics-based machine learning in a single ring network using synthetic dimensions, which allows flexibility and easiness of reconfiguration with complex functionality in achieving desired optical tasks.

The simple kagome-lattice band structure possesses Dirac cones, flat band, and saddle point with van Hove singularities in the electronic density of states, facilitating the emergence of various electronic orders. Here we report a titanium-based kagome metal CsTi$_{3}$Bi$_{5}$ where titanium atoms form a kagome network, resembling its isostructural compound CsV$_{3}$Sb$_{5}$. Thermodynamic properties including the magnetization, resistance, and heat capacity reveal the conventional Fermi liquid behavior in the kagome metal CsTi$_{3}$Bi$_{5}$ and no signature of superconducting or charge density wave (CDW) transition anomaly down to 85 mK. Systematic angle-resolved photoemission spectroscopy measurements reveal multiple bands crossing the Fermi level, consistent with the first-principles calculations. The flat band formed by the destructive interference of hopping in the kagome lattice is observed directly. Compared to CsV$_{3}$Sb$_{5}$, the van Hove singularities are pushed far away above the Fermi level in CsTi$_{3}$Bi$_{5}$, in line with the absence of CDW. Furthermore, the first-principles calculations identify the nontrivial $\mathbb{Z}_2$ topological properties for those bands crossing the Fermi level, accompanied by several local band inversions. Our results suppose CsTi$_{3}$Bi$_{5}$ as a complementary platform to explore the superconductivity and nontrivial band topology.