When a charge current is injected into the surface state of a topological insulator (TI), the resulting shift of the spin-momentum-locked Fermi surface leads to the appearance of a net spin polarization. The helical spin structure of the Dirac-cone surface state of a TI should lead to a fixed sign of this spin polarization for a given current direction, but experimentally both signs that agree and disagree with the theory expectation for the surface state Dirac cone have been observed in the past. Although the origin of the wrong sign has not been conclusively elucidated, this observation points to the possibility that one may switch the spin polarization at will to realize a spin transistor operation. Here we report the observation of both signs of spin polarization in the very same device and demonstrate the tunability between the two by electrostatic gating, which gives a proof of principle of a TI spin transistor. This switching behavior is explained using a minimal model of competing contributions from the topological surface state and trivial Rashba-split states.

Asymmetric synthetic antiferromagnets (SAFs) with perpendicular magnetic anisotropy (PMA) have attracted considerable attention due to the advantages of both high operation speed and easy detection. In this paper, anomalous Hall effect (AHE) and spin-orbit-torque (SOT) effect are investigated for the SAF samples of $[\mathrm{Ni}/\mathrm{Co}{]}_4/\mathrm{Ru}/[\mathrm{Co}/\mathrm{Ni}{]}_3$, which exhibit oscillatory interlayer exchange coupling when varying the $\mathrm{Ru}$ layer thickness $t_{\mathrm{Ru}}$. It is found that the AHE loop amplitude decreases and even changes its polarity as $t_{\mathrm{Ru}}$ exceeds 1.27 nm, indicating the existence of a negative Hall coefficient at the $\mathrm{Ru}/\mathrm{Co}$ interface. The calculated spin Hall angle θ${}_{\mathrm{SH}}$ varies nonmotonically with the increase of $t_{\mathrm{Ru}}$, following a similar variation trend to the antiferromagnetic (AF) coupling field $H_{\mathrm{AF}}$. Specifically, when $H_{\mathrm{AF}}$ reaches its maximum at $t_{\mathrm{Ru}}$ = 0.95 nm, θ${}_{\mathrm{SH}}$ is 7 times higher compared to the case of $H_{\mathrm{AF}}$ = 0, indicating that the greatly enhanced SOT effect is strongly linked to the AF-coupling interaction. Nevertheless, although $H_{\mathrm{AF}}$ increases significantly as the measurement temperature drops from 300 to 10 K, θ${}_{\mathrm{SH}}$ keeps nearly unchanged. Our study demonstrates that the enhanced θ${}_{\mathrm{SH}}$ with AF coupling is primarily determined by the modulation of the spacer-related band structure, rather than a magnetic mechanism of reduced magnon excitations in the magnetic layers. These results of strong AHE and SOT manipulation are valuable for the practical design of SAF-based spintronic devices.

Topological catalysis has attracted significant interest in both topological and catalytic research fields, but the underlying mechanism remains poorly understood, and the influence of topological surface states (TSSs) on catalytic activity has yet to be determined. Herein, we employ ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, a prototypical topological material, to investigate the relationship between TSSs and catalytic activity. We analyze the adsorption energies of key species (e.g., $\mathrm{H}$, $\mathrm{O}$, and $\mathrm{N}$) in heterogeneous catalysis on the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$(111) surface by considering both the presence and absence of TSSs. Our findings reveal that TSSs have no significant impact on adsorption energy, while spin-orbit coupling (SOC) significantly affects it. Given that topological insulators and catalytic materials containing heavy elements generally exhibit strong SOC, it is crucial to consider the role of SOC in catalytic reactions.

Developing thermal analogues of a field-effect transistor could open the door to a low-power and even zero-power communication technology working with heat rather than electricity. These solid-sate devices could also find many applications in the field of active thermal management in numerous technologies (microelectronic, building science, energy harvesting and conversion…). Recent theoretical works have suggested that a photonic transistor made with three terminals can, in principle, be used to switch, modulate, and even amplify heat flux through exchange of thermal photons. Here, we report an experimental demonstration of thermal transistor effect using a noncontact system composed of a temperature-controlled metal-insulator-based material interacting in the far-field regime with two blackbodies held at two different temperatures. We demonstrate that, with a tiny change in the temperature of the active layer, the heat flux received by the cold blackbody can be drastically modified. An amplification parameter of heat flux over 20 is reported.

In this study, we provide an empirical validation of spontaneous synchronization and the exceptional-point- (EP) induced pulse-generation mechanism within the dynamic framework of the breather complex. During the establishment of a nine-breather assembly within a mode-locked fiber laser, we find synchronization in both the breathing frequency and phase. Intriguingly, the formation of these breathers aligns exactly with the junctures where the complex’s breathing frequency either diverges from or is entrained into their subharmonics. We posit that such a pulse-generation mechanism is intrinsically associated with the non-Hermitian EPs or the time-translation symmetry breaking. Our in-depth studies into the deconstruction and subsequent reconstruction of mode locking have unveiled a crucial correlation between synchronization and laser stabilization. These findings could stimulate alternative studies, including ultrafast optics, microcavity combs, ocean breather behaviors, non-Hermitian optics, etc.

We present a detailed investigation of the magnetization dynamics in $\mathrm{Co}$/$\mathrm{Ag}$ nanodots, which due to their size can support standing spin-wave (SSW) modes with complex spectral responses. To interpret the experimentally measured broadband vector network analyzer ferromagnetic resonance data, we compare the spectra of the nanoarray structure with those of the unpatterned $\mathrm{Co}$/$\mathrm{Ag}$ film of identical thickness, which serves as a baseline for obtaining the general magnetic parameters of the system. Using a frequency-domain matrix-free simulation method of the dynamic response, we identify the nature of the excitation modes, which allows us to assess the boundary conditions for the nanodots. We find excellent agreement between the calculated and experimental values for the frequencies of the fundamental (uniformlike) (011) mode. The existence of an edge-localized mode in the experiment has been confirmed and fits very well with theory and micromagnetic simulations, having the form of a flapping mode at the extrema of the nanodot in one of the in-plane directions. Its frequency is below the fundamental mode’s frequency and has been shown to be a consequence of the imaginary wave vector for such localized SSW modes. Higher-order SSW modes can be generated from the theory, which allows us to find a probable mode number for the second bulk SSW (201 or 221 or 131), which lies at frequencies above the fundamental mode.

When the energy of a quantum emitter aligns with the photonic bandgap of the waveguide, variety of distinct quantum optical phenomena emerges. The paradigmatic example of such nontrivial interaction results in the formation of a qubit-photon bound state (QPBS) where a single photon is exponentially localized around the qubit position. Superconducting quantum circuits has been extensively used for studying QPBS where the photonic band gaps are generated in two-dimensional periodic structures such as photonic crystals and metamaterials. Nonetheless, in all the experiments reported so far, the exponential nature of the bound state wave function is justified by making two assumptions (1) that the waveguide is infinite in length and (2) the coupling to the external ports are absent. These assumptions are difficult to achieve for a physical device and the transition from an experimentally realizable finite-size system to the theoretically assumed infinite device size has never been thoroughly understood. Here, we have realized an alternative platform based on a three-dimensional (3D) rectangular waveguide that has a naturally occurring low-frequency cutoff for generating QPBS as proposed in Shahmoon and Kurizki [Phys. Rev. A 87, 033831 (2013)]. In its theoretical description, we explicitly take into consideration the finite nature of the 3D waveguide arising due to its metallic boundaries and coupling to microwave ports and demonstrate how the infinite waveguide limit arises in such a finite system.

A nanoscale dielectric gap clamped between two metal electrodes may undergo a large resistance change from insulating to highly conducting upon applying an electrical stress. This sudden resistive switching is largely exploited in memristors for emulating synapses in neuromorphic neural networks. Here, we show that volatile resistive switching can be accompanied by a release of electromagnetic radiation spanning the visible spectral region. Of note, we find that the spectrum is characterized by photon energies exceeding the maximum kinetic energy of electrons provided by the switching voltage. This so-called overbias emission can be described self-consistently by a thermal radiation model featuring an out-of-equilibrium electron distribution generated in the device with an effective temperature exceeding 2000 K. The emitted spectrum is understood in terms of hot electrons radiatively decaying to resonant optical modes occurring in a nanoscale ${\mathrm{Si}\mathrm{O}}_2$ matrix located between two $\mathrm{Ag}$ electrodes. We further show that the same device can sustain different emission mechanisms depending on the nature, the intricacy and historicity of its memristive gap. Specifically, when operated in a nonvolatile state, we identify inelastic electron tunneling as an additional process providing photon emission from the device. The correlation between resistive switching and the onset of light emission in atomic scale photonic memristor brings alternative venues to generate light on chip and their exploitation in optical interconnects. Photons emitted during memristive switching can also be monitored to follow the neural activation pathways in memristor-based networks.

The lattice strain induced by metallic electrodes can impair the functionality of advanced quantum devices operating with electron or hole spins. Here, we investigate the deformation induced by CMOS-manufactured titanium nitride electrodes on the lattice of a buried 10-nm-thick $\mathrm{Si}/{\mathrm{Si}}_{0.66}{\mathrm{Ge}}_{0.34}$ quantum well by means of nanobeam scanning x-ray diffraction microscopy. We are able to measure $\mathrm{Ti}\mathrm{N}$-electrode-induced local modulations of the strain tensor components in the range of 2–8 × ${10}^{-4}$ with about 60-nm lateral resolution. We evaluate that these strain fluctuations are reflected in local modulations of the potential of the $\mathrm{Si}$ conduction-band minimum larger than 2 meV, which is close to the orbital energy of an electrostatic quantum dot. We observe that the sign of the strain modulations at a given depth of the quantum-well layer depends on the lateral dimensions of the electrodes. Since our work explores the impact of device geometry on the strain-induced energy landscape, it enables further optimization of the design of scaled CMOS-processed quantum devices.

Mott-insulator-to-metal transitions under an applied electric field are currently the subject of numerous fundamental and applied studies. Exploring the electronic parameters contributing to the external control of conductivity of correlated systems like ${\mathrm{V}}_2{\mathrm{O}}_3$ is an indispensable requirement for next-generation Mottronic devices. Here, we demonstrate a resistive-switching (RS) phenomenon, i.e., a flip from the high-resistance state (HRS) to the low-resistance state in a ${\mathrm{V}}_2{\mathrm{O}}_3$ thin film grown on $\mathrm{Si}$ (001) substrate by applying a dc voltage as external perturbation. The RS effect is explained in connection with the electronic structure by overcoming the electronic correlations and, in the HRS, the ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{Si}$ film is realized to lie in the intermediate regime between the Mott-Hubbard and charge-transfer insulating states. Interestingly, our study reveals an electrically induced nonthermal RS effect in the ${\mathrm{V}}_2{\mathrm{O}}_3/\mathrm{Si}$ film in terms of different energetics like on-site Coulomb repulsion (U) and charge-transfer energy (Δ), which regulate the exotic properties of this metal oxide and its functionality.

Quantum-disordered models provide a versatile platform to explore the emergence of quantum excitations in many-body systems. The engineering of spin models at the atomic scale with scanning tunneling microscopy and the local imaging of excitations with electrically driven spin resonance has risen as a powerful strategy to image spin excitations in finite quantum spin systems. Here, focusing on $S=1/2$ lattices as realized by $\mathrm{Ti}$ in $\mathrm{Mg}\mathrm{O}$, we show that dynamical spin excitations provide a robust strategy to infer the nature of the underlying Hamiltonian. We show that finite-size interference of the dynamical many-body spin excitations of a generalized long-range Heisenberg model allows the underlying spin couplings to be inferred. We show that the spatial distribution of local spin excitations in $\mathrm{Ti}$ islands and ladders directly correlates with the underlying ground state in the thermodynamic limit. Using a supervised-learning algorithm, we demonstrate that the different parameters of the Hamiltonian can be extracted by providing the spatially dependent and frequency-dependent local excitations that can be directly measured by electrically driven spin resonance with scanning tunneling microscopy. Our results put forward local dynamical excitations in confined quantum spin models as versatile witnesses of the underlying ground state, providing an experimentally robust strategy for Hamiltonian inference in complex real spin models.

Mechanical resonators that possess coupled modes with harmonic frequency relations have recently sparked interest due to their suitability for controllable energy transfer and non-Hermitian dynamics. Here we show coupling between high-$Q$-factor (greater than ${10}^4$) resonances with a nearly 1:1 frequency relation in spatially symmetric microresonators. We develop and demonstrate a method to analyze their dynamical behavior based on the simultaneous and resonant detection of both spectral peaks, and validate this with experimental results. The frequency difference between the peaks modulates their ringdown, and creates a beat pattern in the linear decay. This method applies to both the externally driven regime and the Brownian-motion (thermal) regime, and allows characterization of both linear and nonlinear parameters. The mechanism behind this method renders it broadly applicable to both optical and electrical readout, as well as to different mechanical systems. This will aid studies using near-degenerate mechanical modes, for example, optomechanical energy transfer, synchronization, and gyroscopic sensors.

Teleporting physical quantities to remote locations remains a key challenge for quantum information science and technology. Quantum teleportation has enabled the transfer of quantum information, but teleportation of quantum physical quantities has not yet been realized. Here we report the realization and observation of quantum energy teleportation on real superconducting quantum hardware. We achieve this by using several IBM superconducting quantum computers. The results are consistent with the exact solution of the theory and are improved by the mitigation of measurement error. Quantum energy teleportation requires only local operations and classical communication. Therefore, our results provide a realistic benchmark that is fully achievable with current quantum computing and communication technologies.

We propose compact plasmonic-power-splitters with arbitrary phase responses in the millimetre waveband based on spoof surface plasmon polaritons (SSPPs). Benefitting from the strong field confinements of SSPPs, the branches of the proposed plasmonic-power-splitters can be flexibly bent to meet the design requirement of various situations, while their transmission performance is nearly not affected. Of note, the output phase responses of the plasmonic-power-splitters can be flexibly controlled by adjusting the SSPP propagation constant of each branch only via optimizing the unit size, without changing the overall layout of the power splitter. At a proof of concept, two eight-way plasmonic-power-splitters with exactly the same layout are designed, simulated and measured. They can achieve eight-way equal output powers, but their output phase shifts are 0° and 45°, respectively, at the center frequency of 26 GHz. We show that the designed power splitters have good power allocation performance in an ultrawideband range from 5 to 30 GHz. Though the phase responses cannot maintain good consistency in such a wide bandwidth, it can be designed at any center frequency in the band. The proposed power splitters show big advantages of path compatibility, high compactness, and customizable phase response, which is promising in large-scale integrated circuits.

The synthesized two-dimensional (2D) Ruddlesden-Popper (RP) all-inorganic mixed halogen perovskite, ${\mathrm{Cs}}_2{\mathrm{Pb}\mathrm{I}}_x{\mathrm{Cl}}_{4-x}$ (x = 2) has attracted extensive attention due to its excellent luminescence properties and environmental stability. However, the regulation of halogen ratio and halogen replacement sites on the luminescence properties of 2D RP inorganic mixed halogen perovskite remains unknown. In this paper, the luminescence properties containing band structures, effective mass, exciton-binding energies, photoluminescence emission energy, and the transition dipole moment of 2D RP perovskite ${\mathrm{Cs}}_2{\mathrm{Pb}\mathrm{I}}_x{\mathrm{Cl}}_{4-x}$ (x = 0,1,2,3,4) were studied via density-functional theory. To systematically represent different replacement sites, according to the halogens on the equatorial plane of the octahedron, we divide it into three types. [(1) the halogens on the equatorial plane are $\mathrm{I}$ atoms; (2) the halogens on the equatorial plane are $\mathrm{Cl}$ atoms; (3) the halogens on the equatorial plane are composed of $\mathrm{I}$ and $\mathrm{Cl}$ atoms]. The calculation results show that for structures with replacement sites of the same kind, the band gap, photoluminescence emission energy, and transition dipole moment decrease with the increase of the proportion of $\mathrm{I}$ atoms, while the opposite is true for exciton-binding energy and effective mass. In addition, among the three types of replacement sites, the quadratic eigenvalue problem-Mix (equatorial plane is composed of $\mathrm{I}$ and $\mathrm{Cl}$) type replacement site is the most conducive to the luminescence performance of the material. Our theoretical study will provide guidance for the design and fabrication of highly luminescent 2D RP perovskite.