Metal monochalcogenide $\mathrm{Ga}\mathrm{Se}$ is a classic layered semiconductor that has received increasing research interest due to its highly tunable electronic and optical properties for ultrathin electronics applications. Despite intense research efforts, a systematic understanding of the layer-dependent electronic and optical properties of $\mathrm{Ga}\mathrm{Se}$ remains to be established, and there appear to be significant discrepancies between different experiments. We have performed GW plus Bethe-Salpeter equation calculations for few-layer and bulk $\mathrm{Ga}\mathrm{Se}$, aiming at understanding the effects of interlayer coupling and dielectric screening on excited-state properties of $\mathrm{Ga}\mathrm{Se}$, and how the electronic and optical properties evolve from strongly two-dimensional-like to intermediate thick layers, and to three-dimensional bulk character. Using a new definition of the exciton binding energy, we are able to calculate the binding energies of all excitonic states. Our results reveal an interesting correlation between the binding energy of an exciton and the spread of its wave function in real and momentum spaces. We find that the existence of (nearly) parallel valence and conduction bands facilitates the formation of excitonic states that spread out in momentum space. Thus, these excitons tend to be more localized in real space and have large exciton binding energies. The interlayer coupling substantially suppresses the Mexican-hat-like dispersion of the top valence band seen in the monolayer system, explaining the greatly enhanced photoluminescence as layer thickness increases. Our results also help resolve apparent discrepancies between different experiments. After including the quasiparticle and excitonic effects as well as the optical activities of excitons, our results compare well with available experimental results.

Using the time dependent Ginzburg-Landau equations, we simulate the inductive responses of a variety of thin-film systems containing patterned antidots with different sizes and shapes. The results for all shapes show that the kinetic inductance diverges as the applied current approaches a critical current that is below the BCS depairing current. Exploiting the similarity of the observed current-voltage behavior to that of Josephson junctions, we obtain an empirical equation that well fits the inductivity curve as a function of the applied current.

Two-dimensional (2D) anisotropic semiconductors, such as black phosphorene, show strong potential in ultrascaled metal-oxide-semiconductor field-effect transistors (MOSFETs) as the anisotropic electronic structure is highly beneficial in boosting the device performance at sub-10-nm gate length regime. Metallic graphenelike borophene can be halogenated to form a stable monolayer family of ${\mathrm{B}}_4{\mathrm{X}}_4$ ($\mathrm{X}$ = $\mathrm{F},\mathrm{Cl},\mathrm{and}\mathrm{Br}$) whose highly anisotropic semiconducting electronic structures suggest a potential in ultrascaled MOSFET applications. Here, we computationally explore the quantum transport properties of ${\mathrm{B}}_4{\mathrm{X}}_4$ monolayers as high-performance (HP) 5-nm MOSFETs. The HP on-state current of the n-type 5-nm monolayer ${\mathrm{B}}_4{\mathrm{X}}_4$ MOSFETs can reach over 3000 µA/µm at 5-nm gate length regime, thus fulfilling the ITRS requirement of HP devices. Of note, by analyzing the physical relationship between the anisotropic electronic structures (transport effective mass $m_{//}$ and density of states $m_{\mathrm{DOS}}$), we show that large electronic anisotropy does not immediately guarantee high performance. An overly large $m_{//}$ or $m_{\mathrm{DOS}}$ would suppress the saturation current and lead to limited HP on-state current of monolayer ${\mathrm{B}}_4{\mathrm{X}}_4$, thus revealing a balance between the effective masses is needed when designing 2D semiconductor MOSFETs. This work provides insights and design guidelines for the development of next-generation nanoelectronic devices based on the exceptional transport properties of 2D anisotropic channel materials.

The study of topological states, which allow transport properties that are robust against impurities and defects in electronic structures, has been recently extended to the realm of elasticity. This work shows that nontrivial topological flexural edge states located on the free boundary of the elastic graphenelike metamaterial can be realized without breaking the time-reversal, mirror, or inversion symmetry of the system. Numerical calculations and experimental studies demonstrate the robust transport of flexural waves along the boundaries of the designed structure. The topological edge states on the free boundary are not limited by the size of the finite structure, which can reduce the scale of the topological state system. In addition, unlike the edge states localized on the free boundary in graphene where the group velocity is zero, the edge states on the elastic metamaterial plate have propagation states with nonzero group velocity. We have introduced the concept of Shannon entropy for elastic waves to assess the frequency range of the edge states in graphenelike elastic metamaterials. This work represents a relevant advance in the study of elastic wave topological states, providing a theoretical basis for engineering applications such as vibration reduction and vibration isolation for mechanical structures.

The variational quantum imaginary time-evolution algorithm is efficient in finding the ground state of a quantum Hamiltonian. This algorithm involves solving a system of linear equations in a classical computer and the solution is then used to propagate a quantum wave function. Here, we show that owing to the noisy nature of current quantum processors, such a quantum algorithm or the family of quantum algorithms will require single- and two-qubit gates with very low error probability to produce reliable results. Failure to meet such a condition will result in erroneous quantum data propagation even for a relatively small quantum circuit ansatz. Specifically, we provide the upper bounds on how the relative error in variational parameters’ propagation scales with the probability of noise in quantum hardware. We also present an exact expression of how the relative error in variational parameter propagation scales with the probability of partially depolarizing noise.

Topological modes in the bandgap are generally localized at the boundaries. However, recent research proposes a new topological mode arising from the non-Hermitian skin effect, whose energy can extend to the bulk, forming the topological extended state. Such a topological mode can increase the space utilization of topological devices, which is worth further exploration and confirmation in classical systems. Here, we propose a topological extended state reshaping in non-Hermitian topolectrical circuits with a skin effect, where the stairlike extended mode is reshaped by controlling the odd-even properties of unit cells in the electric circuit ring. The extended state reshaping is confirmed by measuring the stairlike voltage distribution in the experiment. Our finding enriches the characteristics of extended states, and has potential application in multichannel tunable topological devices based on the stairlike extended mode.

Topological ferromagnets with remarkable transverse-transport properties, low saturation magnetization ($M_{\mathrm{s}}$), and high uniaxial magnetic anisotropy energy ($K_{\mathrm{u}}$) are attracting attention for application in spintronic devices. In this study, the anomalous Nernst effect (ANE) in $\mathrm{Mn}\mathrm{Al}\mathrm{Ge}$ and $(\mathrm{Mn}$-$\mathrm{Cr})\mathrm{Al}\mathrm{Ge}$ films with a pseudo-two-dimensional structure consisting of $\mathrm{Mn}$ ($\mathrm{Mn}$-$\mathrm{Cr}$) and $\mathrm{Al}$-$\mathrm{Ge}$ layers were investigated. The $\mathrm{Mn}\mathrm{Al}\mathrm{Ge}$ and $(\mathrm{Mn}$-$\mathrm{Cr})\mathrm{Al}\mathrm{Ge}$ films with low $M_{\mathrm{s}}$ and high $K_{\mathrm{u}}$ were grown epitaxially on single-crystal $\mathrm{Mg}\mathrm{O}(001$) substrates using sputtering. The relatively large anomalous Hall angles of approximately 0.02 were obtained in both films at 300 K, which is attributed to layered topological nodal lines in these materials. Anomalous Nernst coefficients ($S_{\mathrm{ANE}}$) were −0.13 µV/K for the $\mathrm{Mn}\mathrm{Al}\mathrm{Ge}$ film and −0.50 µV/K for the $(\mathrm{Mn}$-$\mathrm{Cr})\mathrm{Al}\mathrm{Ge}$ film at 300 K. The enhancement of the negative $S_{\mathrm{ANE}}$ by substituting some $\mathrm{Mn}$ with $\mathrm{Cr}$ is caused by the enhancement of the positive Seebeck coefficient and the sign change of the transverse thermoelectric conductivity from positive to negative. These materials with low $M_{\mathrm{s}}$, high $K_{\mathrm{u}}$, and negative $S_{\mathrm{ANE}}$ are suitable for application in thermoelectric conversion devices using an ANE-based thermopile structure.

The presence of an external magnetic field leads to the loss of anisotropic physical information and is responsible for the broadening of spectra in sensing experiments with solid-state quantum sensors. However, the range of applicable sensing protocols at zero field was limited due to the incomplete manipulations. Here we propose and demonstrate a precise geometric control protocol in a spin-1 quantum sensor for zero-field multiquantum gates. By employing specific phased geometric controls, state leakage is prevented at zero field even under low control power, which allows much more complicated multipulse control especially under living biological conditions. Our method offers an approach to implement an arbitrary multiquantum gate on the spin-1 quantum sensor, rendering it a valuable tool for zero-field multipulse quantum technologies, such as nanoscale zero-field multidimensional nuclear magnetic resonance.

Using quantum transport simulations, we study the operating principle of a proposed quantum cascade cooler, a multiple-quantum-well structure whose cooling capabilities rely on combined resonant tunneling and thermionic-emission filtering. We couple charge and heat transport by self-consistently solving nonequilibrium Green’s functions and the heat equation, and we subsequently calculate the thermodynamic properties of the electrons using noninvasive virtual probes. We show that this device exhibits bias-dependent electron-temperature oscillations emerging from electron-phonon interactions and intersubband transitions. Finally, we show the advantages of a multiple-quantum-well structure over a single quantum well and discuss the actual potential for such a structure to effectively cool down the crystal lattice upon optimization.

We report that the photovoltaic (PV) effect in nanoscale monocrystalline lithium niobate (LN) films originates from the Schottky barrier formed at the electrode-LN interface, different from the bulk PV effect reported previously in the bulk crystal. The Schottky barrier height and the depletion layer width at the $\mathrm{Cr}$-LN interface was measured to be 1.15 eV and 16 nm, respectively. The open-circuit voltage and the power conversion efficiency of the PV devices based on LN films were determined to be 0.8 V and 0.1%, respectively, at 325 nm. It was found the PV properties are film-thickness-dependent, mainly due to the increasing contribution of the polarization-induced asymmetric conduction from the bulk layer with the increase of LN film thickness. Furthermore, direct tunneling of electrons was observed to become the dominant conduction mechanism in ultrathin LN films (much less than 16 nm). These results could be useful for developing integrated optoelectronic devices, such as PV devices and photodetectors based on LN films.

We develop perpendicularly magnetized magnetic tunnel junctions consisting of a recording layer exhibiting a low magnetic damping to investigate the influence of magnetic damping on the write-error rate of voltage-driven magnetization switching. The effective magnetic damping is reduced to about one-third that of a conventional $\mathrm{Ta}$/$\mathrm{Co}\text{−}\mathrm{Fe}\text{−}\mathrm{B}$/$\mathrm{Mg}\mathrm{O}$ recording layer by eliminating the spin pumping effect. The low magnetic damping contributes to a 3-orders-of-magnitude reduction in the write-error rate for the longer write pulses, which is explained by the suppression of thermal fluctuation during the switching process. The low magnetic damping also enables a long period of magnetization precession to control the dynamics via the voltage-controlled magnetic anisotropy effect.

Designing an efficient, metal-free, and inexpensive catalyst for the electrochemical hydrogen evolution reaction (HER) is crucial for large-scale clean and green energy production. Recently synthesized 1D biphenylene nanoribbons (BPRs) display a few exciting properties originating from the unique coexistence of four-, six-, and eight-carbon rings. Here we present first-principles calculations of the electronic structure and electrocatalytic activity of variously sized $N$-BPRs ($N$ indicates the width). The electrocatalytic performance is evaluated on the basis of several descriptors, including electronic properties, carrier mobility, Gibbs free energy ($\mathrm{\Delta }{G}_{\mathrm{HER}}$), and exchange-current density. The electronic properties are crucially sensitive to the width (N) of BPRs transiting it from semiconducting to metallic nature at $N=18$. The $p_z$ orbitals of $\mathrm{C}$ atoms from the central tetragonal rings are mainly responsible for the decrease in band gap with increasing width. The room-temperature electron mobility is found to be as high as approximately $2.5\times {10}^4{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, while hole mobility is relatively lower in magnitude. The Gibbs free energy also depends sensitively on the width of BPRs as evident from the $p$-band-center analysis. We propose 15-BPR as the most-promising candidate for electrocatalytic activity, with extremely small overpotential (approximately $0.005$ V) and a high exchange-current density, much better than the state-of-the-art $\mathrm{Pt}$(111). A close inspection of the elementary reactions of the HER (Volmer, Heyrovsky, and Tafel reactions) shows that the Volmer-Tafel mechanism is most dominant for 15-BPR, with the Tafel mechanism as the rate-determining step, with a barrier of 0.56 eV. The present study provides deeper insight into the excellent HER catalytic activity of a newly synthesized BPR that is inexpensive and is expected to hasten experimental validation towards ${\mathrm{H}}_2$ production.

The potential of optical orbital angular momentum (OAM) to create boundless dimensional Hilbert spaces has garnered considerable interest for augmenting the capacity of communication systems. Precise detection and reconfiguration of optical vortices (OVs) carrying distinct topological charges are crucial for leveraging their communicative potential. Here, based on transformation optics (TO), we theoretically propose a straightforward method for OV decomposition and reconfiguration. We first transform spiral vortices into planar waves with varying refraction angles and subsequently restore the vortices at designated image points with the aid of coherent perfect absorbers. Employing Hamiltonian optics, we analyze the trajectory of OV rays at both source and image positions, revealing an efficient reconfiguration of the OAM field that accounts for the phases of the sources. Our findings demonstrate flexible manipulation of OAM through TO, offering substantial advancements in communication technologies, including on-chip signal filtering and demultiplexing.

The silicon vacancy in silicon carbide has emerged as a promising quantum system embedded in an industry-friendly platform due to its long-lived spin qubits that can effectively interface with photonic qubits. However, the unique spin quantum number of 3/2 gives rise to a statistical mixture of the optically initialized ground-state spin sublevels, hindering its successful application as a high-fidelity spin-photon interface. Recent experimental breakthroughs have demonstrated a solution to this challenge by achieving pure-state preparation through simultaneous optical initialization and depletion of selected spin sublevels using electron spin resonance. Nonetheless, the underlying mechanism of this process remains poorly understood, and an efficient method for achieving deterministic initialization has not yet been explored. In this work, we present a comprehensive investigation of the selective initialization process by establishing a complete rate model. We offer a detailed explanation of the underlying mechanism and elucidate the trade-off between initialization fidelities and efficiencies, which are strongly influenced by the experimental parameters employed. Through a thorough exploration of a wide range of experimental parameters, we identify the optimal initialization process that allows for pure-state initialization fidelity exceeding 99%. Our study offers valuable insights into achieving high-fidelity spin-photon interface applications, such as quantum repeaters, based on silicon vacancies in silicon carbide.

The Eötvös-type torsion balance is a well-known gravity gradient instrument for the regional or local geophysical exploration. As a key issue for the gravity gradient measurement, the estimation of the systematic effects in the instrument is rarely discussed as yet. This lack may lead to inconsistencies in the actual gravity gradient measurements. Among the systematic effects, one of the more obvious is the high-order gravitational gradient coupling, which is usually neglected in the measurement equation. This paper focuses on the estimation of such an effect. The coupling between the high-order gravitational gradient and the pendulum used in the instrument is charactered on the basis of the multipole expansion. It is presented that the coupling effect in the two versions of the commonly used Eötvös-type torsion balance can contribute a measurement bias of gravity gradient as large as approximately $20\text{E}$, approximately $10\text{E}$, respectively. The evaluation shows that the high-order gravitational gradient effect can not be ignored in the gravity gradient measurement by the Eötvös-type torsion balance. In addition, such an analysis method for the high-order gravitational gradient effect can also be applied to other types of gravity gradiometer or even gravimeters if required.

This work reports extraordinary topological properties of sound transmission through topological states in sonic crystals denominated by the Suzuki phase, consisting of a rectangular lattice of vacancies created in a triangular lattice. These low-symmetry crystals exhibit unique properties due to the embedded lattice of vacancies. A generalized folding method explains the band structure and the quasi-type-II Dirac point in the Suzuki phase, which is related to the underlying triangular lattice. Analogous to the acoustic valley Hall effect, the Suzuki phase contains three types of topological edge states on the four possible interfaces separating two Suzuki-phase crystals with distinct topological phases. The edge states have defined symmetries with inherent directionality, which affect the topological sound transmission and are different from chirality, valley vorticity, or helicity. Particularly, the existence of topological deaf bands is reported here. The propagation of topological eigenmodes on the same interface is also different; this is quantified using the acoustic Shannon entropy, making the topological transport dependent on the frequency of the edge states. Based on the abundant topological edge states of Suzuki-phase crystals, a multifunctional device with acoustic diodes, multichannel transmission, and selective acoustic transmission can be designed. Numerical simulations and measurements demonstrate the topological transmission. Our work extends the research platform of acoustic topological states to lattices with low symmetry, which opens avenues for enriching topological states with broad engineering applications.

Stochastic magnetic tunnel junctions (SMTJs) using low-barrier nanomagnets have shown promise as fast, energy-efficient, and scalable building blocks for probabilistic computing. Despite recent experimental and theoretical progress, SMTJs exhibiting the ideal characteristics necessary for probabilistic bits ($p$-bits) are still lacking. Ideally, the SMTJs should have (a) voltage bias independence, preventing read disturbance; (b) uniform randomness in the magnetization angle between the two magnetic layers; and (c) fast fluctuations without requiring external magnetic fields, while being robust to magnetic field perturbations. Here, we propose a design that satisfies all of these requirements, using double-free-layer SMTJs with synthetic antiferromagnets (SAFs). We evaluate the proposed SMTJ design with experimentally benchmarked spin-circuit models, accounting for transport physics, coupled with the stochastic Landau-Lifshitz-Gilbert equation for magnetization dynamics. We find that the use of low-barrier SAF layers reduces dipolar coupling, achieving uncorrelated fluctuations at zero-magnetic field, surviving up to diameters exceeding $D\approx 100\mathrm{nm}$ if the nanomagnets can be made thin enough ($\approx 1$–$2\mathrm{nm}$). The double-free-layer structure retains bias independence and the circular nature of the nanomagnets provides near-uniform randomness with fast fluctuations. Combining our full SMTJ model with advanced transistor models, we estimate the energy to generate a random bit to be about $3.6\mathrm{fJ}$, with fluctuation rates of about $3.3\mathrm{GHz}$ per $p$-bit. Our results will guide the experimental development of superior stochastic magnetic tunnel junctions for large-scale and energy-efficient probabilistic computation for problems relevant to machine learning and artificial intelligence.

The development of power-efficient spintronic devices has been a compelling need in the post-CMOS technology era. The effective tuneability of spin-orbit coupling (SOC) in the bulk and at the interfaces of hybrid material stacks is a prerequisite for scaling down the dimensions and power consumption of these devices. In this work, we demonstrate the strong chemisorption of ${\mathrm{C}}_{60}$ (fullerene) molecules when grown on the high-SOC $\beta$-$\mathrm{W}$ layer. The parent ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$/$\beta$-$\mathrm{W}$ ($\mathrm{CFB}/\beta$-W) bilayer exhibits large spin-to-charge interconversion efficiency, which can be ascribed to the interfacial SOC observed at the ferromagnet/heavy-metal interface. Further, the adsorption of ${\mathrm{C}}_{60}$ molecules on $\beta$-$\mathrm{W}$ reduces the effective Gilbert damping by $\sim 15\mathrm{\%}$ in $\mathrm{CFB}/\beta$-$\mathrm{W}$/${\mathrm{C}}_{60}$ heterostructures. The antidamping is accompanied by a gigantic $\sim 115\mathrm{\%}$ enhancement in the spin-pumping-induced output voltage owing to molecular hybridization. The noncollinear density-functional-theory calculations confirm the long-range enhancement of the SOC of $\beta$-$\mathrm{W}$ upon the chemisorption of ${\mathrm{C}}_{60}$ molecules, which in turn can also enhance the SOC at the $\mathrm{CFB}/\beta$-$\mathrm{W}$ interface in $\mathrm{CFB}/\beta$-$\mathrm{W}$/${\mathrm{C}}_{60}$ heterostructures. The combined amplification of the bulk as well as the interfacial SOC upon molecular hybridization stabilizes the antidamping and enhanced spin-to-charge conversion, which can pave the way for the fabrication of power-efficient spintronic devices.