Application of an intense THz field copropagating with the main driving pulse breaks the field symmetry and promotes generation of even optical harmonics naturally forbidden in centrosymmetric crystals. We show that the transient nature of the symmetry switching confines efficient even harmonic generation to the regions close to the crystal surfaces in the case when the length of the crystal significantly exceeds the coherence length of the process. In such a case, efficient generation of the absorption-limited and the absorption-free even harmonics appears to be separated in time by the walk-off time of THz and near-IR driving pulse due to the strong absorption of the above-band-gap harmonics generated close to the front surface of the crystal. By using a THz field with external strength of 7 MV/cm, we demonstrate generation of second and fourth harmonics of a near-IR $1.65\text{−}\mu \mathrm{m}$ driver with efficiency of ${10}^{-4}$ and ${10}^{-7}$ separated by 3.2 ps in 1.4-mm-long CdS crystal. Application of the extreme THz field leads to a comparable intensity of the even and odd harmonics showing the potential of bichromatic pumping for creation of a synthesized medium with controllable nonlinear properties.

This study delves into the interaction between a monolayer of molybdenum disulfide (${\mathrm{MoS}}_2$) and a single perylene orange (PO) molecule, representative of inorganic and organic semiconductor materials, respectively. Investigation of the amalgamation of these materials under mechanical strains reveals significant alterations in the electronic properties of the ${\mathrm{MoS}}_2/\mathrm{PO}$ interface. Tensile strain induces a reduction in the bandgap, while compressive strain initially engenders an increase, followed by a subsequent decrease. Notably, ${\mathrm{MoS}}_2$ undergoes a transition from a direct to an indirect bandgap under both stretching and compression conditions. Remarkably, under specific compression conditions, the ${\mathrm{MoS}}_2/\mathrm{PO}$ system manifests a transition between type II and type I band alignments. The detailed analysis of a range of strain magnitudes yields profound insights into the behavior of ${\mathrm{MoS}}_2$ and ${\mathrm{MoS}}_2/\mathrm{PO}$ systems under mechanical strain, with potential implications for nano- and optoelectronics applications.

Gaussian basis sets are highly appealing for large-scale electronic structure calculations of quantum dots (QDs) due to their smaller basis set size and ease of computing multicenter integrals. Yet the prevailing Gaussian basis sets are commonly designed for atoms or molecules and contain highly diffusive functions, which are not transferable for electronic structure calculations of large-size QDs and bulk solids, thus lacking dimensional-consistency. Herein, we resolve this issue by exploring an inverse design strategy for novel Gaussian basis sets, i.e., we design Gaussian basis set for periodic bulk solid and inversely apply it to confined nanostructures. The key to success is to optimize the exponents of polarization functions in the Gaussian basis set to best reproduce the reference lattice constant and band structure of a given bulk solid calculated by using the plane-wave basis set. While applying this strategy to ten traditional semiconductors of groups IV, II-VI, and III-V, the resulting novel Gaussian basis sets exhibit excellent transferability to nanostructured materials, including a two-dimensional (2D) quantum well (QW) down to the monolayer limit and zero-dimensional (0D) QD down to ultrasmall sizes ($\sim 1\mathrm{nm}$), thus achieving the desired dimensional-consistency. Meanwhile, the resulting relative error in the lattice constant or averaged bond length is mostly below 2%, and the band-gap error below 0.1 eV compared to plane-wave references, thus offering competing accuracy. This work provides an alternative pathway of designing novel Gaussian basis sets capable of treating periodic solids and confined nanomaterials on an equal footing, which is broadly applicable for highly accurate basis set optimization of the existing Gaussian basis sets.

We present a new strategy to amplify the spin-orbit coupling (SOC) effect in a simple metal-based polar superlattices with light elements to create a giant Rashba SOC up to ${\alpha }_R\approx 3.80$ eV Å with negative sign. First-principles calculations demonstrate that the giant ${\alpha }_R$ originates from optimizing the internal electric field, which comes from the polarity, charge transfer, and superlattice systems. This strategy provides an effective way to design a next-generation spintronics device without the use of heavy elements.

Triple-Q density waves are commonly found in various materials, such as charge density waves in transition metal dichalcogenides and spin density waves (skyrmion crystals) in B20 compounds. Compared to single-Q density waves, triple-Q density waves possess an additional internal degree of freedom, a phase shift arising from the phase of the order parameters, in addition to the translations of the density waves. In this study, we systematically investigate the significant effects stemming from both triple-Q charge density waves and spin density waves order parameters, with particular emphasis on potential phase shifts. We demonstrate that these phase shifts play a crucial role in influencing the interference effects of triple-Q density waves on electronic states. Due to such interference, the band geometry in the momentum space becomes nontrivial at the hot spots, where multiband Dirac-type fermions are induced near the Fermi energy. Furthermore, we explicitly establish that the nontrivial band geometry, combined with symmetry breaking induced by phase shifts, leads to a variety of intriguing linear and nonlinear responses.

The synthesis of $\mathrm{Sr}{\mathrm{B}}_3{\mathrm{C}}_3$ and the research on its analogs demonstrate the high-temperature superconductivity of ternary metal-boron-carbon clathrates at ambient or moderate pressure. Here, we explore the stability and superconductivity of calcium-doped and boron-substituted type-VIII carbon clathrates $\mathrm{C}{\mathrm{a}}_4{\mathrm{B}}_x{\mathrm{C}}_{23-x}$ ($x=0-23$) at 25–100 GPa. Based on the structural features and density functional theory (DFT) calculations, we screened 8 388 608 possible B-decorated structures and ultimately identified five thermodynamically metastable superconductors. Among them, $\mathrm{C}{\mathrm{a}}_4{\mathrm{B}}_{10}{\mathrm{C}}_{13}$ (space group $I\overline{4}3m$) exhibited the highest $T_c$ of $\sim 101-109$ K, between 25 and 100 GPa. The high $T_c$ of $\mathrm{C}{\mathrm{a}}_4{\mathrm{B}}_{10}{\mathrm{C}}_{13}$ originates from strong electron-phonon coupling caused by phonon softening and high density of states at the Fermi level. Our findings suggest that metal-doped and boron-substituted carbon clathrates are promising high-temperature superconductors at moderate pressure.

The temperature-dependent $1/f$ noise is reported for AgMn (12 at. %) thin films with multiple thicknesses ranging from 15 to 80 nm. A significant increase in the noise magnitude occurs in the spin-glass state. Analysis of the temperature-dependent exponent provides information on the energy barrier distribution and height, which in turn are related to the spin-glass coherence length. We compare our results with those obtained previously on CuMn (13.5 at. %) thin films with similar thicknesses. We observe a similar trend of the increase of the barrier height with respect to thickness, but with relatively lower values for the AgMn barriers as compared to CuMn.

X-ray photon correlation spectroscopy (XPCS) is a powerful technique for analyzing particle systems by investigating their dynamics in suspensions across a broad range of temporal and spatial scales. This is done by illuminating samples with coherent x-ray beams and calculating the correlation function of the obtained x-ray scattering images. XPCS is uniquely suited for studying Brownian dynamics, consisting of translational and rotational diffusion. While traditional XPCS image analysis techniques can extract translational diffusion components, they are unable to estimate rotational diffusion coefficients. Here, we introduce a methodology that combines the angular-temporal cross-correlation analysis and a algorithmic framework called Multi-Tiered Estimation for Correlation Spectroscopy in 3D for estimating three-dimensional rotational diffusion coefficients from XPCS images of three-dimensional particle systems. We demonstrate our methodology for extracting rotational diffusion coefficients from XPCS data by applying it to simulated noisy x-ray images of systems of crossing nanotubes and proteins that evolve under translational and rotational Brownian motion for different diffusion rates. Our results show that our approach determines rotational diffusion coefficients within a few percent error.

Two-dimensional (2D) magnetic materials empowered with nontrivial band topology may lead to the emergence of exotic quantum states with significant application potentials. Here, we predict a family tree of 2D magnetic materials with tunable topological properties, starting from the parental materials of $\mathrm{Cr}{\mathrm{I}}_3$ and $\mathrm{CrB}{\mathrm{r}}_3$. The underlying design principle is that by substituting the alternating sites of the Cr honeycomb lattice sandwiched between the halogen layers with V or Mn, the parental materials of trivial ferromagnetic insulators are ripe to be converted into topological systems. Specifically, our first-principles calculations show that due to the elegant interplay between band-gap narrowing and spin-orbital coupling, $\mathrm{Cr}{\mathrm{I}}_3$ branches into high-temperature quantum anomalous Hall insulators of $\mathrm{CrV}{\mathrm{I}}_6$ and $\mathrm{CrMn}{\mathrm{I}}_6$ with different topological invariants, while $\mathrm{CrB}{\mathrm{r}}_3$ branches into topological half metals of $\mathrm{CrVB}{\mathrm{r}}_6$ and $\mathrm{CrMnB}{\mathrm{r}}_6$. Those 2D magnets are also shown to be easily exfoliated from their bulk counterparts. The present study is thus geared to advance the field of 2D magnetic materials into the topologically nontrivial realm.

Recent experiments show that the ground state of some layered materials with localized moments is in close proximity to the Kitaev spin liquid, calling for a proper model to describe the measurements. The Kitaev-Hubbard (KHu) model is the minimal model that captures the essential ingredients of these systems; it yields the Kitaev-Heisenberg spin model at the strong coupling limit and contains the charge fluctuations present in these materials as well. Despite its relevance, the phase diagram of the KHu model has not been rigorously revealed yet. In this work, we study the full phase diagram of the KHu model using the ${\mathbb{Z}}_2$ slave-spin mean-field theory as well as the auxiliary field quantum Monte Carlo on rather large systems and at low temperatures. The Mott transition is signaled by a vanishing quasiparticle weight evaluated using the slave-spin construction. Moreover, we demonstrate that there are multiple magnetic phase transitions within the Mott phase including magnetically ordered phases and most notably a quantum spin liquid phase for $1.0\lesssim t^{\prime }/t\lesssim 1.11$ at $U/t=5$.

Following long-standing predictions associated with hydrogen, high-temperature superconductivity has recently been observed in several hydride-based materials. Nevertheless, these high-$T_c$ phases only exist at extremely high pressures, and achieving high transition temperatures at ambient pressure remains a major challenge. Recent predictions of the complex hydride ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ may help overcome this challenge with calculations of high-$T_c$ superconductivity ($65\mathrm{K}<T_c<170\text{K}$) in a material that is stable at atmospheric pressure. In this paper, the synthesis of ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ was targeted over a broad range of $P\text{−}T$ conditions, and the resulting products were characterized using x-ray diffraction (XRD) and vibrational spectroscopy, in concert with first-principles calculations. The results indicate that the charge-balanced complex hydride ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$ is more stable over all conditions tested up to approximately 28 GPa. The resulting hydride is isostructural with the predicted superconducting ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ phase except for a single hydrogen vacancy, which shows a favorable replacement barrier upon insertion of hydrogen into the lattice. Bulk ${\mathrm{Mg}}_2{\mathrm{IrH}}_5$ is readily accessible at mild $P\text{−}T$ conditions and may thus represent a convenient platform to access superconducting ${\mathrm{Mg}}_2{\mathrm{IrH}}_6$ via nonequilibrium processing methods. Finally, the critical factors influencing the calculated range of superconducting transition temperatures for this material are discussed.

Non-Hermiticity is prevalent across various branches of physics, giving rise to a range of unique phenomena with no Hermitian counterparts. Recently, the knot topology and braiding properties of non-Hermitian bands have been experimentally observed in systems such as coupled ring resonators with synthetic dimensions, cavity optomechanical systems, and more. However, these observations have been limited to one-dimensional topological manifolds (string knots) in three-dimensional (3D) space, leaving unanswered the question of whether higher-dimensional topological manifolds in non-Hermitian bands can be realized. In this work, we present the construction of two distinct four-dimensional (4D) topological manifolds—the Klein bottle and spun trefoil knot—formed by two-dimensional (2D) complex non-Hermitian bands in synthetic energy space. Moreover, the sinusoidal torus and self-intersected Roman surface can appear in the 3D projection of these 4D non-Hermitian topological manifolds. Experimentally, we design and fabricate reconfigurable electric circuits to reconstruct 2D non-Hermitian bands and observe these non-Hermitian 4D topological manifolds. The strong alignment between our theoretical predictions and experimental results paves the way for generating surface topologies in non-Hermitian bands and opens avenues for exploring high-dimensional topological manifolds in artificial systems.

Superconducting junctions are essential building blocks for quantum hardware, and their fundamental behavior remains a highly active research field. The behavior of generic junctions is conveniently described by Beenakker's determinant formula, linking the subgap energy spectrum to the scattering matrix characterizing the junction. In particular, the gap closing between bound and continuum states in short junctions follows from unitarity of the scattering matrix, and thus, from probability conservation. In this work, we critically reassess two assumptions: that scattering in short junctions is approximately energy-independent and dominated by planar channels. We argue that strongly energy-dependent scattering follows from finite dispersion of the conductor electrons even when they spend little time within the scattering region, and show that evanescent modes play a central role when cross-channel scattering is important. By generalizing Beenakker's equation and performing a mapping to an effective Hamiltonian, we show that the gap closing is linked to a chiral symmetry. While finite energy dependence in the scattering breaks the chiral symmetry, we show two distinct mechanisms preserving the gap closing, each connected to new types of constraints on energy-dependent scattering matrices beyond unitarity. If the dispersive mode is planar, the gap closing is still preserved through a time-dependent probability conservation analysis of the scattering process. If the dispersive channel is evanescent, we derive a constraint which, notably, cannot follow from probability conservation. We thus demonstrate that Andreev physics reveal a much wider variety of properties of normal-metal scattering than commonly expected. We expect that our findings will have an impact on the dissipative behavior of driven junctions, and offer a different perspective on fundamental properties of scattering matrices.

$M$-type hexaferrite ${\mathrm{BaFe}}_{12}{\mathrm{O}}_{19}$ has recently been identified as a quantum paraelectric with a triangular lattice, exhibiting a low-temperature dielectric plateau attributed to quantum fluctuations. A possible quantum-dipole-liquid ground state has also been proposed. To suppress these quantum fluctuations and approach a quantum critical point, we have tuned the material's quantum paraelectricity through three methods: (i) ${}^{57}\mathrm{Fe}$ isotope substitution, (ii) in-plane compressive strain, and (iii) hydrostatic pressure. We find that 95% ${}^{57}\mathrm{Fe}$ substitution and in-plane strain are more effective in driving the system toward the critical region, enhancing both the relative permittivity and the low-temperature peak. In contrast, hydrostatic pressure moves the system away from the quantum critical point, gradually suppressing the magnitude and plateau feature of the relative permittivity. Our findings highlight the potential of $M$-type hexaferrites for investigating quantum critical phenomena.

In this study, we investigate the transition metal dichalcogenide (TMD) ${\mathrm{NbS}}_2$ with a hypothetical $1T$ structure. This material not only closely resembles the crystal structures of $1T\text{−}{\mathrm{TaS}}_2$ and $1T\text{−}{\mathrm{TaSe}}_2$ but also favors a $\sqrt{13}\times \sqrt{13}$ charge density wave (CDW) configuration, characterized by a single unpaired $4d$ electron in each star-of-David (SoD). This configuration results in an ultraflat half-filled band crossing the Fermi level. The electrons in this band are spatially distributed over the 13 Nb atomic sites within each SoD, consistent with the formation of the CDW. Due to the narrow bandwidth, electrons in this band experience significant electronic correlations, encompassing both local and nonlocal components. Our findings indicate that the nonlocal correlations, which are typically significant in systems comprising transition metal cluster units, contribute to the insulating ground state of $1T\text{−}{\mathrm{NbS}}_2$ in two distinct aspects. Firstly, they further stabilize the $\sqrt{13}\times \sqrt{13}$ CDW among several competing structure instabilities. Secondly, they induce a cluster Mott state. Our conclusions are likely applicable to a broad range of $1T$ TMD monolayer materials, providing new insights into the nature of their insulating ground states.

Recently, the $\alpha \text{−}{T}_3$ model, whose specific lattice structure is determined by the parameter $\alpha$, has attracted broad attention due to the intriguing flat band. Under irradiation of an off-resonant circularly polarized light (CPL), the Floquet $\alpha \text{−}{T}_3$ model experiences a topological phase transition, as $\alpha$ varies from 0 to 1, due to the distortion of the flat band. Interestingly, it is found that the phase boundary becomes tunable by the CPL strength if nonzero on-site energy is considered, not a constant ${\alpha }_c=1/\sqrt{2}$ as reported in previous literatures. To characterize the topological phase transition, we investigate the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between magnetic impurities. It is interestingly found that a sharp dip structure in the RKKY magnitude can well ascertain the boundary of the topological phase transition, and different topological phases can be distinguished by the RKKY oscillation behaviors. Thus, the signatures of the RKKY interaction could provide us an alternative method to characterize the topological phase transition, different from the conventional electrical or optical means.

Breaking lattice symmetry is crucial for generating a nonzero Berry curvature. While manipulating twisting angles between adjacent layers has successfully broken lattice symmetry through strain field and generated nonzero Berry curvature, interlayer sliding in principle offers a promising alternative route. However, realizing uniform interlayer sliding faces experimental challenges due to its energetic instability. In this work, we introduce an experimentally feasible method, using a corrugated substrate to induce an inhomogeneous but energetically more stable interlayer sliding in multilayer graphene. Our simulations demonstrate that inhomogeneous interlayer sliding produces a sizable Berry curvature dipole, which can be further tuned by varying the interlayer sliding distances and potential differences. The resulting Berry curvature dipole magnitude is remarkably up to 100 times greater than the maximum displacement involved in the inhomogeneous sliding. Our results highlight inhomogeneous interlayer sliding as a viable and effective method to induce a significant Berry curvature dipole in graphene systems and propose the experimentally feasible way to realize it.

A Josephson junction, formed between two phase-biased superconductors and a normal metal, hosts a discrete spectrum of Andreev bound states (ABS). In this paper, we develop a theory for long ballistic Andreev interferometers in two-dimensional metals. We consider three frameworks in our theoretical analysis: (i) perturbation theory in the tunneling amplitudes, (ii) nonperturbative transport theory, and (iii) physically motivated approximations to visualize the conductance maps in the (flux, voltage) plane. We find a nonstandard phase-sensitive Andreev reflection process in ballistic interferometers that couples the supercurrent to the nonequilibrium populations of the ABS in the normal region. Furthermore, our model shows that conductance spectroscopy follows the spectrum of the ABS in long junctions. We also discuss our results in terms of the semiclassical theory, the classical orbits being the one-dimensional Andreev tubes. Our theoretical analysis captures the results of recent experiments by the Penn State and Harvard groups.

Periodically driven systems offer a perfect breeding ground for out-of-equilibrium engineering of topological boundary states at zero energy (0 mode), as well as finite energy ($\pi$ mode), with the latter having no static analog. The Floquet operator and the effective Floquet Hamiltonian, which encapsulate the stroboscopic features of the driven system, capture both spectral and localization properties of the 0 and $\pi$ modes but sometimes fail to provide complete topological characterization, especially when 0 and $\pi$ modes coexist. In this work, we utilize the spectral localizer, a powerful local probe that can provide numerically efficient, spatially local, and energy-resolved topological characterization. In particular, we apply the spectral localizer to the effective Floquet Hamiltonian for driven one- and two-dimensional topological systems with no or limited symmetries and are able to assign topological invariants, or local markers, that characterize the 0- and the $\pi$-boundary modes individually and unambiguously. Due to the spatial resolution, we also demonstrate that the extracted topological invariants are suitable for studying driven disordered systems and can even capture disorder-induced phase transitions.