Coherent interactions between different magnetic excitations can lead to formation of magnon band gaps and hybrid magnon modes, which can find their applications in magnonic devices and coherent information processing. In this work, we probe the intrinsic magnon band gap of a layered hybrid perovskite antiferromagnet by its strong coupling to a superconducting resonator. The pronounced temperature tunability of the magnon band gap location allows us to set the photon mode within the gap, leading to a reduction of effective magnon-photon coupling and eventually the disappearance of magnon-photon hybridization. When the resonator mode falls into the magnon band gap, the resonator damping rate increases due to the nonzero coupling to the detuned magnon mode. This allows for quantification of the magnon band gap using an analytical model. Our work brings new opportunities in controlling coherent information processing with quantum properties in complex magnetic materials.

We report extreme-ultraviolet high-harmonic generation (HHG) from liquid isopropanol, extending up to 50 eV, when using 1800-nm carrier envelope phase stable pulses of 1.8 cycles with intensities below the laser breakdown threshold. We study the mechanism of the harmonic emission through its dependence on the driving field and find it to be consistent with a strong-field recombination mechanism. We explore the role of scattering from neighboring molecules in simulations using empirical cross-section data. We find that these simulations, within a full propagation calculation, provide good quantitative agreement with the measured intensity-dependent harmonic cutoffs and demonstrate that HHG emission in the liquid phase can be used to corroborate ultrafast electron-scattering processes.

Our previous study observed the localization-delocalization transition and critical quantum fluctuations of the local density of states (LDOS) on the structurally disordered two-dimensional (2D) semiconductor $\mathrm{Mo}{\mathrm{S}}_2$. This transition corresponds to the metal-insulator transition (MIT) reported in transport measurements. The structural disorder in $\mathrm{Mo}{\mathrm{S}}_2$ caused curvature-induced band gap fluctuations, leading to charge localization and unusual band edge flattening through doping. The critical behavior for the MIT was analyzed using autocorrelation and multifractality of LDOS mapping results. However, the effect of structural disorder on critical points has not been fully explored. Here, we systematically investigated the impact of structural disorder on band tail formation and critical doping concentration by examining the radial-averaged autocorrelation and multifractality of LDOS in 2D semiconductors. Our finding indicates that the radial-averaged autocorrelation and multifractality of LDOS characterize the band tail ranges and band edge flattening in disordered 2D semiconductors. Decaying regions in the radial-averaged autocorrelation profile and first-order derivative of singularity peak positions determine band tail ranges. Increased structural disorder led to larger band tail widths near valence and conduction band edges, while the doping-induced band edge flattening altered band tail widths for each valence and conduction band. As the band edge is flattened due to doping, the LDOS map near the critical energy becomes uniform, exhibiting a divergence in the localization length. The average value of conduction and valence band tail widths remained almost constant regardless of doping control, serving as a representative value for the degree of structural disorder. For the MIT, we found that the critical doping concentration depends on the degree of structural disorder in 2D semiconductors. Our findings provide valuable insights into the fundamental physics of structurally disordered 2D semiconductors in relevance to quantum phase transitions, which could have important implications for designing and optimizing electronic/optoelectronic devices based on 2D materials.

We report on the realization of a graphene billiard with a fourfold rotational symmetry, which has the shape of a billiard with chaotic classical dynamics. The eigenstates are separated according to their transformation properties under rotation by $\frac{\pi }{2}$ into four symmetry classes. These subspectra can be divided into regions around the band edges, where they are governed by the nonrelativistic Schrödinger equation, and a region of low energy-excitations around zero energy, that exhibit a linear dispersion relation and are described by the relativistic Dirac equation for a spin-1/2 quasiparticle. We analyze the spectral properties in these parts and compare them with those for nonrelativistic quantum billiards and relativistic neutrino billiards. In both regions the spectral properties conform with those of nonrelativistic quantum billiards of corresponding shape. Furthermore, we compute wave functions in configurational space and momentum distributions in quasimomentum space and find that the first Brillouin zone is formed by two hexagonal ones that are rotated by ${30}^{\circ }$ with respect to each other. Namely, in the relativistic region the momentum distributions are localized at or near the 12 Dirac points at the corners of these hexagons. At the Van Hove singularities, which separate the nonrelativistic and relativistic regions, they are localized along the isofrequency lines that connect the six saddle points at the centers between two corners for each hexagon. We propose a design of a microwave photonic crystal for the experimental modeling of graphene billiards with fourfold symmetry and present numerical results for its properties.

Reaching an ever shorter duration of isolated attosecond pulses (IAPs) is an ongoing mission in attosecond science. Wide usage of long-wavelength driving lasers has greatly broadened bandwidths for generating IAPs. We propose a strategy to further exploit the ability of a long-wavelength laser in producing short IAPs. We introduce a scaling relationship between IAP duration and a trajectory parameter that is associated with the classical cutoff trajectory of high-order harmonic generation (HHG) in gases. This trajectory parameter can facilitate in shortening IAP duration by shaping laser waveform. We demonstrate the effectiveness of our methods with calculations of HHG from Ne by solving the time-dependent Schrödinger equation. A genetic algorithm is used in search for laser parameters. Macroscopic effects in HHG and attopulse generation are investigated. Our results show that increasing laser intensity and using an additional short-wavelength (e.g., deep ultraviolet) laser pulse together with the infrared are effective ways to shorten IAP duration (from 76 to $47\mathrm{as}$ in our example), for which insightful physical explanations are provided.

MnP is a metal that shows successive magnetic transitions from paramagnetic to ferromagnetic and helical magnetic phases at ambient pressure with decreasing temperature. With applied pressure, the magnetic transition temperatures decrease and superconductivity appears around 8 GPa where the magnetic order is fully suppressed and the quantum critical behavior is observed. These results suggest that MnP is an unconventional superconductor in which magnetic fluctuations may be relevant to the superconducting pairing mechanism. In order to elucidate the magnetic ground state adjacent to the superconducting phase first discovered in Mn-based materials, high-pressure neutron diffraction measurements have been performed in hydrostatic pressure up to 7.5 GPa. The helical magnetic structure with the propagation vector along the $b$ axis, reported previously at 3.8 GPa, was found to be robust up to 7.5 GPa. First-principles and classical Monte Carlo calculations have also been performed to understand how the pressure-driven magnetic phase transitions are coupled with change of the exchange interactions. The calculations, which qualitatively reproduce the magnetic structures as a function of pressure, suggest that the exchange interactions change drastically with applied pressure and the further-neighbor interactions become more influential at high pressures. Combining the experimental and theoretical results, we describe the detail of exchange interactions in the vicinity of the superconducting phase, which is critical to understand the pairing mechanism of the unconventional superconductivity in MnP.

Several quantum protocols, with applications ranging from fundamental studies to cryptographic scenarios, can be enhanced through the generation and manipulation of quantum states that belong to high-dimensional Hilbert spaces. For this reason, it is worth devoting efforts to find more efficient methods for complex qudit-state generation. One-dimensional quantum walks have proved to be efficient and versatile platforms for the engineering of such complex states. Hitherto, however, using their two-dimensional counterpart for this task has remained unexplored. In this paper, we consider two-dimensional quantum walk evolution as a tool for the generation of high-dimensional qudit states. We theoretically prove that a suitable change of the coin operators at each step permits the generation of a subset of qudit states by using less resources with respect to the one-dimensional counterpart. Then, we successfully generate qudit states by exploiting two-dimensional quantum walks on an experimental photonic platform. The walker position is encoded on discrete sets of optical modes carrying quantized amounts of transverse momentum and the mode couplings are actively controlled via liquid-crystal devices. The obtained results provide insight into qudit generation for applications in quantum communication and quantum cryptography.

The effect of branches on the linear rheology of entangled wormlike micelle solutions is modeled by tracking the diffusion of micellar material through branch points. The model is equivalent to a Kirchhoff circuit model with the sliding of an entangled branch along an entanglement tube due to the constrained diffusion of micellar material analogous to the flux of current in the Kirchhoff circuit model. When combined with our previous mesoscopic pointer algorithm for linear micelles that can both break and fuse, the model adds a branch sprouting process and therefore enables simulation of the dynamics of structural change and stress relaxation in ensembles of micelle clusters of different topologies. Applying this model to study the relationships between fluid rheology and microstructure of micelles, our results show that branches change the scaling law exponents for viscosity vs micelle strand length. This contrasts with the longstanding hypothesis that branches affect viscosity and relaxation in the same way that micelle ends do. The model also suggests a process for inferring branching density from salt-dependent linear rheology. This is exemplified by mixed surfactant solutions over a range of salt concentrations with flow properties measured using both mechanical rheometry and diffusing wave spectroscopy. By elucidating the connection between the branching characteristics, such as strand length and branching density, with the nonmonotonic variation of solution viscosity, the above model provides a powerful tool to help extract branching information from rheology.

Wires made of topological insulators (TI) are a promising platform for searching for Majorana bound states. These states can be probed by analyzing the fractional ac Josephson effect in Josephson junctions with the TI wire as a weak link. An axial magnetic field can be used to tune the system from trivial to topologically nontrivial. Here, we investigate the oscillations of the supercurrent in such wire Josephson junctions as a function of the axial magnetic field strength and different contact transparencies. Although the current flows on average parallel to the magnetic field we observe $h/2e, h/4e$, and even $h/8e$ periodic oscillations of the supercurrent in samples with lower contact transparencies. Corresponding tight-binding transport simulations using a Bogoliubov–de Gennes model Hamiltonian yield the supercurrent through the Josephson junctions, showing in particular the peculiar $h/4e$-periodic oscillations observed in experiments. A further semiclassical analysis based on Andreev-reflected trajectories connecting the two superconductors allows us to identify the physical origin of these oscillations. They can be related to flux-enclosing paths winding around the TI nanowire, thereby highlighting the three-dimensional character of the junction geometry compared to common planar junctions.

Particle formation represents a central theme in various branches of physics, often associated to confinement. Here we show that dynamical hadron formation can be spectroscopically detected in an ultracold atomic setting within the most paradigmatic and simplest model of condensed matter physics, the repulsive $\text{SU}\left(N\right)$ Hubbard model. By starting from an appropriately engineered high-energy initial state of the strongly interacting $\text{SU}\left(3\right)$ Hubbard model, doublons (mesons) and trions (barions) naturally emerge during time evolution and thermalize to a negative temperature quantum gas, as demonstrated by extensive one-dimensional simulations and exact diagonalization calculations. For strong interactions, trions become heavy and attract each other strongly. Their residual interaction with doublons generates doublon diffusion, as captured by the evolution of the equal time density correlation function. Although our numerical calculations are performed on one-dimensional chains, many of our conclusions extend to a large variety of initial conditions and hold for other spatial dimensions and all $\mathrm{SU}(N>2$) Hubbard models.

A quantum integrable system slightly perturbed away from integrability is typically expected to thermalize on timescales of order $\tau \sim {\lambda }^{-2}$, where $\lambda$ is the perturbation strength. We here study classes of perturbations that violate this scaling, and exhibit much longer thermalization times $\tau \sim {\lambda }^{-2\ell }$ where $\ell >1$ is an integer. Systems with these “weak integrability breaking” perturbations have an extensive number of quasiconserved quantities that commute with the perturbed Hamiltonian up to corrections of order ${\lambda }^{\ell }$. We demonstrate a systematic construction to obtain families of such weak perturbations of a generic integrable model for arbitrary $\ell$. We then apply the construction to various models, including the Heisenberg, XXZ, and XYZ chains, the Hubbard model, models of spinless free fermions, and the quantum Ising chain. Our analytical framework explains the previously observed evidence of weak integrability breaking in the Heisenberg and XXZ chains under certain perturbations.

A minimalist model of microphysical properties in cloudy Rayleigh-Bénard convection is developed based on mass and number balances for cloud droplets growing by vapor condensation. The model is relevant to a turbulent mixed-layer in which a steady forcing of supersaturation can be defined, e.g., a model of the cloudy boundary layer or a convection-cloud chamber. The model assumes steady injection of aerosol particles that are activated to form cloud droplets, and the removal of cloud droplets through sedimentation. Simplifying assumptions include the consideration of mean properties in steady state, neglect of coalescence growth, and no detailed representation of the droplet size distribution. Closed-form expressions for cloud droplet radius, number concentration, and liquid water content are derived. Limits of fast and slow microphysics, compared to the turbulent mixing time scale, are explored, and resulting expressions for the scaling of microphysical properties in fast and slow regimes are obtained. Scaling of microphysics with layer thickness is also explored, suggesting that liquid water content and cloud droplet number concentration increase, and mean droplet radius decreases with increasing layer thickness. Finally, the analytical model is shown to compare favorably to solutions of the fully-coupled set of governing ordinary differential equations that describe the system, and the predicted power law for liquid water mixing ratio versus droplet activation rate is observed to be consistent with measurements from the Pi convection-cloud chamber.

Nonperturbative resonant multiphoton ionization $(1+1)$ is studied using the resolvent operator technique. Scaling parameters for effective two-level Hamiltonians are computed for hydrogen and helium atoms to provide a quantitative description of Rabi oscillations at XUV wavelengths, which were recently observed using a seeded free-electron laser [S. Nandi et al., Nature (London) 608, 488 (2022)]. The resulting photoelectron spectra exhibit a range of Autler-Townes doublets, which are studied for different intensities, detunings, and interaction times. We identify a photoelectron signature that originates from stabilization against ionization of helium atoms interacting with intense circularly polarized XUV light. Thus, our study shows how it is possible to test the prediction of dressed-atom stabilization by Beers and Armstrong [B. L. Beers and L. Armstrong, Phys. Rev. A 12, 2447 (1975)], without the demanding requirement of atomic saturation in the time domain.

We present a minimal model of ferroelectric large polarons, which are suggested as one of the mechanisms responsible for the unique charge transport properties of hybrid perovskites. We demonstrate that short-ranged charge–rotor interactions lead to long-range ferroelectric ordering of rotors, which strongly affects the carrier mobility. In the nonperturbative regime, where our theory cannot be reduced to any of the earlier models, we reveal that the polaron is characterized by large coherence length and a roughly tenfold increase of the effective mass as compared to the bare mass. These results are in good agreement with other theoretical predictions for ferroelectric polarons. Our model establishes a general phenomenological framework for ferroelectric polarons providing the starting point for future studies of their role in the transport properties of hybrid organic-inorganic perovskites.