High-order Phases Research Articles

High-Order Topological Pumping on a Superconducting Quantum Processor.

High-order topological phases of matter refer to the systems of n-dimensional bulk with the topology of m-th order, exhibiting (n-m)-dimensional boundary modes and can be characterized by topological pumping. Here, we experimentally demonstrate two types of second-order topological pumps, forming four 0-dimensional corner localized states on a 4×4 square lattice array of 16 superconducting qubits. The initial ground state of the system at half-filling, as a product of four identical entangled 4-qubit states, is prepared using an adiabatic scheme. During the pumping procedure, we adiabatically modulate the superlattice Bose-Hubbard Hamiltonian by precisely controlling both the hopping strengths and on-site potentials. At the half pumping period, the system evolves to a corner-localized state in a quadrupole configuration. The robustness of the second-order topological pump is also investigated by introducing different on-site disorder. Our Letter studies the topological properties of high-order topological phases from the dynamical transport picture using superconducting qubits, which would inspire further research on high-order topological phases.

Fractal nature of high-order time crystal phases

Fractal nature of high-order time crystal phases

Suppressing High-Order Phase for Efficient Pure Red Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites are promising for the realization of spectrally stable pure red perovskite light-emitting diodes (PeLEDs) with a single iodide component, because they avoid the halide separation that red three-dimensional perovskites of mixed halides have faced. However, the distribution of high-order phases in solution-processed quasi-2D perovskite films causes the spectral shift away from the pure red region. Here, we introduced a simple approach of adding excessive ligand combinations to redistribute the phase distribution of quasi-2D perovskite and to inhibit the high-order phase. Appropriate excess organic ligands will not affect charge injection but will keep the efficient energy funneling and passivate the defect. The narrowed phase distribution reduced the band tail state and restrained reverse charge transfer, resulting in enhanced radiation recombination. We obtained efficient and spectrally stable pure red PeLEDs at 638 nm (approaching the Rec. 2020 specification) with a peak EQE of 11.8% and maximum luminance of 1688 cd/cm2. This study provides guidance for future developments of highly efficient pure red PeLEDs.

Floquet Quadrupole Photonic Crystals Protected by Space-Time Symmetry

High-order topological phases, such as those with nontrivial quadrupole moments [1,2], protect edge states that are themselves topological insulators in lower dimensions. So far, most quadrupole phases of light are explored in linear optical systems, which are protected by spatial symmetries [3] or synthetic symmetries [1,2,4--7]. Here we present Floquet quadrupole phases in driven nonlinear photonic crystals that are protected by space-time screw symmetries [8]. We start by illustrating space-time symmetries by tracking the trajectory of instantaneous optical axes of the driven media. Our Floquet quadrupole phase is then confirmed in two independent ways: symmetry indices at high-symmetry momentum points and calculations of the nested Wannier bands. Our Letter presents a general framework to analyze symmetries in driven optical materials and paves the way to further exploring symmetry-protected topological phases in Floquet systems and their optoelectronic applications.

Translational Motion Compensation for Maneuvering Target Echoes With Sparse Aperture Based on Dimension Compressed Optimization

Translational motion compensation for maneuvering targets is a challenging step in inverse synthetic aperture radar (ISAR) imaging. On one hand, nonuniform translational motion and rotational motion of maneuvering targets result in nonlinear bending of the range profile and create high-order slow time phases. On the other hand, radar cross section (RCS) fluctuation of targets may cause a sparse aperture and, therefore, sharply weakens the correlation between the pulses. Under this condition, traditional methods of translational motion compensation are sometimes difficult to get ideal results. Therefore, we propose an effective and novel method to achieve translational motion compensation for maneuvering targets with sparse aperture. In this method, the translational and rotational motions are modeled as cubic polynomial and quadratic polynomial, respectively. Based on this model, we use the echo to construct a 1-D optimization to estimate all translational parameters simultaneously and use the root-mean-square prop-momentum gradient descent (RMSprop-MGD) algorithm to solve the optimization to maintain the accuracy of parameter estimation. Finally, we use those translational parameters to compensate for the translational motion. Since this method converts the multiparameter optimization into a 1-D optimization, we named it dimension compressed optimization (DCO). Experimental results of the measured dataset prove that the proposed method is effective for full-aperture echoes, random sparse echoes, and block sparse echoes. Moreover, this method is robust under a low pulse sampling rate and low signal-to-noise ratio (SNR) environment.

Higher-order topological superconductors based on weak topological insulators

High-order topological phases host robust boundary states at the boundary of the boundary, which can be interpreted from their boundary topology. In this work, considering the interplay between superconductors and magnetic fields to gap the surface states of three-dimensional weak topological insulators, we show that second-order topological superconductors (TSCs) featuring helical or chiral Majorana hinge modes and third-order TSC featuring Majorana corner modes can be realized. Remarkably, the higher-order TSCs in our models can be attributed to their certain boundaries, surfaces, or hinges, which naturally behave as first-order TSC in DIII or D symmetry class. Correspondingly, these higher-order TSCs can be characterized by the boundary first-order topological invariants, such as surface Chern numbers or surface $Z_2$ topological invariants for surface TSCs. Our models can effectively capture the topology of iron-based superconductors with desired inverted band structures and superconducting pairings.

Generalized Pancharatnam-Berry Phase in Rotationally Symmetric Meta-Atoms.

Pancharatnam-Berry geometric phase has attracted enormous interest in subwavelength optics and electromagnetics during the past several decades. Traditional theory predicts that the geometric phase is equal to twice the rotation angle of anisotropic elements. Here, we show that high-order geometric phases equal to multiple times the rotation angle could be achieved by meta-atoms with highfold rotational symmetries. As a proof of concept, the broadband angular spin Hall effect of light and optical vortices is experimentally demonstrated by using plasmonic metasurfaces consisting of space-variant nanoapertures with C2, C3, and C5 rotational symmetries. The results provide a fundamentally new understanding of the geometric phase as well as light-matter interaction in nanophotonics.

Dielectric susceptibility of quantum Ising model: Simulated monoclinic A2BX4-type ferroelectrics

To explain the anomalous increase in the permittivity of monoclinic Rb2ZnI4 at low temperatures, the dielectric susceptibilities of modulated structures are calculated. A quantum Ising model is reduced from a lattice Hamiltonian by the mean field approximation and two-quantum-level approximation. The susceptibilities of modulated phases remain to be finite values at zero temperature as in the uniform ferroelectric phase, if the quantum effect works. Furthermore, the susceptibilities of the incommensurate and high-order commensurate phases increase at low temperatures. Since the ferroelectric phase can be realized with accompanying strong discontinuity, such an increase is different from the phenomenon during the lock-in transition. The phase diagram and the temperature dependence of susceptibility are calculated. With the selection of a proper set of parameters, the theoretical results agree qualitatively with experimental reports of (Rb1−xKx)2ZnI4.

Performance and stability of Ruddlesden-Popper La2NiO4+δ oxygen electrodes under solid oxide electrolysis cell operation conditions

Abstract Ruddlesden-Popper La2NiO4+δ (LNO) oxygen electrodes were investigated under solid oxide electrolysis cell (SOEC) operation conditions. The electrochemical performance of LNO was measured in both solid oxide fuel cell (SOFC) and SOEC modes at 750 °C in air. The results suggest that LNO oxygen electrodes exhibit high electrochemical activity and the processes related to oxygen adsorption, dissociation and diffusion dominate the oxygen evolution reaction on the electrodes. Electrical conductivity relaxation (ECR) measurements imply that LNO shows better oxygen surface exchange performance than conventional LSM and LSCF electrodes, because of its special crystal structure with flexible non-stoichiometric oxygen. Significant performance degradation was observed during polarization at 500 mA cm−2 and 750 °C in the SOEC mode for 48 h. XRD and XPS results confirmed that high-order Ruddlesden-Popper La3Ni2O7 and La4Ni3O10 phases have great contributions to the performance degradation of LNO oxygen electrodes related to anodic current polarization at 500 mA cm−2 and 750 °C.

Designing an ultrafast laser virtual laboratory using MATLAB GUIDE

In this work we present a virtual simulator developed using the MATLAB GUIDE environment based on the numerical resolution of the nonlinear Schrödinger equation (NLS) and using the split step method for the study of the spatial–temporal propagation of nonlinear ultrashort laser pulses. This allows us to study the spatial–temporal propagation of ultrafast pulses as well as the influence of high-order spectral phases such as group delay dispersion and third-order dispersion on pulse compression in time. The NLS can describe several nonlinear effects, in particular in this paper we consider the Kerr effect, cross-polarized wave generation and cubic–quintic propagation in order to highlight the potential of this equation combined with the GUIDE environment. Graphical user interfaces are commonly used in science and engineering teaching due to their educational value, and have proven to be an effective way to engage and motivate students. Specifically, the interactive graphical interfaces presented provide the visualization of some of the most important nonlinear optics phenomena and allows users to vary the values of the main parameters involved.

Generation of attosecond pulses in molecular nitrogen

We have generated attosecond pulse trains in an ensemble of randomly aligned nitrogen molecules. Measurements of the high-order harmonic relative phases and amplitudes allow us to reconstruct the temporal profile of the attosecond pulses. We show that in the considered spectral range, the latter is very similar to the pulse train generated in argon under the same conditions. We discuss the possible influence of the molecular structure in the generation process, and how it can induce subtle differences on the relative phases.

Correlations in the electronic properties of AlCuFe quasicrystals and high-order approximants: 57Fe Mössbauer, and 27Al and 65Cu nuclear magnetic resonance studies

We have investigated the local electronic properties and the atomic order in the Al100-x-yCuxFey phases using 57Fe Mössbauer as well as 27Al and 65Cu nuclear magnetic resonance (NMR) spectroscopies. We have studied samples along the existence domains of the icosahedral quasicrystalline (i-) and the high-order approximant phases, given by two close-lying parallel lines in the concentration diagram. In addition, we have also studied a series of intermediate concentrations situated between these lines and retained in a metastable i-phase by quenching. It is found that the 57Fe Mössbauer centre shift (isomer shift) and quadrupole splitting are linearly correlated with each other over the range of compositions and structures for all samples, which reveals systematic changes in the orbital occupations on Fe atoms with composition. In addition, it is found that the 27Al NMR average electronic shift follows this correlation. The results are discussed in terms of the hybridization of iron d states with the p and induced d states of Al. We have studied also a low-order cubic approximant phase containing Si as well as several non-approximant crystalline phases.

Effect of Hydrostatic Pressure on the Low-Temperature Phase Transitions in Rb2ZnBr4

The effect of hydrostatic pressure on the low-temperature structural phase transitions in Rb 2 ZnBr 4 has been investigated by the use of neutron scattering technique. The phase III-to-IV transition temperature, T 3 =112 K at atmospheric pressure, increased by applying pressure with a rate of 7 K/kbar. The phase IV-to-V transition temperature, T 4 =76 K at atmospheric pressure, decreased by applying pressure with a rate of -45 K/kbar. At high pressure, two high-order pseudo-commensurate phases characterized by wave vectors q z ≃ \(\frac{3}{11}\) and \(\frac{4}{15}\) were observed in addition to the already known commensurate ones of \(q_z=\frac{2}{7}\) and \(\frac{1}{4}\). The space group of the commensurate phase of \(q_z=\frac{1}{4}\) under high pressure was suggested to be P 2 1 / c 11 from the extinction rule.

Structural study of approximant phases of Al-Cu-Fe quasicrystals under high pressure

X-ray-diffraction experiments under high-pressure conditions were performed on two high-order approximant phases of the icosahedral Al-Cu-Fe quasicrystal. The rhombohedral and pentagonal samples were compressed under quasihydrostatic conditions up to 35 GPa. We did not observe clear evidence for structural transformation in either sample. The most prominent feature observed was a broadening of the Bragg peaks with increasing pressure. This behavior has been compared with the one exhibited by the parent related structure $(i\ensuremath{-}\mathrm{Al}\ensuremath{-}\mathrm{Cu}\ensuremath{-}\mathrm{Fe})$ and by a low-order cubic approximant structure $(\ensuremath{\alpha}\ensuremath{-}\mathrm{Al}\ensuremath{-}\mathrm{Cu}\ensuremath{-}\mathrm{Fe}\ensuremath{-}\mathrm{Si}).$ The modifications in the diffraction patterns are preserved after pressure release. The peak broadening has been related with the development of a particular phason-strain field. This kind of interaction is explained with the help of group-theoretical arguments proposed by Ishii.

Diamond and Diamond-like-Carbon Growth on Si (100) by Hot Filament-Assisted RF Plasma CVD

Diamond and diamond-like carbon (DLC) crystallites can be grown on a Si (100) substrate by hot filament-assisted RF plasma CVD in a low-vacuum (2-Torr) environment from C2H2 without using hydrogen. The deposition was carried out at 900°C onto the precleaned diamond polished Si (100) substrate. XRD and Raman spectra revealed the presence of diamond, graphite, lonsdaleite, and high-order polymeric hydrocarbon phases. The morphology observed by SEM shows typical habit and facets of the diamond crystallites grown on silicon. An attempt was made to explain some discrepancies observed in the XRD and Raman spectra of our multiphasic DLC films.

Lattice dynamics of YBa 2Cu 3O 7− x in oxygen-vacancy ordered ortho-II and ortho-III superstructures

A lattice-dynamics of YBa 2Cu 3O 7− x in superstructures ortho-II and ortho-III of oxygen ordering ( x=0.5 and x=0.33) is calculated in the frameworks of shell model with transferable interatomic potential parameters. Frequencies and eigenvectors for 75 vibration modes of ortho-II and 114 phonons of ortho-III are analysed and their connection with the phonon dispersion in YBa 2Cu 3O 7 and YBa 2Cu 3O 6 is investigated. In spite of the great complication of phonon spectra due to a multiplication of a unit cell in superstructures ortho-II and ortho-III a lot of their long-wave phonons are still close to the short-wave eigenmodes of ortho-I and are not expected to be observable in optical experiments. All Γ-phonons of ortho-I lattice manifest themselves in the long-wave spectra of high-order phases. The intrinsic Γ-modes of apical oxygen of YBa 2Cu 3O 6 arise in both superstructures as well. Only a restricted set of long-wave phonons can be regarded as the inherent ortho-II and ortho-III modes and could be useful as the reference vibrations for the purpose of superstructure characterization.

Interpretation of high-order commensurate phases for an argon monolayer adsorbed on Pt(111).

Interpretation of high-order commensurate phases for an argon monolayer adsorbed on Pt(111).

Effect of hydrostatic pressure on the modulated structure of deuterated betaine calcium chloride dihydrate.

In this work we present a study of elastic neutron scattering in deuterated betaine calcium chloride dihydrate under hydrostatic pressure. This study provides clear evidence for the existence of a large number of high-order commensurate phases induced by pressure. Structural branching processes as predicted by the analysis of axial next-nearest-neighbor Ising models have been observed.

Effect of hysteresis on the phase transition between high-order commensurate phases

We argue that the phase transition between two high-order commensurate phases and the transition between two modulation wave vectors in the incommensurate phase, can be of the first order. The transition starts from the nucleation of stripple, critical energy of which increases with increasing modulation amplitude. High nucleation energy involves a considerable hysteresis, width of which might even exceed the stability intervals of the high-order commensurate phases. Hence, diffraction measurements made on such states do not allow to detect all high-order commensurate phases.

Structure of monolayer Ar on Pt(111): Possible realization of a devil's staircase in two dimensions.

The structure of Ar physisorbed on Pt(111) in the submonolayer-coverage regime has been explored by thermal He-atom scattering. On the clean Pt(111) surface Ar condenses in a hexagonal close-packed phase aligned with the substrate. At coverages \ensuremath{\Theta}\ensuremath{\lesssim}0.7 ML the Ar adlayer lattice parameter is about 3.81 \AA{}. When the Ar coverage increases above 0.75 ML a first-order phase transition into a compressed hexagonal Ar phase with a lattice constant of 3.70 \AA{} is observed. From thermal-expansion measurements and the appearance of superlattice diffraction peaks, the compressed phase is demonstrated to be a high-order commensurate phase, characterized by a (4\ifmmode\times\else\texttimes\fi{}4)R0\ifmmode^\circ\else\textdegree\fi{} commensurate unit cell containing nine argon atoms. We have found experimental evidence for further high-order commensurate phases also in the low-Ar-coverage regime. Therefore the phase diagram of the Ar/Pt(111) physisorption system is likely to be a realization of a devil's staircase in two dimensions.