Lattice Polarization Research Articles

Ultrahigh-Density Polar Vortex Lattice in Square-Shaped Moiré Bilayers of Lead Chalcogenides.

Nanoscale exotic polar topological structures, such as vortices and skyrmions, hold promise for next-generation electronic devices, yet their spontaneous formation in 2D van der Waals (vdW) materials remains quite challenging. Herein, we demonstrate from first-principles that ultrahigh-density polar vortices emerge in the square moiré bilayer formed by twisting two layers of centrosymmetric PbS with the D4h point group. The emerged ferroelectricity arises from the inherent complex strain associated with the twisted structures, and the resulting electron polarization is much greater than that obtained in sliding ferroelectricity. Notably, the engineered strain patterns are characterized by peculiar inhomogeneous in-plane fields with a checkerboard distribution of uniaxial tension. This nanoscale nonuniform strain produces an ultrahigh-density vortex polarization lattice. The results from our study not only reveals a new mechanism for electric polarization and polar topologies in moiré bilayers but also provides opportunities for designing 2D ultrahigh-density electric devices.

ScAlInN/GaN heterostructures grown by molecular beam epitaxy

Rare-earth (RE) elements doped III-nitride semiconductors have garnered attention for their potential in advanced high-frequency and high-power electronic applications. We report on the molecular beam epitaxy of quaternary alloy ScAlInN, which is an encouraging strategy to improve the heterointerface quality when grown at relatively low temperatures. Monocrystalline wurtzite phase and uniform domain structures are achieved in ScAlInN/GaN heterostructures, featuring atomically sharp interface. ScAlInN (the Sc content in the ScAlN fraction is 14%) films with lower In contents (less than 6%) are nearly lattice matched to GaN, exhibiting negligible in-plane strain, which are excellent barrier layer candidates for GaN high electron mobility transistors (HEMTs). Using a 15-nm-thick Sc0.13Al0.83In0.04N as a barrier layer in GaN HEMT, a two-dimensional electron gas density of 4.00 × 1013 cm−2 and a Hall mobility of 928 cm2/V s, with a corresponding sheet resistance of 169 Ω/□, have been achieved. This work underscores the potential of alloy engineering to adjust lattice parameters, bandgap, polarization, interfaces, and strain in emerging RE-III-nitrides, paving the way for their use in next-generation optoelectronic, electronic, acoustic, and ferroelectric applications.

Energy level spectrum and lattice polarization of polaron in metal halide perovskite parabolic quantum wells

In this study, polaron effect in 2D metal halide perovskite materials (TMHPMs), which naturally form quantum well (QW) structures, has been investigated. Polarization of carriers and lattice within these structures was explored based on unitary transformation and variational methods. Specifically, lattice polarization and energy level transition spectra of strong coupling polaron in parabolic potential metal halide perovskite QWs (MAPbCl3, MAPbBr3, and MAPbI3) were studied. Also, we calculated ground and first excited state energies, excitation energy, transition frequency, and vibration frequency of a TMHPM QWs. Our results indicated that parabolic potential confinement intensity affected related physical quantities, which provided insight to investigate metal halide perovskite materials and polaron effect.

Lattice Polarity Manipulation of AlN Films on SiC Substrates for N-Polar GaN HEMTs

Lattice Polarity Manipulation of AlN Films on SiC Substrates for N-Polar GaN HEMTs

Horizontal Lithium Electrodeposition on Atomically Polarized Monolayer Hexagonal Boron Nitride.

Both uncontrolled Li dendrite growth and corrosion are major obstacles to the practical application of Li-metal batteries. Despite numerous attempts to address these challenges, effective solutions for dendrite-free reversible Li electrodeposition have remained elusive. Here, we demonstrate the horizontal Li electrodeposition on top of atomically polarized monolayer hexagonal boron nitride (hBN). Theoretical investigations revealed that the hexagonal lattice configuration and polarity of the monolayer hBN, devoid of dangling bonds, reduced the energy barrier for the surface diffusion of Li, thus facilitating reversible in-plane Li growth. Moreover, the single-atom-thick hBN deposited on a Cu current collector (monolayer hBN/Cu) facilitated the formation of an inorganic-rich, homogeneous solid electrolyte interphase layer, which enabled the uniform Li+ flux and suppressed Li corrosion. Consequently, Li-metal and anode-free full cells containing the monolayer hBN/Cu exhibited improved rate performance and cycle life. This study suggests that the monolayer hBN is a promising class of underlying seed layers to enable dendrite- and corrosion-free, horizontal Li electrodeposition for sustainable Li-metal anodes in next-generation batteries.

Realization of N-polarity GaN films on graphene/SiC substrates by interfacial atomic manipulation

Growth of N-polarity GaN on a two-dimensional (2D) material is of significance for the development of high-performance nitride devices such as red light-emitting diodes. However, the realization of N-polarity GaN on a 2D material is a challenge. In this work, we successfully achieve N-polarity GaN on graphene/SiC substrates through interfacial atomic manipulation. Our results show that the growth conditions of the AlN buffer play an important role in the lattice polarity of nitride film grown on 2D graphene. A low growth temperature of AlN buffer leads to a metal-polarity nitride film, while a high growth temperature of it leads to a mix-polarity nitride film. The underlying mechanism is revealed by first-principles calculations. Under the guidance of the calculations results, the preflow of trimethylaluminum source is introduced prior to the high-temperature AlN buffer growth to manipulate the interfacial atoms between the AlN buffer and graphene/SiC. With this method, we successfully realize the fabrication of N-polarity GaN on graphene/SiC by metalorganic chemical vapor deposition. This work provides a new route for the development of high-performance N-polarity nitride devices on graphene/SiC substrates.

Electronic structure orientation as a map of in-plane antiferroelectricity in β'-In2Se3.

Antiferroelectric (AFE) materials are excellent candidates for sensors, capacitors, and data storage due to their electrical switchability and high-energy storage capacity. However, imaging the nanoscale landscape of AFE domains is notoriously inaccessible, which has hindered development and intentional tuning of AFE materials. Here, we demonstrate that polarization-dependent photoemission electron microscopy can resolve the arrangement and orientation of in-plane AFE domains on the nanoscale, despite the absence of a net lattice polarization. Through direct determination of electronic transition orientations and analysis of domain boundary constraints, we establish that antiferroelectricity in β'-In2Se3 is a robust property from the scale of tens of nanometers to tens of micrometers. Ultimately, the method for imaging AFE domain organization presented here opens the door to investigations of the influence of domain formation and orientation on charge transport and dynamics.

Motivic Geometry of two-Loop Feynman Integrals

Abstract We study the geometry and Hodge theory of the cubic hypersurfaces attached to two-loop Feynman integrals for generic physical parameters. We show that the Hodge structure attached to planar two-loop Feynman graphs decomposes into mixed Tate pieces and the Hodge structures of families of hyperelliptic, elliptic or rational curves depending on the space-time dimension. For two-loop graphs with a small number of edges, we give more precise results. In particular, we recover a result of Bloch (Double box motive. SIGMA 2021;17,048) that in the well-known double-box example, there is an underlying family of elliptic curves, and we give a concrete description of these elliptic curves. We show that the motive for the non-planar two-loop tardigrade graph is that of a K3 surface. In an appendix by Eric Pichon-Pharabod, we argue via high-precision numerical computations that the Picard number of this K3 surface is generically 11 and we compute the expected lattice polarization. Lastly, we show that generic members of the ice cream cone family of graph hypersurfaces correspond to the pairs of sunset Calabi–Yau varieties.

Self-Trapped Exciton Emission in Highly Polar 0D Hybrid Ammonium/Hydronium-Based Perovskites Triggered by Antimony Doping.

Various monovalent cations are employed to construct metal halide perovskites with various structures and functionalities. However, perovskites based on highly polar A-site cations have seldom been reported. Here, a novel hybrid 0D (NH4)x(OH3)3-xInCl6 perovskite with highly polar hydronium OH3+ cations is introduced in this study. Upon doping with Sb3+, hybrid 0D (NH4)x(OH3)3-xInCl6 single crystals exhibited highly efficient broadband yellowish-green (550 nm) and red (630 nm) dual emissions with a PLQY of 86%. The dual emission arises due to Sb3+ occupying two sites within the crystal lattice that possess different polarization environments, leading to distinct Stokes shift energies. The study revealed that lattice polarity plays a significant role in the self-trapped exciton emission of Sb3+-doped perovskites, contributing up to 25% of the Stokes shift energy for hybrid 0D (NH4)x(OH3)3-xInCl6:Sb3+ as a secondary source, in addition to the Jahn-Teller deformation. These findings highlight the potential of Sb3+-doped perovskites for achieving tunable broadband emission and underscore the importance of lattice polarity in determining the emission properties of perovskite materials.

DFT and TD-DFT studies of perovskite materials LiAX3 (A=Ge, Sn; X= F, Cl, Br, I) in reference to their solar cell applications

Halide perovskite materials have attracted a huge interest of researchers due to their fascinating optoelectronic properties. In this report, structural, electronic, optical, and thermoelectric properties of Li-based perovskite materials LiAX3 (A = Ge, Sn; X = F, Cl, Br, I) are analyzed using Density Functional Theory (DFT). Functionals- B3LYP/LanL2DZ, B3LYP/def2-TZVP and B3LYP/LanL08 within the DFT framework are applied for geometry optimization of these perovskites. The results show a marked variation in magnitude of HOMO-LUMO energy gap of LiGeX3 and LiSnX3 with respect to different functionals viz. B3LYP/LanL2DZ, B3LYP/def2-TZVP and B3LYP/LanL08. LiGeF3 and LiSnF3 show the maximum values of HOMO-LUMO energy gap. The computed energy gap lies in the range required for perovskite materials to exhibit solar cell applications. A number of CDFT-based descriptors and Optical properties of LiAX3 are also studied and reported accordingly. Our computed results show that lattice constants, volume, formation energy, polarizability, refractive index, dielectric constant, entropy, heat capacity and wavelength of LiAX3 increases from F to I, whereas, HOMO-LUMO energy gap, electronegativity, electrophilicity index, optical electronegativity, vibrational frequencies, peak IR intensity, vibrational energy, total energy, zero-point vibrational energy, Gibbs free energy and photon energy decreases in the reverse direction.

Phase transformation, lattice evolution and microwave dielectric properties of three Y–Al oxides ceramics

The present work begins with the investigation of a large number of studies that give the phase diagram of Y–Al–O ternary compounds. Furthermore, the phase compositions of the Y2O3–Al2O3 system at different temperatures are obtained by high-temperature in situ XRD detection. The constitutive relationships between the lattice properties, grain development, polarizability, internal strain and microwave dielectric properties of the three Y–Al oxides (Y4Al2O9, YAlO3, Y3Al5O12) are elaborated in detail. As an ideal candidate crystalline material for terahertz wave transmission dielectric devices, yttrium-aluminum-garnet ceramics have a dielectric constant of 11.7 in the real part and a Q × f value of 214,735 GHz at high-frequency band (THz).

A Bound Exciton Resonance Modulated by Bulk and Localized Coherent Phonons in Double Perovskites.

Optically excited electronic excitations are coupled to the soft and polar halide perovskite lattice, generating coherent phonons after subpicosecond interband laser-excitation. In Ag-based halide double perovskites, Ag-vacancies can bind free excitons, resulting in a pronounced bound exciton resonance. Here, we report the detection of three modulation frequencies corresponding to coherent phonons in Ag-based double perovskite nanocrystals at distinct spectral positions at the bound exciton resonance. Two of them are found in oscillatory spectral shifts of the bound exciton resonance and are identified as Cs- and Br-related bulk phonons. Surprisingly, a third frequency is observed as an intensity modulation. We argue that this amplitude oscillation is a consequence of an optically generated vibronic wave packet localized at a Ag-vacancy. Consequently, the localized coherent phonon modulates the giant oscillator strength of the bound exciton. This optically induced and spatially localized lattice shaking could potentially be useful for initiating photochemical reactions with atomic precision.

Secondary‐Bond‐Driven Construction of a Polar Material Exhibiting Strong Broad‐Spectrum Second‐Harmonic Generation and Large Birefringence

AbstractConsiderable effort has been invested in the development of non‐centrosymmetric (NCS) inorganic solids for ferroelectricity‐, piezoelectricity‐ and, particularly, optical nonlinearity‐related applications. While great progress has been made, a persistent problem is the difficulty in constructing NCS materials, which probably stems from non‐directionality and unsaturation of the ionic bonds between metal counter‐cations and covalent anionic modules. We report herein a secondary‐bond‐driven approach that circumvents the cancellation of dipole moments between adjacent anionic modules that has plagued second‐harmonic generation (SHG) material design, and which thereby affords a polar structure with strong SHG properties. The resultant first NCS counter‐cation‐free iodate, VO2(H2O)(IO3) (VIO), a new class of iodate, crystallizes in a polar lattice with VO2(H2O)(IO3)] zigzag chains connected by weak hydrogen bonds and intermolecular forces. VIO exhibits very large SHG responses (18 × KH2PO4 @ 1200 nm, 1.5 × KTiOPO4 @ 2100 nm) and sufficient birefringence (0.184 @ 546 nm). Calculations and crystal structure analysis attribute the large SHG responses to consistent polarization orientations of the VO2(H2O)(IO3)] chains controlled by secondary bonds. This study highlights the advantages of manipulating the secondary bonds in inorganic solids to control NCS structure and optical nonlinearity, affording a new perspective in the development of high‐performance NLO materials.

Secondary-Bond-Driven Construction of a Polar Material Exhibiting Strong Broad-Spectrum Second-Harmonic Generation and Large Birefringence.

Considerable effort has been invested in the development of non-centrosymmetric (NCS) inorganic solids for ferroelectricity-, piezoelectricity- and, particularly, optical nonlinearity-related applications. While great progress has been made, a persistent problem is the difficulty in constructing NCS materials, which probably stems from non-directionality and unsaturation of the ionic bonds between metal counter-cations and covalent anionic modules. We report herein a secondary-bond-driven approach that circumvents the cancellation of dipole moments between adjacent anionic modules that has plagued second-harmonic generation (SHG) material design, and which thereby affords a polar structure with strong SHG properties. The resultant first NCS counter-cation-free iodate, VO2 (H2 O)(IO3 ) (VIO), a new class of iodate, crystallizes in a polar lattice with VO2 (H2 O)(IO3 )] zigzag chains connected by weak hydrogen bonds and intermolecular forces. VIO exhibits very large SHG responses (18 × KH2 PO4 @ 1200 nm, 1.5 × KTiOPO4 @ 2100 nm) and sufficient birefringence (0.184 @ 546 nm). Calculations and crystal structure analysis attribute the large SHG responses to consistent polarization orientations of the VO2 (H2 O)(IO3 )] chains controlled by secondary bonds. This study highlights the advantages of manipulating the secondary bonds in inorganic solids to control NCS structure and optical nonlinearity, affording a new perspective in the development of high-performance NLO materials.

Improving energy storage performance of barium titanate-based ceramics by doping MnO2

MnO2 was used as a sintering additive to reduce sintering temperature of the 0.92(Ba0.94Li0.02La0.04)(Mg0.04Ti0.96)O3-0.08Bi(Zn1/2Ti1/2)O3 (0.92BLLMT-0.08BZT) ceramic thick film and promote sintering process. At the same time, MnO2 doping is beneficial for reducing dielectric loss and leakage current, and improving insulation performance, thus, breakdown field strength (BDS) of ceramics is increased. In addition, MnO2 doping introduces defect energy levels, and increases lattice distortion and polarization intensity, thereby changing the crystal structure and microstructure morphology, and improving energy storage density and thermal stability. The BDS reaches 650 kV/cm electric field with 0.5 mol% MnO2 doping, where the ceramic thick film achieves a discharge density (Wdis) of 5.51 J/cm3, ultra-high power density (PD = 443.87 MW/cm3) and current density (CD = 1365.74 A/cm2). The ceramic thick film exhibits good thermal stability with Wdis change rate of only 16.47 % within room temperature to 170 °C under 200 kV/cm. Such excellent comprehensive performance can be attributed to the decrease of grain size, defect concentration, and leakage current, and the formation of polar nano regions in the BT-based ceramics caused by MnO2 doping and cations substitution at A-site and B-site of the perovskite structure. This study provides valuable insights for the research of lead-free dielectric ceramic capacitors, and the 0.92BLLMT-0.08BZT-0.5 mol% Mn ceramic thick film presents good development prospect in high-power pulse energy storage system.

Enhanced carrier transport in CsxSnBry perovskite by reducing electron-phonon coupling under compressive strain

Low-toxicity and environmentally friendly tin-based perovskite materials are attractive substitutes for lead halide perovskites in photovoltaic and optoelectronic devices. However, the polar perovskite lattice coupled with charge carrier, and strong polar optical phonon scattering severely affect the carrier transport. Here, we perform the first-principles calculation, and demonstrate that the carrier mobility can be significantly enhanced by applying compressive strain to the lattice, which can be attributed to the reduction of the electron-phonon coupling. Pressure-induced electron-phonon coupling strength evolutions correlate well with the polar optical phonon scattering changes. The maximum carrier mobility is 11 cm2 V−1s−1 and 143 cm2 V−1s−1 of Cs2SnBr6 with the unstrained and strained structure (13 % compression). The carrier mobility of CsSnBr3 with 1 % compression is improved due to a significant dielectric response induced by the dynamic lone pair activity of CsSnBr3. These studies indicate that compressive strain can significantly alter the structure and carrier transport characteristics of tin-based perovskite materials, which are important for photovoltaics and optoelectronics.

Unveiling interface structure and polarity of wurtzite ZnO film epitaxially grown on a-plane sapphire substrate

Atomic-scale structure properties of the epitaxial growth of the wurtzite ZnO film prepared on an a-plane sapphire (α-Al2O3) substrate have been investigated by using aberration-corrected transmission electron microscopy. The crystallographic orientation relationship of (0001)[1¯1¯20]ZnO//(112¯0)[0001]α-Al2O3 has been determined between the ZnO film and the α-Al2O3 substrate. Two types of oxygen-terminated a-plane α-Al2O3 substrate surfaces have been characterized, which leads to the formation of different heterointerface structures and ZnO domains with opposite lattice polarity. The coalescence of opposite polarity domains results in the appearance of inversion domain boundaries (IDBs) on prismatic planes, and kinks occur on basal planes during the propagation of IDBs within the film. Additionally, the structure of stacking mismatch boundaries in the film with threefold coordinated Zn and O atoms has been resolved. We believe that these findings can be helpful to advance the understanding of the complex propagation of planar defects (e.g., IDBs and stacking faults) in wurtzite films and the interface structure and polarity of wurtzite films on the a-plane sapphire substrate.

Lattice constant and polarization-independent high transmission in tellurium-based dielectric metasurfaces

High-refractive-index dielectric metasurfaces give rise to unprecedented control of light manipulation, such as control of phase, polarization and amplitude, giving rise to interesting properties, such as directional beam steering, polarization detectors and sensors. Dielectric metasurfaces of sub-wavelength dimensions have tremendous applications in the field of optics, such as negative refractive index, cloaking, perfect absorbers and reflectors. The study of light–matter interactions in such materials has gained impetus due to the formation of novel states, such as anapoles, and transparent states obtained by interference between resonant electric, magnetic and higher-order modes. In this article, we investigate the light–matter interaction of an array of periodic dielectric metasurfaces made from high-refractive-index tellurium in cubic geometries and study its electromagnetic response as a function of the lattice constant, angle of incidence and angle of polarization. More specifically, we observe a non-resonant transparent state at 60.69 THz, which is independent of both the lattice constant and polarization of the input radiation. Moreover, this state shows high transmission for a broad range of incident angles with potential applications as optical filters. It also depends on the incident polarization, thus acting as a perfect polarization detector. Detailed investigations of scattering parameters, the spatial distribution of electric and magnetic fields in the near- and far-field regions and detailed multipole analysis are carried out to analyze the electromagnetic response of the metasurface.

Stabilizing confined quasiparticle dynamics in one-dimensional polar lattice gases

Stabilizing confined quasiparticle dynamics in one-dimensional polar lattice gases

Strain-Control of Cycloidal Spin Order in a Metallic Van der Waals Magnet.

The manipulation of magnetism through strain control is a captivating area of research with potential applications for low-power devices that do not require dissipative currents. Recent investigations of insulating multiferroics have unveiled tunable relationships among polar lattice distortions, Dzyaloshinskii-Moriya interactions (DMI), and cycloidal spin orders that break inversion symmetry. These findings have raised the possibility of utilizing strain or strain gradient to manipulate intricate magnetic states by changing polarization. However, the effectiveness of manipulating cycloidal spin orders in "metallic" materials with screened magnetism-relevant electric polarization remains uncertain. In this study, the reversible strain control of cycloidal spin textures in a metallic van der Waals magnet, Cr1/3 TaS2 , through the modulation of polarization and DMI induced by strain is demonstrated. With thermally-induced biaxial strains and isothermally-applied uniaxial strains, systematic manipulation of the sign and wavelength of the cycloidal spin textures is realized, respectively. Additionally, unprecedented reflectivity reduction under strain and domain modification at a record-low current density are also discovered. These findings establish a connection between polarization and cycloidal spins in metallic materials and present a new avenue for utilizing the remarkable tunability of cycloidal magnetic textures and optical functionality in van der Waals metals with strain.