Three-dimensional Electronic Structure Research Articles

QuanDB: a quantum chemical property database towards enhancing 3D molecular representation learning

Previous studies have shown that the three-dimensional (3D) geometric and electronic structure of molecules play a crucial role in determining their key properties and intermolecular interactions. Therefore, it is necessary to establish a quantum chemical (QC) property database containing the most stable 3D geometric conformations and electronic structures of molecules. In this study, a high-quality QC property database, called QuanDB, was developed, which included structurally diverse molecular entities and featured a user-friendly interface. Currently, QuanDB contains 154,610 compounds sourced from public databases and scientific literature, with 10,125 scaffolds. The elemental composition comprises nine elements: H, C, O, N, P, S, F, Cl, and Br. For each molecule, QuanDB provides 53 global and 5 local QC properties and the most stable 3D conformation. These properties are divided into three categories: geometric structure, electronic structure, and thermodynamics. Geometric structure optimization and single point energy calculation at the theoretical level of B3LYP-D3(BJ)/6-311G(d)/SMD/water and B3LYP-D3(BJ)/def2-TZVP/SMD/water, respectively, were applied to ensure highly accurate calculations of QC properties, with the computational cost exceeding 107 core-hours. QuanDB provides high-value geometric and electronic structure information for use in molecular representation models, which are critical for machine-learning-based molecular design, thereby contributing to a comprehensive description of the chemical compound space. As a new high-quality dataset for QC properties, QuanDB is expected to become a benchmark tool for the training and optimization of machine learning models, thus further advancing the development of novel drugs and materials. QuanDB is freely available, without registration, at https://quandb.cmdrg.com/.

Three-dimensional electronic structure of the superconductor Sn4Sb3 by angle-resolved photoemission spectroscopy

The layered material Sn4Sb3 exhibits superconductivity with 1.47 K and is proposed to be a topological superconductor candidate. In this study, we investigate the electronic structure of Sn4Sb3 using angle-resolved photoemission spectroscopy and density functional theory (DFT) calculations. Despite its layered structure, the band structure of Sn4Sb3 shows strong kz dependence, leading to the formation of a three-dimensional Fermi surface. The electronic bands exhibit three-fold symmetry at most kz planes and six-fold symmetry at the Γ and Z planes. These observations are consistent with DFT calculations, except for the presence of additional flat-like bands located 500 meV below the Fermi level. The photon energy dependence measurement show noticeable kz dispersion in one of the splitted branches, suggesting a bulk origin of the feature, and negligible kz dispersion in another branch, implying the surface origin of the state.

High-energy photoemission final states beyond the free-electron approximation

Three-dimensional (3D) electronic band structure is fundamental for understanding a vast diversity of physical phenomena in solid-state systems, including topological phases, interlayer interactions in van der Waals materials, dimensionality-driven phase transitions, etc. Interpretation of ARPES data in terms of 3D electron dispersions is commonly based on the free-electron approximation for the photoemission final states. Our soft-X-ray ARPES data on Ag metal reveals, however, that even at high excitation energies the final states can be a way more complex, incorporating several Bloch waves with different out-of-plane momenta. Such multiband final states manifest themselves as a complex structure and added broadening of the spectral peaks from 3D electron states. We analyse the origins of this phenomenon, and trace it to other materials such as Si and GaN. Our findings are essential for accurate determination of the 3D band structure over a wide range of materials and excitation energies in the ARPES experiment.

Itinerant to relocalized transition of f electrons in the Kondo insulator CeRu4Sn6

The three-dimensional electronic structure and the nature of Ce 4f electrons of the Kondo insulator CeRu4Sn6 are investigated by angle-resolved photoemission spectroscopy, utilizing tunable photon energies. Our results reveal (i) the three-dimensional k-space nature of the Fermi surface, (ii) the localized-to-itinerant transition of f electrons occurs at a much high temperature than the hybridization gap opening temperature, and (iii) the "relocalization" of itinerant f electrons below 25 K, which could be the precursor to the establishment of magnetic order.

Coherent Interlayer Coupling in Quasi-Two-Dimensional Dirac Fermions in α-(BEDT-TTF)2I3

Theoretical and experimental studies have supported that the electronic structure of $\alpha$-(BEDT-TTF)$_2$I$_3$ under pressure is described by two-dimensional Dirac fermions. When the interlayer tunneling is coherent, the electronic structure of the system becomes three-dimensional, and we expect the peak structure to appear in the interlayer resistivity under magnetic fields. We theoretically and experimentally show that the peak appears in the interlayer resistivity at low temperatures and high magnetic fields. From the experiment, we estimate that the magnitude of the interlayer tunneling is $t_1 \sim 1$ meV. Our result opens the door to investigating the three-dimensional electronic structure of $\alpha$-(BEDT-TTF)$_2$I$_3$.

Nature of quasiparticle interference in three dimensions

Quasiparticle interference (QPI) imaging is a powerful tool for the study of the low-energy electronic structure of quantum materials. However, the measurement of QPI by scanning tunneling microscopy (STM) is restricted to surfaces and is thus inherently constrained to two dimensions. QPI has proved immensely successful for the study of materials that exhibit a quasi-two-dimensional electronic structure, yet it raises questions about how to interpret QPI in materials that have a highly three-dimensional electronic structure. In this paper, we address this question and establish the methodology required to simulate and understand QPI arising from three-dimensional systems as measured by STM. We calculate the continuum surface Green's function in the presence of a defect, which captures the role of the surface and the vacuum decay of the wave functions. We find that defects at different depths from the surface will produce unique sets of scattering vectors for three-dimensional systems, which nevertheless can be related to the three-dimensional electronic structure of the bulk material. We illustrate the consequences that the three-dimensionality of the electronic structure has on the measured QPI for a simple cubic nearest-neighbor tight-binding model, and then demonstrate application to a real material using a realistic model for PbS. Our method unlocks the use of QPI imaging for the study of quantum materials with three-dimensional electronic structures and introduces a framework to generically account for ${k}_{z}$ dispersions within QPI simulations.

Novel stylophora coral-like furan-based Ni/Co bimetallic metal organic framework for high-performance capacitive storage and non-enzymatic glucose electrochemical sensing

With the development of power supplies for wearable devices, electrode materials with dual functions have received extensive attention. Herein, we report a strategy of preparing stylophora coral-like Ni/Co bimetal metal organic framework (MOF) with furan-based derivatives as ligands through the simple solvothermal method, which can be utilized as a dual-function electrode material to build supercapacitors and non-enzymatic glucose sensing. It can be found that the high molecular stacking properties of the rigid furan ring skeleton combined with the unique stylophora coral-like morphology can greatly improve the charge transfer efficiency of the electrode reaction process, and the structure of the bimetallic node can effectively adjust the three-dimensional electronic structure, making high capacitive performance during charge storage. The specific capacitance of the furan-based bimetallic MOF material is as high as 531 C g−1 at a current density of 1 A g−1 with a high capacitance retention rate of 83.4% after 5000 cycles. In addition, the glucose sensing performance is analyzed and an outstanding sensitivity value of 366 µA mM−1 cm−2 is achieved with a low limit of detection (2 μM). The as-synthesized furan-based bimetallic MOF material is a promising candidate for electrochemical supercapacitors and efficient glucose detection.

Research on Three-Dimensional Electronic Navigation Chart Hybrid Spatial Index Structure Based on Quadtree and R-Tree

The three-dimensional (3D) visualization of the electronic navigation chart (ENC) can reflect the marine environment and various marine features truly, accurately, and directly, to reduce misoperation during chart use and improve the convenience of using the chart. Due to a large amount of ENC data, complex data structure, and uneven distribution in 3D space, the construction and real-time rendering of 3D ENCs depend on the retrieval speed of 3D spatial data. Improving the spatial retrieval efficiency of 3D ENC data is helpful for the rapid rendering of a 3D scene. In this paper, based on the S-100 universal hydrological data model (S-100) and the 3D characteristics to classify the ENC features and create the 3D ENC data set, a hybrid spatial index structure is proposed based on quadtree and R-tree and ENC features data structure, using the smallest minimum bounding box (SMBB) and classification retrieval methods to optimize the spatial index structure. All the ENC features are rendered in a 3D marine scene. By analyzing the overlap of ENC features and testing the efficiency of spatial index structure, the results show that this method can effectively reduce the overlap rate of index nodes and improve the efficiency of data retrieval, realize the effective management of 3D ENC data, and improve the drawing speed of 3D ENCs.

Three-dimensional electronic structure of LiFeAs

Amongst the iron-based superconductors, LiFeAs is unrivalled in the simplicity of its crystal structure and phase diagram. However, our understanding of this canonical compound suffers from conflict between mutually incompatible descriptions of the material's electronic structure, as derived from contradictory interpretations of the photoemission record. Here, we explore the challenge of interpretation in such experiments. By combining comprehensive photon energy- and polarization- dependent angle-resolved photoemission spectroscopy (ARPES) measurements with numerical simulations, we establish the providence of several contradictions in the present understanding of this and related materials. We identify a confluence of surface-related issues which have precluded unambiguous identification of both the number and dimensionality of the Fermi surface sheets. Ultimately, we arrive at a scenario which supports indications of topologically non-trivial states, while also being incompatible with superconductivity as a spin-fluctuation driven Fermi surface instability.

Electronic structure and open-orbit Fermi surface topology in isostructural semimetals NbAs2 and W2As3 with extremely large magnetoresistance

In transition-metal dipnictides TmPn2 (Tm = Ta and Nb; Pn = P, As, and Sb), the origin of extremely large magnetoresistance (XMR) is yet to be studied by the direct visualization of the experimental band structures. Here, using angle-resolved photoemission spectroscopy, we map out the three-dimensional electronic structure of NbAs2. The open-orbit topology contributes to a non-negligible part of the Fermi surfaces (FSs), like that of the isostructural compound MoAs2, where the open FS is proposed to likely explain the origin of XMR. We further demonstrate the observation of open characters in the overall FSs of W2As3, which is also a XMR semimetal with the same space group of C12/m1 as the TmPn2 family and MoAs2. Our results suggest that the open-orbit FS topology may be a shared feature between XMR materials with the space group of C12/m1 and, thus, could possibly play a role in determining the corresponding XMR effect together with the electron–hole compensation.

Visualizing the out-of-plane electronic dispersions in an intercalated transition metal dichalcogenide

Layered transition metal dichalcogenides have rich phase diagram and they feature two dimensionality on numerous physical properties. Co1/3NbS2 is one of the newest members of this family where Co atoms are intercalated into the Van der Waals gaps between NbS2 layers. We study the three-dimensional electronic band structure of Co1/3NbS2 using both surface and bulk sensitive angle-resolved photoemission spectroscopy. We show that the electronic bands do not fit into the rigid-band-shift picture after the Co intercalation. Instead, Co1/3NbS2 displays a different orbital character near the Fermi level compared to the pristine NbS2 compound and has a clear band dispersion in kz direction despite its layered structure. Our photoemission study demonstrates the out-of-plane electronic correlations introduced by the Co intercalation, thus offering a new perspective on this compound. Finally, we propose how Fermi level tuning could lead to exotic phases such as spin density wave instability.

Electronic structure of URu2Si2 in paramagnetic phase: three-dimensional angle resolved photoelectron spectroscopy study

The three-dimensional (3D) electronic structure of the hidden order compound URu2Si2 in a paramagnetic phase was revealed using a 3D angle-resolved photoelectron spectroscopy where the electronic structure of the entire Brillouin zone is obtained by scanning both incident photon energy and detection angles of photoelectrons. The quasi-particle bands with enhanced contribution from the U 5f state were observed near E F, formed by the hybridization with the Ru 4d states. The energy dispersion of the quasi-particle band is significantly depend on k z , indicating that they inherently have a 3D nature. The band-structure calculation qualitatively explain the characteristic features of the band structure and Fermi surface although the electron correlation effect strongly renormalizes the quasi-particle bands. The 3D and strongly-correlated nature of the quasi-particle bands in URu2Si2 is an essential ingredient for modeling its hidden-order transition.

A comprehensive ARPES study on the type-II Dirac semimetal candidate Ir1−xPtxTe2

The transition metal dichalcogenide Ir1−xPtxTe2 displays both superconductivity and a topological band structure. Using angle-resolved photoemission spectroscopy, we obtain a comprehensive understanding of the three-dimensional electronic structure in the normal state of Ir1−xPtxTe2 for doping levels from x = 0.1 to 0.4, which spans the composition range of a superconducting state to a non-superconducting state. Many features of the electronic structure can be attributed to strong Te–Te interactions between the layers of the layered crystal structure and can be resolved by photon energy dependent measurements. We demonstrate that the type-II Dirac fermions can be successfully tuned via Pt doping, where the Dirac point lies close to the Fermi level for x = 0.1. The band evolution vs doping provides a clearer understanding of the relationship between the superconductivity and electronic structure. In addition, the β band in the superconducting samples locates the system close to a type-II van Hove singularity, where spin triplet paring symmetry has been predicted. Our results provide a comprehensive understanding of the band structure of Ir1−xPtxTe2, and we discuss the possibilities of the existence of topological superconductivity in this system.

Three-dimensional and temperature-dependent electronic structure of the heavy-fermion compound CePt2In7 studied by angle-resolved photoemission spectroscopy

The three-dimensional electronic structure and Ce 4f electrons of the heavy fermion superconductor CePt2In7 is investigated. Angle-resolved photoemission spectroscopy using variable photon energy establishes the existence of quasi-two and three dimensional Fermi surface topologies. Temperature-dependent 4d-4f on-resonance photoemission spectroscopies reveal that heavy quasiparticle bands begin to form at a temperature well above the characteristic (coherence) temperature T*. T* emergence may be closely related to crystal electric field splitting, particularly the low-lying heavy band formed by crystal electric field splitting.

Strong spin-orbit coupling and Dirac nodal lines in the three-dimensional electronic structure of metallic rutile IrO2

Using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we have studied the bulk and surface electronic structure of metallic rutile $5d$ transition metal oxide ${\mathrm{IrO}}_{2}$ that harbors both edge and corner sharing Ir-O octahedrons. We observe strong modulation of the band structure by spin-orbit coupling (SOC). The measured band structure is well reproduced by our ab initio calculation without band renormalization, suggesting the absence of the SOC-enhanced correlation effect in ${\mathrm{IrO}}_{2}$. In accordance with the calculation, we visualize two types of Dirac nodal lines (DNLs) protected by mirror symmetry and nonsymmorphic crystal symmetry, respectively. SOC gaps the first type of DNLs, which may contribute largely to the strong spin Hall effect. The second type of DNLs at the edges of Brillouin zone, however, remain intact against SOC. Our results not only provide important insights into the exotic transport properties of ${\mathrm{IrO}}_{2}$, but also shed light on the understanding of the role of SOC in the iridate family.

Parasitic parameter extraction and analysis of high voltage SiC intelligent power module for three-phase motor control applications

Parasitic parameter extraction of intelligent power module is crucial to analyze transient noise, ground bounce, voltage and current overshoot. This paper investigates the relationship between the physical layout of a high voltage SiC intelligent power module and its equivalent circuit parasitic parameters. An accurate three-dimensional electronic structure of the high voltage SiC intelligent power module is provided and the parasitic elements are extracted from the three-dimensional physical layout model for crucial graphic patterns. Parameter extraction results are compared and studied with different parameter values of heatsink plate and copper layer in this research. The effects of different values of these two parameters on AC parasitic resistance and inductance are evaluated.

Spontaneous Thermal Hall Effect in Three-dimensional Chiral Superconductors with Gap Nodes

Generic chiral superconductors with three-dimensional electronic structure have nodal gaps and are not strictly topological. Nevertheless, they exhibit a spontaneous thermal Hall effect (THE), i.e. a transverse temperature gradient in response to a heat current even in the absence of an external magnetic field. While in some cases this THE can be quantized analogous to the Quantum Hall effect, this is not the case for nodal superconductors in general. In this study we determine the spontaneous THE for tight binding models with tetragonal and hexagonal crystal symmetry with chiral $p$- and d-wave superconducting phase. At the zero-temperature limit, the thermal Hall conductivity $ \kappa_{xy} $ provides information on the structure of the gap function on the Fermi surface and the Andreev bound states on the surface. The temperature dependence at very low temperatures is determined by the types of gap nodes, point or line nodes, leading to characteristic power law behaviors in the temperature, as known for other quantities such as specific heat or London penetration depth. The generic behavior is discussed on simple models analytically, while the analysis of the tight-binding models is given numerically.

Engineering Carrier Effective Masses in Ultrathin Quantum Wells of IrO_{2}.

The carrier effective mass plays a crucial role in modern electronic, optical, and catalytic devices and is fundamentally related to key properties of solids such as the mobility and density of states. Here we demonstrate a method to deterministically engineer the effective mass using spatial confinement in metallic quantum wells of the transition metal oxide IrO_{2}. Using a combination of insitu angle-resolved photoemission spectroscopy measurements in conjunction with precise synthesis by oxide molecular-beam epitaxy, we show that the low-energy electronic subbands in ultrathin films of rutile IrO_{2} have their effective masses enhanced by up to a factor of 6 with respect to the bulk. The origin of this strikingly large mass enhancement is the confinement-induced quantization of the highly nonparabolic, three-dimensional electronic structure of IrO_{2} in the ultrathin limit. This mechanism lies in contrast to that observed in other transition metal oxides, in which mass enhancement tends to result from complex electron-electron interactions and is difficult to control. Our results demonstrate a general route towards the deterministic enhancement and engineering of carrier effective masses in spatially confined systems, based on an understanding of the three-dimensional bulk electronic structure.

Three-dimensional Fermi surface of 2H−NbSe2 : Implications for the mechanism of charge density waves

We investigate the three-dimensional electronic structure of the seminal charge-density-wave (CDW) material 2H-NbSe$_2$ by soft x-ray angle-resolved photoelectron spectroscopy and density-functional theory. Our results reveal the pronounced 3D character of the electronic structure formed in the quasi-two-dimensional layered crystal structure. In particular, we find a strong dispersion along $k_z$ excluding a nesting-driven CDW formation based on experimental data. The 3D-like band structure of 2H-NbSe$_2$ has strong implications for the intriguing phase competition of CDW order with superconductivity.

Undistorted linear Bi chains with hypervalent bonding in La3TiBi5 from single-crystal X-ray diffraction.

The crystal structure of the lanthanum titanium bismuthide La3TiBi5 (Pearson code hP18, Wyckoff sequence b d g2) has been established from single-crystal X-ray diffraction data and analyzed in detail using first-principles calculations. There are no anomalies pertaining to the atomic displacement parameter of the Ti site, previously reported based on a powder X-ray diffraction analysis of this compound. The anionic substructure contains columns of face-sharing TiBi6 octahedra and linear Bi chains. Due to a significant La(5d) and Bi(6p) orbital mixing, a perfectly one-dimensional character of the Bi chains is not realised, while a three-dimensional electronic structure is established instead. The latter fact explains the stability of the polyanionic pnictide units against Peierls distortions. The hypervalent bonding in the Bi chains is reflected in a rather long Bi-Bi distance of 3.2264 (4) Å and a typical pattern of bonding and antibonding interactions, as revealed by electronic structure calculations.