Phonons as bosons are different from electrons as fermions. Unlike interatomic electron hopping that can be either positive or negative and further tuned by spin-orbit coupling, interatomic spring constant is positive, or the structure of atomic lattices would be dynamically unstable. Surprisingly, we found that topological phonon flat bands (FBs) can manifest either a positive or negative interatomic spring constant that couples the FB-modes of opposite chirality, as exemplified by first-principles calculations of a 2D material of Kagome-BN. To reveal its physical origin, we first establish a fundamental correspondence between a collective lattice-coupling (CLC) variable of two quasi-particle states (e.g., electronic states or phonon modes) of opposite parity in a periodic lattice with band topology. Topological semimetals arise with zero CLC at special k-points protected by symmetry; while positive and negative CLC at these k-points gives rise to normal and topological insulators, respectively. Then, we show topological FB has a special form of CLC that vanishes at all k-points as characterized by its real-space wave function, and multi-atom FB phonon mode can manifest effectively a negative interatomic spring constant. Our findings shed new light on our fundamental understanding of topology and provide a practical design principle for creating artificial bosonic topological states.

Chiral exact flat bands (FBs) at charge neutrality have attracted much recent interest, presenting an intriguing condensed-matter system to realize exact many-body phenomena, as specifically shown in "magic angle" twisted bilayer graphene for superconductivity and triangulene-based superatomic graphene for excitonic condensation. Yet, no generic physical model to realize such FBs has been developed. Here we present a new mathematical theorem, called bipartite double cover (BDC) theorem, and prove that the BDC of line-graph (LG) lattices hosts at least two chiral exact FBs of opposite chirality, i.e., yin-yang FBs, centered-around/at charge neutrality (E = 0) akin to the "chiral limit" of twisted bilayer graphene. We illustrate this theorem by mapping it exactly onto tight-binding lattice models of the BDC of LGs of hexagonal lattice for strong topological and of triangular lattice for fragile topological FBs, respectively. Moreover, we use orbital design principle to realize such exotic yin-yang FBs in non-BDC lattices to instigate their real material discovery. This work not only enables the search for exact chiral FBs at zero energy beyond moiré heterostructures, but also opens the door to discovering quantum semiconductor features with FB-enabled strongly correlated carriers.

We developed a new tool to assess the severity of osteoporotic vertebral fracture using radiographs of the spine. Our technique can be used in patient care by helping to stratify patients with osteoporotic vertebral fractures into appropriate treatment pathways. It can also be used for research purposes. The aim of our study was to propose a semi-quantitative (SQ) grading scheme for osteoporotic vertebral fracture (OVF) on anteroposterior (AP) radiographs. On AP radiographs, the vertebrae are divided into right and left halves, which are graded (A) vertical rectangle, (B) square, (C) traverse rectangle, and (D) trapezoid; whole vertebrae are graded (E) transverse band or (F) bow-tie. Type A and B were compared with normal and Genant SQ grade 1 OVF, Type C and D with grade 2 OVF, and Type E and F with grade 3 OVF. Spine AP radiographs and lateral radiographs of 50 females were assessed by AP radiographs SQ grading. After training, an experienced board-certified radiologist and a radiology trainee assessed the 50 AP radiographs. The height-to-width ratio of the half vertebrae varied 1.32–1.48. On lateral radiographs, 84 vertebrae of the 50 patients had OVFs (38 grade 1, 24 grade 2, and 22 grade 3). On AP radiographs, the radiologist correctly assigned 84.2

This study takes Cushing's syndrome, a rare disease, as a model, and adopts the path of "Plan, Do, Check, Action" (PDCA) to explore new methods to optimize the clinical path, can improve the quality and efficiency of diagnosis and treatment of rare diseases. After sorting out the problems existing in the previous diagnosis and treatment mode, our team optimizes the path in various ways and establishes a standard operation procedure (SOP) for the new path. In the evaluation of the optimized mode, 55 patients with Cushing's syndrome were admitted to the Department of Endocrinology, Peking Union Medical College Hospital, including 19 males and 36 females, aged (41.8±14.4) years (6-68 years). The pathway group (28 cases) and the control group (27 cases) were divided according to whether they were included in the new path management at the time of admission, and the effect of path optimization was assessed in terms of time, efficacy, safety and cost. The results showed that compared with the control group, the pathway group had a shorter time of hospitalization in the Department of Endocrinology and critical tests, such as blood cortisol rhythm, low-dose dexamethasone inhibition test, and bilateral inferior petrosal sinus sampling (all P<0.05). There was no significant differences in the decrease of total cortisol after operation, the incidence of postoperative complications, and hospitalization expenses (all P>0.05). The optimized path improves the medical efficiency while ensuring medical quality, safety and no increase in cost. This study proposes PDCA path optimization for complex diseases and establishes SOP process, which provides experience in management optimization for the patient-centered and clinical path-oriented diagnosis and treatment mode of rare diseases.

The experimental realization of p -orbital systems is desirable because p -orbital lattices have been proposed theoretically to host strongly correlated electrons that exhibit exotic quantum phases. Here, we synthesize a two-dimensional Fe-coordinated bimolecular metal-organic framework which constitutes a honeycomb lattice of 1,4,5,8,9,12-hexaazatriphenylene molecules and a Kagome lattice of 5,15-di(4-pyridyl)-10,20-diphenylporphyrin molecules on a Au(111) substrate. Density-functional theory calculations show that the framework features multiple well-separated spin-polarized Kagome bands, namely Dirac cone bands and Chern flat bands, near the Fermi level. Using tight-binding modelling, we reveal that these bands are originated from two effects: the low-lying molecular orbitals that exhibit p -orbital characteristics and the honeycomb-Kagome lattice. This study demonstrates that p -orbital Kagome bands can be realized in metal-organic frameworks by using molecules with molecular orbitals of p -orbital like symmetry.

Nodal ring phonons with topologically nontrivial properties have triggered much interest in recent years. Unlike fermions inevitably affected by the spin-orbit interaction, nodal ring phonons are topologically robust. In this paper, we investigate the classification of nodal rings in phonon systems based on symmetry arguments and $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ models. We identify that all the nodal ring phonons can be categorized into three types, i.e., in-plane nodal rings protected by mirror symmetry, twisted nodal rings protected by inversion and time-reversal symmetries, and the hybrid type protected by a combination of these symmetries. On the basis of first-principles calculations, we propose that these three types of nodal ring phonons can emerge in two different phases of silver oxide. The calculation results also show clear drumheadlike surface states along high-symmetry paths and nontrivial arc states in the isofrequency surfaces. This work exposes various appearances of nodal rings and also promotes the development of topological phonons.

Objective:To determine the clinical features and genetic characters of patients with chronic enteropathy associated SLCO2A1 gene (CEAS). Methods:Five CEAS patients diagnosed at Peking Union Medical College Hospital from January 2012 to December 2019 were enrolled in this study. The clinical manifestations, laboratory test, radiological and endoscopic findings, gene detections, treatments and prognosis of these patients were reviewed and analyzed.Results:Five male patients presented gastrointestinal symptoms after puberty, including abdominal pain, diarrhea, intermittent melena or hematochezia, incomplete bowel obstruction, anemia, hypoalbuminemia and hypokalemia. The whole gastrointestinal tract except esophagus could be involved, especially the stomach and ileum. Intestinal lesions were characterized by multiple shallow ulcers with stenosis in the layers of mucosa and submucosa. Five patients were all accompanied with primary hypertrophic osteoarthropathy (PHO), and 1 with myelofibrosis and thoracic duct dysplasia. All patients were homozygous or compound heterozygous mutations of SLCO2A1 gene. Conventional treatment of inflammatory bowel disease and COX-2 inhibitors were ineffective. Conclusions:CEAS is an autosomal recessive genetic disease which widely involves the gastrointestinal tract, and can be associated with skin and bone involvement. There is no effective treatment for CEAS at present. CEAS is a different entity from other inflammatory gastrointestinal diseases.

Dirac semimetals associated with bulk Dirac fermions are well known in topological electronic systems. In sharp contrast, three-dimensional (3D) Dirac phonons in crystalline solids are still unavailable. Here we perform symmetry arguments and first-principles calculations to systematically investigate 3D Dirac phonons in all space groups with inversion symmetry. The results show that there are two categories of 3D Dirac phonons depending on their protection mechanisms and positions in momentum space. The first category originates from the four-dimensional irreducible representations at the high symmetry points. The second category arises from the phonon branch inversion, and the symmetry guarantees Dirac points to be located along the high symmetry lines. Furthermore, we reveal that nonsymmorphic symmetries and the combination of inversion and time-reversal symmetries play essential roles in the emergence of 3D Dirac phonons. Our work not only offers a comprehensive understanding of 3D Dirac phonons but also provides significant guidance for exploring Dirac bosons in both phononic and photonic systems.

Realization of the Kagome antiferromagnetic (KAF) lattice is of high interest because the geometric frustration in the Kagome lattice is expected to give rise to highly degenerated ground states that may host exotic phases such as quantum spin liquid. Here we demonstrate the design and synthesis of a single-layer two-dimensional metal-organic framework (2D-MOF) containing a Kagome lattice of Fe(II) ions assembled on a Au(111) surface. First-principles calculations reveal that the Fe(II) ions are at a high spin state of S = 2 and are coupled antiferromagnetically with nearest-neighboring exchange J1 = 5.8 meV. The ground state comprises various degenerated spin configurations including the well-known q = 0 and q = √3 × √3 phases. Remarkably, we observe a spin excitation at 6 meV using tunneling spectroscopy. This work points out a feasible route toward realizing spin 1/2 KAF, a candidate quantum spin liquid system, by replacing Fe(II) by Cu(II) in the same structure.

Maffucci syndrome is characterized by the presence of multiple enchondromas associated with multiple hemangiomas (figure 1). Enchondromas are common benign cartilage tumors of bone. They can occur as solitary lesions or as multiple lesions in enchondromatosis (Schwartz 1987, Kaplan 1993). When hemangiomata are associated, the condition is known as Maffucci syndrome (figure 2). The patients are normal at birth and the syndrome manifests during childhood and puberty. The enchondromas affect the extremities and their distribution is asymmetrical. The most common sites of enchondromas are the metacarpal bones and phalanges of the hands. The feet are less commonly afflicted. Clinical problems caused by enchondromas include skeletal deformity and the potential for malignant change to osteosarcoma (figure 3). The risk for sarcomatous degeneration of enchondromas, hemangiomas, or lymphangiomas is 15-30%. Maffucci syndrome is also associated with a higher risk of CNS, pancreatic, and ovarian malignancies (Ono 2012) (figure 4).

Two-dimensional (2D) non-covalent and covalent networks are interesting because their tailorable architectures offer fresh applications in sensing, catalysis, gas storage, and topological structures. So far, rational design of these networks has been explored exclusively involving organic molecules based on the concept of modular assembly. Here, we demonstrate that, by using molecular-beam epitaxy, we can isolate inorganic blocks to form a 2D porous gold-phosphorus network (AuPhoN), wherein blue phosphorene (blueP) subunits are linked by gold atoms on an Au surface. We provide evidence that such metal-phosphorus networks are tunable in their chemical functionalities and electronic properties by simply altering the linkers and subunits. Our work provides insights to tailor low-dimension architectures of inorganic networks that maintain good long-range order and are stable over a wide temperature range.

The realization of topological quantum states in devices is an important subject. According to whether or not the time-reversal symmetry is broken, topological materials can be classified into magnetic and nonmagnetic ones. In particular, magnetic topological materials are of importance, in which the coexistence of nontrivial band topology and magnetic orders gives exotic spintronics-related applications. However, experimental observations of magnetic topological quantum states are extremely difficult. In this Perspective, we review the recent progress to explore and design magnetic topological oxides such as topological semimetals and three-dimensional quantum anomalous Hall insulators, which are robustly stable against oxidation at ambient conditions. Most of these materials possess high Curie temperatures and are widely used in industrial applications, stimulating considerable experimental interest. Moreover, further discussions related to the topological classification and topological transitions are also present.

By combining first-principles calculations and symmetry arguments, we propose that the half-metallic phase of K2Cr8O16 presents ferromagnetic Weyl fermions. In particular, K2Cr8O16 possesses two pairs of Weyl nodes, which originate from two groups of nodal lines connected by the mirror reflection symmetry. We show that the non-trivial topological properties of K2Cr8O16 come from the partially occupied t2g states of Cr, and we also demonstrate that such exotic topological feature is robust. The topological surface states and corresponding Fermi arcs are revealed. As K2Cr8O16 is a realistic and widely studied material, our results suggest that K2Cr8O16 is an ideal candidate for studying ferromagnetic Weyl fermions. In addition, K2Cr8O16 possesses several interesting phenomena, such as the co-existence of charge density wave and Weyl fermions, even pairs of FM Weyl points, and tunable distribution of Weyl points, which will attract intensive attentions in this field.

AbstractA 2D metal–organic framework (2D‐MOF) was formed on a Cu(111) substrate using benzenehexol molecules. By means of a combination of scanning tunneling microscopy and spectroscopy, X‐ray photoelectron spectroscopy and density‐functional theory, the structure of the 2D‐MOF is determined to be Cu3(C6O6), which is stabilized by O–Cu–O bonding motifs. We find that upon adsorption on Cu(111), the 2D‐MOF features a semiconductor band structure with a direct band gap of 1.5 eV. The O–Cu–O bonds offer efficient charge delocalization, which gives rise to a highly dispersive conduction band with an effective mass of 0.45 me at the band bottom, implying a high electron mobility in this material.

Type-III nodal ring associated with a flat band without dispersion, whose nodes are the critical states between type-I and type-II Dirac/Weyl nodes, is of great interest. Here, we propose a strategy to explore and design materials that can realize the type-III nodal-ring phonons by introducing two-dimensional (2D) lattices with ideal flat band. As a concrete example, we show by first-principles calculations that the Laves phase AB(2) with C14 structure possesses ideal type-III nodal-ring phonons. The flat phonon band related to type-III nodal-ring phonons originates from their 2D triangular and kagome layers in the Laves phase AB(2). The type-III nodal-ring phonons with nontrivial Berry phase lie on a reflection-invariant plane, which are protected by the inversion and time-reversal symmetries. In addition, the drumhead surface states and unique surface arcs are clearly visible, which facilitate experimental observations. Our work enriches the classification of topological quantum phases, and provides a feasible strategy in designing flat-band related topological phases.

AbstractWe investigate the on‐surface [2+2] cycloaddition reaction of 2,3,6,7,10,11‐hexabromotriphenylene (HBTP) on Ag(111), Cu(111), Au(111), and Cu‐dosed Au(111) surfaces using STM and DFT simulation focusing on the organometallic intermediates. The fully debrominated HBTP molecules form an organo‐silver framework on Ag(111) and an organo‐copper framework on Cu(111), both incorporating multinuclear metal adatom clusters. The organo‐silver framework is converted into porous covalent networks via [2+2] cycloaddition above 240 °C. In contrast, the organo‐copper framework is very stable and does not undergo [2+2] cycloaddition even at 300 °C. On Au(111), no organo‐gold intermediate of [2+2] cycloaddition is observed. After loading Cu onto Au(111), the partially debrominated HBTP molecules bind to Cu adatom dimers to form multinuclear organo‐copper complexes at 100 °C which undergo [2+2] cycloaddition at 140 °C. This study shows that the choice of surface can direct the reaction pathway.

As a paradigmatic phenomenon in condensed matter physics, the quantum anomalous Hall effect (QAHE) in stoichiometric Chern insulators has drawn great interest for years. Using model Hamiltonian analysis and first-principles calculations, we establish a topological phase diagram and map different 2D configurations to it, which are taken from the recently grown magnetic topological insulators MnBi_{4}Te_{7} and MnBi_{6}Te_{10} with superlatticelike stacking patterns. These configurations manifest various topological phases, including the quantum spin Hall effect with and without time-reversal symmetry and QAHE. We then provide design principles to trigger the QAHE by tuning experimentally accessible knobs, such as the slab thickness and magnetization. Our work reveals that superlatticelike magnetic topological insulators with tunable exchange interactions are an ideal platform to realize the long-sought QAHE in pristine compounds, paving a new path within the area of topological materials.

The self-assembly of indeno [1,2-b]fluorene-6,12-dione (IFDO) absorbed on Au(111) was investigated by scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations.It was found that IFDO molecules assembled into one-dimensional molecular chains along the herringbone structures on the Au(111) surface.The lowest unoccupied molecular orbital of IFDO molecules in the assembled structures, relative to isolated molecules, shifts towards Fermi level.The degree of molecular orbital shift, varying from 0.16 to 0.32 eV, depends on the pattern and number of hydrogen bonds formed between the detected IFDO molecule and its neighboring ones.Both transient and induced polarization of neighboring IFDO molecules contribute to the total polarization energy which leads to molecular orbital shift observed by experiments.The former makes the dominant contribution, while the effect of the latter is appreciable especially for molecules composing the defect structures.

Weyl points are often believed to appear in pairs with opposite chirality. In this work, we show by first-principles calculations and symmetry analysis that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion are simultaneously present between two specific phonon branches in realistic materials with trigonal or hexagonal lattices. These phonon Weyl points are guaranteed to locate at high-symmetry points due to the screw rotational symmetry, forming a unique triangular Weyl complex. In sharp contrast to conventional Weyl systems with surface arcs terminated at the projections of a pair of Weyl points with opposite chirality, the phonon surface arcs of the unconventional triangular Weyl complex connect the projections of one double Weyl point and two single Weyl points. Importantly, the phonon surface arcs originating from the triangular Weyl complex are extremely long and span the entire surface Brillouin zone. Furthermore, there are only nontrivial phonon surface states across the isofrequency surface, which facilitates their detection in experiments and further applications. Our work not only offers the promising triangular phonon Weyl complex but also provides guidance for exploring triangular Weyl bosons in both phononic and photonic systems.

We synthesize four- and six-member cyclic products via sequential multi-step aryl-aryl coupling reactions of 2,3,6,7,10,11-hexabromotriphenylene molecules on a Au(111) surface. The final products as well as the organo-gold intermediate structures are identified using scanning tunneling microscopy and density-functional theory simulation. By adjusting reaction temperature and post-annealing temperature, we enhance/suppress the yields of the four-member and six-member cyclic products. We propose an underlying mechanism which is associated with different reaction kinetics of the first-order and second-order reactions. This work exemplifies intricate kinetically-controlled on-surface synthesis when multiple reactions of different reaction order are involved.