Topological phase transition and texture inversion in a tunable topological insulator

The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. By directly measuring the topological quantum numbers and invariants, we report the observation of a phase transition in a tunable spin-orbit system, BiTl(S(1-δ)Se(δ))(2), in which the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit three-dimensional vectorial textures, which collectively feature a chirality transition as the spin momentum-locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena.     

Quantum spin Hall effect and topological phase transition in HgTe quantum wells

We show that the quantum spin Hall (QSH) effect, a state of matter with topological properties distinct from those of conventional insulators, can be realized in mercury telluride-cadmium telluride semiconductor quantum wells. When the thickness of the quantum well is varied, the electronic state changes from a normal to an "inverted" type at a critical thickness d(c). We show that this transition is a topological quantum phase transition between a conventional insulating phase and a phase exhibiting the QSH effect with a single pair of helical edge states. We also discuss methods for experimental detection of the QSH effect.     

The coexistence of superconductivity and topological order in the Bi₂Se₃ thin films

Three-dimensional topological insulators (TIs) are characterized by their nontrivial surface states, in which electrons have their spin locked at a right angle to their momentum under the protection of time-reversal symmetry. The topologically ordered phase in TIs does not break any symmetry. The interplay between topological order and symmetry breaking, such as that observed in superconductivity, can lead to new quantum phenomena and devices. We fabricated a superconducting TI/superconductor heterostructure by growing dibismuth triselenide (Bi(2)Se(3)) thin films on superconductor niobium diselenide substrate. Using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we observed the superconducting gap at the Bi(2)Se(3) surface in the regime of Bi(2)Se(3) film thickness where topological surface states form. This observation lays the groundwork for experimentally realizing Majorana fermions in condensed matter physics.     

Interaction-driven spectrum reconstruction in bilayer graphene

The nematic phase transition in electronic liquids, driven by Coulomb interactions, represents a new class of strongly correlated electronic ground states. We studied suspended samples of bilayer graphene, annealed so that it achieves very high quasiparticle mobilities (greater than 10(6) square centimers per volt-second). Bilayer graphene is a truly two-dimensional material with complex chiral electronic spectra, and the high quality of our samples allowed us to observe strong spectrum reconstructions and electron topological transitions that can be attributed to a nematic phase transition and a decrease in rotational symmetry. These results are especially surprising because no interaction effects have been observed so far in bilayer graphene in the absence of an applied magnetic field.     

Two-dimensional nematic colloidal crystals self-assembled by topological defects

The ability to generate regular spatial arrangements of particles is an important technological and fundamental aspect of colloidal science. We showed that colloidal particles confined to a few-micrometer-thick layer of a nematic liquid crystal form two-dimensional crystal structures that are bound by topological defects. Two basic crystalline structures were observed, depending on the ordering of the liquid crystal around the particle. Colloids inducing quadrupolar order crystallize into weakly bound two-dimensional ordered structure, where the particle interaction is mediated by the sharing of localized topological defects. Colloids inducing dipolar order are strongly bound into antiferroelectric-like two-dimensional crystallites of dipolar colloidal chains. Self-assembly by topological defects could be applied to other systems with similar symmetry.     

Topological transitions in metamaterials

Light-matter interactions can be controlled by manipulating the photonic environment. We uncovered an optical topological transition in strongly anisotropic metamaterials that results in a dramatic increase in the photon density of states-an effect that can be used to engineer this interaction. We describe a transition in the topology of the iso-frequency surface from a closed ellipsoid to an open hyperboloid by use of artificially nanostructured metamaterials. We show that this topological transition manifests itself in increased rates of spontaneous emission of emitters positioned near the metamaterial. Altering the topology of the iso-frequency surface by using metamaterials provides a fundamentally new route to manipulating light-matter interactions.     

Quantum phase extraction in isospectral electronic nanostructures

Quantum phase is not directly observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures with matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these "quantum drums"-degenerate two-dimensional electron states on the copper(111) surface confined by individually positioned carbon monoxide molecules-reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction.     

刺云实胶对魔芋葡甘聚糖分子链拓扑缠结的分析

将魔芋葡甘聚糖(KGM)与刺云实胶(TG)以一定的比例复配,通过旋转流变仪测定KGM-TG复配体系的相关流变特性,结合分子动力学和拓扑分析学研究KGM和TG分子的作用方式,探讨刺云实胶对魔芋葡甘聚糖分子链拓扑缠结的作用机理。结果表明,刺云实胶与KGM分子间存在协同增效作用,分子链间的主要作用是氢键作用力,刺云实胶的添加使得KGM分子链间的拓扑缠结强度与密度的增强,复配体系的力学性能得到加强。从分子作用本质上验证了刺云实胶与KGM之间流变性能的理化实验结果。     

Quantum phase interference and parity effects in magnetic molecular clusters

An experimental method based on the Landau-Zener model was developed to measure very small tunnel splittings in molecular clusters of eight iron atoms, which at low temperature behave like a nanomagnet with a spin ground state of S = 10. The observed oscillations of the tunnel splittings as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum interference of two tunnel paths of opposite windings. Transitions between quantum numbers M = -S and (S - n), with n even or odd, revealed a parity effect that is analogous to the suppression of tunneling predicted for half-integer spins. This observation is direct evidence of the topological part of the quantum spin phase (Berry phase) in a magnetic system.     

Topological defects coupling smectic modulations to intra-unit-cell nematicity in cuprates

We study the coexisting smectic modulations and intra-unit-cell nematicity in the pseudogap states of underdoped Bi(2)Sr(2)CaCu(2)O(8+δ). By visualizing their spatial components separately, we identified 2π topological defects throughout the phase-fluctuating smectic states. Imaging the locations of large numbers of these topological defects simultaneously with the fluctuations in the intra-unit-cell nematicity revealed strong empirical evidence for a coupling between them. From these observations, we propose a Ginzburg-Landau functional describing this coupling and demonstrate how it can explain the coexistence of the smectic and intra-unit-cell broken symmetries and also correctly predict their interplay at the atomic scale. This theoretical perspective can lead to unraveling the complexities of the phase diagram of cuprate high-critical-temperature superconductors.     

三次Hamiltonian对称系统的全局拓扑结构

研究一类三次Hamiltonian对称系统(1)，通过对系统的有限奇点和无穷远奇点的分析，给出了系统所有可能的全局拓扑结构。     

Low-voltage organic transistors on plastic comprising high-dielectric constant gate insulators

The gate bias dependence of the field-effect mobility in pentacene-based insulated gate field-effect transistors (IGFETs) was interpreted on the basis of the interaction of charge carriers with localized trap levels in the band gap. This understanding was used to design and fabricate IGFETs with mobility of more than 0.3 square centimeter per volt per second and current modulation of 10(5), with the use of amorphous metal oxide gate insulators. These values were obtained at operating voltage ranges as low as 5 volts, which are much smaller than previously reported results. An all-room-temperature fabrication process sequence was used, which enabled the demonstration of high-performance organic IGFETs on transparent plastic substrates, at low operating voltages for organic devices.     

Effects of cis arrangement of chromatin insulators on enhancer-blocking activity

Chromatin boundary elements or insulators are believed to regulate gene activity in complex genetic loci by organizing specialized chromatin structures. Here, we report that the enhancer-blocking activity of the Drosophila suHw insulator is sensitive to insulator copy number and position. Two tandem copies of suHw were ineffective in blocking various enhancers from a downstream promoter. Moreover, an enhancer was blocked more effectively from a promoter by two flanking suHw insulators than by a single intervening one. Thus, insulators may modulate enhancer-promoter interactions by interacting with each other and facilitating the formation of chromatin loop domains.     

Emerging chirality in artificial spin ice

Artificial spin ice, made up of planar nanostructured arrays of simple ferromagnetic bars, is a playground for rich physics associated with the spin alignment of the bars and spin texture associated with the magnetic frustration at the bar vertices. The phase diagram is exotic, showing magnetic monopole-like defects and liquid and solid phases of spins arranged in loop states with predicted chiral order. We show that magnetotransport measurements in connected honeycomb structures yield the onset of an anomalous Hall signal at 50 kelvin. The temperature scale can be attributed to the long-range dipolar ice phase. The topological Hall signal arises because chiral loops form at the sample edges, indicating a generic route to exotic states via nanoarray edge structure.     

黄酮类化合物槲皮素与甲基丙烯酸分子识别机理研究

在B3LYP/6-311＋＋G（d,p）水平下采用密度泛函理论,计算得甲基丙烯酸与槲皮素分子间结合能为-21.09 kJ/mol;采用自然键轨道理论与电子拓扑研究分析了分子间作用的本质。     

Specificity and stability in topology of protein networks

Molecular networks guide the biochemistry of a living cell on multiple levels: Its metabolic and signaling pathways are shaped by the network of interacting proteins, whose production, in turn, is controlled by the genetic regulatory network. To address topological properties of these two networks, we quantified correlations between connectivities of interacting nodes and compared them to a null model of a network, in which all links were randomly rewired. We found that for both interaction and regulatory networks, links between highly connected proteins are systematically suppressed, whereas those between a highly connected and low-connected pairs of proteins are favored. This effect decreases the likelihood of cross talk between different functional modules of the cell and increases the overall robustness of a network by localizing effects of deleterious perturbations.     

An in vivo map of the yeast protein interactome

Protein interactions regulate the systems-level behavior of cells; thus, deciphering the structure and dynamics of protein interaction networks in their cellular context is a central goal in biology. We have performed a genome-wide in vivo screen for protein-protein interactions in Saccharomyces cerevisiae by means of a protein-fragment complementation assay (PCA). We identified 2770 interactions among 1124 endogenously expressed proteins. Comparison with previous studies confirmed known interactions, but most were not known, revealing a previously unexplored subspace of the yeast protein interactome. The PCA detected structural and topological relationships between proteins, providing an 8-nanometer-resolution map of dynamically interacting complexes in vivo and extended networks that provide insights into fundamental cellular processes, including cell polarization and autophagy, pathways that are evolutionarily conserved and central to both development and human health.     

Quasi-particle properties from tunneling in the v = 5/2 fractional quantum Hall state

Quasi-particles with fractional charge and statistics, as well as modified Coulomb interactions, exist in a two-dimensional electron system in the fractional quantum Hall (FQH) regime. Theoretical models of the FQH state at filling fraction v = 5/2 make the further prediction that the wave function can encode the interchange of two quasi-particles, making this state relevant for topological quantum computing. We show that bias-dependent tunneling across a narrow constriction at v = 5/2 exhibits temperature scaling and, from fits to the theoretical scaling form, extract values for the effective charge and the interaction parameter of the quasi-particles. Ranges of values obtained are consistent with those predicted by certain models of the 5/2 state.     

High-resolution inkjet printing of all-polymer transistor circuits

Direct printing of functional electronic materials may provide a new route to low-cost fabrication of integrated circuits. However, to be useful it must allow continuous manufacturing of all circuit components by successive solution deposition and printing steps in the same environment. We demonstrate direct inkjet printing of complete transistor circuits, including via-hole interconnections based on solution-processed polymer conductors, insulators, and self-organizing semiconductors. We show that the use of substrate surface energy patterning to direct the flow of water-based conducting polymer inkjet droplets enables high-resolution definition of practical channel lengths of 5 micrometers. High mobilities of 0.02 square centimeters per volt second and on-off current switching ratios of 10(5) were achieved.