Ubiquitous coexisting electron-mode couplings in high-temperature cuprate superconductors.

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of [Formula: see text]70-meV nodal dispersion kink and [Formula: see text]40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electron-mode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at [Formula: see text]70meV and [Formula: see text]40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the well-known "peak-dip-hump" structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of "peak-double dip-double hump" finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the [Formula: see text]70-meV and [Formula: see text]40-meV energy scales and their evolutions with momentum, doping and temperature. They provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity.

Probing the photocurrent in two-dimensional titanium disulfide.

Generating photocurrent in a condensed matter system involves the excitation, relaxation, and transportation of charge carriers. As such, it is viewed a potent method for probing the dynamics of non-equilibrium carriers and the electronic band structure of solid state materials. In this research, we analyze the photoresponse of the mechanically exfoliated titanium disulfide (TiS2), a transition metal dichalcogenide whose classification as either a semimetal or a semiconductor has been the subject of debate for years. The scanning photocurrent microscopy and the temperature-dependent photoresponse characterization expose the appearance of a photovoltaic current primarily from the metal/TiS2junction in an unbiased sample, while negative photoconductivity due to the bolometric effect is observed in the conductive TiS2channel. The optoelectronic experimental results, combined with electrical transport characterization and angle-resolved photoemission spectroscopy measurements, indicate that the TiS2employed in this study is likely a heavily-doped semiconductor. Our findings unveil the photocurrent generation mechanism of two dimensional TiS2, highlighting its prospective optoelectronic applications in the future.

Genome-Wide Identification and Analysis of the WRKY Gene Family in Asparagus officinalis.

In recent years, the related research of the WRKY gene family has been gradually promoted, which is mainly reflected in the aspects of environmental stress and hormone response. However, to make the study of the WRKY gene family more complete, we also need to focus on the whole-genome analysis and identification of the family. In previous studies, the whole WRKY gene family of Arabidopsis, legumes and other plants has been thoroughly studied. However, since the publication of Asparagus officinalis genome-wide data, there has never been an analysis of the whole WRKY gene family. To understand more broadly the function of the WRKY gene family, the whole genome and salt stress transcriptome data of asparagus were used for comprehensive analysis in this study, including WRKY gene family identification, phylogenetic tree construction, analysis of conserved mods and gene domains, extraction of cis-acting elements, intron/exon analysis, species collinearity analysis, and WRKY expression analysis under salt stress. The results showed that a total of 70 genes were selected and randomly distributed on 10 chromosomes and one undefined chromosome. According to the functional classification of Arabidopsis thaliana, the WRKY family of asparagus was divided into 11 subgroups (C1-C9, U1, U2). It is worth considering that the distribution rules of gene-conserved motifs, gene domains and introns/exons in the same subfamily are similar, which suggests that genes in the same subfamily may regulate similar physiological processes. In this study, 11 cis-acting elements of WRKY family were selected, among which auxin, gibberellin, abscisic acid, salicylic acid and other hormone-regulated induction elements were involved. In addition, environmental stress (such as drought stress and low-temperature response) also accounted for a large proportion. Interestingly, we analyzed a total of two tandem duplicate genes and 13 segmental duplication genes, suggesting that this is related to the amplification of the WRKY gene family. Transcriptome data analysis showed that WRKY family genes could regulate plant growth and development by up-regulating and down-regulating gene expression under salt stress. Volcanic maps showed that 3 and 15 AoWRKY genes were significantly up-regulated or down-regulated in NI&NI+S and AMF&AMF+S, respectively. These results provide a new way to analyze the evolution and function of the WRKY gene family, and can provide a reference for the production and research of asparagus.

The priming effects of plant leachates on dissolved organic matter degradation in water depend on leachate type and water stability.

The modification of dissolved organic matter (DOM) degradation by plant carbon inputs represents a critical biogeochemical process that controls carbon dynamics. However, the priming effects (PEs) different plant tissues induce on the degradation of DOM pools with different stabilities remain unknown. In this study, PEs, induced by different tissue leachates of Phragmites australis, were evaluated via changes in DOM components and properties of both fresh and tidal water (with different stabilities). The results showed that DOM derived from different plant tissue leachates differed in composition and bioavailability. Inputs of tissue leachates induced PEs with different intensities and directions (negative or positive) on DOM degradation of fresh and tidal water. In fresh water, the PEs of leaf and root leachates were significantly higher than those of stem and rhizome leachates. The PE direction changed for DOM degradation between fresh and tidal water. The addition of leaf and root leachates tended to induce positive PEs on DOM degradation of fresh water, while resulting in negative PEs on DOM degradation of tidal water. Negative PEs for tidal water DOM may be due to preferential utilization of microbes, high salinity, and/or the promotion of exogenous DOM production from plant tissues. The results indicate that intensity and direction of PEs induced by plant leachates depend on both leachate type and water stability. The findings highlight the necessity to examine the nature of exogenous and native DOM when interpreting the interactive processes that regulate DOM degradation.

Genome-Wide Identification and Analysis of the R2R3-MYB Gene Family in Theobroma cacao.

The MYB gene family is involved in the regulation of plant growth, development and stress responses. In this paper, to identify Theobroma cacao R2R3-MYB (TcMYB) genes involved in environmental stress and phytohormones, we conducted a genome-wide analysis of the R2R3-MYB gene family in Theobroma cacao (cacao). A total of 116 TcMYB genes were identified, and they were divided into 23 subgroups according to the phylogenetic analysis. Meanwhile, the conserved motifs, gene structures and cis-acting elements of promoters were analyzed. Moreover, these TcMYB genes were distributed on 10 chromosomes. We conducted a synteny analysis to understand the evolution of the cacao R2R3-MYB gene family. A total of 37 gene pairs of TcMYB genes were identified through tandem or segmental duplication events. Additionally, we also predicted the subcellular localization and physicochemical properties. All the studies showed that TcMYB genes have multiple functions, including responding to environmental stresses. The results provide an understanding of R2R3-MYB in Theobroma cacao and lay the foundation for a further functional analysis of TcMYB genes in the growth of cacao.

Highly Efficient Multiphoton Absorption of Zinc-AIEgen Metal-Organic Frameworks.

A series of luminescent frameworks was synthesized from the selective combination of aggregation induced emission (AIE)-linker tetra-(4-carboxylphenyl)ethylene (H4 TCPE) and Zn2+ . Complex 1 was formed by the close packing of Zn-TCPE hinge, and isostructural complexes 2-5 were constructed by the linkage of Zn-TCPE layer and pillar ligands. These complexes exhibit highly efficient multiphoton excited photoluminescence (MEPL) and concomitant third-harmonic generation (THG). The multiphoton absorption (MPA) parameters of 1 are superior to other multiphoton emission materials including the perovskite nanocrystals. The incorporation of pillar linkers slows down the charge transfer between layers of Zn-TCPE, and the aromatic core of pillar linkers has a great influence on the MPA performance of the corresponding frameworks.

Genome-Wide Identification and Analysis of the GRAS Transcription Factor Gene Family in Theobroma cacao.

GRAS genes exist widely and play vital roles in various physiological processes in plants. In this study, to identify Theobroma cacao (T. cacao) GRAS genes involved in environmental stress and phytohormones, we conducted a genome-wide analysis of the GRAS gene family in T. cacao. A total of 46 GRAS genes of T. cacao were identified. Chromosomal distribution analysis showed that all the TcGRAS genes were evenly distributed on ten chromosomes. Phylogenetic relationships revealed that GRAS proteins could be divided into twelve subfamilies (HAM: 6, LISCL: 10, LAS: 1, SCL4/7: 1, SCR: 4, DLT: 1, SCL3: 3, DELLA: 4, SHR: 5, PAT1: 6, UN1: 1, UN2: 4). Of the T. cacao GRAS genes, all contained the GRAS domain or GRAS superfamily domain. Subcellular localization analysis predicted that TcGRAS proteins were located in the nucleus, chloroplast, and endomembrane system. Gene duplication analysis showed that there were two pairs of tandem repeats and six pairs of fragment duplications, which may account for the rapid expansion in T. cacao. In addition, we also predicted the physicochemical properties and cis-acting elements. The analysis of GO annotation predicted that the TcGRAS genes were involved in many biological processes. This study highlights the evolution, diversity, and characterization of the GRAS genes in T. cacao and provides the first comprehensive analysis of this gene family in the cacao genome.

Genome-Wide Identification and Analysis of the MADS-Box Gene Family in Theobroma cacao.

The MADS-box family gene is a class of transcription factors that have been extensively studied and involved in several plant growth and development processes, especially in floral organ specificity, flowering time and initiation and fruit development. In this study, we identified 69 candidate MADS-box genes and clustered these genes into five subgroups (Mα: 11; Mß: 2; Mγ: 14; Mδ: 9; MIKC: 32) based on their phylogenetical relationships with Arabidopsis. Most TcMADS genes within the same subgroup showed a similar gene structure and highly conserved motifs. Chromosomal distribution analysis revealed that all the TcMADS genes were evenly distributed in 10 chromosomes. Additionally, the cis-acting elements of promoter, physicochemical properties and subcellular localization were also analyzed. This study provides a comprehensive analysis of MADS-box genes in Theobroma cacao and lays the foundation for further functional research.

In-Plane Anisotropic Nonlinear Optical Properties of Two-Dimensional Organic-Inorganic Hybrid Perovskite.

Two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) with superior nonlinear optical (NLO) properties show great versatility in frequency upconversion applications. Optical anisotropy plays an indispensable role in interpreting the interactions between incoming photons and crystal structure. Recently, the in-plane anisotropic NLO properties of 2D OIHPs have been reported and attracted much attention. However, the structure-related NLO anisotropy of the 2D OIHP framework is not well-established. Here, NLO properties of (C6H5(CH2)2NH3)2PbI4 (PEPI), (C6H11NH3)2PbI4 (C6H11), and (C4H9NH3)2PbI4 (C4PI) were systematically studied to interrogate the correlation between the in-plane anisotropic NLO responses and its lattice structure. In-plane nonparametric NLO responses, e.g., two-photon photoluminescence (2PPL) and three-photon photoluminescence (3PPL), manifest similar anisotropy configurations for PEPI, C6H11, and C4PI regardless of aromatic, cyclic, or linear organic molecules; however, the anisotropies of THG signals are strongly dependent on the specific crystal structures of the individual flakes, and they are much higher than that of the multiphoton excited photoluminescence.

Thermodynamics Controlled Sharp Transformation from InP to GaP Nanowires via Introducing Trace Amount of Gallium.

Growth of high-quality III-V nanowires at a low cost for optoelectronic and electronic applications is a long-term pursuit of research. Still, controlled synthesis of III-V nanowires using chemical vapor deposition method is challenge and lack theory guidance. Here, we show the growth of InP and GaP nanowires in a large area with a high density using a vacuum chemical vapor deposition method. It is revealed that high growth temperature is required to avoid oxide formation and increase the crystal purity of InP nanowires. Introduction of a small amount of Ga into the reactor leads to the formation of GaP nanowires instead of ternary InGaP nanowires. Thermodynamic calculation within the calculation of phase diagrams (CALPHAD) approach is applied to explain this novel growth phenomenon. Composition and driving force calculations of the solidification process demonstrate that only 1 at.% of Ga in the catalyst is enough to tune the nanowire formation from InP to GaP, since GaP nucleation shows a much larger driving force. The combined thermodynamic studies together with III-V nanowire growth studies provide an excellent example to guide the nanowire growth.

Valence band dispersion measurements of perovskite single crystals using angle-resolved photoemission spectroscopy.

The electronic structure of a cleaved perovskite (CH3NH3PbBr3) single crystal was studied in an ultra-high vacuum (UHV) system using angle-resolved photoemission spectroscopy (ARPES) and inverse photoelectron spectroscopy (IPES). Highly reproducible dispersive features of the valence bands were observed with symmetry about the Brillouin zone center and boundaries. The largest dispersion width was found to be ∼0.73 eV and ∼0.98 eV along the ΓX and ΓM directions, respectively. The effective mass of the holes was estimated to be ∼0.59m0. The quality of the surface was verified using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The elemental composition was investigated using high resolution X-ray photoelectron spectroscopy (XPS). The experimental electronic structure shows a good agreement with the theoretical calculation.

Imaging the three-dimensional Fermi-surface pairing near the hidden-order transition in URu2Si2 using angle-resolved photoemission spectroscopy.

We report angle-resolved photoemission spectroscopy experiments probing deep into the hidden-order state of URu(2)Si(2), utilizing tunable photon energies with sufficient energy and momentum resolution to detect the near Fermi-surface (FS) behavior. Our results reveal (i) the full itinerancy of the 5f electrons, (ii) the crucial three-dimensional k-space nature of the FS and its critical nesting vectors, in good comparison with density-functional theory calculations, and (iii) the existence of hot-spot lines and pairing of states at the FS, leading to FS gapping in the hidden-order phase.

Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi2Sr2-xLaxCuO(6+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

Coexistence of Fermi arcs and Fermi pockets in a high-T(c) copper oxide superconductor.

In the pseudogap state of the high-transition-temperature (high-T(c)) copper oxide superconductors, angle-resolved photoemission (ARPES) measurements have seen Fermi arcs-that is, open-ended gapless sections in the large Fermi surface-rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested by recent quantum oscillation measurements. The Fermi arcs cannot be understood in terms of existing theories, although there is a solution in the form of conventional Fermi surface pockets associated with competing order, but with a back side that is for detailed reasons invisible to photoemission probes. Here we report ARPES measurements of Bi(2)Sr(2-x)La(x)CuO(6+delta) (La-Bi2201) that reveal Fermi pockets. The charge carriers in the pockets are holes, and the pockets show an unusual dependence on doping: they exist in underdoped but not overdoped samples. A surprise is that these Fermi pockets appear to coexist with the Fermi arcs. This coexistence has not been expected theoretically.

High energy dispersion relations for the high temperature Bi2Sr2CaCu2O8 superconductor from laser-based angle-resolved photoemission spectroscopy.

Laser-based angle-resolved photoemission spectroscopy measurements have been carried out on the high energy electron dynamics in Bi2Sr2CaCu2O8 high temperature superconductor. Our superhigh resolution data, momentum-dependent measurements, and complete analysis provide important information to judge the nature of the high energy dispersion and kink. Our results rule out the possibility that the high energy dispersion from the momentum distribution curve (MDC) may represent the true bare band as believed in previous studies. We also rule out the possibility that the high energy kink represents electron coupling with some high energy modes as proposed before. Through detailed MDC and energy distribution curve analyses, we propose that the high energy MDC dispersion may not represent intrinsic band structure.

Development of a vacuum ultraviolet laser-based angle-resolved photoemission system with a superhigh energy resolution better than 1 meV.

The design and performance of the first vacuum ultraviolet (VUV) laser-based angle-resolved photoemission (ARPES) system are described. The VUV laser with a photon energy of 6.994 eV and bandwidth of 0.26 meV is achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2. The new VUV laser-based ARPES system exhibits superior performance, including superhigh energy resolution better than 1 meV, high momentum resolution, superhigh photon flux, and much enhanced bulk sensitivity, which are demonstrated from measurements on a typical Bi2Sr2CaCu2O8 high temperature superconductor. Issues and further development related to the VUV laser-based photoemission technique are discussed.

Identification of a new form of electron coupling in the Bi2Sr2CaCu2O8 superconductor by laser-based angle-resolved photoemission spectroscopy.

Laser-based angle-resolved photoemission measurements with superhigh resolution have been carried out on an optimally doped Bi(2)Sr(2)CaCu(2)O(8) high temperature superconductor. New high energy features at approximately 115 meV and approximately 150 meV, in addition to the prominent approximately 70 meV one, are found to develop in the nodal electron self-energy in the superconducting state. These high energy features, which cannot be attributed to electron coupling with single phonon or magnetic resonance mode, point to the existence of a new form of electron coupling in high temperature superconductors.