In polar semiconductors and oxides, the long-range nature of the electron-phonon (e-ph) interaction is a bottleneck to compute charge transport from first principles. Here, we develop an efficient ab initio scheme to compute and converge the e-ph relaxation times (RTs) and electron mobility in polar materials. We apply our approach to GaAs, where by using the Boltzmann equation with state-dependent RTs, we compute mobilities in excellent agreement with experiment at 250-500 K. The e-ph RTs and the phonon contributions to intravalley and intervalley e-ph scattering are also analyzed. Our work enables efficient ab initio computations of transport and carrier dynamics in polar materials. DOI: 10.1103/PhysRevB.94.201201 Semiconductors with polar bonds, such as III-V and II-VI compounds, and oxides, are important in condensed matter physics and for technological applications. Charge transport in these polar materials plays a key role in electronics, optoelectronic, photovoltaics, and photocatalysis. Novel experiments [1,2] are dramatically advancing the understanding of charge transport in polar materials. Yet, their microscopic interpretation requires detailed knowledge of the carrier scattering processes. Since fabricating pure crystals is challenging for many polar materials, extracting intrinsic charge transport properties from experiment is nontrivial; questions related to the role of doping, impurities, and defects often arise when interpreting transport measurements.Ab initio computational approaches to study the carrier transport and scattering mechanisms are uniquely poised to advance the understanding of polar materials. Ab initio calculations of carrier mobility [3][4][5][6][7][8][9] and scattering [10][11][12][13] are a recent development, and have been reported so far only for a few metals and nonpolar semiconductors. However, the mobility in polar semiconductors and oxides, which is the focus of this Rapid Communication, is still typically investigated with semiempirical models [1,14]. One major challenge in computing transport in polar materials is the Fröhlich interaction [15], a long-range coupling between electrons and longitudinal optical (LO) phonons. Electronphonon (e-ph) scattering due to LO modes, and in general to polar phonons (PPs), is typically the main carrier scattering mechanism in polar materials, but it cannot yet be included in ab initio transport calculations.When computed directly using density functional perturbation theory (DFPT) [16], the e-ph matrix elements correctly include the Fröhlich interaction for arbitrary values of the phonon wave vector q. Yet, the very large number of e-ph matrix elements necessary to converge the mobility and the e-ph relaxation times (RTs) [10-12] make direct DFPT calculations impractical due to computational cost. For metals and nonpolar semiconductors, in which the e-ph interaction is short ranged, Wannier interpolation [17] can be employed to obtain e-ph matrix elements on fine Brillouin zone (BZ) grids. In polar materials, Wannier interpolati...

Using first-principles calculations within density functional theory, we investigate the intrinsic spin Hall effect in monolayers of group-VI transition-metal dichalcogenides M X2 (M = Mo, W and X = S, Se). M X2 monolayers are direct band-gap semiconductors with two degenerate valleys located at the corners of the hexagonal Brillouin zone. Because of the inversion symmetry breaking and the strong spin-orbit coupling, charge carriers in opposite valleys carry opposite Berry curvature and spin moment, giving rise to both a valley-Hall and a spin-Hall effect. We also show that the intrinsic spin Hall conductivity in inversion-symmetric bulk dichalcogenides is an order of magnitude smaller compared to monolayers. Our result demonstrates monolayer dichalcogenides as an ideal platform for the integration of valleytronics and spintronics.

Perturbo is a software package for first-principles calculations of charge transport and ultrafast carrier dynamics in materials. The current version focuses on electron-phonon interactions and can compute phonon-limited transport properties such as the conductivity, carrier mobility and Seebeck coefficient. It can also simulate the ultrafast nonequilibrium electron dynamics in the presence of electron-phonon scattering. Perturbo uses results from density functional theory and density functional perturbation theory calculations as input, and employs Wannier interpolation to reduce the computational cost. It supports norm-conserving and ultrasoft pseudopotentials, spin-orbit coupling, and polar electron-phonon corrections for bulk and 2D materials. Hybrid MPI plus OpenMP parallelization is implemented to enable efficient calculations on large systems (up to at least 50 atoms) using high-performance computing. Taken together, Perturbo provides efficient and broadly applicable ab initio tools to investigate electron-phonon interactions and carrier dynamics quantitatively in metals, semiconductors, insulators, and 2D materials.

Self-incompatibility S-locus–encoded F-box (SLF) proteins have been identified in Antirrhinum and several Prunus species. Although they appear to play an important role in self-incompatible reaction, functional evidence is lacking. Here, we provide several lines of evidence directly implicating a role of AhSLF-S2 in self-incompatibility in Antirrhinum. First, a nonallelic physical interaction between AhSLF-S2 and S-RNases was demonstrated by both coimmunoprecipitation and yeast two-hybrid assays. Second, AhSLF-S2 interacts with ASK1- and CULLIN1-like proteins in Antirrhinum, and together, they likely form an Skp1/Cullin or CDC53/F-box (SCF) complex. Third, compatible pollination was specifically blocked after the treatment of the proteasomal inhibitors MG115 and MG132, but they had little effect on incompatible pollination both in vitro and in vivo, indicating that the ubiquitin/26S proteasome activity is involved in compatible pollination. Fourth, the ubiquitination level of style proteins was increased substantially after compatible pollination compared with incompatible pollination, and coimmunoprecipitation revealed that S-RNases were ubiquitinated after incubating pollen proteins with compatible but not with incompatible style proteins, suggesting that non-self S-RNases are possibly degraded by the ubiquitin/26S proteasome pathway. Fifth, the S-RNase level appeared to be reduced after 36 h of compatible pollination. Taken together, these results show that AhSLF-S2 interacts with S-RNases likely through a proposed SCFAhSLF-S2 complex that targets S-RNase destruction during compatible rather than incompatible pollination, thus providing a biochemical basis for the inhibition of pollen tube growth as observed in self-incompatible response in Antirrhinum

Recently, we have provided evidence that the polymorphic self-incompatibility (S) locus-encoded F-box (SLF) protein AhSLF-S 2 plays a role in mediating a selective S-RNase destruction during the self-incompatible response in Antirrhinum hispanicum. To investigate its role further, we first transformed a transformation-competent artificial chromosome clone (TAC26) containing both AhSLF-S 2 and AhS 2 -RNase into a self-incompatible (SI) line of Petunia hybrida. Molecular analyses showed that both genes are correctly expressed in pollen and pistil in four independent transgenic lines of petunia. Pollination tests indicated that all four lines became self-compatible because of the specific loss of the pollen function of SI. This alteration was transmitted stably into the T1 progeny. We then transformed AhSLF-S 2 cDNA under the control of a tomato (Lycopersicon esculentum) pollen-specific promoter LAT52 into the self-incompatible petunia line. Molecular studies revealed that AhSLF-S 2 is specifically expressed in pollen of five independent transgenic plants. Pollination tests showed that they also had lost the pollen function of SI. Importantly, expression of endogenous SLF or SLF-like genes was not altered in these transgenic plants. These results phenocopy a well-known phenomenon called competitive interaction whereby the presence of two different pollen S alleles within pollen leads to the breakdown of the pollen function of SI in several solanaceaous species. Furthermore, we demonstrated that AhSLF-S 2 physically interacts with PhS 3 -RNase from the P. hybrida line used for transformation. Together with the recent demonstration of PiSLF as the pollen determinant in P. inflata, these results provide direct evidence that the polymorphic SLF including AhSLF-S 2 controls the pollen function of S-RNase-based self-incompatibility.

Quantum spin Hall (QSH) insulators have gapless topological edge states inside the bulk band gap, which can serve as dissipationless spin current channels. The major challenge currently is to find suitable materials for this topological state. Here, we predict a new large-gap QSH insulator with bulk direct band gap of ∼0.18 eV, in single-layer Bi 4 Br 4 , which could be exfoliated from its three-dimensional bulk material due to the weakly-bonded layered structure. The band gap of single-layer Bi 4 Br 4 is tunable via strain engineering, and the QSH phase is robust against external strain. Moreover, because this material consists of special one-dimensional molecular chain as its basic building block, the single layer Bi 4 Br 4 could be torn to ribbons with clean and atomically sharp edges. These nano-ribbons, which have singleDirac-cone edge states crossing the bulk band gap, are ideal wires for dissipationless transport.

Gene duplication plays a fundamental role in evolution by providing the genetic material from which novel functions can arise. Newly duplicated genes can be maintained by subfunctionalization (the duplicated genes perform different aspects of the original gene's function) and/or neofunctionalization (one of the genes acquires a novel function). PLENA in Antirrhinum and AGAMOUS in Arabidopsis are the canonical C-function genes that are essential for the specification of reproductive organs. These functionally equivalent genes encode closely related homeotic MADS-box transcription factors. Using genome synteny, we confirm phylogenetic analyses showing that PLENA and AGAMOUS are nonorthologous genes derived from a duplication in a common ancestor. Their respective orthologs, SHATTERPROOF in Arabidopsis and FARINELLI in Antirrhinum, have undergone independent subfunctionalization via changes in regulation and protein function. Surprisingly, the functional divergence between PLENA and FARINELLI, is morphologically manifest in both transgenic Antirrhinum and Arabidopsis. This provides a clear illustration of a random evolutionary trajectory for gene functions after a duplication event. Different members of a duplicated gene pair have retained the primary homeotic functions in different lineages, illustrating the role of chance in evolution. The differential ability of the Antirrhinum genes to promote male or female development provides a striking example of subfunctionalization at the protein level.

Metformin is a biguanide drug that has been used to treat type 2 diabetes mellitus for more than 60 years. The United Kingdom Prospective Diabetic Study (UKPDS) has shown metformin to improve mortality rates in diabetes patients, and recent studies suggest metformin has additional effects in treating cancer, obesity, nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), and metabolic syndrome. Metformin has also been shown to alleviate weight gain associated with antipsychotic medication. Metformin has recently been extensively studied and emerging evidence suggests metformin decreases hepatocyte triglyceride accumulation in NAFLD and prevents liver tumorigenesis. Interestingly, studies have also shown metformin reduces visceral fat, suppresses white-adipose-tissue (WAT) extracellular matrix remodeling, and inhibits obesity-induced inflammation. However, clinical evidence for using metformin to treat NAFLD, cancer, metabolic syndrome, or to prevent hepatocellular carcinoma in NAFLD patients is lacking. This review therefore addresses the potential beneficial effects of metformin on NAFLD, its role in protecting against cardiac ischemia–reperfusion (I/R) injury, atherosclerosis, glucotoxicity, and lipotoxicity induced oxidative and ER stress in pancreatic β-cell dysfunction, as well as its underlying molecular mechanisms of action.