Experimental observation of topological Fermi arcs in type-II Weyl semimetal MoTe2

Weyl semimetal is a new quantum state of matter [1-12] hosting the condensed matter physics counterpart of relativisticWeyl fermion [13] originally introduced in high energy physics. The Weyl semimetal realized in the TaAs class features multiple Fermi arcs arising from topological surface states [10, 11, 14-16] and exhibits novel quantum phenomena, e.g., chiral anomaly induced negative mag-netoresistance [17-19] and possibly emergent supersymmetry [20]. Recently it was proposed theoretically that a new type (type-II) of Weyl fermion [21], which does not have counterpart in high energy physics due to the breaking of Lorentz invariance, can emerge as topologically-protected touching between electron and hole pockets. Here, we report direct spectroscopic evidence of topological Fermi arcs in the predicted type-II Weyl semimetal MoTe2 [22-24]. The topological surface states are confirmed by directly observing the surface states using bulk-and surface-sensitive angle-resolved photoemission spectroscopy (ARPES), and the quasi-particle interference (QPI) pattern between the two putative Fermi arcs in scanning tunneling microscopy (STM). Our work establishes MoTe2 as the first experimental realization of type-II Weyl semimetal, and opens up new opportunities for probing novel phenomena such as exotic magneto-transport [21] in type-II Weyl semimetals.Comment: submitted on 01/29/2016. Nature Physics, in press. Spectroscopic evidence of the Fermi arcs from two complementary surface sensitive probes - ARPES and STS. A comparison of the calculated band structure for T_d and 1T' phase to identify the topological Fermi arcs in the T_d phase is also included in the supplementary informatio

Structural and vibrational study of pseudocubic CdIn2Se4 under compression

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp5077565We report a comprehensive experimental and theoretical study of the structural and vibrational properties of a-CdIn2Se4 under compression. Angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy evidence that this ordered-vacancy compound with pseudocubic structure undergoes a phase transition (7 GPa) toward a disordered rocksalt structure as observed in many other ordered-vacancy compounds. The equation of state and the pressure dependence of the Raman-active modes of this semiconductor have been determined and compared both to ab initio total energy and lattice dynamics calculations and to related compounds. Interestingly, on decreasing pressure, at similar to 2 GPa, CdIn2Se4 transforms into a spinel structure which, according to calculations, is energetically competitive with the initial pseudocubic phase. The phase behavior of this compound under compression and the structural and compressibility trends in AB(2)Se(4) selenides are discussed.This study was supported by the Spanish government MEC under Grant Nos: MAT2013-46649-C4-3-P, MAT2013-46649-C4-2-P, MAT2010-21270-C04-03/04, and CTQ2009-14596-C02-01, by MALTA Consolider Ingenio 2010 Project (CSD2007-00045) and by Generalitat Valenciana (GVA-ACOMP-2013-1012). A.M. and P.R-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster, and also to S. Munoz-Rodriguez for providing a data-parsing application. J.A.S. acknowledges Juan de la Cierva fellowship program for financial support.Santamaría Pérez, D.; Gomis, O.; Pereira, ALJ.; Vilaplana Cerda, RI.; Popescu, C.; Sans Tresserras, JÁ.; Manjón Herrera, FJ.... (2014). Structural and vibrational study of pseudocubic CdIn2Se4 under compression. Journal of Physical Chemistry C. 118(46):26987-26999. https://doi.org/10.1021/jp5077565S26987269991184

Fractional deuteration applied to biomolecular solid-state NMR spectroscopy

Solid-state Nuclear Magnetic Resonance can provide detailed insight into structural and dynamical aspects of complex biomolecules. With increasing molecular size, advanced approaches for spectral simplification and the detection of medium to long-range contacts become of critical relevance. We have analyzed the protonation pattern of a membrane-embedded ion channel that was obtained from bacterial expression using protonated precursors and D2O medium. We find an overall reduction of 50% in protein protonation. High levels of deuteration at Hα and Hβ positions reduce spectral congestion in (1H,13C,15N) correlation experiments and generate a transfer profile in longitudinal mixing schemes that can be tuned to specific resonance frequencies. At the same time, residual protons are predominantly found at amino-acid side-chain positions enhancing the prospects for obtaining side-chain resonance assignments and for detecting medium to long-range contacts. Fractional deuteration thus provides a powerful means to aid the structural analysis of complex biomolecules by solid-state NMR

The Key Residue for Substrate Transport (Glu¹⁴) in the EmrE Dimer Is Asymmetric

Transport proteins exhibiting broad substrate specificities are major determinants for the phenomenon of multidrug resistance. The Escherichia coli multidrug transporter EmrE, a 4-transmembrane, helical 12-kDa membrane protein, forms a functional dimer to transport a diverse array of aromatic, positively charged substrates in a proton/drug antiport fashion. Here, we report (13)C chemical shifts of the essential residue Glu(14) within the binding pocket. To ensure a native environment, EmrE was reconstituted into E. coli lipids. Experiments were carried out using one- and two-dimensional double quantum filtered (13)C solid state NMR. For an unambiguous assignment of Glu(14), an E25A mutation was introduced to create a single glutamate mutant. Glu(14) was (13)C-labeled using cell-free expression. Purity, labeling, homogeneity, and functionality were probed by mass spectrometry, NMR spectroscopy, freeze fracture electron microscopy, and transport assays. For Glu(14), two distinct sets of chemical shifts were observed that indicates structural asymmetry in the binding pocket of homodimeric EmrE. Upon addition of ethidium bromide, chemical shift changes and altered line shapes were observed, demonstrating substrate coordination by both Glu(14) in the dimer