Raman scattering in correlated thin films as a probe of chargeless surface states

Several powerful techniques exist to detect topologically protected surface states of weakly-interacting electronic systems. In contrast, surface modes of strongly interacting systems which do not carry electric charge are much harder to detect. We propose resonant light scattering as a means of probing the chargeless surface modes of interacting quantum spin systems, and illustrate its efficacy by a concrete calculation for the 3D hyperhoneycomb Kitaev quantum spin liquid phase. We show that resonant scattering is required to efficiently couple to this model's sublattice polarized surface modes, comprised of emergent Majorana fermions that result from spin fractionalization. We demonstrate that the low-energy response is dominated by the surface contribution for thin films, allowing identification and characterization of emergent topological band structures.Comment: 7 pages, 4 figures; added supplemental materia

Phylogenomic analysis of lactobacillus curvatus reveals two lineages distinguished by genes for fermenting plant-derived carbohydrates

Lactobacillus curvatus is a lactic acid bacterium encountered in many different types of fermented food (meat, seafood, vegetables, and cereals). Although this species plays an important role in the preservation of these foods, few attempts have been made to assess its genomic diversity. This study uses comparative analyses of 13 published genomes (complete or draft) to better understand the evolutionary processes acting on the genome of this species. Phylogenomic analysis, based on a coalescent model of evolution, revealed that the 6,742 sites of single nucleotide polymorphism within the L. curvatus core genome delineate two major groups, with lineage 1 represented by the newly sequenced strain FLEC03, and lineage 2 represented by the type-strain DSM20019. The two lineages could also be distinguished by the content of their accessory genome, which sheds light on a long-term evolutionary process of lineage-dependent genetic acquisition and the possibility of population structure. Interestingly, one clade from lineage 2 shared more accessory genes with strains of lineage 1 than with other strains of lineage 2, indicating recent convergence in carbohydrate catabolism. Both lineages had a wide repertoire of accessory genes involved in the fermentation of plant-derived carbohydrates that are released from polymers of α/β-glucans, α/β-fructans, and N-acetylglucosan. Other gene clusters were distributed among strains according to the type of food from which the strains were isolated. These results give new insight into the ecological niches in which L. curvatus may naturally thrive (such as silage or compost heaps) in addition to fermented food.Fil: Teran, Lucrecia Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; ArgentinaFil: Coeuret, Gwendoline. Institut National de la Recherche Agronomique; FranciaFil: Raya, Raul Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Centro de Referencia para Lactobacilos; ArgentinaFil: Zagorec, Monique. Institut National de la Recherche Agronomique; FranciaFil: Champomier-Vergès, Marie-Christine. Institut National de la Recherche Agronomique; FranciaFil: Chaillou, Stéphane. Institut National de la Recherche Agronomique; Franci

Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate γ\gamma-Li2_2IrO3_3

Honeycomb iridates such as $\gamma$-Li$_2$IrO$_3$ are argued to realize Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly other couplings. While systems with pure Kitaev interactions are candidates to realize a quantum spin liquid ground state, in $\gamma$-Li$_2$IrO$_3$ it has been shown that the balance of magnetic interactions leads to the incommensurate spiral spin order at ambient pressure below 38 K. We study the fragility of this state in single crystals of $\gamma$-Li$_2$IrO$_3$ using resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to 3.0 GPa. RXS is a direct probe of the underlying electronic order, and we observe the abrupt disappearance of the $q$=(0.57, 0, 0) spiral order at a critical pressure $P_c = 1.5\$GPa with no accompanying change in the symmetry of the lattice. This dramatic disappearance is in stark contrast with recent studies of $\beta$-Li$_2$IrO$_3$ that show continuous suppression of the spiral order in magnetic field; under pressure, a new and possibly nonmagnetic ground state emerges