Incommensurate charge-stripe correlations in the kagome superconductor CsV3_3Sb5−x_{5-x}Snx_x

We track the evolution of charge correlations in the kagome superconductor CsV$_3$Sb$_5$ as its parent, long-ranged charge density order is destabilized. Upon hole-doping doping, interlayer charge correlations rapidly become short-ranged and their periodicity is reduced by half along the interlayer direction. Beyond the peak of the first superconducting dome, the parent charge density wave state vanishes and incommensurate, quasi-1D charge correlations are stabilized in its place. These competing, unidirectional charge correlations demonstrate an inherent electronic rotational symmetry breaking in CsV$_3$Sb$_5$, independent of the parent charge density wave state and reveal a complex landscape of charge correlations across the electronic phase diagram of this class of kagome superconductors. Our data suggest an inherent 2$k_f$ charge instability and the phenomenology of competing charge instabilities is reminiscent of what has been noted across several classes of unconventional superconductors.Comment: 6 pages, 4 figure

Fermi surface mapping and the nature of charge density wave order in the kagome superconductor CsV3_3Sb5_5

The recently discovered family of AV$_3$Sb$_5$ (A: K, Rb Cs) kagome metals possess a unique combination of nontrivial band topology, superconducting ground states, and signatures of electron correlations manifest via competing charge density wave order. Little is understood regarding the nature of the charge density wave (CDW) instability inherent to these compounds and the potential correlation with the accompanying onset of a large anomalous Hall response. To understand the impact of the CDW order on the electronic structure in these systems, we present quantum oscillation measurements on single crystals of CsV$_3$Sb$_5$. Our data provides direct evidence that the CDW invokes a substantial reconstruction of the Fermi surface pockets associated with the vanadium orbitals and the kagome lattice framework. In conjunction with density functional theory modeling, we are able to identify split oscillation frequencies originating from reconstructed pockets built from vanadium orbitals and Dirac-like bands. Complementary diffraction measurements are further able to demonstrate that the CDW instability has a correlated phasing between neighboring V$_3$Sb$_5$ planes. These results provide critical insights into the underlying CDW instability in AV$_3$Sb$_5$ kagome metals and support minimal models of CDW order arising from within the vanadium-based kagome lattice.Comment: 12 pages, 9 figure

Frustrated charge order and cooperative distortions in ScV6Sn6

Here we study the stability of charge order in the kagome metal ScV6Sn6. Synchrotron x-ray diffraction measurements reveal high-temperature, short-range charge correlations at the wave vectors along q=(1/3,1/3,1/2) whose inter-layer correlation lengths diverge upon cooling. At the charge order transition, this divergence is interrupted and long-range order freezes in along q=(1/3,1/3,1/3), as previously reported, while disorder enables the charge correlations to persist at the q=(1/3,1/3,1/2) wave vector down to the lowest temperatures measured. Both short-range and long-range charge correlations seemingly arise from the same instability and both are rapidly quenched upon the introduction of larger Y ions onto the Sc sites. Our results validate the theoretical prediction of the primary lattice instability at q=(1/3,1/3,1/2), and we present a heuristic picture for viewing the frustration of charge order in this compound

GREEK-BERT: The Greeks visiting Sesame Street

Transformer-based language models, such as BERT and its variants, have achieved state-of-the-art performance in several downstream natural language processing (NLP) tasks on generic benchmark datasets (e.g., GLUE, SQUAD, RACE). However, these models have mostly been applied to the resource-rich English language. In this paper, we present GREEK-BERT, a monolingual BERT-based language model for modern Greek. We evaluate its performance in three NLP tasks, i.e., part-of-speech tagging, named entity recognition, and natural language inference, obtaining state-of-the-art performance. Interestingly, in two of the benchmarks GREEK-BERT outperforms two multilingual Transformer-based models (M-BERT, XLM-R), as well as shallower neural baselines operating on pre-trained word embeddings, by a large margin (5%-10%). Most importantly, we make both GREEK-BERT and our training code publicly available, along with code illustrating how GREEK-BERT can be fine-tuned for downstream NLP tasks. We expect these resources to boost NLP research and applications for modern Greek.Comment: 8 pages, 1 figure, 11th Hellenic Conference on Artificial Intelligence (SETN 2020

Loss of CD103+ DCs and Mucosal IL-17+ and IL-22+ Lymphocytes is Associated with Mucosal Damage in SIV Infection

HIV/SIV disease progression is associated with multifocal damage to the GI tract epithelial barrier that correlates with microbial translocation and persistent pathological immune activation but the underlying mechanisms remain unclear. Investigating alterations in mucosal immunity during SIV infection, we found that damage to the colonic epithelial barrier was associated with loss of multiple lineages of IL-17-producing lymphocytes, cells that microarray analysis showed express genes important for enterocyte homeostasis, including IL-22. IL-22-producing lymphocytes were also lost after SIV infection. Potentially explaining coordinate loss of these distinct populations, we also observed loss of CD103+ DCs after SIV infection which associated with loss of IL-17 and IL-22-producing lymphocytes. CD103+ DCs expressed genes associated with promotion of IL-17/IL-22+ cells, and co-culture of CD103+ DCs and naïve T-cells led to increased IL17A and RORc expression in differentiating T-cells. These results reveal complex interactions between mucosal immune cell subsets providing potential mechanistic insights into mechanisms of mucosal immune dysregulation during HIV/SIV infection, and offer hints for development of novel therapeutic strategies to address this aspect of AIDS virus pathogenesis

YbV3_3Sb4_4 and EuV3_3Sb4_4, vanadium-based kagome metals with Yb2+^{2+} and Eu2+^{2+} zig-zag chains

Here we present YbV$_3$Sb$_4$ and EuV$_3$Sb$_4$, two new compounds exhibiting slightly distorted vanadium-based kagome nets interleaved with zig-zag chains of divalent Yb$^{2+}$ and Eu$^{2+}$ ions. Single crystal growth methods are reported alongside magnetic, electronic, and thermodynamic measurements. YbV$_3$Sb$_4$ is a nonmagnetic metal with no collective phase transitions observed between 60mK and 300K. Conversely, EuV$_3$Sb$_4$ is a magnetic kagome metal exhibiting easy-plane ferromagnetic-like order below $T_\text{C}$=32K with signatures of noncollinearity under low field. Our discovery of YbV$_3$Sb$_4$ and EuV$_3$Sb$_4$ demonstrate another direction for the discovery and development of vanadium-based kagome metals while incorporating the chemical and magnetic degrees of freedom offered by a rare-earth sublattice

Metabolite Damage and Damage Control in a Minimal Genome

Analysis of the genes retained in the minimized Mycoplasma JCVI-Syn3A genome established that systems that repair or preempt metabolite damage are essential to life. Several genes known to have such functions were identified and experimentally validated, including 5-formyltetrahydrofolate cycloligase, coenzyme A (CoA) disulfide reductase, and certain hydrolases. Furthermore, we discovered that an enigmatic YqeK hydrolase domain fused to NadD has a novel proofreading function in NAD synthesis and could double as a MutT-like sanitizing enzyme for the nucleotide pool. Finally, we combined metabolomics and cheminformatics approaches to extend the core metabolic map of JCVI-Syn3A to include promiscuous enzymatic reactions and spontaneous side reactions. This extension revealed that several key metabolite damage control systems remain to be identified in JCVI-Syn3A, such as that for methylglyoxal. IMPORTANCE Metabolite damage and repair mechanisms are being increasingly recognized. We present here compelling genetic and biochemical evidence for the universal importance of these mechanisms by demonstrating that stripping a genome down to its barest essentials leaves metabolite damage control systems in place. Furthermore, our metabolomic and cheminformatic results point to the existence of a network of metabolite damage and damage control reactions that extends far beyond the corners of it that have been characterized so far. In sum, there can be little room left to doubt that metabolite damage and the systems that counter it are mainstream metabolic processes that cannot be separated from life itself