2,889 research outputs found
Orbital Fulde-Ferrell pairing state in moir\'e Ising superconductors
In this work, we study superconducting moir\'e homobilayer transition metal
dichalcogenides where the Ising spin-orbit coupling (SOC) is much larger than
the moir\'e bandwidth. We call such noncentrosymmetric superconductors, moir\'e
Ising superconductors. Due to the large Ising SOC, the depairing effect caused
by the Zeeman field is negligible and the in-plane upper critical field
() is determined by the orbital effects. This allows us to study the
effect of large orbital fields. Interestingly, when the applied in-plane field
is larger than the conventional orbital , a finite-momentum pairing
phase would appear which we call the orbital Fulde-Ferrell (FF) state. In this
state, the Cooper pairs acquire a net momentum of where is
the momentum shift caused by the magnetic field and denotes the layer
separation. This orbital field-driven FF state is different from the
conventional FF state driven by Zeeman effects in Rashba superconductors.
Remarkably, we predict that the FF pairing would result in a giant
superconducting diode effect under electric gating when layer asymmetry is
induced. An upturn of the as the temperature is lowered, coupled with
the giant superconducting diode effect, would allow the detection of the
orbital FF state.Comment: 6 pages, 4 figures, plus Supplementary Materia
Nonlinear Hall Effects in Strained Twisted Bilayer WSe
Recently, it has been pointed out that the twisting of bilayer WSe would
generate topologically non-trivial flat bands near the Fermi energy. In this
work, we show that twisted bilayer WSe (tWSe) with uniaxial strain
exhibits a large nonlinear Hall (NLH) response due to the non-trivial Berry
curvatures of the flat bands. Moreover, the NLH effect is greatly enhanced near
the topological phase transition point which can be tuned by a vertical
displacement field. Importantly, the nonlinear Hall signal changes sign across
the topological phase transition point and provides a way to identify the
topological phase transition and probe the topological properties of the flat
bands. The strong enhancement and high tunability of the NLH effect near the
topological phase transition point renders tWSe and related moire materials
new platforms for rectification and second harmonic generations.Comment: 5 pages, 3 figures. Comments are welcom
Sliding Dynamics of Current-Driven Skyrmion Crystal and Helix in Chiral Magnets
The skyrmion crystal (SkX) and helix (HL) phases, present in typical chiral
magnets, can each be considered as forms of density waves but with distinct
topologies. The SkX exhibits gyrodynamics analogous to electrons under a
magnetic field, while the HL state resembles topological trivial spin density
waves. However, unlike the charge density waves, the theoretical analysis of
the sliding motion of SkX and HL remains unclear, especially regarding the
similarities and differences in sliding dynamics between these two spin density
waves. In this work, we systematically explore the sliding dynamics of SkX and
HL in chiral magnets in the limit of large current density. We demonstrate that
the sliding dynamics of both SkX and HL can be unified within the same
theoretical framework as density waves, despite their distinct microscopic
orders. Furthermore, we highlight the significant role of gyrotropic sliding
induced by impurity effects in the SkX state, underscoring the impact of
nontrivial topology on the sliding motion of density waves. Our theoretical
analysis shows that the effect of impurity pinning is much stronger in HL
compared with SkX, i.e., (,
: susceptibility to the impurity potential, () is
the Gilbert damping). Moreover, the velocity correction is mostly in the
transverse direction to the current in SkX. These results are further
substantiated by realistic Landau-Lifshitz-Gilbert simulations.Comment: 6 pages, 3 figures, plus supplementary materia
Berry curvature, spin Hall effect and nonlinear optical response in moir\'e transition metal dichalcogenide heterobilayers
Recently, the topological flat bands and spin Hall effect have been
experimentally observed in the AB-stacked MoTe/WSe heterostructures. In
this work, we systematically study the Berry curvature effects in moir\'{e}
transition metal dichalcogenide (TMD) heterobilayers. We point out that the
moir\'{e} potential of the remote conduction bands would induce a sizable
periodic pseudo-magnetic field (PMF) on the valence band. This periodic PMF
creates net Berry curvature flux in each valley of the moir\'{e} Brillouin
zone. The combination of the effect of the Berry curvature and the spin-valley
locking can induce the spin Hall effect being observed in the experiment.
Interestingly, the valley-contrasting Berry curvature distribution generated by
the PMF can be probed through shift currents, which are DC currents induced by
linearly polarized lights through nonlinear responses. Our work shed lights on
the novel quantum phenomena induced by Berry curvatures in moir\'e TMD
heterobilayers.Comment: 10 pages, 7 figure
Suppression of epidemic spreading in complex networks by local information based behavioral responses
This work was funded by the National Natural Science Foundation of China (Grant Nos. 61473001, 11105025, and 11331009) and the Doctoral Research Foundation of Anhui University (Grant No. 02303319). Y.C.L. was supported by AFOSR under Grant No. FA9550-10-1-0083.Peer reviewedPublisher PD
Comparative and phylogenomic studies on the mitochondrial genomes of Pentatomomorpha (Insecta: Hemiptera: Heteroptera)
<p>Abstract</p> <p>Background</p> <p>Nucleotide sequences and the gene arrangements of mitochondrial genomes are effective tools for resolving phylogenetic problems. Hemipteroid insects are known to possess highly reorganized mitochondrial genomes, but in the suborder Heteroptera (Insecta: Hemiptera), there was only one complete mitochondrial genome sequenced without gene rearrangement and the phylogeny of infraorder Pentatomomorpha in Heteroptera was still uncertain.</p> <p>Results</p> <p>Fifteen mitochondrial genomes of the suborder Heteroptera were sequenced. Gene rearrangements were found as follows: 1) <it>tRNA-I </it>and <it>tRNA-Q </it>switched positions in Aradidae, 2) <it>tRNA-T </it>and <it>tRNA-P </it>switched positions in Largidae and Pyrrhocoridae. Two recombination events were found in Alydidae and Malcidae. The other mt-genomes were organized in the same way as observed in <it>Drosophila yakuba</it>. The phylogenetic analyses of infraorder Pentatomomorpha based on the nucleotide sequence raised the hypothesis of (Aradoidea + (Pentatomoidea + (Pyrrhocoroidea + (Lygaeoidea + Coreoidea)))). The rearrangement of <it>tRNA-T </it>and <it>tRNA-P </it>also linked Largidae and Pyrrhocoridae together. Furthermore, the conserved sequence block in the unusual intergenic spacers between <it>tRNA-H </it>and <it>ND4 </it>favored the monophyly of Lygaeoidea. Tetranucleotide ATCA was inferred to be the initiation codon of <it>ND2 </it>in Cydnidae. No correlation was found between the rates of nucleotide substitution and gene rearrangement. CG content was significantly correlated with the nucleotide substitution rate of each gene. For ND1, there was a positive correlation (<it>P </it>< 0.01) between amino acids variations and hydrophobicity, but a negative correlation (<it>P </it>< 0.01) for ND6. No conserved sequence was found among the control regions and these regions were not always the most AT-rich region of the mt-genome.</p> <p>Conclusion</p> <p>Heteropteran insects are extremely complex groups worthy of further study because of the unusual tetranucleotide initiation codon and their great mt-genomic diversity, including gene rearrangements and recombinations. The mt-genome is a powerful molecular marker for resolving phylogeny at the level of the superfamily and family. Gene rearrangements were not correlated with nucleotide substitution rates. CG content variation caused the different evolutionary patterns among genes. For ND1, in many polar or nonpolar regions the specific identity of the amino acid residues might be more important than maintaining the polarity of these regions, while the opposite is true for ND6. Most sequences of the control regions did not appear to be important for regulatory functions. Finally, we suggest that the term "AT-rich regions" should not be used.</p
Phylogenetic analysis of the true water bugs (Insecta: Hemiptera: Heteroptera: Nepomorpha): evidence from mitochondrial genomes
<p>Abstract</p> <p>Background</p> <p>The true water bugs are grouped in infraorder Nepomorpha (Insecta: Hemiptera: Heteroptera) and are of great economic importance. The phylogenetic relationships within Nepomorpha and the taxonomic hierarchies of Pleoidea and Aphelocheiroidea are uncertain. Most of the previous studies were based on morphological characters without algorithmic assessment. In the latest study, the molecular markers employed in phylogenetic analyses were partial sequences of 16S rDNA and 18S rDNA with a total length about 1 kb. Up to now, no mitochondrial genome of the true water bugs has been sequenced, which is one of the largest data sets that could be compared across animal taxa. In this study we analyzed the unresolved problems in Nepomorpha using evidence from mitochondrial genomes.</p> <p>Results</p> <p>Nine mitochondrial genomes of Nepomorpha and five of other hemipterans were sequenced. These mitochondrial genomes contain the commonly found 37 genes without gene rearrangements. Based on the nucleotide sequences of mt-genomes, Pleoidea is not a member of the Nepomorpha and Aphelocheiroidea should be grouped back into Naucoroidea. Phylogenetic relationships among the superfamilies of Nepomorpha were resolved robustly.</p> <p>Conclusion</p> <p>The mt-genome is an effective data source for resolving intraordinal phylogenetic problems at the superfamily level within Heteroptera. The mitochondrial genomes of the true water bugs are typical insect mt-genomes. Based on the nucleotide sequences of the mt-genomes, we propose the Pleoidea to be a separate heteropteran infraorder. The infraorder Nepomorpha consists of five superfamilies with the relationships (Corixoidea + ((Naucoroidea + Notonectoidea) + (Ochteroidea + Nepoidea))).</p
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