Genome Sequence Resource of Fusarium proliferatum f. sp. malus domestica MR5, the Causative Agent of Apple Replant Disease.

Apple replant disease (ARD) caused by the fungal pathogen Fusarium proliferatum f. sp. malus domestica (Fpmd) MR5 brings annual losses to apple production within China. However, the genomic information of the pathogen is not yet available. Here, we obtained the whole-genome sequence of the highly virulent Fpmd MR5 using the Illumina PE150 platform. The genome size was 42.76 Mb and consisted of 9,047 genes. The GC content was 48.80%, and several genes potentially associated with pathogenicity were identified, such as carbohydrate-active enzymes, secreted proteins, and secondary metabolite gene clusters. There were 260 specific virulence factor genes, mainly related to fungal vegetative growth and the production of cell wall-degrading enzymes. These data will aid future studies investigating host-pathogen interactions and help us develop suitable disease management strategies.

Discovery of Fusarium proliferatum f. sp. malus domestica Causing Apple Replant Disease in China.

Apple replant disease (ARD) is the most serious threat facing the apple industry globally. ARD is mainly manifested as decreased plant growth, serious root rot disease, and considerable yield loss. Microbial factors are the dominant factors leading to the occurrence of ARD. Research on soil-borne pathogenic fungi leading to the occurrence of ARD in China is limited. In the present study, we selected 16 replanting orchards from the Northwest Loess region and around the Bohai Gulf. Diseased roots and rhizosphere soil from healthy apple trees and trees showing ARD symptoms were sampled at random. High-throughput sequencing was used to study the fungal communities in the rhizosphere soil, which showed that the composition of the rhizosphere soil fungal community of ARD-symptomatic and healthy apple trees was different. Nectriaceae at the family level and Fusarium at the genus level dominated the rhizosphere soil fungal community in the two regions, while for healthy apple trees, the relative abundance of Mortierella, Minimedusa, Tetracladium, and Chaetomium was higher. Tissue separation and serial dilution were used to separate fungi, and a total of 89 genera and 219 species were obtained, most of which were Fusarium. Fusarium was further confirmed to be the most abundant pathogen species leading to the occurrence of ARD in China through pathogenicity assays. A pathogenicity assay was carried out by the dip-and-cut technique using different host plants. It was found that Fusarium MR5 showed strong aggressiveness to apple rootstocks. Diseased seedlings specifically exhibited chlorosis of the leaves, browning from the edge of the leaf, followed by rolling and yellowing of the leaves, resulting in wilting and eventually death. Strain MR5 was preliminarily identified as F. proliferatum according to the morphological and cultural characteristics. A maximum likelihood analysis of identities based on six gene sequence (ITS, TUB2, IGS, mtSSU, RPB2, and the TEF gene) alignments between the MR5 strain and other strains showed 99 to 100% homology with F. proliferatum. Based on our test results, strain MR5 was identified as F. proliferatum f. sp. malus domestica, which is of great significance for finding new measures to control ARD in China.

Directional massless Dirac fermions in a layered van der Waals material with one-dimensional long-range order.

One or a few layers of van der Waals (vdW) materials are promising for applications in nanoscale electronics. Established properties include high mobility in graphene, a large direct gap in monolayer MoS2, the quantum spin Hall effect in monolayer WTe2 and so on. These exciting properties arise from electron quantum confinement in the two-dimensional limit. Here, we use angle-resolved photoemission spectroscopy to reveal directional massless Dirac fermions due to one-dimensional confinement of carriers in the layered vdW material NbSi0.45Te2. The one-dimensional directional massless Dirac fermions are protected by non-symmorphic symmetry, and emerge from a stripe-like structural modulation with long-range translational symmetry only along the stripe direction as we show using scanning tunnelling microscopy. Our work not only provides a playground for investigating further the properties of directional massless Dirac fermions, but also introduces a unique component with one-dimensional long-range order for engineering nano-electronic devices based on heterostructures of vdW materials.

Reduction of the Spin Susceptibility in the Superconducting State of Sr_{2}RuO_{4} Observed by Polarized Neutron Scattering.

Recent observations [A. Pustogow et al., Nature (London) 574, 72 (2019).NATUAS0028-083610.1038/s41586-019-1596-2] of a drop of the ^{17}O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr_{2}RuO_{4} challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering (PNS) to show that there is a 34±6% drop in the magnetic susceptibility at the Ru site below the superconducting transition temperature. We measure at lower fields H∼1/3H_{c2} than a previous PNS study allowing the suppression to be observed. The PNS measurements show a smaller susceptibility suppression than NMR measurements performed at similar field and temperature. Our results rule out the chiral odd-parity d=z[over ^](k_{x}±ik_{y}) state and are consistent with several recent proposals for the order parameter including even-parity B_{1g} and odd-parity helical states.

Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity.

Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.

A magnetic topological semimetal Sr1-yMn1-zSb2 (y, z < 0.1).

Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal Sr1-yMn1-zSb2 (y, z < 0.1) with nearly massless relativistic fermion behaviour (m∗ =  0.04 - 0.05m0, where m0 is the free-electron mass). This material exhibits a ferromagnetic order for 304 K  <  T  <  565 K, but a canted antiferromagnetic order with a ferromagnetic component for T  <  304 K. The combination of relativistic fermion behaviour and ferromagnetism in Sr1-yMn1-zSb2 offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.

Absence of a Large Superconductivity-Induced Gap in Magnetic Fluctuations of Sr_{2}RuO_{4}.

Inelastic neutron scattering experiments on Sr_{2}RuO_{4} determine the spectral weight of the nesting induced magnetic fluctuations across the superconducting transition. There is no observable change at the superconducting transition down to an energy of ∼0.35 meV, which is well below the 2Δ values reported in several tunneling experiments. At this and higher energies magnetic fluctuations clearly persist in the superconducting state. Only at energies below ∼0.3 meV can evidence for partial suppression of spectral weight in the superconducting state be observed. This strongly suggests that the one-dimensional bands with the associated nesting fluctuations do not form the active, highly gapped bands in the superconducting pairing in Sr_{2}RuO_{4}.

Colossal Magnetoresistance in a Mott Insulator via Magnetic Field-Driven Insulator-Metal Transition.

We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca_{3}Ru_{2}O_{7}. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.

Drastic Pressure Effect on the Extremely Large Magnetoresistance in WTe2: Quantum Oscillation Study.

The quantum oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, in which extremely large magnetoresistance was discovered recently. By analyzing the Shubnikov-de Haas oscillations, four Fermi surfaces are identified, and two of them are found to persist to high pressure. The sizes of these two pockets are comparable, but show increasing difference with pressure. At 0.3 K and in 14.5 T, the magnetoresistance decreases drastically from 1.25×10(5)% under ambient pressure to 7.47×10(3)% under 23.6 kbar, which is likely caused by the relative change of Fermi surfaces. These results support the scenario that the perfect balance between the electron and hole populations is the origin of the extremely large magnetoresistance in WTe2.

Measurement of coherent polarons in the strongly coupled antiferromagnetically ordered iron-chalcogenide Fe1.02Te using angle-resolved photoemission spectroscopy.

The nature of metallicity and the level of electronic correlations in the antiferromagnetically ordered parent compounds are two important open issues for the iron-based superconductivity. We perform a temperature-dependent angle-resolved photoemission spectroscopy study of Fe(1.02)Te, the parent compound for iron chalcogenide superconductors. Deep in the antiferromagnetic state, the spectra exhibit a "peak-dip-hump" line shape associated with two clearly separate branches of dispersion, characteristics of polarons seen in manganites and lightly doped cuprates. As temperature increases towards the Néel temperature (T(N)), we observe a decreasing renormalization of the peak dispersion and a counterintuitive sharpening of the hump linewidth, suggestive of an intimate connection between the weakening electron-phonon (e-ph) coupling and antiferromagnetism. Our finding points to the highly correlated nature of the Fe(1.02)Te ground state featured by strong interactions among the charge, spin, and lattice and a good metallicity plausibly contributed by the coherent polaron motion.

Friedel-like oscillations from interstitial iron in superconducting Fe(1+y)Te0.62Se0.38.

Using polarized and unpolarized neutron scattering, we show that interstitial Fe in superconducting Fe(1+y)Te(1-x)Se(x) induces a magnetic Friedel-like oscillation that diffracts at Q⊥=(1/2 0) and involves >50 neighboring Fe sites. The interstitial >2µ(B) moment is surrounded by compensating ferromagnetic four-spin clusters that may seed double stripe ordering in Fe(1+y)Te. A semimetallic five-band model with (1/2 1/2) Fermi surface nesting and fourfold symmetric superexchange between interstitial Fe and two in-plane nearest neighbors largely accounts for the observed diffraction.

Superconducting spin smecticity evidencing the Fulde-Ferrell-Larkin-Ovchinnikov state in Sr2RuO4.

Translational symmetry breaking is antagonistic to static fluidity but can be realized in superconductors, which host a quantum-mechanical coherent fluid formed by electron pairs. A peculiar example of such a state is the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, induced by a time-reversal symmetry-breaking magnetic field applied to spin-singlet superconductors. This state is intrinsically accompanied by the superconducting spin smecticity, spin density-modulated fluidity with spontaneous translational-symmetry breaking. Detection of such spin smecticity provides unambiguous evidence for the FFLO state, but its observation has been challenging. Here, we report the characteristic "double-horn" nuclear magnetic resonance spectrum in the layered superconductor Sr2RuO4 near its upper critical field, indicating the spatial sinusoidal modulation of spin density that is consistent with superconducting spin smecticity. Our work reveals that Sr2RuO4 provides a versatile platform for studying FFLO physics.

Lattice distortions and the metal-insulator transition in pure and Ti-substituted Ca3Ru2O7.

We report pair distribution function studies on the relationship between the metal-insulator transition (MIT) and lattice distortions in pure and Ti-substituted bilayer Ca3Ru2O7. Structural refinements performed as a function of temperature, magnetic field and length scale reveal the presence of lattice distortions not only within but also orthogonal to the bilayers. Because of the distortions, the local and average crystal structure differ across a broad temperature region extending from room temperature to temperatures below the MIT. The coexistence of distinct lattice distortions is likely to be behind the marked structural flexibility of Ca3Ru2O7under external stimuli. This observation highlights the ubiquity of lattice distortions in an archetypal Mott system and calls for similar studies on other families of strongly correlated materials.

From (pi,0) magnetic order to superconductivity with (pi,pi) magnetic resonance in Fe(1.02)Te(1-x)Se(x).

The iron chalcogenide Fe(1+y)(Te(1-x)Se(x)) is structurally the simplest of the Fe-based superconductors. Although the Fermi surface is similar to iron pnictides, the parent compound Fe(1+y)Te exhibits antiferromagnetic order with an in-plane magnetic wave vector (pi,0) (ref. 6). This contrasts the pnictide parent compounds where the magnetic order has an in-plane magnetic wave vector (pi,pi) that connects hole and electron parts of the Fermi surface. Despite these differences, both the pnictide and chalcogenide Fe superconductors exhibit a superconducting spin resonance around (pi,pi) (refs 9, 10, 11). A central question in this burgeoning field is therefore how (pi,pi) superconductivity can emerge from a (pi,0) magnetic instability. Here, we report that the magnetic soft mode evolving from the (pi,0)-type magnetic long-range order is associated with weak charge carrier localization. Bulk superconductivity occurs as magnetic correlations at (pi,0) are suppressed and the mode at (pi, pi) becomes dominant for x>0.29. Our results suggest a common magnetic origin for superconductivity in iron chalcogenide and pnictide superconductors.

Coupled electronic and magnetic relaxation in Fe1+yTe: direct evidence for the interaction between itinerant carriers and local moments.

Iron chalcogenides are of particular interests among iron-based superconductors due to their distinct properties such as high-Tcon FeSe monolayer and competing magnetic correlations in Fe1+yTe. Here we report unusual transport properties observed near the critical composition of Fe1+yTe (y∼ 0.09) where competing magnetic correlations exist. The resistivity exhibits surprising temperature-dependent relaxation behavior belowTN, resulting in the increase of resistivity with time for 35 K

Spin-valley locking and bulk quantum Hall effect in a noncentrosymmetric Dirac semimetal BaMnSb2.

Spin-valley locking in monolayer transition metal dichalcogenides has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. Here, we report spin-valley locking in a Dirac semimetal BaMnSb2. This is revealed by comprehensive studies using first principles calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy measurements. Moreover, this material also exhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy extracted from the QHE is close to 2. This result, together with the Landau level spin splitting, further confirms the spin-valley locking picture. In the extreme quantum limit, we also observed a plateau in the z-axis resistance, suggestive of a two-dimensional chiral surface state present in the quantum Hall state. These findings establish BaMnSb2 as a rare platform for exploring coupled spin and valley physics in bulk single crystals and accessing 3D interacting topological states.

Suppression of proximity effect and the enhancement of p-wave superconductivity in the Sr2RuO4-Ru system.

We report unexpected phenomena observed on the Sr2RuO4-Ru eutectic phase featuring Ru islands embedded in a bulk crystal of the chiral p-wave superconductor Sr2RuO4. It was found that the Sr2RuO4/Ru interface is atomically sharp, terminated uniformly by a Sr/O layer. Surprisingly, the proximity-induced p-wave superconducting energy gap predicted by theory was not detected inside Ru islands. Our results suggest that the previously observed enhancement of superconductivity in this eutectic phase occurs away from rather than near the Sr2RuO4/Ru interface, where dislocations and phonon hardening were found.

Structure characterization of human cytomegalovirus UL131A, UL130 and UL128 genes in clinical strains in China.

Human cytomegalovirus (HCMV) genetic determinants of endothelial cell tropism, leukocytes and dendritic cells have been identified in the genes UL131A, UL130, and UL128. We examined the structure of these three genes in HCMV. Eighteen low-passage clinical isolates and five non-passage strains from congenitally HCMV-infected infants in China were used to assess the structures of the UL131A, UL130, and UL128 genes and to find possible relationships between sequence polymorphism and different signs of HCMV disease. Comparisons were made between the UL131A, UL130, and UL128 genes of clinical strains and published sequences of Towne and Merlin strains. The UL131A coding region in the clinical strains was similar to that of Towne and Merlin strains, while UL130, and UL128 coding regions in the clinical strains were parallel with those of Towne and Merlin, respectively. Sequence comparison indicated that the UL130, and UL128 genes encode chemokine-like proteins in the clinical strain; the transmembrane regions of UL131A, and UL130 were conserved in all clinical and reference strains. The three genes of clinical strains from infants with different signs of HCMV disease had similar structure characterization. We conclude that the UL131A, UL130, and UL128 genes are highly conserved in these clinical strains. No correlation was found between the structure of the three genes and variations in HCMV disease. The finding of chemokine-like domains in UL130, and UL128 putative proteins suggests that the predicted products play a role in HCMV infectivity.

Insulator-metal transition induced by electric voltage in a ruthenate Mott insulator.

We report the observation of electric-voltage induced insulator-metal phase transition in a ruthenate Mott insulator Ca3(Ru0.9Ti0.1)2O7. We show that the electric field effect dominates and leads to a sharp phase transition at measurement temperatures far below the Mott transition, whereas the thermal effect becomes more significant and broadens the phase transition as the measurement temperature approaches the insulator-metal transition. The electric field induced insulator-metal transition is presumably attributed to the avalanche breakdown of the correlated insulating state when driven out of equilibrium. This work highlights the strategy of using electric voltage to control the phase transition of this system in addition to other nonthermal parameters such as magnetic field and pressure reported previously.

Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3.

Topological materials which are also superconducting are of great current interest, since they may exhibit a non-trivial topologically-mediated superconducting phase. Although there have been many reports of pressure-tuned or chemical-doping-induced superconductivity in a variety of topological materials, there have been few examples of intrinsic, ambient pressure superconductivity in a topological system having a stoichiometric composition. Here, we report that the pure intermetallic CaSn3 not only exhibits topological fermion properties, but also has a superconducting phase at ~1.178 K under ambient pressure. The topological fermion properties, including the nearly zero quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron motions, were revealed from the de Haas-van Alphen (dHvA) quantum oscillation studies of this material. Although CaSn3 was previously reported to be superconducting with T c = 4.2 K, our studies show that the T c = 4.2 K superconductivity is extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk superconducting transition occurs at 1.178 K. These findings make CaSn3 a promising candidate for exploring new exotic states arising from the interplay between non-trivial band topology and superconductivity, e.g. topological superconductivity (TSC).