Elucidating the microscopic origin of nematic order in iron-based superconducting materials is important because the interactions that drive nematic order may also mediate the Cooper pairing 1 .Nematic order breaks fourfold rotational symmetry in the iron plane, which is believed to be driven by either orbital or spin degrees of freedom [1][2][3][4][5] . However, as the nematic phase often develops at a temperature just above or coincides with a stripe magnetic phase transition, experimentally determining the dominant driving force of nematic order is difficult 1,6 . Here, we use neutron scat- tering to study structurally the simplest iron-based superconductor FeSe (ref. 7), which displays a nematic (orthorhombic) phase transition at T s = 90 K, but does not order antiferromagnetically.Our data reveal substantial stripe spin fluctuations, which are coupled with orthorhombicity and are enhanced abruptly on cooling to below T s . Moreover, a sharp spin resonance develops in the superconducting state, whose energy (∼ 4 meV) is consistent with an electron boson coupling mode revealed by scanning tunneling spectroscopy 8 , thereby suggesting a spin fluctuation-mediated signchanging pairing symmetry. By normalizing the dynamic susceptibility into absolute units, we show that the magnetic spectral weight in FeSe is comparable to that of the iron arsenides 9,10 . Our findings support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations 1,2,11-14 .Most parent compounds of iron-based superconductors exhibit a stripe-type long-range antiferromagnetic (AFM) order which is pre-empted by a nematic order: a correlation of electronic states which breaks rotational, but not translational, symmetry. Superconductivity emerges when the magnetic and nematic order are partially or completely suppressed by chemical doping or by the application of pressure 1,6 . The stripe AFM order consists of columns of parallel spins along the orthorhombic b direction, together with antiparallel spins along the a direction. Similar to the stripe AFM order, the nematic order also breaks the fourfold rotational symmetry, which is signaled by the tetragonal to orthorhombic structure phase transition and pronounced in-plane anisotropy of electronic and magnetic properties 1,6,[15][16][17][18] . It has been proposed that nematicity could be driven either by orbital or spin fluctuations, and that orbital fluctuations tend to lead to a sign-preserving s ++ -wave pairing, while spin fluctuations favor a sign-changing s ± -wave or d-wave pairing [1][2][3][4][5][6]14,19,20 . However, as orbital and spin degrees of freedom are coupled and could be easily affected by the nearby stripe magnetic order, it remains elusive which of them is the primary driving force of nematicity [1][2][3][4][5]14,19 .FeSe (T c ≈ 8 K) has attracted great attention not only because of the simple crystal structure (Fig. 1a), 3 but also because it displays a variety of exotic properties unprecedented for other iron based superconduc...

A large and high-quality single crystal (Li 0.84 Fe 0.16 )OHFe 0.98 Se, the optimal superconductor of newly reported (Li 1-x Fe x )OHFe 1-y Se system, has been successfully synthesized via a hydrothermal ion-exchange technique. The superconducting transition temperature (T c ) of 42 K is determined by magnetic susceptibility and electric resistivity measurements, and the zero-temperature upper critical magnetic fields are evaluated as 79 and 313 Tesla for the field along the c-axis and the ab-plane, respectively. The ratio of out-of-plane to in-plane electric resistivity,ρ c /ρ ab , is found to increases with decreasing temperature and to reach a high value of 2500 at 50 K, with an evident kink occurring at a characteristic temperature T*=120 K. The negative in-plane Hall coefficient indicates that electron carriers dominate in the charge transport, and the hole contribution is significantly reduced as the temperature is lowered to approach T*. From T* down to T c , we observe the linear temperature dependences of the in-plane electric resistivity and the magnetic susceptibility for the FeSe layers. Our findings thus reveal that the normal state of (Li 0.84 Fe 0.16 )OHFe 0.98 Se becomes highly two-dimensional and anomalous prior to the superconducting transition, providing a new insight into the mechanism of high-T c superconductivity.

In most existing theories for iron-based superconductors, spin-orbit coupling (SOC) has been assumed to be insignificant. Here, we use spin-polarized inelastic neutron scattering to show that collective low-energy spin excitations in the orthorhombic (or "nematic") phase of FeSe possess nearly no in-plane component. Such spin-space anisotropy is present over an energy range greater than the superconducting gap 2Δ sc and gets fully inherited in the superconducting state, resulting in a c-axis polarized "spin resonance" without any noticeable isotropic spectral-weight rearrangement related to the superconductivity, which is distinct from observations in the superconducting iron pnictides. The contrast between the strong suppression of long-range magnetic order in FeSe and the persisting large spin-space anisotropy, which cannot be explained microscopically by introducing single-ion anisotropy into local-moment spin models, demonstrates the importance of SOC in an itinerant-electron description of the low-energy spin excitations. Our result helps to elucidate the nearby magnetic instabilities and the debated interplay between spin and orbital degrees of freedom in FeSe. The prominent role of SOC also implies a possible unusual nature of the superconducting state.

Grain length (size) and weight are essential components of crop yield. To date, many QTLs/genes for these traits have been identified. GS3 encodes a putative transmembrane protein and functions as a negative regulator, and its larger-grain allele contains a nonsense mutation causing a 178-aa truncation (Fan et al., 2006). GL3.1/qGL3 encodes a putative protein phosphatase and also acts as a negative regulator of grain size (Qi et al., 2012;Zhang et al., 2012). Another negative regulator of grain size and weight is TGW6, which hydrolyzes indole-3-acetic acid (IAA)-glucose into IAA and glucose (Ishimaru et al., 2013). In contrast, GW6a is a positive regulator of grain weight, which encodes a novel histone H4 acetyltransferase (Song et al., 2015). Copy number variation at the GL7/GW7 locus causes elevated expression of GL7 and thus an increase in grain length (Wang et al., 2015a(Wang et al., , 2015b. GL2/GS2 encodes the plant-specific transcription factor OsGRF4, and its larger-grain allele harbors a mutation preventing cleavage by miR396c, resulting in elevated GL2/GS2 expression (Hu et al., 2015;Che et al., 2016). GLW7 encodes the plantspecific transcription factor OsSPL13, and high OsSPL13 expression is associated with larger grains (Si et al., 2016). These findings have greatly enhanced our understanding of grain length and weight regulation; however, there are still gaps in integrating these factors into genetic network(s). Here, we report a thorough dissection of the QTL composition of grain size and the characterization of a novel QTL, qTGW3, that regulates grain length and weight in rice.

Simple basic zirconium carbonate exhibits high catalytic activity at low temperatures for hydrogen transfer of biomass-derived carboxides.

Chemical substitution during growth is a well-established method to manipulate electronic states of quantum materials, and leads to rich spectra of phase diagrams in cuprate and iron-based superconductors. Here we report a novel and generic strategy to achieve nonvolatile electron doping in series of (i.e. 11 and 122 structures) Fe-based superconductors by ionic liquid gating induced protonation at room temperature. Accumulation of protons in bulk compounds induces superconductivity in the parent compounds, and enhances the T c largely in some superconducting ones. Furthermore, the existence of proton in the lattice enables the first proton nuclear magnetic resonance (NMR) study to probe directly superconductivity. Using FeS as a model system, our NMR study reveals an emergent high-T c phase with no coherence peak which is hard to measure by NMR with other isotopes. This novel electric-field-induced proton evolution opens up an avenue for manipulation of competing electronic states (e.g. Mott insulators), and may provide an innovative way for a broad perspective of NMR measurements with greatly enhanced detecting resolution.

A flux-free solution to the growth of large and composition homogeneous superconducting FeSe crystal is reported for the first time, which is based on the traveling-solvent floating-zone technique. The size of the crystal samples prepared by this approach is up to 15×6×2 mm 3 , being far bigger than previously reported in all dimensions, and the main phase of the crystals is of a single preferred orientation along the tetragonal (101) plane. X-ray diffraction analysis identifies the main phase to be the superconducting tetragonal β-FeSe.The superconducting transition temperature (T C ) is determined to be 9.4 K by AC magnetic susceptibility and electronic transport measurements. A nearly perfect diamagnetic shielding of -97% is observed, indicating a bulk superconductivity in the crystal sample. Keywords:Iron-based superconductor; FeSe; crystal growth; traveling-solvent floating-zone method. solvent were ground and mixed with an agate mortar and pestle in glove box filled with argon gas. The mixtures were then pressed into separate columnar shapes before sealed in an evacuated quartz tube and heated at 700 for 10 hours ℃ . The obtained products were once again well ground, sealed in evacuated quartz tube and heated at 700 ºC for 10 hours. After that, the materials were ground into fine powders in the glove box. The preparation of dense and homogeneous feed rods is one of the key factors in achieving a stable and continuous TSFZ growth. The fine powders of 8 g in mass used for the feed rod was loaded into a tubular balloon and pressed under a high hydrostatic pressure over 5 kbar for 2 minutes to form a compact cylindrical rod of 8 cm in length. The feed rod was then sealed in evacuated quartz tube and was finally sintered at 750 for 3 hours. ℃ The solvent used for the TSFZ growth was prepared through the same procedures as that of the feed rod and was finally pressed and sintered together with the feed rod.An optical floating-zone furnace (Crystal Systems Inc., Model FZ-T-10000-H) with 4×150 W halogen lamps as infrared radiation sources was used for TSFZ growth. The crystal was grown in a highly purified argon flow at a zone traveling rate of 0.6 mm/h, using a previously grown FeSe crystal as a seed crystal which is oriented along the tetragonal (101) plane.During the crystal growth the upper feed rod and the lower grown ingot were rotated in opposite directions to improve growth conditions. The composition of as-prepared crystals was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES).Powder and single crystal x-ray diffraction measurements were carried out at room temperature on an x-ray diffractometer (MXP18A-HF) using Cu K α radiation, with 2θ ranging from 10º to 80º and a 2θ scanning step of 0.01º. Experiments of x-ray rocking curve were performed on a double-crystal diffractometer (Delta-X HRXRD) equipped with a Ge (004) monochromator (α~10") under a power of 1.6 kW. The AC magnetic susceptibility was determined on Quantum Design MPMS XL-1 with a frequency of 997.34 Hz an...

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