S. M. Feng

Pressure-induced superconductivity in topological parent compound Bi2Te3

We report a successful observation of pressure-induced superconductivity in a topological compound Bi2Te3 with Tc of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.

Li(Zn,Mn)As as a new generation ferromagnet based on a I–II–V semiconductor

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li(1+y)(Zn(1-x)Mn(x))As in bulk materials. Ferromagnetism with a critical temperature of up to 50u2009K is observed in nominally Li-excess (y=0.05-0.2) compounds with Mn concentrations of x=0.02-0.15, which have p-type metallic carriers. This is presumably due to excess Li in substitutional Zn sites. Semiconducting LiZnAs, ferromagnetic Li(Zn,Mn)As, antiferromagnetic LiMnAs, and superconducting LiFeAs systems share square lattice As layers, which may enable development of novel junction devices in the future.

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3

Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10u2005GPa proceeded by a pressure induced insulator to metal like transition at ~3u2005GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0u2005K with pressure up to 40u2005GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10u2005GPa and 20u2005GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

The comprehensive phase evolution for Bi2Te3 topological compound as function of pressure

The recently discovered three-dimensional topological insulator Bi2Te3 is studied as function of pressure in terms of crystal structures, resistance, and Hall coefficient. The superconductivity is found in phase I (ambient phase) Bi2Te3 with Tcu2009∼u20093u2009K, which is related to the topological features. The evolution of crystal structure with pressure is investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring at about 8u2009GPa, 13u2009GPa, and 16u2009GPa, respectively. Furthermore, the high pressure phases of Bi2Te3 are also superconducting but with much higher Tcu2009∼u20098u2009K. The superconducting transitions are compared with those for Bi, Te elements. A global phase diagram of Bi2Te3 as function of pressure up to 30u2009GPa is obtained.

Ferroelectricity of multiferroic hexagonal TmMnO3 ceramics synthesized under high pressure

Dense hexagonal TmMnO3 ceramics were synthesized by solid-state reaction technique combined with high-pressure treatment which significantly increased the density of ceramic samples. The crystal structure of the hexagonal TmMnO3 oxide was refined by using Rietveld analysis based on powder x-ray diffraction experiment. We observed obvious dielectric peaks through dielectric measurement on the specimen subjected to postannealing in oxygen atmosphere. A ferroelectric-paraelectric transition around 348°C is identified. Polarization-electric field hysteresis (P-E) loop measurement proved the ferroelectricity of the sample at room temperature.

Large magneto (thermo) dielectric effect in multiferroic orthorhombic LuMnO3

We have investigated the relation between ferroelectric and magnetic orders of orthorhombic (o-) LuMnO3 ceramics. The increase of dielectric constant ɛ exceeds 82% near incommensurate to commensurate E-type antiferromagnetic (AFM) spin ordering transition temperature TL, reflecting a large magneto (thermo) dielectric response. Meanwhile, distinct anomalies and thermal hysteresis behavior are observed near this temperature in both temperature dependence of ɛ and specific heat Cp, indicating a strong coupling between FE and magnetic orders in o-LuMnO3. Comparing to o-HoMnO3, TmMnO3, and YbMnO3 with similar E-type AFM ground state, o-LuMnO3 has the largest magneto (thermo) dielectric effect

Efficient generation of mouse models of human diseases via ABE- and BE-mediated base editing.

A recently developed adenine base editor (ABE) efficiently converts A to G and is potentially useful for clinical applications. However, its precision and efficiency in vivo remains to be addressed. Here we achieve A-to-G conversion in vivo at frequencies up to 100% by microinjection of ABE mRNA together with sgRNAs. We then generate mouse models harboring clinically relevant mutations at Ar and Hoxd13, which recapitulates respective clinical defects. Furthermore, we achieve both C-to-T and A-to-G base editing by using a combination of ABE and SaBE3, thus creating mouse model harboring multiple mutations. We also demonstrate the specificity of ABE by deep sequencing and whole-genome sequencing (WGS). Taken together, ABE is highly efficient and precise in vivo, making it feasible to model and potentially cure relevant genetic diseases.CRISPR-based base editors allow for single nucleotide genome editing in a range of organisms. Here the authors demonstrate the in vivo generation of mouse models carrying clinically relevant mutations using C→T and A→G editors.

Effect of pressure on a "111"-type iron pnictide superconductor

The behavior of superconductivity of “111”-type iron pnictide superconductors, namely, LiFeAs, NaFeAs and LiFeP, is investigated at different pressures through electrical resistance measurements. For LiFeAs and LiFeP, the superconducting transition temperature T c decreases monotonously with increasing pressure, with the pressure coefficient of dT c /dP being−1.38 and−1.26 K/GPa, respectively. The T c of NaFeAs increases to a maximum value with the pressure increasing to 3 GPa; further increasing the pressure suppresses T c with the slope of dT c /dP about−3.40 K/GPa.

Pressure-induced phase transition in Ho0.8Dy0.2MnO3 multiferroic compound

The multiferroic Ho0.8Dy0.2MnO3 compound crystallizing into hexagonal perovskite was investigated by using an in situ high pressure Raman scattering method at room temperature. It is found that with increasing pressure, the compound started to transform from hexagonal-type into an orthorhombic-type perovskite near 9.8GPa. The phase transition process is analyzed.

The effects of high pressure on the ferroelectric properties of nano-BaTiO3 ceramics

Temperature dependence of the dielectric constant of nano-grain BaTiO3 (BTO) ceramic has been investigated under hydrostatic pressure up to 5 GPa. We show that the paraelectric-ferroelectric phase transition temperature, which is represented by TC (Curie temperature point), decreases with pressure at a rate of dTC/dσ = -40.0 K/GPa for coarse grain ceramic and -34.3 K/GPa for ceramic with 60nm size grains. For the paraelectric-ferroelectric phase transition temperature, the variation of inter-granular stress with reducing grain size is considered the main factor causing the decrease of TC and the change of dTC/dσ. Adding the hydrostatic-pressure and inter-granular stress contributions to a Ginsburg-Landau-Devonshire (GLD) type thermodynamic theory provides a satisfactory explanation to our experimental results. Based on the GLD theory, a phase diagram, reflecting the relationship among the transition temperature, grain size and hydrostatic-pressure, has been established, which matches well with our experimental results.