In this work, the Ba9Sn3Te15 compound has been synthesized for the first time under high pressure and high temperature conditions. Single-crystal X-ray diffraction analysis shows that Ba9Sn3Te15 crystallizes into a hexagonal structure with a space group of Pc2 (188) and lattice parameters of a = b = 10.2403(1) Å, and c = 20.7720(2) Å. The crystal structure contains trimeric one-dimensional chains with face-sharing SnTe6 octahedrons stacked along the c-axis. These chains are arranged in a triangular lattice in the ab plane. The energy dispersive X-ray spectroscopy measurement for a single crystal of Ba9Sn3Te15 shows approximately 6% vacancies on the Sn sites. The anion Te can be substituted by Se to form Ba9Sn3(Te1−xSex)15 with x = 0–1. The resistivity and Seebeck coefficient measurements were performed. Ba9Sn3Te15 behaves similar to a semiconductor with a band gap of approximately 24 meV. When Se is doped, the resistivity increases and the band gap is enhanced to 508 meV for x = 1. The Seebeck coefficient ranges from 31 μV K−1 to 90.7 μV K−1. Ab initio calculations were also performed to study the density of states and band structures for Ba9Sn3Te15 and Ba9Sn3Se15.

2D transition-metal dichalcogenides (TMDCs) are currently the key to the development of nanoelectronics. However, TMDCs are predominantly nonmagnetic, greatly hindering the advancement of their spintronic applications. Here, an experimental realization of intrinsic magnetic ordering in a pristine TMDC lattice is reported, bringing a new class of ferromagnetic semiconductors among TMDCs. Through van der Waals (vdW) interaction engineering of 2D vanadium disulfide (VS2), dual regulation of spin properties and bandgap brings about intrinsic ferromagnetism along with a small bandgap, unravelling the decisive role of vdW gaps in determining the electronic states in 2D VS2. An overall control of the electronic states of VS2 is also demonstrated: bond-enlarging triggering a metal-to-semiconductor electronic transition and bond-compression inducing metallization in 2D VS2. The pristine VS2 lattice thus provides a new platform for precise manipulation of both charge and spin degrees of freedom in 2D TMDCs availing spintronic applications.

We report the ferromagnetism with Cure temperature Tc at 230 K in a new diluted magnetic semiconductor (DMS) (Ba0.7K0.3)(Zn0.85Mn0.15)2As2 isostructural to ferropnictide 122 superconductors synthesized via low temperature sintering. Spin is doped by isovalence substitution of Mn2+for Zn2+, while charge is introduced by heterovalence substitution of K1+ for Ba2+ in (Ba0.7K0.3)(Zn0.85Mn0.15)2As2 DMS, being different from (Ga,Mn)As where both spin & charge are induced simultaneously by heterovalence substation of Mn2+ for Ga3+. The (Ba0.7K0.3)(Zn0.85Mn0.15)2As2 DMS shows spontaneous magnetization following T3/2 dependence expected for a homogeneous ferromagnet with saturation moment 1.0μB for each Mn atom.

The recent discovery of iron ferropnictide superconductors has received intensive concern in connection with magnetically involved superconductors. Prominent features of ferropnictide superconductors are becoming apparent: the parent compounds exhibit an antiferromagnetic ordered spin density wave (SDW) state, the magnetic-phase transition is always accompanied by a crystal structural transition, and superconductivity can be induced by suppressing the SDW phase via either chemical doping or applied external pressure to the parent state. These features generated considerable interest in the interplay between magnetism and structure in chemically doped samples, showing crystal structure transitions always precede or coincide with magnetic transition. Pressure-tuned transition, on the other hand, would be more straightforward to superconducting mechanism studies because there are no disorder effects caused by chemical doping; however, remarkably little is known about the interplay in the parent compounds under controlled pressure due to the experimental challenge of in situ measuring both of magnetic and crystal structure evolution at high pressure and low temperatures. Here we show from combined synchrotron Mössbauer and X-ray diffraction at high pressures that the magnetic ordering surprisingly precedes the structural transition at high pressures in the parent compound BaFe2As2, in sharp contrast to the chemical-doping case. The results can be well understood in terms of the spin fluctuations in the emerging nematic phase before the long-range magnetic order that sheds light on understanding how the parent compound evolves from a SDW state to a superconducting phase, a key scientific inquiry of iron-based superconductors.

The effect of pressure on the crystalline structure and superconducting transition temperature (Tc) of the 111-type Na1–xFeAs system using in situ high-pressure synchrotron X-ray powder diffraction and diamond anvil cell techniques is studied. A pressure-induced tetragonal to tetragonal isostructural phase transition was found. The systematic evolution of the FeAs4 tetrahedron as a function of pressure based on Rietveld refinements on the powder X-ray diffraction patterns was obtained. The nonmonotonic Tc(P) behavior of Na1–xFeAs is found to correlate with the anomalies of the distance between the anion (As) and the iron layer as well as the bond angle of As–Fe–As for the two tetragonal phases. This behavior provides the key structural information in understanding the origin of the pressure dependence of Tc for 111-type iron pnictide superconductors. A pressure-induced structural phase transition is also observed at 20 GPa.

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.

•Superconductivity was found in Cu intercalated Bi2Te3 topological insulators induced via pressures.•The copper atoms are intercalated between Te(2) and Te(2) layers confirmed by X-ray diffraction experiment.•The superconductivity of Cu0.14Bi2Te3 occurs before the pressure point of the structural transition.Copper intercalated Bi2Te3 topological single crystal Cu0.14Bi2Te3 was grown using Bridgman method. The transport properties were studied by temperature dependent resistance measurements at various pressures. Pressure induced superconductivity was found with Tc for ambient phase ∼6 K. The evolutions of crystal structure with pressure were investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring above 9.8 GPa. The superconducting properties of Cu0.14Bi2Te3 are compared with that of undoped topological compound Bi2Te3.

•We synthesized the Sr2CuO3.4 superconductor with a new La214 type modulation structure.•The new modulation structure shows superconducting transition with Tc 48K.•The new modulation structure is related to the distribution of apical oxygen, of Pmmm symmetry.A Sr2CuO3+δ superconductor with a new modulated structure has been synthesized using high pressure technique. Two superconducting transitions with Tc ∼ 75 K and ∼ 48 K respectively were found in Sr2CuO3+δ superconductor. The superconducting volume fraction is calculated to be 85% at 2 K, which is much higher than anyone else reported before. A new type of modulated phase with a periodicity of 2√2ap × 2√2ap × cp of Pmmm symmetry is found in the sample by using transmission electron microscopy. Our experimental results suggest that the new Pmmm modulated phase is responsible for superconductivity with Tc at 48 K, while C2/m modulated phase for that with Tc at 75 K found previously.