Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS_(2)

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.

Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd_(2)As_(2)

Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism.Recent studies suggest that EuCd_(2)As_(2) is an antiferromagnetic topological material.Here by carrying out thorough magnetic,electrical and thermodynamic property measurements,we discover a long-time relaxation of the magnetic susceptibility in EuCd_(2)As_(2).The(001)in-plane magnetic susceptibility at 5 K is found to continuously increase up to∼10%over the time of∼14 hours.The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field.These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cup- rate high temperature superconductors is what determines the maximum transition temperature （Tc,max）, which varies from less than 30 to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size （ACT）, indicating a clear anticorrelation between AcT and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high To mechanism from doped Mott insulator perspective.

Superconductivity of a cuprate with compressed local octahedron

Since the historical discovery of high Tc superconductivity(HTS)of La2CuO4 in 1986[1],the superconductivity me chanism of copper oxides remains one of the biggest mysteries in the field of condensed matter physics[2-10].High-Tc cuprates crystallize into layered perovskite structure,as well as copper oxygen octahedron coordination.In octahedron symmetry,the 3d orbitals of Cu^2+with a 3d^9 configuration degenerate into two top eg and three lower t2g orbitals.

A novel approach in preparing polymer/nano-CaCO_(3) composites

An novel compounding process using nano-CaCO_(3) aqueous suspension for preparing polymer/nano-CaCO_(3) composites with nanoparticles dispersed at the nanoscale is reported.The process is called the mild mixing method.In this method,the pre-dispersed nano-particle suspensions are blended with melting polymers in a weak shearing field using an extruder,followed by removing the water from the vent.The four typical poly-meric nanocomposites were prepared by mild mixing method.The dispersion of nano-CaCO_(3) in the matrix of the polymer at the nanoscale was confirmed by scanning electron microscopy(SEM).The molecular weights of polycarbonate(PC)and its nanocomposite showed that the degradation had not occurred during the mild mixing processing.The mechanical properties of the composite with 1.5 wt-% nano-CaCO_(3) improve slightly.It proved that this approach is suitable for the preparation of nano-composites based on both polar and non-polar polymers.

High-pressure synthesis,crystal structure and physical properties of a new Cr-based arsenide La3CrAs5

In La-Cr-As system,the first ternary compound La3CrAs5 has been successfully synthesized under highpressure and high-temperature conditions.La3CrAs5 crystallizes into a hexagonal Hf5Sn3Cu-anti type structure with a space group of P63/mcm(No.193)and lattice parameters of a=b=8.9845A and c=5.8897A.The structure contains facesharing octahedral CrAs6 chains along the c-axis,which are arranged triangularly in the ab-plane and separated by a significantly large distance of 8.9845A.The magnetic properties,resistivity and specific heat measurements were performed.La3CrAs5 exhibits a metallic state with Fermi liquid behavior at low temperatures and undergoes a ferromagnetic transition at Curie temperature TC^50 K.First-principles theoretical studies were conducted to calculate its band structure and density of states(DOS),which indicated that the non-negligible contribution of La to the DOS near the Fermi level caused La3CrAs5 to be a three-dimensional(3D)metal.The crystal orbital Hamilton population(-COHP)was also calculated to explain the global stability and bonding characteristics in the structure of La3CrAs5.

Orbital selection of the double [CuO2] layer compound Ca3Cu2O4Cl2

The discovery of high-temperature copper oxide superconductors(HTS)by Bednorz and Muller[1]in 1986 opened up a new field of superconductivity.Since then,several different families of materials have been discovered with greatly increased superconducting critical temperature(Tc)[2].Oxychloride cuprates,Can+1CunO2wCl2,are one such type of parent compound of high Tc cuprate superconductors.There are two members in this family known so far that can exist at ambient pressure:Ca2CuO2Cl2(single[Cu02]layer CCOC)and Ca3Cu2O4Cl2(double[CuO2]layer CCOC).Both are composed of a[CuO2]plane with the apical oxygen replaced by chlorine atoms.