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We report a comprehensive study on a layered-structure compound of NaZn4As3, which has been predicted to be an ideal topological semimetal (TSM) candidate. It is found that NaZn4As3 undergoes a structural transformation from high temperature rhombohedral to a low temperature monoclinic phase. The electric resistivity exhibits a metal-to-insulator-like transition at around 100 K, and then develops a plateau at low temperature, which might be related to the protected topologically conducting surface states. Our first-principles calculation confirms further that NaZn4As3 is a topological insulator (TI) for both different phases rather than a previously proposed TSM. The Hall resistivity reveals that the hole carriers dominate the transport properties for the whole temperature range investigated. Furthermore, an obvious kink possibly associated to the structure transition has been detected in thermopower around ~ 170 K. The large thermopower and moderate κ indicate that NaZn4As3 and /or its derivatives can provide a good platform for optimizing and studying the thermoelectric performance.

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr2. It crystallizes in a C15-type (cubic MgCu2-type, space group F d 3 ¯ m ) structure in which the Ir atoms form a kagome lattice, with cell parameters a = b = c = 7.3596(1) Å. Resistivity and magnetic susceptibility measurements indicate that ZrIr2 is a type-II superconductor with a transition temperature of 4.0 K. The estimated lower and upper critical fields are 12.8 mT and 4.78 T, respectively. Heat capacity measurements confirm the bulk superconductivity in ZrIr2. ZrIr2 is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change ΔC e/γ T c ∼ 1.86 and the coupling strength Δ0/k B T c ∼ 1.92. First-principles calculations suggest that ZrIr2 has three-dimensional Fermi surfaces with simple topologies, and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals. Similar to SrIr2 and ThIr2, spin–orbit coupling has dramatic influences on the band structure in ZrIr2.

We report the microwave synthesis and the doping effect of Mo3−x Re x Al2C (0 ≤ x ≤ 0.3) superconductor. Re doping into Mo3Al2C results in a regular shrinkage of the lattice, marked by the linear decrease of lattice parameter a from 6.868(1) Å (for Mo3Al2C) to 6.846(2) Å (for Mo2.7Re0.3Al2C). Upon Re doping, T c of Mo3−x Re x Al2C first increases and then decreases, with the maximum T c = 9.14 K at the optimal doping level of x = 0.09. Our report provides a convenient method to synthesize Mo3−x Re x Al2C within minutes, and also marks the first Re doping study with enhanced superconductivity on the non-centrosymmetric superconductor Mo3Al2C.

In this article, the Sm-doping single crystals Ca1 − x Sm x Fe2As2 (x = 0 ~ 0.2) were prepared by the CaAs flux method, and followed by a rapid quenching treatment after the high temperature growth. The samples were characterized by structural, resistive, and magnetic measurements. The successful Sm-substitution was revealed by the reduction of the lattice parameter c, due to the smaller ionic radius of Sm3+ than Ca2+. Superconductivity was observed in all samples with onset T c varying from 27 K to 44 K upon Sm-doping. The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples. Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x > 0.10. The doping dependences of the c-axis length and onset T c were summarized. The high-T c observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution.