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We report the discovery of superconductivity on the border of antiferromagnetic order in a quasi-one-dimensional material RbMn6Bi5 via measurements of resistivity and magnetic susceptibility under high pressures. Its phase diagram of temperature versus pressure resembles those of many magnetism-mediated superconducting systems. With increasing pressure, its antiferromagnetic ordering transition with T N = 83 K at ambient pressure is first enhanced moderately and then suppressed completely at a critical pressure of P c ≈ 13 GPa, around which bulk superconductivity emerges and exhibits a dome-like T c(P) with a maximal T c onset ≈ 9.5 K at about 15 GPa. In addition, the superconducting state around P c is characterized by a large upper critical field μ 0 H c2(0) exceeding the Pauli paramagnetic limit, implying a possible unconventional paring mechanism. The present study, together with our recent work on KMn6Bi5 (the maximum T c onset ≈ 9.3 K), makes A Mn6Bi5 (A = alkali metal) a new family of Mn-based superconductors with relatively high T c. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structure, and superconductivity of Ti4Ir2O. The title compound crystallizes in an η -carbide type structure of the space group F d 3 ÂŻ m (No. 227), with lattice parameters a = b = c = 11.6194(1) Ă.... The superconducting temperature T c is found to be 5.1â€"5.7 K. Most surprisingly, Ti4Ir2O hosts an upper critical field of 16.45 T, which is far beyond the Pauli paramagnetic limit. Strong coupled superconductivity with evidences for multigap is revealed by the measurements of heat capacity and upper critical field. First-principles calculations suggest that the density of states near the Fermi level originates from the hybridization of Ti-3 d and Ir-5 d orbitals, and the effect of spin-orbit coupling on the Fermi surfaces is prominent. Large values of the Wilson ratio (R W ∼ 3.9), the Kadowakiâ€"Woods ratio [ A / Îł 2 ∼ 9.0 Ă— 10âˆ'6 μΩâ‹...cm/(mJâ‹...molâˆ'1â‹...Kâˆ'1)2], and the Sommerfeld coefficient (Îł = 33.74 mJâ‹...molâˆ'1â‹...Kâˆ'2) all suggest strong electron correlations (similar to heavy fermion systems) in Ti4Ir2O. The violation of Pauli limit is possibly due to a combination of strong-coupled superconductivity and large spin-orbit scattering. With these intriguing behaviors, Ti4Ir2O serves as a candidate for unconventional superconductor. [ABSTRACT FROM AUTHOR]

We report the microwave synthesis and the doping effect of Mo3−xRexAl2C (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) Ĺ (for Mo3Al2C) to 6.846(2) Ĺ (for Mo2.7Re0.3Al2C). Upon Re doping, Tc of Mo3−xRexAl2C first increases and then decreases, with the maximum Tc = 9.14 K at the optimal doping level of x = 0.09. Our report provides a convenient method to synthesize Mo3−xRexAl2C within minutes, and also marks the first Re doping study with enhanced superconductivity on the non-centrosymmetric superconductor Mo3Al2C. [ABSTRACT FROM AUTHOR]

We report the tip-induced superconductivity on the topological semimetal NbSb2, similar to the observation on TaAs2 and NbAs2. Belonging to the same family of MPn2, all these materials possess similar band structures, indicating that the tip-induced superconductivity may be closely related to their topological nature and share a common mechanism. Further analysis suggests that a bulk band should play the dominant role in such local superconductivity most likely through interface coupling. In addition, the compatibility between the induced superconductivity and tips' ferromagnetism gives an evidence for its unconventional nature. These results provide further clues to elucidate the mechanism of the tip-induced superconductivity observed in topological materials. [ABSTRACT FROM AUTHOR]

We report a comprehensive high-pressure study on the monoclinic TlFeSe2 single crystal, which is an antiferromagnetic insulator with quasi-one-dimensional crystal structure at ambient pressure. It is found that TlFeSe2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above Pc ≈ 13 GPa, accompanied with a large volume collapse of ΔV/V0 = 8.3%. In the low-pressure monoclinic phase, the insulating state is easily metallized at pressures above 2 GPa; while possible superconductivity with K is found to emerge above 30 GPa in the high-pressure phase. Such a great tunability of TlFeSe2 under pressure indicates that the ternary AFeSe2 system (A = Tl, K, Cs, Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition, dimensionality crossover, and superconductivity. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a new ternary molybdenum pnictide superconductor, Cs2Mo3As3. The powder x-ray diffraction analysis reveals the quasi-one-dimensional (Q1D) hexagonal crystal structure formed by Cs+ and infinite (Mo3As3)2− chains as indicated by the wire-like grain morphology. Electrical resistivity and magnetic susceptibility characterizations exhibit superconductivity with the onset transition temperature at 11.5 K, which is the highest in all Q1D superconductors reported so far. An upper critical magnetic field of about 61.7 T at zero temperature was extrapolated from the resistivity measurement under a magnetic field, which is much higher than the Pauli paramagnetic limit, and the reason for such a high upper critical field may lie in its unconventional nature of superconducting pairing symmetry. The discovery of Cs2Mo3As3 inspires the search for new superconductors for future high field applications. [ABSTRACT FROM AUTHOR]

Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5 × √5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of KxFe2-ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5 × √5 order is highly developed. Superconductivity occurs in such a metallic phase. [ABSTRACT FROM AUTHOR]

A series of layered (Sr1-xKx)Fe2As2 compounds with nominal x = 0-0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc [?] 38 K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor. [ABSTRACT FROM AUTHOR]

We synthesize a set of Pd-doped polycrystalline samples PdxNdSeTe2 and measure their physical properties. Compared with pure NdSeTe2, the charge density wave (CDW) order is continuously suppressed with the Pd-intercalation. Bulk superconductivity first appears at x = 0.06 with Tc nearly 2.5K, coexisting with a CDW transition at 176K. Further Pd-doping enhances Tc, until it reaches the maximum value 2.84K at x=0.1, meanwhile the CDW transition vanishes. The upper critical field for the optimal doping sample Pd0.1NdSeTe2 is determined from the R-H measurement, which is estimated to be 0.6 T. These results provide another kind of ideal compound for studying the interplay between CDW and superconductivity systematically. [ABSTRACT FROM AUTHOR]

We report both 23Na and 75As nuclear magnetic resonance (NMR) studies on hole-doped Ca1[?]xNaxFe2As2 superconducting single crystals (x [?] 0.67) with the superconducting temperature Tc = 32 K. Singlet superconductivity is suggested by a sharp drop of the Knight shift 75K below Tc. The spin-lattice relaxation rate 1/T1 does not show the Slichter--Hebel coherence peak, which suggests an unconventional pairing. The penetration depth is estimated to be 0.24 um at temperature T = 2 K. Here 1/75T1T shows an anisotropic behavior and a prominent low-temperature upturn, with 75T1 denoting the 75As spin-lattice relaxation time and T the temperature, which indicates strong low-energy antiferromagnetic spin fluctuations and supports a magnetic origin of superconductivity. [ABSTRACT FROM AUTHOR]

We report the tip-induced superconductivity on the topological semimetal NbSb2, similar to the observation on TaAs2 and NbAs2. Belonging to the same family of MPn2, all these materials possess similar band structures, indicating that the tip-induced superconductivity may be closely related to their topological nature and share a common mechanism. Further analysis suggests that a bulk band should play the dominant role in such local superconductivity most likely through interface coupling. In addition, the compatibility between the induced superconductivity and tips' ferromagnetism gives an evidence for its unconventional nature. These results provide further clues to elucidate the mechanism of the tip-induced superconductivity observed in topological materials. [ABSTRACT FROM AUTHOR]

We report a comprehensive high-pressure study on the monoclinic TlFeSe2 single crystal, which is an antiferromagnetic insulator with quasi-one-dimensional crystal structure at ambient pressure. It is found that TlFeSe2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above Pc ≈ 13 GPa, accompanied with a large volume collapse of ΔV/V0 = 8.3%. In the low-pressure monoclinic phase, the insulating state is easily metallized at pressures above 2 GPa; while possible superconductivity with K is found to emerge above 30 GPa in the high-pressure phase. Such a great tunability of TlFeSe2 under pressure indicates that the ternary AFeSe2 system (A = Tl, K, Cs, Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition, dimensionality crossover, and superconductivity. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Here we report the discovery of the first ternary molybdenum pnictide based superconductor K 2 Mo 3 As 3. Polycrystalline samples were synthesized by the conventional solid state reaction method. X-ray diffraction analysis reveals a quasi-one-dimensional hexagonal crystal structure with (Mo 3 As 3)2− linear chains separated by K+ ions, similar as previously reported K 2 Cr 3 As 3 , with the space group of P -6 m 2 (No. 187) and the refined lattice parameters a = 10.145(5) Å and c = 4.453(8) Å. Electrical resistivity, magnetic susceptibility, and heat capacity measurements exhibit bulk superconductivity with the onset T c at 10.4 K in K 2 Mo 3 As 3 which is higher than the isostructural Cr-based superconductors. Being the same group VIB transition elements and with similar structural motifs, these Cr and Mo based superconductors may share some common underlying origins for the occurrence of superconductivity and need more investigations to uncover the electron pairing within a quasi-one-dimensional chain structure. [ABSTRACT FROM AUTHOR]

Abstract We report the discovery and characterization of a novel 112-type iron pnictide EuFeAs 2 , with La-doping induced superconductivity in a series of Eu 1− x La x FeAs 2. The polycrystalline samples were synthesized through solid state reaction method only within a very narrow temperature window around 1073 K. Small single crystals were also grown from a flux method with the size about 100 μm. The crystal structure was identified by single crystal X-ray diffraction analysis as a monoclinic structure with space group of P 2 1 / m. From resistivity and magnetic susceptibility measurements, we found that the parent compound EuFeAs 2 shows distinct anomalies probably due to the Fe2+ related antiferromagnetic/structural phase transition near 110 K and the Eu2+ related antiferromagnetic phase transition near 40 K. La-doping suppressed both phase transitions to lower temperatures and induced superconducting transitions with a T c ∼ 11 K for Eu 0.85 La 0.15 FeAs 2. [ABSTRACT FROM AUTHOR]

Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5 × √5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of KxFe2-ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5 × √5 order is highly developed. Superconductivity occurs in such a metallic phase. [ABSTRACT FROM AUTHOR]

• The synthesis method of a new compound Mo 5 GeB 2 is reported. Ball-milling helps to get rid of binary borides. • Mo 5 GeB 2 is the first ternary phase in Mo–Ge–B system. • Mo 5 GeB 2 is a type-II superconductor with T c = 5.8 K. • Mo 5 GeB 2 is a fully gapped s -wave BCS superconductor with an intermediate coupling. We report the crystal structure and superconductivity of a new ternary boride Mo 5 GeB 2. Mo 5 GeB 2 crystallizes in a Cr 5 B 3 -type structure with a space group of I 4/ mcm (No. 140). The lattice parameters are a = 6.0721(1) Å, and c = 11.1173(2) Å. A type-II superconductivity of T c = 5.8 K is revealed by resistivity, magnetization, and heat capacity measurements. The upper and lower critical fields are 0.52 T and 77.1 mT, respectively. The temperature dependence of low temperature specific heat follows the description of a BCS superconductor with an isotropic s -wave gap (Δ 0 = 0.93 meV). However, both the values of the normalized specific heat change (Δ C e / γT c = 1.63) and the coupling strength (Δ 0 / k B T c = 1.87) exceed the BCS weak-coupling limit, indicating an intermediate coupling in Mo 5 GeB 2. [ABSTRACT FROM AUTHOR]