We performed a comprehensive study of the vanadium-based anti-post-perovskite compounds V3XC (X = Ge, P, As) and V3XN (X = Ga, Ge, P, As). It was clarified that V3PN and V3AsN exhibit superconducting transitions at 4.2 and 2.6 K, respectively, whereas the other compounds not show superconducting transition above 1.8 K. We further investigated substitution effects on superconductivity in V3PN, and found that the superconducting transition temperature (Tc) shows a dome-shaped curve with maximum Tc values of 5.45 K at x = 0.05 and 5.82 K at x = 0.10 for V3P1−xAsxN and V3P1−xSbxN, respectively. In these optimal compositions, clear implications of the phonon softening and the enhanced electron–phonon coupling were revealed by the analysis of specific heat data. Our findings showed that structural instability is one of the important factors for tuning superconducting properties in vanadium-based superconductors with an anti-post-perovskite structure.
RhSn is a topological semimetal with chiral fermions. At ambient pressure, it exhibits large positive magnetoresistance (MR) and field-induced resistivity upturn at low temperatures. Here we report on the electrical transport properties of RhSn single crystal under various pressures. We find that with increasing pressure the temperature-dependent resistivity
Structural, magnetic, electrical, and thermal transport properties of antiperovskite compounds AlNxMn3 (x=1,1.1,1.2) have been investigated systematically. With increasing x, the lattice constant increases monotonously while the Curie temperature TC decreases. Both the high TC and small coercive fields consistently indicate AlNxMn3 may be a promising high-temperature soft magnetic material. The resistivity displays T2-dependence below 30 K and the Kadowaki–Woods ratio is about 107.7 μΩ cm/K2, indicating a possible strongly correlated Fermi-liquid behavior in AlNMn3. Further analysis suggests that the electron-type carriers are dominant and the thermal conductivity mainly originates from the lattice contribution.
The temperature dependences of magnetization, electrical transport, and thermal transport properties of antiperovskite compound SnCMn3 have been investigated systematically. A positive magnetoresistance (∼11%) is observed around the ferrimagnetic-paramagnetic transition (TC∼280 K) in the field of 50 kOe, which can be attributed to the field-induced magnetic phase transition. The abnormalities of resistivity, Seebeck coefficient, normal Hall effect, and thermal conductivity near TC are suggested to be associated with an abrupt reconstruction of electronic structure. Further, our results indicate an essential interaction among lattice, spin, and charge degrees of freedom around TC. Such an interaction among various degrees of freedom associated with sudden phase transition is suggested to be characteristic of Mn-based antiperovskite compounds.
The anisotropic superconducting state properties in Cu(0.03)TaS(2) have been investigated by magnetization, magnetoresistance and specific heat measurements. They clearly show that Cu(0.03)TaS(2) undergoes a superconducting transition at T(C) = 4.03 K. The obtained superconducting parameters demonstrate that Cu(0.03)TaS(2) is an anisotropic type-II superconductor. Combining specific heat jump ΔC/γ(n)T(C) = 1.6(4), gap ratio 2Δ/k(B)T(C) = 4.0(9) and the estimated electron-phonon coupling constant λ∼0.68, the superconductivity in Cu(0.03)TaS(2) is explained within the intermediate coupling BCS scenario. First-principles electronic structure calculations suggest that copper intercalation of 2H-TaS(2) causes a considerable increase of the Fermi surface volume and the carrier density, which suppresses the CDW fluctuation and favors the raise of T(C).
Abstract Among the metal hydrides, Th 4 H 15 is the first reported superconductor with a relatively high T c ≈ 8 K at ambient pressure. Here we report on the synthesis and characterization of a low- T c superconducting modification of Th 4 H 15 , which is obtained via hydrogenating Th metal at 5 GPa and 800 °C by using the ammonia borane as the hydrogen source. Measurements of resistivity, magnetic susceptibility, and specific heat confirm that the obtained Th 4 H 15 sample shows a bulk superconducting transition at T c ≈ 6 K, which is about 2 K lower than that reported previously. Various characteristic superconducting parameters have been extracted for this compound and unusual lattice dynamics were evidenced from the specific-heat analysis.
In this paper, we report the effects of carbon content on crystal structure, magnetic and electrical/thermal transport properties in antiperovskite compounds GaCxFe3 (0.15 ≤ x ≤ 0.3). Our experimental results indicate that all the physical properties we measured are sensitive to the carbon concentration for GaCxFe3. With decreasing the carbon content x, the Curie temperature (TC), saturated magnetization, and coercive force (HC) increase while the lattice constant, Debye temperature, and resistivity decrease gradually. Further analysis suggests that the serial GaCxFe3 can be a new kind of promising high-temperature soft magnetic material considering their high-TC (∼788 K) and low-HC (∼22 Oe). Interestingly, the low-temperature resistivity exhibits an abnormal semiconducting behavior below a characteristic temperature for each of GaCxFe3 (0.15 ≤ x ≤ 0.3). This abnormality of resistivity may be attributed to a combination of the renormalized electron-electron interaction and the weak-localization. Furthermore, the studies of the thermal transport and the Hall measurement suggest that the type of dominant carriers in GaCxFe3 changes gradually from hole- to electron-type with decreasing x.
The advances in the field of unconventional superconductivity are largely driven by the discovery of novel superconducting systems. Here we report on the discovery of superconductivity on the border of antiferromagnetic order in a quasi-one-dimensional RbMn6Bi5 via measurements of resistivity and magnetic susceptibility under high pressures. With increasing pressure, its antiferromagnetic transition with TN = 83 K at ambient pressure is first enhanced moderately and then suppressed completely at a critical pressure of Pc = 13 GPa, around which bulk superconductivity emerges and exhibits a dome-like Tc(P) with a maximal Tc_onset = 9.5 K at about 15 GPa. Its temperature-pressure phase diagram resembles those of many magnetism-mediated superconducting systems. In addition, the superconducting state around Pc is characterized by a large upper critical field {\mu}0Hc2(0) exceeding the Pauli limit, elaborating a possible unconventional paring mechanism. The present study, together with our recent work on KMn6Bi5 (Tcmax = 9.3 K), makes AMn6Bi5 (A= Alkali metal) a new family of Mn-based superconductors with relatively high Tc.
Many exotic phenomena in strongly correlated electron systems, such as unconventional superconductivity, metal-insulator transition, and quantum criticality, take place in the intermediate regime between localized and itinerant electronic state. To understand the electronic behaviors near the localized-to-itinerant crossover remains a challenging problem in condensed matter physics. The Ru5+ cubic pyrochlores A2Ru2O7 (A=Cd, Cd, Hg) constitute such a system that the Ru-4d electrons acquire characters of both itinerancy and localization. In addition, the magnetic Ru5+ ions that are situated on the vertices of corner-shared tetrahedral lattice are expected to experience strong geometrical frustration given an antiferromagnetic (AF) arrangement. In this work, we investigate the cubic pyrochlore Cd2Ru2O7, which develops a peculiar metallic state below the AF transition. We synthesize a series of Pb-doped Cd2-xPbxRu2O7 (0 x 2) polycrystalline samples under high-pressure condition, and study the effects of Pb doping on their crystal structure and physical properties. Although the Pb2Ru2O7 pyrochlore is a Pauli paramagnetic metal, we find that the substitution of 10% Pb2+ for Cd2+ in Cd1.8Pb0.2Ru2O7 converts the metallic state of Cd2Ru2O7 into an insulating ground state, in a manner similar to the consequence of exerting hydrostatic pressure or substituting 10% Ca2+ for Cd2+ ions as we found recently. We propose that the electronic state of Cd2Ru2O7 be located at the itinerancy to localization crossover, and the introduction of chemical disorder via Pb2+ substitution may enhance the localized character and induce the metal-to-insulator transition. Our results further demonstrate that the cubic Ru5+ pyrochlore oxides offer an important paradigm for studying the exotic physics of correlated electrons on the border of (de)localization in the presence of strong geometrical frustration.
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