High pressure study of the normal and superconducting states of the layered pnictide oxide Ba1−xNaxTi2Sb2O withx= 0, 0.10, and 0.15 (original) (raw)
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Superconductivity, charge- or spin-density wave, and metal-nonmetal transition in BaTi2(Sb1−xBix)2O
Physical Review B, 2013
We have performed an isovalent substitution study in a layered titanium oxypnictide system BaTi2(Sb1−xBix)2O (0≤ x ≤ 0.40) by the measurements of x-ray diffraction, electrical resistivity and magnetic susceptibility. The parent compound BaTi2Sb2O is confirmed to exhibit superconductivity at 1.5 K as well as charge-or spin-density wave (CDW/SDW) ordering below 55 K. With the partial substitution of Sb by Bi, the lattice parameters a, c and c/a all increase monotonically, indicating a negative chemical pressure and lattice distortion for the (super)conducting Ti2Sb2O-layers. The Bi doping elevates the superconducting transition temperature to its maximum Tc=3.7 K at x =0.17, and then Tc decreases gradually with further Bi doping. A metal-to-nonmetal transition takes place around x=0.3, and superconductivity at ∼1 K survives at the nonmetal side. The CDW/SDW anomaly, in comparison, is rapidly suppressed by the Bi doping, and vanishes for x ≥0.17. The results are discussed in terms of negative chemical pressure and disorder effect.
Pressure-induced superconductivity in Ba 0.5 Sr 0.5 Fe 2 As 2
2012
High-pressure electrical resistance measurements have been performed on single crystal Ba 0.5 Sr 0.5 Fe 2 As 2 platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ~31 K and zero resistance at ~22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing in pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, e.g., Ba 1-x. Sr x Fe 2 As 2 (0 < x <1), can also exhibit superconductivity under high pressure.
Pressure-induced superconductivity and structural transitions in Ba(Fe0.9Ru0.1)2As2
The European Physical Journal B, 2014
High-pressure electrical resistance and x-ray diffraction measurements have been performed on ruthenium-doped Ba(Fe 0.9 Ru 0.1) 2 As 2 , up to pressures of 32 GPa and down to temperatures of 10 K, using designer diamond anvils under quasi-hydrostatic conditions. At 3.9 GPa, there is an evidence of pressure-induced superconductivity with T C onset of 24 K and zero resistance at T C zero 14.5 K. The superconducting transition temperature reaches maximum at ~ 5.5 GPa and decreases gradually with increase in pressure before completely disappearing above 11.5 GPa. Upon increasing pressure at 200 K, an isostructural phase transition from a tetragonal (I4/mmm) phase to a collapsed tetragonal phase is observed at 14 ± 1 GPa and the collapsed phase persists up to at least 30 GPa. The changes in the unit cell dimensions are highly anisotropic across the phase transition and are qualitatively similar to those observed in undoped BaFe 2 As 2 parent.
Pressure-induced superconductivity in BaFe2As2 single crystal
The evolution of pressure-induced superconductivity in single crystal as well as polycrystalline samples of BaFe2As2 have been investigated through temperature-dependent electrical resistivity studies in the 0-7 GPa pressure range. While the superconducting transition remains incomplete in the polycrystalline sample, a clear pressure-induced superconductivity with zero resistivity at the expense of magnetic transition, associated with spin density wave (SDW), is observed in the single-crystal sample. The superconducting transition temperature (TC) is seen to increase upto a moderate pressure of about ∼ 1.5 GPa and decreases monotonically beyond this pressure. The SDW transition temperature TSDW decreases rapidly with increasing pressure and vanishes above ∼ 1.5GPa.
Ba 1– x Na x Ti 2 Sb 2 O (0.0 ≤ x ≤ 0.33): A Layered Titanium-Based Pnictide Oxide Superconductor
Journal of the American Chemical Society, 2012
A new layered Ti-based pnictide oxide superconductor, Ba1-xNaxTi2Sb2O (0.0 ≤ x≤ 0.33), is reported. X-ray studies reveal it crystallizes in the tetragonal CeCr2Si2C structure. The undoped parent compound, BaTi2Sb2O (P4/mmm; a=4.1196(1)Å; c=8.0951(2)Å), exhibits a CDW/SDW transition at 54K. Upon chemical doping with Na, the CDW/SDW transition is systematically suppressed and superconductivity arises with the critical temperatures, Tc, increasing to 5.5 K. Bulk superconductivity is confirmed by resistivity, magnetic and heat capacity measurements. Like the high-Tc cuprates and the iron pnictides, superconductivity in BaTi2Sb2O arises from an ordered state. Similarities and differences to the cuprate and iron pnictide superconductors are discussed.
Pressure-induced spin-density-wave transition in superconducting Mo3Sb7
We report a novel pressure-induced spin-density-wave transition in the superconductor Mo3Sb7 figured our by measurements of the electrical resistivity and magnetization under hydrostatic pressure. The critical temperature of superconducting Mo3Sb7 is found to increase with increasing pressure, from 2.15 K at 0.2 kbar up to 2.37 K at 22 kbar. Above 4.5 kbar, superconductivity exists in parallel with a pressure-induced spin-density wave state, revealed by a sharp jump in the electrical resistivity and a maximum in the magnetization at the phase transition temperature T_SDW. The application of pressure shifts T_SDW to lower temperatures, from 6.6 K at 4.5 kbar down to 6.15 K at 22 kbar. A strong magnetic field dependence of T_SDW and a maximum seen in the magnetization indicate an antiferromagnetic character of T_SDW. The pressure dependence of T_c and T_SDW suggests a competition of the SDW and the superconducting states in this system. Comment: 12 pages, 4 figures. submitted to PRL
Physical Review B, 2013
We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi2Sb2O doped with sodium. The temperature and field dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal state Sommerfeld constant, the heat capacity jump at Tc, and the electron-phonon coupling constant are in favor of a conventional weak coupling superconductivity mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first principle calculations.