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Register a new userComparative High Field Magneto-Transport of Rare Earth Oxypnictides with Maximum Transition Temperatures
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The recent discovery of a new class of superconducting oxypnictides with high transition temperatures may have profound implications for understanding unconventional high-temperature superconductivity. Like the cuprates, the oxypnictides seem to manifest an interleaving of charge donor and superconducting layers emerging upon doping of an antiferromagnetic parent semi-metal. Here we report magneto-transport measurements of three rare earth (Re = La, Nd, Sm) oxypnicide compounds with the transition temperatures near the maximum reported to date, in very high DC and pulsed magnetic fields up to 45 and 54 T, respectively. Our resistivity, Hall coefficient and critical magnetic fields data suggest that these oxypnictide superconductors bridge the gap between MgB$_2$ and YBaCu$_3$O$_{7-x}$ as far as electromagnetic and vortex properties are concerned.
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We report high field magneto transport of Sm/PrFeAsO. Below spin density wave transition (TSDW), the magneto-resistance (MR) of Sm/PrFeAsO is positive and increasing with decreasing temperature. The MR of SmFeAsO, is found 16%, whereas the same is 21.5% in case of PrFeAsO, at 2.5 K under applied magnetic field of 14 Tesla (T). In case of SmFeAsO, the variation of isothermal MR with field below 20 K is nonlinear at lower magnetic fields (< 2 Tesla) and the same is linear at moderately higher magnetic fields (H geq 3.5 T). On the other hand PrFeAsO shows almost linear MR at all temperatures below 20 K. The anomalous behavior of MR being exhibited in PrFeAsO is originated from Dirac cone states. The stronger interplay of Fe and Pr ordered moments is responsible for this distinct behavior. PrFeAsO also shows a hump in resistivity (R-T) with possible conduction band (FeAs) mediated ordering of Pr moments at around 12 K. However the same is absent in SmFeAsO even down to 2 K. Our results of high field magneto-transport of up to 14 Tesla brings about clear distinction between ground states of SmFeAsO and PrFeAsO.
High-pressure superconductivity in a rare-earth doped Ca0.86Pr0.14Fe2As2 single crystalline sample has been studied up to 12 GPa and temperatures down to 11 K using designer diamond anvil cell under a quasi-hydrostatic pressure medium. The electrical resistance measurements were complemented by high pressure and low temperature x-ray diffraction studies at a synchrotron source. The electrical resistance measurements show an intriguing observation of superconductivity under pressure, with Tc as high as ~51 K at 1.9 GPa, presenting the highest Tc reported in the intermetallic class of 1-2-2 iron-based superconductors. The resistive transition observed suggests a possible existence of two superconducting phases at low pressures of 0.5 GPa: one phase starting at Tc1 ~48 K, and the other starting at Tc2~16 K. The two superconducting transitions show distinct variations with increasing pressure. High pressure low temperature structural studies indicate that the superconducting phase is a collapsed tetragonal ThCr2Si2-type (122) crystal structure. Our high pressure studies indicate that high Tc state attributed to non-bulk superconductivity in rare-earth doped 1-2-2 iron-based superconductors is stable under compression over a broad pressure range.
In this work we study the effect of the rare earth element in iron oxypnictides of composition REFeAsO (RE=rare earth). On one hand we carry out Density Functional Theory calculations of the band structure, which evidence the multiband character of these compounds and the presence of Dirac cones along the Y-{Gamma} and Z-R directions of the reciprocal space. On the other hand, we explore transport behavior by means of resistivity, Hall resistance and magnetoresistance measurements, which confirm the dominant role of Dirac cones. By combining our theoretical and experimental approaches, we extract information on effective masses, scattering rates and Fermi velocities for different rare earth elements.
Here, we present the comparative study of magnetotransport properties of recently discovered Ta2PdTe6 and Nb2PdS5 superconductors. The XRD and magnetotransport measurements are performed on these samples to investigate structure and superconducting properties as well as normal state transport properties of these compounds. Both the compounds are crystallized in monoclinic structure within space group C2m. Here, we observe superconductivity in both the compounds Ta2PdTe6 (Tc =4.4 K) and Nb2PdS5 (Tc =6.6 K). We see a linear magnetoresistance in Ta2PdTe6 as well as violation of Kohler rule in same compound. On the other hand, we find the absence of same in Nb2PdS5 compound.
Recently the superconductivity has been discovered in the rock-salt structured binary lanthanum monoxide LaO through the state-of-the-art oxide thin-film epitaxy. This work reveals the normal state of superconducting LaO to be a $Z_2$ nontrivial topological metal that the Dirac point protected by the crystal symmetry is located at around the Fermi energy. By analysing the orbital characteristics, the nature of topological band structure of LaO originates from the intra-atomic transition in energy from outer shell La 5$d$ to inner shell 4$f$ orbitals driven by the strong octahedral crystal-field. Furthermore, the appearance of novel surface states unambiguously demonstrates the topological signature of LaO. Our theoretical findings not only shed light into the understanding of exotic quantum behaviors in LaO superconductor with intimate correlation between 4$f$ and 5$d$ orbitals in La, but also provide an exciting platform to explore the interplay of intriguing nontrivial topology and superconductivity.
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