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Kushwaha, S. K.

Publications and source records attributed to Kushwaha, S. K..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Universal superconductivity phase diagram for pressurized tetradymite topological insulators

Two different superconducting phases exist at high pressures in the optimized tetradymite topological insulators Bi 2 Te 2 Se (BTS) and Bi 1.1 Sb 0.9 Te 2 S (BSTS) are demonstrated in this work. The superconducting phases emerge at structural phase transitions; the first at ~ 8.4 GPa for BTS and ~ 12.4 GPa for BSTS, and the second at 13.6 GPa for BTS and 20.4 GPa, for BSTS. Electronic structure calculations show that these phases do not have topological character. Comparison of our results with prior work on Bi 2 Se 3 , Bi 2 Te 3 , and (Bi, Sb) 2 (Se,Te) 3 enable us to uncover a universal phase diagram for pressure-induced superconductivity in tetradymites, providing a basis for understanding the relationships between topological behavior, crystal structure, and superconductivity for these materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Tuning the electronic and the crystalline structure of LaBi by pressure: From extreme magnetoresistance to superconductivity

Here, extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi. By increasing pressure, we observe the disappearance of XMR followed by the appearance of superconductivity at P ≈ 3.5 GPa. We find a region of coexistence between superconductivity and XMR in LaBi in contrast to other superconducting XMR materials. The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures, P ≈ 11 GPa, we find a structural transition from the face-centered cubic lattice to a primitive tetragonal lattice, in agreement with theoretical predictions. The relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Superconductivity in CaBi 2

We observed superconductivity with critical temperature T c = 2.0 K in self-flux-grown single crystals of CaBi 2 . This material adopts the ZrSi 2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi 2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T c is ΔC/γT c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol -1 K -2 and the Debye temperature Θ D = 157 K. The electron–phonon coupling strength is λ el–ph = 0.59, and the thermodynamic critical field H c is low, between 111 and 124 Oe CaBi 2 is a moderate coupling type-I superconductor. Our results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin–orbit coupling and electronic property anisotropy. Furthermore, we find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗