Crystal growth, characterization and advanced study of the noncentrosymmetric superconductor Mo${}_3$Al${}_2$C

Abstract

We report on the first successful growth of single crystals of the noncentrosymmetric superconductor Mo${}_3$Al${}_2$C obtained by means of a cubic-anvil, high-pressure and high-temperature technique. Composition, structure, and normal-state transport properties of the crystals were studied by means of X-ray diffraction, energy-dispersive X-ray spectroscopy, magnetic susceptibility and resistivity measurements as a function of temperature. Variations in critical temperature ($T_c$) between 8.6 and 9.3 K were observed, probably due to the slightly different carbon stoichiometry of the samples. Single-crystal X-ray refinement confirmed the high structural perfection of the grown crystals. Remarkably, the refined Flack parameter values for all the measured crystals using a $P{4}_{1}32$ space-group model were consistently close to either 0 or 1, hence indicating that the considered crystals belong to two enantiomorphic space groups, $P{4}_{1}32$ and $P{4}_{3}32$. An anomaly in the resistivity is observed at about 130 K, most likely associated with the onset of a charge-density-wave phase. The superconducting properties (and in particular the symmetry, the amplitude and the temperature dependence of the superconducting gap) were studied by using - for the first time in this compound - point contact Andreev-reflection spectroscopy. The results confirm that Mo${}_3$Al${}_2$C is a moderately strongly-coupled superconductor with $2\Delta /k_B{T}_c\simeq 4$ and unambiguously prove that the order parameter has an s-wave symmetry despite the asymmetric spin-orbit coupling arising from the lack of inversion symmetry.

12 pages, 12 figures, revtex format

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• Exploring 2D Materials by High Pressure Synthesis: hBN, Mg-hBN, b-P, b-AsP, and GeAs
• Crystal growth and characterization of the antiperovskite superconductor MgC1-xNi3-y
• High-pressure hydrothermal growth and characterization of Sr3Os4O14 single crystals
• Polar charge density wave in a superconductor with crystallographic chirality
• $s$-wave superconductivity in the noncentrosymmetric W${}_3$Al${}_2$C superconductor: An NMR study
• High-pressure high-temperature solution growth, structural, and superconducting properties of Fe-substituted MgB2 single crystals
• High-pressure self-flux growth and characterization of Li-deficient Li0.95FeAs single crystals
• Phonon anomalies within the polar charge density wave phase of the structurally chiral superconductor Mo${}_3$Al${}_2$C
• Superconductivity of Co-Doped CaKFe4As4 Investigated via Point-Contact Spectroscopy and London Penetration Depth Measurements
• Discovery of a new magnesium iron boride Mg4Fe1.1B13.9 in the Mg-Fe-B-N system