Crystal growth, structure, and superconducting properties of the β-pyrochlore KOs2O6

Abstract

Single crystals of KOs2O6 have been grown in a sealed quartz ampoule. Detailed single crystal x-ray diffraction studies at room temperature show Bragg peaks that violate Fd3¯m symmetry. With a comparative structure refinement the structure is identified as noncentrosymmetric (F4¯3m). Compared to the ideal β-pyrochlore lattice (Fd3¯m), both Os tetrahedral and O octahedral networks exhibit breathing mode like volume changes accompanied by strong anisotropic character of the K channels. The crystals show metallic conductivity and a sharp transition to the superconducting state at Tc=9.65K. Superconducting properties have been investigated by magnetization measurements performed in a temperature range from 2to12K and in magnetic fields from 0to60kOe. The temperature dependence of the upper critical field Hc2(T) has been determined and the initial slope (dHc2∕dT)Tc=−33.3kOe∕K has been obtained near Tc. The upper critical field at zero temperature was estimated to be Hc2(0)≅230kOe, which is a value close to the Pauli paramagnetic limiting field Hp(0)≅250kOe. Then, the Ginzburg–Landau (GL) coherence length ξGL(0)≈3.8nm was calculated, and the Maki parameter α≈√2 was obtained, suggesting the possibility that KOs2O6 might behave unconventionally at low temperatures and high magnetic fields.

Source-reported materials — not catalogue approval

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