Specific-heat studies of the spin-orbit interaction in noncentrosymmetric Li2(Pd1−xPtx)3B (x=0,0.5,1) superconductors

Abstract

The temperature- and field-dependent specific heat C(T,H) measurement on the noncentrosymmetric superconductors Li2Pd3B, Li2Pt3B, and Li2(Pd0.5Pt0.5)3B were carried out over a wide range of T and H. C(T,H) of the limit compounds is found to be distinctly different: within the superconducting phase, the electronic specific heat of the Pd-based compound follows CeS(T<Tc=6.95K,0T)=3exp[−16.4∕T]J∕molK while for the Pt-based compound CeS(T<Tc=2.56K,0T)=αT2mJ∕molK, where α=7.3mJ∕molK3. An increase in H tends to reduce weakly the exponential argument and the coefficient of the quadratic term. The above-mentioned findings are in agreement with the description that, due to the difference in the strength of the spin-orbit coupling, the pairing symmetry in the Pd- (Pt-) based compound is predominately a spin-singlet (spin-triplet) state. Within the very low-temperature range, the field-induced normal-state of the Pd-based limit manifests CN(T,7T>Hc2)=9.3T+1.1T3mJ∕molK while that of the Pt-based isomorph shows CN(T,7T>Hc2)=9.3T+0.92T3mJ∕molK. For the intermediate alloy Li2(Pt0.5Pd0.5)3B, C(T,H) mimics that of the Pt-based compound; specifically, CeS(T<Tc=3.9K,0T)=αT2mJ∕molK where α=4.6(2)mJ∕molK3. The ratio of the coefficients of the quadratic terms in Li2(Pt0.5Pd0.5)3B and Li2Pt3B, αPt0.5Pd0.5∕αPt, is equal to ZPt0.5Pd0.52∕ZPt2, confirming that the line nodes are driven by the spin-orbit interaction. The finding that these nodes can survive even in a 50% Pd-diluted material gives extra support to the reported claim that the x-dependent evolution of Tc, Hc1, Hc2, and (∂Hc2∕∂T)Tc is almost linear.

Source-reported materials — not catalogue approval

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