Fermi-surface evolution in Yb-substituted CeCoIn₅

We report results of systematic de Haas–van Alphen (dHvA) studies on Ce_1−xYb_xCoIn₅ single crystals with varyingYb concentration. For x = 0.1, the well-known Fermi surfaces and the heavy effective masses of CeCoIn₅ (x = 0) have changed only slightly.We start to observe changes of the Fermi-surface topology at x = 0.2 leading to a drastic reconstruction above x = 0.55. At these concentrations, the effective masses are reduced considerably to values between 0.7 and 2.6 free electron masses. For both YbCoIn₅ and CeCoIn₅, the angular-resolved dHvA frequencies can be very well described by conventional density-functional theory calculations. Projection of the Bloch states onto atomic Yb-4f orbitals yields a 4f occupation of 13.7 electrons, in agreement with previous experimental results indicating an intermediate Yb valence of +2.3.