Ultrasonic observation of small Fermi surfaces in LaTIn₅ (T = Co, Rh, Ir)

We performed high-field ultrasonic measurements on LaTIn5 (T = Co, Rh, Ir) to reveal the origin of the small Fermi surface that was recently observed in LaRhIn5 with an oscillation frequency of 6.8 T. We observed quantum oscillations originating from this Fermi surface in LaRhIn5. In addition, we revealed that LaCoIn5 and LaIrIn5 exhibit quantum oscillations with frequencies below 100 T, indicating hidden Fermi surfaces in these compounds. Furthermore, Co-substituted LaRhIn5 exhibited quantum oscillations with a frequency of 10 T. Our results suggest that the small Fermi surface originates from bulk properties and that 3d electrons of the transition metal contribute to its formation.