Ultrasonic observation of small Fermi surfaces in La$T$In${}_5$ ($T$ = Co, Rh, Ir)

We performed high-field ultrasonic measurements on La$T$In${}_5$ ($T$ = Co, Rh, Ir) to reveal the origin of the small Fermi surface that was recently observed in LaRhIn${}_5$ with an oscillation frequency of 6.8 T. We observed quantum oscillations originating from this Fermi surface in LaRhIn${}_5$. In addition, we revealed that LaCoIn${}_5$ and LaIrIn${}_5$ exhibit quantum osciilations with frequencies below 100 T, indicating hidden Fermi surfaces in these compounds. Furthermore, Co-substituted LaRhIn${}_5$ 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.