Origin of the 30 T transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CeRhIn</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math> in tilted magnetic fields

We present a comprehensive ultrasound study of the prototypical heavy-fermion material CeRhIn_5 examining the origin of the enigmatic 30 T transition. For a field applied at 2^\circfrom the caxis, we observed two sharp anomalies in the sound velocity, at B_m \approx20 T and B^* \approx30 T, in all the symmetry-breaking ultrasound modes at low temperatures. The lower-field anomaly corresponds to the well-known first-order...