Quantum criticality and Fermi surface topology in CeRhIn$_5$

In the heavy fermion compound CeRhIn$_5$, superconductivity occurs upon partially suppressing the antiferromagnetic state via applying pressure. At the quantum critical point ($p_c$=2.3GPa), observations of a Fermi surface change from a small Fermi volume to a large one [1] seems to favor the scenario of local quantum criticality [2]. In this talk, we will present the first experimental evidence of a magnetic field induced quantum phase transition in CeRhIn$_5$ by measuring the ac specific heat and the de Hass van Alphen effect using the facilities of pulsed magnetic field at Los Alamos. The antiferromagnetic transition of CeRhIn$_5$ is eventually suppressed at a critical field of $H_c\simeq 50$ T. A dramatic change of the Fermi surface is found close to $H_c$, but still on the antiferromagnetic side. At sufficiently low temperatures, the Fermi surface in the antiferromagnetic state undergo a topological change from a small Fermi volume to a large one with increasing magnetic field, the latter being kept unchanged in the paramagnetic state at fields above $H_c$. These findings seem to support a different scenario for the field induced quantum phase transition in CeRhIn$_5$, e.g., the spin-density-wave-type quantum criticality. [1] H. Shishido et. al., J. Phys. Soc. Jpn. 74, 1103 (2005). [2] Q. Si et al., Nature 413, 804 (2001).