P1: Quantum critical point scenarios in heavy-fermion systems

P. Gegenwart, F. Steglich, C. Geibel, M. Brando

Quantum criticality in f-electron based heavy-fermion (HF) systems arises from the competition of the on-site Kondo with the intersite exchange interaction. The essential question is how the heavy quasiparticles evolve if these materials are tuned from the paramagnetic into the antiferromagnetically ordered state.

The traditional picture describes a spin-density-wave transition at which the quasiparticles retain their itinerant character. Unconventional quantum criticality, which qualitatively differs from the predictions of standard theory, may arise due to a destruction of Kondo screening, leading to a decomposition of the heavy quasiparticles into conduction electrons and local magnetic moments.

In order to identify the conditions for the formation of unconventional quantum criticality, we perform a comparative study on already known antiferromagnetic quantum critical HF metals, e.g. YbRh2Si2 and CeRhIn5, as well as on new ones to be discovered in this project, by means of low-temperature thermodynamic, magnetic, transport as well as de Haas-van Alphen experiments. Our study will also include ferromagnetic quantum phase transitions which are very scarce in f-electron HF systems