Novel types of quantum criticality in heavy-fermion systems

Quantum criticality arises from continuous changes of matter at absolute zero temperature. It can have vast reaching influence on wide regions of phase space and is often connected to the occurrence of non-Fermi liquid behavior and unconventional superconductivity. Various different types of quantum criticality have been observed over the last years and 4f-electron based heavy-fermion metals have become prototype materials in which quantum criticality is easily realized by application of pressure or magnetic field, as well as suitable changes in chemical composition. Using low-temperature thermodynamic, magnetic and transport experiments on clean prototype materials we investigate novel types of quantum criticality arising from ferromagnetic fluctuations and strong geometrical frustration, as well as quantum criticality hidden by unconventional superconductivity.