| The study of quantum phase transitions has received a large amount of attention owing to the fact that a range of anomalous properties appear to be linked to the occurrence of quantum fluctuations. CeCoIn5 is a recently discovered heavy-fermion metal with an unconventional superconducting state below Tc = 2.3 K and a range of properties unexplained by the conventional Fermi liquid theory of metals. As a member of the CeMIn5 family (where M = Co, Ir or Rh), the anomalous transport, magnetic and thermodynamics properties of CeCoIn5 are thought to arise from an antiferromagnetic instability which has yet to be identified.; This study reports measurements of heat and charge transport in CeCoIn 5, as a function of temperature T, magnetic field H and orientation of current J with respect to the crystal axes, which have unearthed a host of incredible properties. These include the identification of a field-tuned quantum critical point (QCP) which coincides with the upper critical field of the superconducting state at Hc2 = 5 T. As evidenced by divergences of the T2 coefficients of both electrical and thermal resistivities in the field-induced Fermi liquid state, the nature of this QCP is further elucidated by the observed relation between Delta H/T scaling and an anomalous T2/3 dependence of resistivity in the high-field non-Fermi liquid regime of J ⊥ [001] transport. Additional measurements of antiferromagnetic CeRhIn5 were also performed in order to shed light on the similarities and differences throughout this series of compounds.; As a function of current orientation, qualitatively different behaviour is observed both in temperature and field dependences of transport. Whereas the temperature dependence of resistivity evolves with field for J ⊥ [001] transport, it remains linear in temperature for the J || [001] orientation, as observed in both the heat and charge channels. At the critical field, a test of the Wiedemann-Franz law in the T → 0 limit has revealed a stunning anisotropy: the Wiedemann-Franz law is obeyed by J ⊥ [001] currents, whereas a 27% violation occurs for J || [001] currents. These observations suggest the existence of two distinct QCPs which influence correspondingly different conduction bands, highlighting the multi-band nature of quantum criticality in CeCoIn5. |
