### Abstract

The physics of quantum critical phase transitions connects
to some of the most difficult problems in condensed matter
physics, including metal–insulator transitions, frustrated
magnetism and high-temperature superconductivity. Near a
quantum critical point, a new kind of metal emerges, the thermodynamic
and transport properties of which do not fit into
the unified phenomenology for conventional metals—the Landau
Fermi-liquid theory—characterized by a low-temperature
limiting T-linear specific heat and a T2 resistivity1. Studying
the evolution of the temperature dependence of these
observables as a function of a control parameter leads to
the identification of both the presence and the nature of the
quantum phase transition in candidate systems. In this study
we measure the transport properties of BaFe2(As1-xPx)2 below
the critical temperature Tc by suppressing superconductivity
with high magnetic fields. At sufficiently low temperatures,
the resistivity of all compositions (x >0:31) crosses over from
a linear to a quadratic temperature dependence, consistent
with a low-temperature Fermi-liquid ground state. As compositions
with optimal Tc are approached from the overdoped
side, this crossover becomes steeper, consistent with models
of quantum criticality where the effective Fermi temperature
TF goes to zero.

Original language | English |
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Pages (from-to) | 194 |

Number of pages | 197 |

Journal | Nature Physics |

Volume | 10 |

Issue number | 3 |

DOIs | |

Publication status | Published - Mar 2014 |