Abstract

In the first part of my talk, I will present recent achievement in thermoelectricity measurements in pulsed magnetic field. We have investigated the so-called ‘metamagnetic transition’ around H=35 T in the heavy fermion URu2Si2. Both Nernst coefficient and thermopower show an anomaly at the transition, which allow us to reconstruct the phase diagram at low temperature and high magnetic field. Data provide significant information about the ‘hidden order’ in URu2Si2. High magnetic fields can also be used to quench superconductivity in underdoped cuprates and therefore to investigate the nature of the ground state. We have studied the magnetoresistance of high-quality single crystals of YBa2Cu3Oy and YBa2Cu4O8 up to 60 T. In contrast to other cuprates, where localization masks the intrinsic low-temperature properties of the entire underdoped region, the metallic regime in the present materials extends deep into the so-called pseudogap phase. We argue that these are the defining low-energy properties of the electron system as it evolves towards the Mott insulator, in the absence of disorder and competing phases.