Laboratoire de Physique et d'Etude des Matériaux, ESPCI Paris
The phase diagram of underdoped superconducting cuprates is known to be extremely rich and complex. In addition to a transition from an antiferromagnetic insulator at half-doping to a strange metal at optimal doping, and the opening of a pseudogap in the density of states, the normal state is also the location for a charge ordering and a Fermi surface reconstruction. By analyzing La1-xSrxCuO4 thin films resistivity under high pulsed magnetic field for various doping, I will carefully inspect the behavior of superconducting thermal and quantum fluctuations and the existence of quantum critical points. I will extract a systematic (H,T) phase diagram and discuss the interplay between charge ordering and superconductivity. In particular I will relate our findings to a theoretical model proposed by J. Lorenzana and A. Attanasi, which enables to demonstrate that disorder can induce a charge-density-wave to become superconducting. This paradoxical e?ect occurs close to the phase boundary between CDW and SC and is analogous to the occurrence of supersolid effects in 4He. It originates from the topological stabilization of filamentary superconductivity at the interfaces of different CDW domains at low temperature and intermediate/large magnetic fields. By comparing experimental and theoretical phase diagrams I will show that the previously observed two-step phase transition in under-doped films is related to the interplay between superconducting fluctuations and CDW. I will then analyze the doping dependence of this diagram and show that p=1/8 is specific for this CDW/SC competition at least in LSCO, since the coexistence takes place at zero magnetic field for this specific doping.
Prof. Brigitte Leridon is a Centre national de la recherche scientifique (CNRS) full-time researcher and a group leader in Laboratoire de Physique et d’Etude des Matériaux, ESPCI Paris. She is the reviewer of RRL, PRB, Science, etc. She won the Jean Langlois Prize for scientific research in 2017. Her recent research highlights include: two-step insulator/superconductor transition in high-Tc superconductor, incipient inhomogeneities and zero-dimensional fluctuations in ultrathin NgN, discovery of a new superionic conductor with colossal permittivity, etc.