High-Tc superconductivity in strongly overdoped cuprates – SUPERSTRONG

Until recently, it was commonly believed that superconducting cuprates become conventional Fermi-liquid metals upon overdoping the CuO2 plane at p > 0.27 hole/Cu. In fact, this overdoped region has been little studied in the past, so the above Fermi-liquid scenario was never verified in a systematic manner.

Recently, we discovered high-temperature superconductivity in Cu0.75Mo0.25Sr2YCu2O7.54, where high-pressure synthesis enabled us to achieve strong overdoping, with p=0.46 hole/Cu. This unexpected result, later confirmed in other cuprates, has put into question the validity of the current phenomenological description of cuprates.

The open question we intend to address in the present proposal is whether the normal state of strongly overdoped cuprates is a Fermi liquid, which would invalidate the paradigm that superconductivity in cuprates arises from an unconventional non-Fermi-liquid state. In order to answer this fundamental question, we take advantage of the long-standing expertise of our DEMARE group in cuprates and in high-pressure synthesis of materials to study systematically the thermodynamic, electronic and transport properties of the 3 overdoped systems (Cu,Mo)Sr2YCu2O7+x, YBa2Cu3O7+x and YSr2Cu3O7+x as a function of doping x.

Some of these studies shall be carried out on high-purity polycrystalline samples already available, while angular resolved photoemission spectroscopy and optical conductivity studies require sizable single crystals that we plan to grow using a high-pressure synthesis technique controlled by means of a unique combination of in situ X-ray diffraction, tomography and calorimetric measurements.

The members of the DEMARE group have complementary expertise ranging from materials synthesis to characterisation and theory required to implement successfully the above work plan. Funding is requested to enable an effective use of a specially designed press for high-pressure synthesis, to cover the costs of consumables and to support a PhD.