Investigating quantum phase transitions using designer-anvil pressure cells

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Discovery in correlated electron systems research occurs on the boundary of known low temperature states. Next to applied magnetic field, pressure, which affords precise control over the lattice density, is the vehicle of choice for traversing quantum matter phase diagrams and seeking out novel states of matter. This project represents a radical departure in high pressure anvil cell technology: We will structure leads and detection circuits into ceramic anvils by microlithographic methods. The resulting designer anvils provide the reliability, ease of use and versatility necessary for a novel investigation into the high-pressure superconducting state of the archetypal correlated electron superconductor CeCu2Si2. In this intriguing material it appears that two distinct mechanisms can induce superconductivity in different regions of the pressure-temperature phase diagram. Both interactions originate in the Coulomb repulsion between electrons, but one - an effective magnetic interaction - dominates when the material is tuned close to the onset of magnetic order, while the other - an effective charge density interaction - prevails close to a putative transition of the lattice, in which the unit cell volume and hence the lattice density undergoes a weak first order change. In order to investigate the density change quantum phase transition in CeCu2Si2 and in related materials, a detailed study of the pressure dependence of resistivity, heat capacity and thermal expansion will be carried out into the 100 kbar regime. While the investigated pairing mechanism may have ramifications throughout the strongly correlated electron field, including the high-Tc superconductors, the envisaged high pressure technology will be beneficial for a large community of researchers interested in transport or thermodynamic experiments under anvil cell conditions.