Influence of Pressure on the Structure and Electronic Properties of the Layered Superconductor Y2C2I2

The structural properties under hydrostatic pressure up to 3 GPa of the layered rare earth carbide halide superconductor Y2C2I2 are studied by neutron powder diffraction at room temperature. The compressibilities are anisotropic, such that the compressibility perpendicular to the layers being approximately twice as large as within the layers. The atomic positional parameters determined from the powder diffraction patterns as a function of pressure were used as the basis for highly resolved electronic structure calculations. These reveal the electronic density of states at E_F to increase with pressure. As is shown quantitatively, this effect outweighs the pressure induced lattice stiffening effects and is responsible for the pressure induced increase and saturation of Tc towards 2 GPa.