The cuprate phase diagram and the influence of nanoscale inhomogeneities

TL;DR

This paper investigates the complex phase diagram of high Tc cuprate superconductors, focusing on nanoscale inhomogeneities and their role in distinguishing pseudogap phenomena from superconducting gaps, linking the pseudogap to spin singlet formation.

Contribution

The study clarifies the influence of nanoscale inhomogeneities on the phase diagram and separates pseudogap effects from superconducting gaps using a mean field approach linked to the $t-J$ model.

Findings

Nanoscale inhomogeneities affect the interpretation of the phase diagram.

The pseudogap is associated with spin singlet formation.

The gap magnitude correlates with the Heisenberg exchange interaction $J$.

Abstract

The phase diagram associated with the high Tc superconductors is complicated by an array of different ground states. The parent material represents an antiferromagnetic insulator but with doping superconductivity becomes possible with transition temperatures previously thought unattainable. The underdoped region of the phase diagram is dominated by the so-called pseudogap phenomena whereby in the normal state the system mimics superconductivity in its spectra response but does not show the complete loss of resistivity associated with the superconducting state. An understanding of this regime presents one of the great challenges for the field. In the present study we revisit the structure of the phase diagram as determined in photoemission studies. By careful analysis of the role of nanoscale inhomogeneities in the overdoped region we are able to more carefully separate out the gaps due to the pseudogap phenomena from the gaps due to the superconducting transition. Within a mean field description we are thus able to link the magnitude of the gap directly to the Heisenberg exchange interaction term, $J\sum{s_i \cdot s_j}$, contained in the $t-J$ model. This approach provides a clear indication that the pseudogap is that associated with spin singlet formation.