Interplay between pair- and charge-density-wave orders in underdoped cuprates

Abstract

We analyze the interplay between charge-density-wave (CDW) and pair-density-wave (PDW) orders within the spin-fermion model for the cuprates. We specifically consider CDW order with transferred momenta $(\pm Q,0)$/$(0,\pm Q)$, and PDW order with total momenta $(0,\pm Q)/(\pm Q,0)$. We show that both emerge in the spin-fermion model near the onset of antiferromagnetism. We further argue that the two orders are nearly degenerate due to an approximate SU(2) particle-hole symmetry of the model. The ${\rm SU}(2)$ symmetry becomes exact if one neglects the curvature of the Fermi surface in hot regions, in which case ${\rm U}(1)$ CDW and PDW order parameters become components of an SO(4)-symmetric PDW/CDW "super-vector". We develop a Ginzburg-Landau theory for PDW/CDW order parameters and find two possible ground states: a "stripe" state, and a "checkerboard" state. We show that the ${\rm SO}(4)$ symmetry between CDW and PDW is broken by two effects. One is the inclusion of Fermi surface curvature, which selects a PDW order immediately below the instability temperature. Another is the overlap between different hot regions, which favors CDW order at low temperatures. For the stripe state, we show that the competition between the two effects gives rise to a first-order transition from PDW to CDW inside the ordered state. We also argue that beyond mean-field theory, the onset temperature for CDW order is additionally enhanced due to feedback from a preemptive breaking of ${\mathbb Z}_2$ time-reversal symmetry. We discuss the ground state properties of a pure PDW state and a pure CDW state, and show that the PDW checkerboard state yields a vortex-anti-vortex lattice. For the checkerboard state, we considered a situation when both CDW and PDW orders are present at low $T$ and show that the presence of both condensates induces a long sought chiral $s+id_{xy}$ superconductivity.