Cuprate superconductors in the vicinity of a Pomeranchuk instability

We propose that cuprate superconductors are in the vicinity of a spontaneous dd-wave type Fermi surface symmetry breaking, often called a dd-wave Pomeranchuk instability. This idea is explored by means of a comprehensive study of magnetic excitations within the slave-boson mean-field theory of the tt–JJ model. We can naturally understand the pronounced xyxy anisotropy of magnetic excitations in untwinned YBa2Cu3OyYBa2Cu3Oy and the sizable change of incommensurability of magnetic excitations at the transition temperature to the low-temperature tetragonal lattice structure in La2-xBaxCuO4La2-xBaxCuO4. In addition, the present theoretical framework allows the understanding of the similarities and differences of magnetic excitations in Y-based and La-based cuprates.