Theory of reduced singlet pairing without the underlying state of charge stripes in the high-temperature superconductor YBa_2Cu_3O_6.45

TL;DR

This paper proposes that in YBa_2Cu_3O_6.45, reduced singlet pairing enhances a competing order, explaining the observed anisotropy in magnetic excitations without the need for charge stripe states.

Contribution

It introduces a theoretical framework linking reduced singlet pairing to enhanced magnetic anisotropy, without assuming underlying charge stripe order.

Findings

Enhanced xy anisotropy in magnetic excitations at low temperature and energy.

Reduced singlet pairing correlates with increased d-wave Pomeranchuk instability.

Explains experimental observations without charge stripe states.

Abstract

Recently, a strongly enhanced xy anisotropy of magnetic excitations was observed in YBa_2Cu_3O_y (YBCO_y) with y=6.45 and Tc=35 K [Science 319, 597 (2008)]. Unlike the observation in YBCO_6.6 and YBCO_6.85, the anisotropy grows to be pronounced at lower temperature and at lower energy, and is not suppressed by the onset of superconductivity. We propose that the effect of singlet pairing is substantially reduced in YBCO_6.45. This reduction concomitantly enhances an order competing with singlet pairing, a strong tendency of the so-called d-wave Pomeranchuk instability, leading to the magnetic excitations observed experimentally.