A two-pronged approach to the cuprate pseudogap: A comparison of mode-coupling and first-principles (SCAN) results

Density functional theory using the new SCAN exchange-correlation functional has successfully described the antiferromagnetic ground states of undoped cuprate superconductors. In YBa₂Cu₃O₇ (YBCO₇), the energy landscape involves a competition between many different nearly degenerate states – a mixture of antiferromagnetic and stripe states[1]. The organizing principle of these states remains Mott-like: the lower-energy phases tend to have a larger planar copper magnetic moment. In particular, all these phases have substantially lower energy than the nonmgnetic Fermi liquid phase found in most previous DFT calculations, showing that it can play no role in the low-energy properties of YBCO₇.
The contrasting behaviors of YBCO₆ and YBCO₇ are reminiscent of the Mott-Slater crossover found in a mode-coupling model of the cuprates[2]. I will demonstrate how these two approaches illuminate each other, leading to a picture of the pseudogap as a gapped paramagnetic metal with only short-range order (SRO) over a broad temperature range. This work provides a realistic model for the cuprate pseudogap phase with implications for superconducting pairing.
[1] Y. Zhang et al., arXiv:1809.8457.
[2] R.S. Markiewicz et al., Scientific Reports 7, 44008 (2017).