Hidden antiferromagnetism and pseudogap from fluctuating stripes

One of the central mysteries of hole-doped cuprates is the pseudogap phase, whose unusual properties are believed to be essential for understanding high-temperature superconductivity. While a broad variety of theoretical proposals have been put forward in the past decades, a unified view connecting the pseudogap to other observed phases, like antiferromagnetic (AFM) and stripe phases, has remained elusive. In this talk, I will begin by briefly summarizing the key characteristics of the pseudogap phase and providing an overview of existing theoretical scenarios. I will then propose a scenario in which the the AFM, stripe, and pseudogap phases all share a common origin: The spins in the material form an ordered AFM background, on top of which fluctuating domain walls exist that can disrupt and obscure long-range order. I will argue that these fluctuating domain walls may be at the heart of the pseudogap phase. They break down magnetic order in real space, leaving only short-range AFM correlations detectable in experiments. Furthermore, these fluctuations can give rise to a topological phase (an odd Z2 spin liquid) that supports a small Fermi surface, consistent with experimental data. At a (hidden) quantum critical point, hidden AFM order fully dissolves, restoring spin symmetry without a divergent correlation length.

One key experiment for indicating the LC is the nonlinear response [2] in 2022. They measured the non-reciprocal voltage, which is proportional to the square of the electric field E, it was found that the resistivity is proportional to the magnetic field B_x and J_z. Furthermore, it was discovered that the resistivity is proportional to B_z, which was traditionally considered a material-dependent constant, jumps depending on the B_z. Such a jump behavior cannot be accounted for in the conventional polar-type nonlinear response theory (please refer to [3]). In this study [5], we start from the Boltzmann equation under the LC order and go beyond the conventional approximation by considering higher-order terms in relaxation-time [4], developing a theoretical formula for this jump-type nonlinear response. As a result, we found that the jump term, which could not be explained by the conventional Drude term, can be explained by the higher-order term. Furthermore, by applying the obtained formula to a two-orbital 12-site Kagome model and performing numerical analysis, we found that the dominant component of the nonlinear conductivity is large at band crossing points, and even larger at points where the orbital character changes sharply. This behavior can be understood using the concept of quantum geometry, where the conductivity resonates with the LC gap size. (The present nonlinear conductivity is considers as "quasi"-quantum geometry, as its dimension differs by the 1/E.)

[1] C. Mielke et al., Nature 602, 245 (2022)
[2] C. Guo et al., Nature 611, 461 (2022)
[3] Y. Tokura, et al., Nat. Commun.9, 3740 (2018)
[4] X. Liu et al., arXiv: 2303.10164 (2023)
[5] R. Tazai et al., arXiv:2408.04233