Speaker
Description
Despite the complexity of high-$T_c$ cuprates, we have identified a series of surprisingly simple and universal behaviors [1-7]. Building on these findings, we show [8,9] that the phenomenology of cuprates across the phase diagram can be fully described by two relatively simple relations:
$\hspace{2cm}$$1 + p = n_{loc} + n_{eff}\;\; (1)\hspace{2cm} \rho_S = n_{eff}\cdot(O_S\,n_{loc})\;\; (2)$
where $p$ is the doping, $n_{eff}$ is the density of Fermi-liquid carriers, $n_{loc}$ is the density of (Mott-like) localized charge, while $\rho_S$ is the superfluid density and $O_S$, is compound-dependent constant fine-tuned by the local crystal structure [9]. Importantly, all terms can be experimentally determined directly.
Murunskite (K$_2$FeCu$_3$S$_4$) can be viewed as a bridging compound between cuprate and iron-pnictide superconductors [10]. It is isostructural to iron-pnictides but, like parent cuprate compounds, it is a $\sim 1$ eV insulator, as determined from optical conductivity. Long-range magnetic order is observed below $97$ K, with a nearly commensurate quarter-zone wave vector, as determined by neutron studies [11]. Mössbauer and XPS measurements reveal that the magnetic transition is accompanied by an orbital transition. Remarkably, full orbital and spin order is achieved at $30$ K, despite the presence of two distinct magnetic Fe sites at higher temperatures, where Fe is randomly distributed among non-magnetic Cu.
We will argue that understanding the role of the localized hole ($O_S$ $n_{loc}$) within the CuO$_2$ unit in cuprates, as well as the very local magnetic interactions in murunskite, is key to understanding these materials—and may provide valuable insights for other functional materials as well.
References
[1] N. Barišić et al., “Evidence for a universal Fermi-liquid scattering rate throughout the phase diagram of the copper-oxide superconductors,” New Journal of Physics, vol. 21, no. 11., p. 113007, 2019. https://doi.org/10.1088/1367-2630/ab4d0f
[2] Y. Li et al., “Hole pocket–driven superconductivity and its universal features in the electron-doped cuprates,” Science Advances, vol. 5, no. 2., 2019. https://doi.org/10.1126/sciadv.aap7349
[3] N. Barišić et al., “Universal sheet resistance and revised phase diagram of the cuprate high-temperature superconductors,” Proceedings of the National Academy of Sciences, vol. 110, no. 30., pp. 12235–12240, 2013. https://doi.org/10.1073/pnas.1301989110
[4] S. I. Mirzaei et al., “Spectroscopic evidence for Fermi liquid-like energy and temperature dependence of the relaxation rate in the pseudogap phase of the cuprates,” Proceedings of the National Academy of Sciences, vol. 110, no. 15., pp. 5774–5778, 2013. https://doi.org/10.1073/pnas.1218846110
[5] M. K. Chan et al., “In-Plane Magnetoresistance Obeys Kohler’s Rule in the Pseudogap Phase of Cuprate Superconductors,” Physical Review Letters, vol. 113, no. 17., 2014. https://doi.org/10.1103/physrevlett.113.177005
[6] P. Popčević et al., “Percolative nature of the direct-current paraconductivity in cuprate superconductors,” npj Quantum Materials, vol. 3, no. 1., 2018. https://doi.org/10.1038/s41535-018-0115-2
[7] C. M. N. Kumar et al., “Characterization of two electronic subsystems in cuprates through optical conductivity,” Physical Review B, vol. 107, no. 14., 2023. https://doi.org/10.1103/physrevb.107.144515
[8] D. Pelc, P. Popčević, M. Požek, M. Greven, and N. Barišić, “Unusual behavior of cuprates explained by heterogeneous charge localization,” Science Advances, vol. 5, no. 1., 2019. https://doi.org/10.1126/sciadv.aau4538
[9] N. Barišić & D. K. Sunko. J Supercond. Nov. Magn. 35, 1781 (2022). doi : 10.1007/s10948-022-06183-y
[10] D.Tolj et. al., Appl. Mater. Today 24, 101096 (2021). doi : 10.1016/j.apmt.2021.101096
[11] D. Tolj et. al., arXiv:2406.17108 (2024). doi : 10.48550/arXiv.2406.17108.
