Charge trapping and super-Poissonian noise centers in a cuprate superconductor

We present new insight into the mystery of highly anisotropic transport in the cuprates and how they can trap additional charges. Above the superconducting transition these materials are perfectly metallic along the crystal planes (ab-plane), but are insulating in the c-axis, with ratios between in-plane and perpendicular resistance exceeding 10⁴. This anisotropy has been identified as one of the key mysteries in the cuprates and has been connected to the mechanism of high-temperature superconductivity. Here, we employ our newly developed scanning noise spectroscopy technique, for which we combined a scanning tunneling microscope (STM) with a novel MHz frequency amplifier to bring noise-spectroscopy measurements to the atomic scale [1]. We discover surprising deviations from the expected Poissonian noise of uncorrelated electrons. A behavior that can only happen in highly polarizable insulators and represents strong evidence for trapping of charge in the charge reservoir layers of the cuprates. We will show how these new observations connect to the mystery of anisotropic transport in high-temperature superconductors and shed new light onto this issue [2].

[1] KM Bastiaans et al. Rev.Sci.Instrum. 89, 093709 (2018)
[2] KM Bastiaans, D Cho et al. Nature Physics AOP