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Noisy defects in a high temperature superconductor


High temperature superconductivity in copper oxide materials is achieved through adding oxygen atoms, or dopants, to the system. Using current-noise measurements at the atomic scale, researchers at the LPS have unveiled unusual charge dynamics for specific dopant environments.

Charge dynamics in a cuprate superconductor. (a) Atomic lattice of Bi2Sr2CaCu2O8+x and (b) current-noise image taken on the same location. The current noise is strongly enhanced on a number of atomic scale sites. (c) The abrupt increase in noise (blue trace) from Poissonian (dashed black) coincides with a drop in the differential conductance (red) and can be explained by charging and de-charging of an oxygen dopant on sub-microsecond time-scales.

Dopants and impurities are crucial in shaping the ground-state of host materials : semiconducting technology is based on their ability to donate or trap electrons, and in many correlated electron systems they are used to transform materials of little interest into exotic matter. A prime example is the copper oxide high temperature superconductors, which are insulators without the addition of dopants. To understand the role of dopants in this transformation at the microscopic level, local atomic scale techniques such as scanning tunnelling microscopy are crucial. However, due to limited time resolution, most of these studies focus on the effect of dopants on the electronic properties averaged over time. Using newly developed circuitry, researchers from the LPS are now able to study the electronic dynamics of optimally doped Bi2Sr2CaCu2O8+x using current-noise measurements. They visualise sub-nanometre-sized objects where the tunnelling-current noise is enhanced by at least an order of magnitude. They showed that these objects are previously-undetected oxygen dopants whose ionisation and local environment lead to unconventional charge dynamics, resulting in correlated tunnelling events. The ionisation of these dopants opens up new routes to dynamically control doping at the atomic scale, enabling the direct visualisation of the effects of local charging on e.g. high-Tc superconductivity.

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Reference

Noisy defects in the high-Tc superconductor Bi2Sr2CaCu2O8+x
F. Massee, Y. K. Huang, M. S. Golden and M. Aprili
Nature Communications (2019)
doi:10.1038/s41467-019-08518-1

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Freek Massee