Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 3: Superconductivity: Properties and Electronic Structure

TT 3.5: Talk

Monday, September 5, 2022, 10:30–10:45, H23

Local measurements of (super-)conducting microstructure in Rb_xFe_2−ySe₂ — •Donald M Evans¹, Stephan Krohns¹, Dorina Croitori², Vladimir Tsurkan^1,2, and István Kézsmárki¹ — ¹Experimental Physics V, University of Augsburg, 86135 Germany — ²Institute of Applied Physics, MD 2028 Chisinau, Moldova.

There are many reports on the bulk coexistence of competing orders in iron-based superconductors. In some of these systems, such as RbFe₂Se₂, this is because even single crystals spontaneously phase separate into a superconducting phase made up of micron scale islands, within an antiferromagnetic host matrix. Such phase coexistence makes any bulk data challenging to interpret and, rather, requires local measurement techniques.

In this work, we use low-temperature conducting atomic force microscopy (cAFM) to map the local current response of the superconducting islands in RbFe₂Se₂. Below T_c (∼ 32 K) these islands show large current values, as expected for a superconductor. Unexpectedly, there is no distinct change in these current values when heating through Tc: rather, the high currents persist within the islands until they becoming as insulating as the bulk matrix at ∼ 150 K. This enhanced conductivity vanishes in response to external magnetic fields. This implies that the reported bulk Tc is the temperature at which the superconductivity is strong enough to connect the islands, i.e. the percolation limit, while the superconductivity within individual islands persists to higher temperatures. This work shows the strength of cAFM to understand the local properties of inhomogeneous superconductors.