Regensburg 2022 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 7: Fluctuations, Noise, Magnetotransport, and Related Topics

TT 7.2: Vortrag

Montag, 5. September 2022, 15:15–15:30, H23

Revealing channel polarization of atomic contacts of ferromagnets and strong paramagnets by shot-noise measurements — Martin Prestel, •Marcel Strohmeier, Wolfgang Belzig, and Elke Scheer — University of Konstanz, 78457 Konstanz, Germany

We report measurements of the shot noise of atomic contacts using the mechanically controllable break junction (MCBJ) technique at low temperatures. In accordance with theoretical predictions [1, 2] single-atom contacts of the ferromagnets Co and Gd with conductance smaller than the conductance quantum show reduced noise compared to the expectation for the spin-degenerate single-channel transport. Additionally we focus on the strong paramagnets Pt [3], Pd [4], and Ir [5], where a nonmonotonic magnetoresistance has been reported for atomic contacts, interpreted as emerging magnetic ordering in small dimension, which is triggered by the vicinity of the respective bulk metals to a Stoner instability. Our recent measurements on Pd, Pt, and Ir reveal noise levels which are above, but close to the threshold to the spin-degenerate single-channel situation [6]. An anticorrelation between the minimum noise and the bulk Stoner parameter of these elements is observed. We discuss by how far this might indicate that spin polarization is reflected in the noise signal.

[1] Olivera et al., PRB 95, 075409 (2017)

[2] Häfner et al., PRB 77, 104409 (2008)

[3] Strigl et al., Nature Comm. 6, 6172 (2015)

[4] Strigl et al., PRB 94, 144431 (2016)

[5] Prestel et al., PRB 100, 214439 (2019)

[6] Prestel et al., PRB 104, 115434 (2021)