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arXiv · 2301.03928

Microstructuring YbRh2Si2 for resistance and noise measurements down to ultra-low temperatures

Alexander Steppke·Sandra Hamann·Markus König·Andrew P. Mackenzie·Kristin Kliemt·Cornelius Krellner·Marvin Kopp·Martin Lonsky·Jens Müller·Lev V. Levitin·John Saunders·Manuel Brando
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Abstract

The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh2Si2 at an extremely low temperature of 2 mK has inspired efforts to perform high-resolution electrical resistivity measurements down to this temperature range in highly conductive materials. Here we show that control over the sample geometry by microstructuring using focused-ion-beam (FIB) techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNR) tenfold, without adverse effects to sample quality. In five experiments we show four-terminal sensing resistance and magnetoresistance measurements which exhibit sharp phase transitions at the N\'eel temperature, and Shubnikov-de-Haas (SdH) oscillations between 13 T and 18 T where we identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance fluctuation (noise) spectroscopy that would not be possible for bulk crystals, and confirmed intrinsic 1/f-type fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase of T_N from 67 mK up to 188 mK while still showing clear signatures of the phase transition and SdH oscillations. SQUID-based thermal noise spectroscopy measurements in a nuclear demagnetisation refrigerator down to 0.95 mK, show a sharp superconducting transition at T_c = 1.2 mK. These experiments demonstrate microstructuring as a powerful tool to investigate the resistance and the noise spectrum of highly conductive correlated metals over wide temperature ranges.

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Alexander Steppke, Sandra Hamann, Markus König, Andrew P. Mackenzie, Kristin Kliemt, Cornelius Krellner, Marvin Kopp, Martin Lonsky, Jens Müller, Lev V. Levitin, John Saunders, Manuel Brando. 2023-01-10. Microstructuring YbRh2Si2 for resistance and noise measurements down to ultra-low temperatures. https://doi.org/10.1088/1367-2630%2Faca8c6

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