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

Abstract

<jats:title>Abstract</jats:title><jats:p>The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh<jats:sub>2</jats:sub>Si<jats:sub>2</jats:sub> 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 techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNRs) 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 Néel 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 <jats:inline-formula><jats:tex-math><?CDATA $1/f$?></jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mn>1</mml:mn><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mi>f</mml:mi></mml:math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="njpaca8c6ieqn1.gif" xlink:type="simple" /></jats:inline-formula>-type fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase of <jats:inline-formula><jats:tex-math><?CDATA $T_{N}$?></jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:msub><mml:mi>T</mml:mi><mml:mrow><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:msub></mml:math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="njpaca8c6ieqn2.gif" xlink:type="simple" /></jats:inline-formula> from 67 mK up to 188 mK while still showing clear signatures of the phase transition and SdH oscillations. Superconducting quantum interference device-based thermal noise spectroscopy measurements in a nuclear demagnetization refrigerator down to 0.95 mK, show a sharp superconducting transition at <jats:inline-formula><jats:tex-math><?CDATA $T_{c} = 1.2$?></jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:msub><mml:mi>T</mml:mi><mml:mrow><mml:mi mathvariant="normal">c</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>1.2</mml:mn></mml:math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="njpaca8c6ieqn3.gif" xlink:type="simple" /></jats:inline-formula> 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.</jats:p>

Topics

• resistivity
• phase
• experiment
• phase transition
• superconductivity
• superconductivity
• spectroscopy