A spatially resolved optical method to measure thermal diffusivity
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We describe an optical method to directly measure the position-dependent thermal diffusivity of reflective single crystal samples across a broad range of temperatures for condensed matter physics research. Two laser beams are used, one as a source to locally modulate the sample temperature, and the other as a probe of sample reflectivity, which is a function of the modulated temperature. Thermal diffusivity is obtained from the phase delay between source and probe signals. We combine this technique with a microscope setup in an optical cryostat, in which the sample is placed on a three-axis piezo-stage, allowing for spatially resolved measurements. Furthermore, we demonstrate experimentally and mathematically that isotropic in-plane diffusivity can be obtained when overlapping the two laser beams instead of separating them in the traditional way, which further enhances the spatial resolution to a micron scale, especially valuable when studying inhomogeneous or multidomain samples. We discuss in detail the experimental conditions under which this technique is valuable and demonstrate its performance on two stoichiometric bilayer ruthenates: Sr3Ru2O7 and Ca3Ru2O7. The spatial resolution allowed us to study the diffusivity in single domains of the latter, and we uncovered a temperature-dependent in-plane diffusivity anisotropy. Finally, we used the enhanced spatial resolution enabled by overlapping the two beams to measure the temperature-dependent diffusivity of Ti-doped Ca3Ru2O7, which exhibits a metal–insulator transition. We observed large variations of transition temperature over the same sample, originating from doping inhomogeneity and pointing to the power of spatially resolved techniques in accessing inherent properties.
Sun , F , Mishra , S , McGuinness , P H , Filipiak , Z H , Marković , I , Sokolov , D A , Kikugawa , N , Orenstein , J W , Hartnoll , S A , Mackenzie , A P & Sunko , V 2023 , ' A spatially resolved optical method to measure thermal diffusivity ' , Review of Scientific Instruments , vol. 94 , no. 4 , 043003 . https://doi.org/10.1063/5.0098800
Review of Scientific Instruments
Copyright © 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
DescriptionFunding: V.S. is supported by the Miller Institute for Basic Research in Science, University of California, Berkeley. N.K. is supported by a KAKENHI Grants-in-Aid for Scientific Research (Grant Nos. 17H06136, 18K04715, and 21H01033), a Core-to-Core Program (Grant No. JPJSCCA20170002) from the Japan Society for the Promotion of Science (JSPS), and a JST-Mirai Program (Grant No. JPMJMI18A3). A.P.M. and S.M. acknowledge the financial support of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—TRR 288-422213477 (project A10).
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