A spatially resolved optical method to measure thermal diffusivity

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...

Full description

Saved in:

Bibliographic Details
Published in:	Review of scientific instruments 2023-04, Vol.94 (4)
Main Authors:	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.
Format:	Article
Language:	eng
Subjects:	Anisotropy Condensed matter physics Diffusivity Inhomogeneity Laser beams Metal-insulator transition Position measurement Scientific apparatus & instruments Single crystals Spatial resolution Temperature Temperature dependence Thermal diffusivity Titanium Transition temperature
Online Access:	Get full text
Tags:	Add Tag No Tags, Be the first to tag this record!

Description
Summary:	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.
ISSN:	0034-6748 1089-7623