Highly sensitive lock-in thermoreflectance temperature measurement using thermochromic liquid crystal

We show that the temperature measurement sensitivity in the lock-in thermoreflectance (LITR) can be improved by incorporating a thermochromic liquid crystal (TLC) into a transducer. The quantitatively estimated thermoreflectance coefficient of a TLC/Pt hybrid film depends on the excitation frequency and reaches >2 x 10(-2) K-1 at low excitation frequencies, which is two orders of magnitude greater than typical values of 10(-4) for metallic films. Using the TLC/Pt film, we detected the temperature changes due to Joule heating and the spin Peltier effect with the temperature resolution of similar to 10 mu K by the LITR method. We also performed the same measurements for an Au film and found that the temperature resolution for the TLC/Pt film is increased by a factor of >10 compared with that for the Au film despite the low reflected light intensity of the TLC/Pt film.

Automated summary

We find that the temperature measurement sensitivity in LITR can be improved by incorporating a thermochromic liquid crystal (TLC) into a transducer. The estimated thermoreflectance coefficient of a TLC/Pt hybrid film reaches >2 x 10(-2) K-1 at low excitation frequencies, which is two orders of magnitude greater than typical metallic films. Using the TLC/Pt film, we were able to detect temperature changes with a resolution of about 10 μK due to Joule heating and the spin Peltier effect, surpassing the resolution achieved with an Au film despite the lower reflected light intensity of the TLC/Pt film.