Development of microwave surface elastoresistivity measurement technique under tunable strain

By integrating a dielectric microwave resonator with a piezoelectric-based strain device, we develop an in situ strain-tunable microwave spectroscopy technique that enables contactless measurements of superconducting properties under strain. In the slightly overdoped iron-based superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$, we successfully observe a systematic strain dependence of the superconducting transition, manifested as changes in the quality factor and resonance frequency shifts. Both compressive and tensile anisotropic lattice distortions along the [110]${_{\rm T}}$ direction suppress superconductivity, consistent with standard transport measurements, highlighting the pivotal role of nematic fluctuations in the superconducting mechanism. Our strain-tunable cavity therefore serves as a powerful, contactless probe of fundamental superconducting material properties under strain and may also potentially facilitate the design of hybrid quantum systems with strain-controlled quantum degrees of freedom.