Superconductivity in the Tungsten Bronzes

Via pulsed laser deposition and post-annealing, high quality K-doped WO$_{\mathrm{3-y}}$ films with reproducible transport properties are obtained. A home built two-coil mutual inductance setup is used to probe the behavior of the films in the superconducting and normal state. The inverse penetration depths and dissipation peaks are measured as a function of temperature and field. Separately, via thin film deposition techniques, we report for the first time stable crystalline hexagonal WO$_{\mathrm{3}}$ on substrates. In order to tune the physical properties of the undoped material, we utilized an ionic liquid gating technique. We observe an insulator-to-metal transition, showing the ionic liquid gate to be a viable technique to alter the electrical transport properties of this material. By comparing the alkali and ionic liquid gated WO$_{\mathrm{3}}$, we conclude with some remarks regarding how superconductivity arises in this system.