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In bulk ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, the strong sensitivity of the superconducting transition temperature $T_{\text{c}}$to nonmagnetic impurities provides robust evidence for a superconducting order parameter that changes sign around the Fermi surface. In superconducting epitaxial thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, the relationship between $T_{\text{c}}$and the residual resistivity ${\rho }_0$, which in bulk samples is taken to be a proxy for the low-temperature elastic scattering rate, is far less clear. Using high-energy electron irradiation to controllably introduce point disorder into bulk single-crystal and thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, we show that $T_{\text{c}}$is suppressed in both systems at nearly identical rates. This suggests that part of ${\rho }_0$in films comes from defects that do not contribute to superconducting pairbreaking and establishes a quantitative link between the superconductivity of bulk and thin-film samples. Published by the American Physical Society2024 

Abstract The quest to improve transparent conductors balances two key goals: increasing electrical conductivity and increasing optical transparency. To improve both simultaneously is hindered by the physical limitation that good metals with high electrical conductivity have large carrier densities that push the plasma edge into the ultra-violet range. Technological solutions reflect this trade-off, achieving the desired transparencies only by reducing the conductor thickness or carrier density at the expense of a lower conductance. Here we demonstrate that highly anisotropic crystalline conductors offer an alternative solution, avoiding this compromise by separating the directions of conduction and transmission. We demonstrate that slabs of the layered oxides Sr₂RuO₄and Tl₂Ba₂CuO_6+δare optically transparent even at macroscopic thicknesses >2 μm for c-axis polarized light. Underlying this observation is the fabrication of out-of-plane slabs by focused ion beam milling. This work provides a glimpse into future technologies, such as highly polarized and addressable optical screens. 

Abstract One of the main developments in unconventional superconductivity in the past two decades has been the discovery that most unconventional superconductors form phase diagrams that also contain other strongly correlated states. Many systems of interest are therefore close to more than one instability, and tuning between the resultant ordered phases is the subject of intense research 1 . In recent years, uniaxial pressure applied using piezoelectric-based devices has been shown to be a particularly versatile new method of tuning 2,3 , leading to experiments that have advanced our understanding of the fascinating unconventional superconductor Sr 2 RuO 4 (refs.  4–9 ). Here we map out its phase diagram using high-precision measurements of the elastocaloric effect in what we believe to be the first such study including both the normal and the superconducting states. We observe a strong entropy quench on entering the superconducting state, in excellent agreement with a model calculation for pairing at the Van Hove point, and obtain a quantitative estimate of the entropy change associated with entry to a magnetic state that is observed in proximity to the superconductivity. The phase diagram is intriguing both for its similarity to those seen in other families of unconventional superconductors and for extra features unique, so far, to Sr 2 RuO 4 . 

Unambiguous identification of the superconducting order parameter symmetry in ${\text{Sr}}_2{\text{RuO}}_4$has remained elusive for more than a quarter century. While a chiral p-wave ground state analogue to superfluid³He-A was ruled out only very recently, other proposed triplet-pairing scenarios are still viable. Establishing the condensate magnetic susceptibility reveals a sharp distinction between even-parity (singlet) and odd-parity (triplet) pairing since the superconducting condensate is magnetically polarizable only in the latter case. Here field-dependent¹⁷O Knight shift measurements, being sensitive to the spin polarization, are compared to previously reported specific heat measurements for the purpose of distinguishing the condensate contribution from that due to quasiparticles. We conclude that the shift results can be accounted for entirely by the expected field-induced quasiparticle response. An upper bound for the condensate magnetic response of <10% of the normal state susceptibility is sufficient to exclude all purely odd-parity candidates.