Doping studies and superconductivity in Ru-doped Zr$_{\mathrm{5}}$Ge$_{\mathrm{3}}$ system

Searching for new superconducting materials with distinct crystal structures has been proven to be fruitful in achieving higher transition temperature T$_{\mathrm{c}}$, as seen in cuprates and Fe pnictides. The hexagonal Mn$_{\mathrm{5}}$Si$_{\mathrm{3}}$-type structure, with a large amount of compounds crystallizing in this structure and similar structural derivatives, will be an ideal model system to search for new superconductors. Herein, we are reporting firstly a new superconductor Zr$_{\mathrm{5}}$Ge$_{\mathrm{2.5}}$Ru$_{\mathrm{0.5}}$ with T$_{\mathrm{c\thinspace }}$\textasciitilde 5.7K from our systematic Ru-doping studies at three selected doping sites for the Zr$_{\mathrm{5}}$Ge$_{\mathrm{3}}$ system. Interestingly, with the same Ru-doping, superconductivity is only selectively induced with doping at Ge site, but remains absent down to 1.8K with doping at Zr site or interstitial site. The bulk superconductivity nature for Ru-doped Zr$_{\mathrm{5}}$Ge$_{\mathrm{2.5}}$Ru$_{\mathrm{0.5}}$ sample has been confirmed from magnetic, electrical transport, and heat capacity measurements. The high upper critical field, enhanced electron correlation, extremely small electron-phonon coupling, have indicated possible unconventional superconductivity in this system. Detailed synthesis and characterization will be presented and discussed.