Single crystal growth of superconducting UTe by molten salt flux method

Sakai, Hironori   ; Opletal, P.  ; Tokiwa, Yoshifumi  ; Yamamoto, Etsuji  ; Tokunaga, Yo  ; Kambe, Shinsaku  ; Haga, Yoshinori   

The molten salt flux method is applied as a new synthetic route for the single crystals of the spin-triplet superconductor UTe. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at K, which is the highest reported for this compound. The obtained crystals show a remarkably large residual resistivity ratio with respect to the room temperature value and a small residual electronic contribution in specific heat well below . These results indicate that the increase of in UTe can be achieved by reducing the disorder associated with uranium vacancies. The excess uranium in the molten salt acts as a reducing agent, preventing tetravalent uranium from becoming pentavalent and suppressing creation of uranium vacancies. At the same time, the relatively low growth temperature can suppress Te volatilization.