Single crystal growth of superconducting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>UTe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> by molten salt flux method
H. Sakai, Petr Opletal, Y. Tokiwa, Etsuji Yamamoto, Y. Tokunaga, S. Kambe, Yoshinori Haga
Abstract
The molten salt flux method is applied as a synthetic route for the single crystals of the spin-triplet superconductor ${\mathrm{UTe}}_{2}$. The single crystals under an optimized growth condition with excess uranium exhibit a superconducting transition at ${T}_{\mathrm{c}}=2.1\phantom{\rule{4pt}{0ex}}\mathrm{K}$, which is the highest ${T}_{\mathrm{c}}$ 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 ${T}_{\mathrm{c}}$. These results indicate that the increase of ${T}_{\mathrm{c}}$ in ${\mathrm{UTe}}_{2}$ 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.