  Here we report the TiVNbTa medium-entropy alloy (MEA) superconductor with the
mixed 3d - 5d elements synthesized by an arc-melting method. The TiVNbTa
material has a body-centered cubic structure. The superconducting properties of
TiVNbTa were studied by resistivity, magnetic susceptibility, and specific heat
measurements. The experimental results show that the bulk superconducting phase
transition temperature of TiVNbTa is about 4.65 K, and the upper and lower
critical fields are 49.3(4) mT and 5.9(5) T, respectively, which indicates
TiVNbTa is a type-II superconductor. First-principles calculations show that
the d electrons of Ti, V, Nb, and Ta atoms play a significant role near the
Fermi level. The results show TiVNbTa is a traditional s-wave superconductor.
