[en] We search for pair production of supersymmetric top quarks (t-tilde₁), followed by R-parity violating decay t-tilde₁→τb with a branching ratio β, using 322 pb^-1 of pp collisions at √(s)=1.96 TeV collected by the upgraded Collider Detector at Fermilab. Two candidate events pass our final selection criteria, consistent with the standard model expectation. We set upper limits on the cross section σ(t-tilde₁t-tilde₁)xβ² as a function of the top-squark mass m(t-tilde₁). Assuming β=1, we set a 95% confidence level limit m(t-tilde₁)>153 GeV/c². The limits are also applicable to the case of a third-generation scalar leptoquark (LQ₃) decaying LQ₃→τb