Moving flux quanta, driven by high density currents in low-impurity samples of V$_{3}$Si, LuNi$_{2}$B$_{2}$C, and NbSe$_{2}$ : Ordered flow and core-size effects

There is incomplete understanding about the dissipative motion of magnetic flux quanta in type II superconductors, especially under large Lorentz forces. This is mainly due to the technical challenges involving the application of large electric currents and the rarity of samples wherein flux quanta are relatively free to move -- i.e., samples with weak ``pinning'' -- which commonly make it impossible to observe dynamic phases. Progress towards overcoming these challenges is described, along with clear observations of flux-flow phases in high-quality samples of three ``low $T_{c}$'' superconductors, V$_{3}$Si, LuNi$_{2}$B$_{2}$C, and NbSe$_{2}$. Evidence of the rarely observed Bardeen-Stephen flux flow -- a highly ordered, collective motion of flux quanta in near-unison -- will be presented. These observations have also enabled an examination of a model by Kogan and Zelezhina [Kogan and Zhelezina, \textit{Phys Rev B} \textbf{71}, 134505 (2005)] predicting the effect of a field-dependent flux \textit{core size }on ordered flux flow, as will be discussed. \textit{Funded by the U. of South Alabama and by the Research Corporation. We thank P. Canfield and L. Delong for samples and helpful discussions. }