Hall coefficient in the ground state of the charge stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ single crystals

Temperature dependence of the Hall coefficient, $R_{\rm H}$, has been investigated in charge-spin stripe-ordered La-214 high- $T_{\rm c}$ superconductors [1]. Using the simplest stripe-ordered system of La$_{2-x} $Ba$_x$CuO$_4$, it has been clarified for the first time, to our knowledge, that both the behavior of $R_{\rm H}$ and its sign exhibit significant dependences on the hole concentration. That is, $R_{\rm H}$ is zero in the ground state of the charge- spin stripe order at $x=1/8$, while it is negative in the less- stabilized state of the charge stripe for $x<1/8$. These are interpreted as being due to the delicate balance of the contributions of the hole-like Fermi surface and the possible electron pocket, suggested from the recent quantum- oscillation experiments [2], arising from the formation of the charge-spin stripe order. \\[4pt] [1] T. Adachi {\it et al}., arXiv: 0909.3452. \\[0pt] [2] N. Doiron-Leyraud {\it et al}., Nature (London) {\bf 447}, 565 (2007).