Magnetic-field-induced stripe order and a 2D vortex glass phase in La$_{1.905}$Ba$_{0.095}$CuO$_4$*

We have measured the resistivity parallel and perpendicular to the CuO$_2$ planes in La$_{1.905}$Ba$_{0.095}$CuO$_4$ ($T_c = 32$ K) as a function of perpendicular magnetic field. We have discovered a significant regime of field and temperature where the perpendicular resistivity is finite (and large) but the parallel resistivity is zero. This regime appears to correspond to a quasi-two-dimensional vortex glass phase, a state that theory predicts cannot exist at finite temperature. It seems to be stabilized by field-induced charge and spin stripe order, which we have detected with x-ray and neutron diffraction, respectively.