  In correlated electron materials, electrons often self-organize and form a
variety of patterns with potential ordering of charges, spins, and orbitals,
which are believed to be closely connected to many novel properties of these
materials including superconductivity, metal-insulator transitions, and the CMR
effect. How these real-space patterns affect the conductivity and other
properties of materials (which are usually described in momentum space) is one
of the major challenges of modern condensed matter physics. Moreover, although
the presence of static stripes is indisputable, the existence (and potential
impacts) of fluctuating stripes in such compounds is a subject of great debate.
Here we present the electronic excitations of
La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x ~ 0.59) probed by angle-resolved
photoemission (ARPES), from which we demonstrate that a novel type of ordering,
termed bi-stripes, can exhibit either static or fluctuating order as a function
of temperature. We found that the static bi-stripe order is especially damaging
to electrical conductivity, completely localizing the electrons in the
bi-stripe regions, while the fluctuating stripes can coexist with mobile
carriers. This physics drives a novel phase transition with colossal
conductivity changes as a function of temperature. Our finding suggests that
quantum stripes can give rise to electronic properties significantly different
from their static counterparts. Inducing transition between them can turn on
remarkable electronic phenomena, enriching our understanding of correlated
electron systems as well as opening a window for potential applications in
electronic devices.
