  The presence of electron correlations in a system with topological order can
lead to exotic ground states. Considering single crystals of LaAgSb2 which has
a square net crystal structure, one finds multiple charge density wave
transitions (CDW) as the temperature is lowered. We find large planar Hall
(PHE) signals in the CDW phase, which are still finite in the high temperature
phase though they change sign. Optimising the structure within first-principles
calculations, one finds an unusual chiral metallic phase. This is because as
the temperature is lowered, the electrons on the Ag atoms get more localized,
leading to stronger repulsions between electrons associated with atoms on
different layers. This leads to successive layers sliding with respect to each
other, thereby stabilising a chiral structure in which inversion symmetry is
also broken. The large Berry curvature associated with the low temperature
structure explains the low temperature PHE. At high temperature the PHE arises
from the changes induced in the tilted Dirac cone in a magnetic field. Our work
represents a route towards detecting and understanding the mechanism in a
correlation driven topological transition through electron transport
measurements, complemented by ab-initio electronic structure calculations.
