The origin of the weakly insulatinglike behavior revealed when magnetic fields ($H$) suppress superconductivity in underdoped cuprates has been a longtime mystery. Surprisingly, similar behavior observed recently in La-214 cuprates with striped spin and charge orders is consistent with a metallic, as opposed to insulating, high-field normal state. Here we report a striking finding of the vanishing of the Hall coefficient ($R_mathrm{H}$) in this field-revealed normal state for all $T<(2-6)T_{c}^{0}$, where $T_{c}^{0}$ is the zero-field superconducting transition temperature. In standard models, $R_mathrm{H}$ can only vanish accidentally, and thus $R_mathrm{H}=0$ observed over a wide range of $T$ and $H$ has to imply that charge conjugation (i.e. particle-hole) symmetry is dynamically generated. This is a robust, new fundamental property of the normal state of cuprates with intertwined orders.
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