Restoring the Planckian regime via suppression of charge density waves in an underdoped cuprate superconductor

The normal state of cuprates is dominated by the strange metal phase that, near optimal doping, shows a linear temperature dependence of the resistivity persisting down to the lowest $T$, when superconductivity is suppressed. For underdoped cuprates this behavior is lost below the pseudogap temperature $T$*, where Charge Density Wave (CDW) together with other intertwined local orders characterize the ground state. Here we show that the $T$-linear resistivity of highly strained, ultrathin and underdoped YBa$_2$Cu$_3$O$_{7-\delta}$ films is restored when the CDW amplitude, detected by Resonant Inelastic X-ray scattering, is suppressed. This observation points towards an intimate connection between the onset of CDW and the departure from $T$-linear resistivity in underdoped cuprates, a link that was missing until now. It also illustrates the potentiality of strain control to manipulate the ground state of quantum materials.