Scale-invariant magnetoresistance in a cuprate superconductor

摘要

The anomalous metallic state in high-temperature superconducting cuprates ismasked by the onset of superconductivity near a quantum critical point. Use ofhigh magnetic fields to suppress superconductivity has enabled a detailed studyof the ground state in these systems. Yet, the direct effect of strong magneticfields on the metallic behavior at low temperatures is poorly understood,especially near critical doping, $x=0.19$. Here we report a high-fieldmagnetoresistance study of thin films of \LSCO cuprates in close vicinity tocritical doping, $0.161\leq x\leq0.190$. We find that the metallic stateexposed by suppressing superconductivity is characterized by amagnetoresistance that is linear in magnetic field up to the highest measuredfields of $80$T. The slope of the linear-in-field resistivity istemperature-independent at very high fields. It mirrors the magnitude anddoping evolution of the linear-in-temperature resistivity that has beenascribed to Planckian dissipation near a quantum critical point. Thisestablishes true scale-invariant conductivity as the signature of the strangemetal state in the high-temperature superconducting cuprates.