Unlocking the mystery of the strange metal state has become the focal point of high-Tcresearch, not because of its importance for superconductivity, but because it appears to represent a truly... Show moreUnlocking the mystery of the strange metal state has become the focal point of high-Tcresearch, not because of its importance for superconductivity, but because it appears to represent a truly novel phase of matter dubbed "quantum supreme matter. " Detected originally through high magnetic field, transport experiments, signatures of this phase have now been uncovered with a variety of probes. Our high resolution optical data of the low-Tccuprate superconductor, Bi2-xPbxSr2-yLayCuO6+delta allows us to probe this phase over a large energy and temperature window. We demonstrate that the optical signatures of the strange metal phase persist throughout the phase diagram. The strange metal signatures in the optical conductivity are twofold: (i) a low energy Drude response with Drude width on the order of temperature and (ii) a high energy conformal tail with a doping dependent power-law exponent. While the Drude weight evolves monotonically throughout the entire doping range studied, the spectral weight contained in the high energy conformal tail appears to be doping and temperature independent. Our analysis further shows that the temperature dependence of the optical conductivity is completely determined by the Drude parameters. Our results indicate that there is no critical doping level inside the superconducting dome where the carrier density starts to change drastically and that the previously observed "return to normalcy " is a consequence of the increasing importance of the Drude component relative to the conformal tail with doping. Importantly, both the doping and temperature dependence of the resistivity are largely determined by the Drude width. Show less
Ayres, J.; Berben, M.; Culo, M.; Hsu, Y.T.; Heumen, E. van; Huang, Y.; ... ; Hussey, N.E. 2021
Strange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity(1-6), an inverse Hall angle that varies as temperature squared(7-9) and a linear-in... Show moreStrange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity(1-6), an inverse Hall angle that varies as temperature squared(7-9) and a linear-in-field magnetoresistance(10-13). Identifying the origin of these collective anomalies has proved fundamentally challenging, even in materials such as the hole-doped cuprates that possess a simple bandstructure. The prevailing consensus is that strange metallicity in the cuprates is tied to a quantum critical point at a doping p* inside the superconducting dome(14,15). Here we study the high-field in-plane magnetoresistance of two superconducting cuprate families at doping levels beyond p*. At all dopings, the magnetoresistance exhibits quadrature scaling and becomes linear at high values of the ratio of the field and the temperature, indicating that the strange-metal regime extends well beyond p*. Moreover, the magnitude of the magnetoresistance is found to be much larger than predicted by conventional theory and is insensitive to both impurity scattering and magnetic field orientation. These observations, coupled with analysis of the zero-field and Hall resistivities, suggest that despite having a single band, the cuprate strange-metal region hosts two charge sectors, one containing coherent quasiparticles, the other scale-invariant 'Planckian' dissipators.Measurements of high-field magnetotransport in overdoped cuprates indicate that the strange-metal regime exists beyond the critical doping, and that it has both coherent and incoherent contributions. Show less
