Evidence for Quantum Criticality (QC) and Universal Field-Induced Quantum Fluctuations (QF) in Cuprate Superconductivity (SC)*

We present experimental evidence for universal field-induced QF among cuprate superconductors as the result of their proximity to QC and the coexistence of SC and competing orders. We employ various experimental techniques to derive the in-plane magnetic irreversibility field in hole- and electron-type cuprate superconductors of varying doping levels and numbers of CuO$_{2}$ layers per unit cell, and we find strong suppression of the extrapolated zero-temperature in-plane irreversibility field relative to the paramagnetic field in all cuprates, suggesting universal field-induced QF. The irreversibility fields follow a universal dependence on a parameter that combines the effect of the doping level, electronic anisotropy, and charge imbalance in multi-layer samples.