We use ionic liquid-assisted electric field effect to tune the carrier density in an electron-doped cuprate ultrathin film and cause a two-dimensional superconductor-insulator transition (SIT). The low upper critical field in this system allows us to perform magnetic field (B)-induced SIT in the liquid-gated superconducting film. Finite-size scaling analysis indicates that SITs induced both by electric and magnetic field are quantum phase transitions and the transitions are governed by percolation effects -quantum mechanical in the former and classical in the latter case. Compared to the hole-doped cuprates, the SITs in electron-doped system occur at critical sheet resistances (R c ) much lower than the pair quantum resistance R Q =h/(2e) 2 =6.45 kΩ, suggesting the possible existence of fermionic excitations at finite temperature at the insulating phase near SITs. Two-dimensional superconductor-insulator quantum phase transitions in an electron-doped cuprate Supplemental Material

The ability to control a magnetic phase with an electric field is of great current interest for a variety of low power electronics in which the magnetic state is used either for information storage or logic operations. Over the past several years, there has been a considerable amount of research on pathways to control the direction of magnetization with an electric field. More recently, an alternative pathway involving the change of the magnetic state (ferromagnet to antiferromagnet) has been proposed. In this paper, we demonstrate electric field control of the Anomalous Hall Transport in a metamagnetic FeRh thin film, accompanying an antiferromagnet (AFM) to ferromagnet (FM) phase transition. This approach provides us with a pathway to "hide" or "reveal" a given ferromagnetic region at zero magnetic field. By converting the AFM phase into the FM phase, the stray field, and hence sensitivity to external fields, is decreased or eliminated. Using detailed structural analyses of FeRh films of varying crystalline quality and chemical order, we relate the direct nanoscale origins of this memory effect to site disorder as well as variations of the net magnetic anisotropy of FM nuclei. Our work opens pathways toward a new generation of antiferromagnetic -ferromagnetic interactions for spintronics.In recent years, the ever increasing need for large scale data storage in computing systems has kindled significant interest in new materials and new physical phenomena that could lead to denser and more energy efficient memory systems. One approach is the heat assisted magnetic recording (HAMR) for which low Neel temperature AFMs have been suggested to play a key role 1 . In this context, the AFM to FM phase transition makes FeRh a serious contender for insertion into heterostructures utilizing exchange bias. Typically, in magnetic systems, defects impede domain wall motion, increase the coercivity, lower magnetization, and decrease spin polarization. Going beyond this traditional thinking, in this work we demonstrate that it is possible to exploit crystalline defects in FeRh to