Bimodal ionic photomemristor based on a high-temperature oxide superconductor/semiconductor junction

Hybrid Ferroelectric Tunnel Junctions: State of the Art, Challenges, and Opportunities

Ferroelectric tunnel junctions (FTJs) harness the combination of ferroelectricity and quantum tunneling and thus herald opportunities in next-generation nonvolatile memory technologies. Recent advancements in the fabrication of ultrathin heterostructures have enabled the integration of ferroelectrics with various functional materials, forming hybrid tunneling-diode junctions. These junctions benefit from the modulation of the functional layer/ferroelectric interface through ferroelectric polarization, thus enabling further modalities and functional capabilities in addition to tunneling electroresistance. This Perspective aims to provide in-depth insight into the physical phenomena of several typical ferroelectric hybrid junctions, ranging from ferroelectric/dielectric, ferroelectric/multiferroic, and ferroelectric/superconducting to ferroelectric/2D materials, and finally their expansion into the realm of ferroelectric resonant tunneling diodes (FeRTDs). This latter aspect, i.e., resonant tunneling, offers an approach to exploiting tunneling behavior in ferroelectric heterostructures. We discuss examples that have successfully shown room-temperature ferroelectric control of parameters such as the resonant peak, tunnel current ratio at peak, and negative differential resistance. We conclude the Perspective by summarizing the challenges and highlighting the opportunities for the future development of hybrid FTJs, with a special emphasis on a possible type of FeRTD device. The prospects for enhanced performance and expanded functionality ignite tremendous excitement in hybrid FTJs and FeRTDs for future nanoelectronics.

Disentangling Photodoping, Photoconductivity, and Photosuperconductivity in the Cuprates

The normal-state conductivity and superconducting critical temperature of oxygen-deficient YBa_{2}Cu_{3}O_{7-δ} can be persistently enhanced by illumination. Strongly debated for years, the origin of those effects-termed persistent photoconductivity and photosuperconductivity (PPS)-has remained an unsolved critical problem, whose comprehension may provide key insights to harness the origin of high-temperature superconductivity itself. Here, we make essential steps toward understanding PPS. While the models proposed so far assume that it is caused by a carrier-density increase (photodoping) observed concomitantly, our experiments contradict such conventional belief: we demonstrate that it is instead linked to a photo-induced decrease of the electronic scattering rate. Furthermore, we find that the latter effect and photodoping are completely disconnected and originate from different microscopic mechanisms, since they present different wavelength and oxygen-content dependences as well as strikingly different relaxation dynamics. Besides helping disentangle photodoping, persistent photoconductivity, and PPS, our results provide new evidence for the intimate relation between critical temperature and scattering rate, a key ingredient in modern theories on high-temperature superconductivity.