Juan Jiang

Realizing non-volatile control of superconductivity is a key step toward integrating memory and quantum functionality in future information technologies. KTaO₃-based heterostructures uniquely host interfacial two-dimensional superconductivity and quantum paraelectric lattice background. The coupling between these two degrees of freedom potentially provides a promising route to encode memory into the superconducting state. Here we reveal two intertwined phenomena in AlOₓ/KTaO₃ heterostructures: a gate-imprinted memory in which electrostatic gate cycling promotes superconductivity, and its erasure by optical illumination at cryogenic temperatures. These phenomena arise from a previously unrecognized interplay between the superconducting interface and emergent lattice excitations including polar-nanoregion reorientation and charge trapping/detrapping by oxygen vacancies. These results demonstrate configurable superconductivity at correlated oxide interfaces, opening a pathway to enrich dissipationless transport with non-volatile controls for superconducting elements.

Despite extensive progress in iron-based superconductors, how interlayer coupling affects superconductivity remains a key unresolved issue. Here, using angle-resolved photoemission spectroscopy, we successfully resolve the electronic structure of a surface-decoupled FeAs monolayer in KCa₂Fe₄As₄F₂, a rare example in iron pnictides. This allows for a direct, side-by-side comparison between the basic FeAs unit and its bulk bilayer counterpart within a single sample. Two distinct superconducting phases are identified: a bulk bilayer phase with Tc ∼ 34 K and a surface-decoupled monolayer phase with a smaller gap vanishing at ∼18 K. In addition to probable enhanced fluctuations in single-layer FeAs, we propose that this Tc difference may originate from either interfacial effect, such as phonon-mediated assistance from the CaF layers or electronic interlayer hopping within the bilayer unit. Our work offers a refined framework for understanding the superconductivity in multilayer iron-based superconductors.

The van der Waals room-temperature ferromagnet Fe_{5}GeTe_{2} has garnered considerable research interest due to its intriguing magnetic and transport properties, as well as its potential applications, yet their microscopic origin remains unclear. Using angle-resolved photoemission spectroscopy and density functional theory calculations, we resolve an electronic structure corresponding to the up-up-up-type configuration. Pronounced Fermi surface reconstruction and a 25 meV dispersion kink referring to the strong electron-magnon coupling have been observed near T_{1}∼105 K, coincident with anomalies in resistivity and magnetic susceptibility. Our calculations identify the emergence of Fe(1) sublattice spin order as the driving force behind both phenomena. These findings reveal the decisive role of sublattice-dependent magnetism in governing the coupled electronic and magnetic properties of Fe_{5}GeTe_{2}, establishing sublattice engineering as a pathway for tuning correlated behavior in two-dimensional magnets.

Chromium nitride (CrN) is a prototypical correlated antiferromagnet in which magnetic ordering is concomitant with a structural transition in its bulk form, yet its low-energy electronic structure in thin films remains largely unexplored. Here we investigate high-quality epitaxial CrN/MgO (001) thin films using angle-resolved photoemission spectroscopy (ARPES). Transport measurements reveal that the films remain metallic and undergo a magnetic transition without detectable structural distortion. ARPES directly resolves a shallow electron-like band crossing the Fermi level ( E _F ), forming a small Fermi surface that persists across the Néel temperature ( T _N ). A pronounced redistribution of spectral weight is observed, which may be related to the magnetic transition. Comparison with first-principles calculations shows that electronic correlations are essential to reproduce the observed band topology, establishing epitaxial CrN as a correlated antiferromagnetic (AFM) metal. These results help understand the interplay between magnetism, correlations, and lattice constraints in CrN, offering an example of tailoring electronic and magnetic properties in correlated AFM thin films.

Dimensionality and electronic correlations are crucial elements of many quantum material properties. An example is the change of the electronic structure accompanied by the loss of quasiparticles when a metal is reduced from three dimensions to a lower dimension, where the Coulomb interaction between carriers becomes poorly screened. Here, using angle-resolved photoemission spectroscopy, we report an orbital-selective decoherence of spectral density in the perovskite nickelate LaNi O 3 toward the monolayer limit. The spectral weight of the d z 2 band vanishes much faster than that of the d x 2 − y 2 band as the thickness of the LaNi O 3 layer is decreased to a single unit cell, indicating a stronger correlation effect for the former upon dimensional confinement. Dynamical mean-field theory calculations show an orbital-selective Mott transition largely due to the localization of d z 2 electrons along the c axis in the monolayer limit. This orbital-selective correlation effect underpins many macroscopic properties of nickelates, such as metal-to-insulator transition and superconductivity, where most theories are built upon a d x 2 − y 2 – d z 2 two-band model.

Epitaxial growth serves as a critical platform for tailoring electronic interactions. Here, we synthesized high-quality Nd_1-xSr_xNiO₃ thin films on (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃ (LSAT) (001) and SrTiO₃ (STO) (001) substrates and systematically investigated the effects of substrate strain and chemical doping on their low-energy electronic structures using angle-resolved photoemission spectroscopy (ARPES). Transport measurements reveal that Sr doping strongly suppresses the metal-insulator transition (MIT) temperature T_MIT on both substrates, with accelerated suppression in STO (001)-grown samples. Our ARPES results reveal that beyond a chemical potential shift, Sr doping significantly alters the effective mass, with a larger change observed in Nd_1-xSr_xNiO₃/STO (001) than in LSAT-based films. These findings indicate that Sr doping, combined with epitaxial strain, alters the correlation strength, thereby modifying the MIT. Our results unravel the intricate interplay among multiple degrees of freedom in Nd_1-xSr_xNiO₃ thin films, deepening the understanding of nickelate-based heterostructure design and engineering.