Engineering topics

Li, Yangyang

Publications and source records attributed to Li, Yangyang.

5 records

DOE OSTI2024

Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO 3 thin films grown on a series of single crystal substrates. Unlike films synthesized on other substrates, NdNiO 3 on SrTiO 3 (NNO/STO) gives rise to a unique band structure which features an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by the orbital hybridization between Ti 3d orbitals of the STO substrate and O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. Further, these findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin-films, thereby offering key insights into tuning their interfacial properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Engineering structural homogeneity and magnetotransport in strained Nd 2 Ir 2 O 7 films

The 5d pyrochlore iridate family (R 2 Ir 2 O 7 , where R is a rare earth ion) has garnered significant attention due to its topological properties, such as Weyl semimetallic phases and axion insulator. However, the investigation of these properties has been impeded by severe iridium loss during growth, which results in the formation of defects and impurities. Herein, we demonstrate a method for controlling impurities and defects in strained Nd 2 Ir 2 O 7 (NIO-227) films by compensating for iridium loss during growth. By increasing the amount of IrO 2 target ablated, we enhance the morphological quality and electrical transport properties of the fabricated films. Furthermore, our results show that the anomalous Hall effects of the films have a strong dependency on the amount of IrO 2 target ablated, which is attributed to the structural inhomogeneity in the NIO-227 films. Our work provides a way to control defects and impurities and would promote the investigation of topological phases in the family R 2 Ir 2 O 7 .

36 MATERIALS SCIENCE↗

DOE OSTI2022

Higher harmonics in planar Hall effect induced by cluster magnetic multipoles

Antiferromagnetic (AFM) materials are attracting tremendous attention due to their spintronic applications and associated novel topological phenomena. However, detecting and identifying the spin configurations in AFM materials are quite challenging due to the absence of net magnetization. Herein, we report the practicality of utilizing the planar Hall effect (PHE) to detect and distinguish “cluster magnetic multipoles” in AFM Nd 2 Ir 2 O 7 (NIO-227) fully strained films. By imposing compressive strain on the spin structure of NIO-227, we artificially induced cluster magnetic multipoles, namely dipoles and A 2 - and T 1 -octupoles. Importantly, under magnetic field rotation, each magnetic multipole exhibits distinctive harmonics of the PHE oscillation. Moreover, the planar Hall conductivity has a nonlinear magnetic field dependence, which can be attributed to the magnetic response of the cluster magnetic octupoles. Our work provides a strategy for identifying cluster magnetic multipoles in AFM systems and would promote octupole-based AFM spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Ultra-flat and long-lived plasmons in a strongly correlated oxide

Plasmons in strongly correlated systems are attracting considerable attention due to their unconventional behavior caused by electronic correlation effects. Recently, flat plasmons with nearly dispersionless frequency-wave vector relations have drawn significant interest because of their intriguing physical origin and promising applications. However, these flat plasmons exist primarily in low-dimensional materials with limited wave vector magnitudes (q< ~0.7 Å –1 ). Here, we show that long-lived flat plasmons can propagate up to ~1.2 Å –1 in α-Ti 2 O 3 , a strongly correlated three-dimensional Mott-insulator, with an ultra-small energy fluctuation (<40 meV). The strong correlation effect renormalizes the electronic bands near Fermi level with a small bandwidth, which is responsible for the flat plasmons in α-Ti 2 O 3 . Moreover, these flat plasmons are not affected by Landau damping over a wide range of wave vectors (q < ~1.2 Å –1 ) due to symmetry constrains on the electron wavefunctions. Our work provides a strategy for exploring flat plasmons in strongly correlated systems, which in turn may give rise to novel plasmonic devices in which flat and long-lived plasmons are desirable.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Perspective on solid-phase epitaxy as a method for searching novel topological phases in pyrochlore iridate thin films

Pyrochlore iridates exhibit various novel topological phenomena due to their topology and electron correlation. Notably, pyrochlore iridate was the first proposed material system shown to host the time-reversal symmetry broken Weyl semimetal phase. After this profound theoretical proposal, extensive experimental attempts have been made to synthesize high-quality samples in both bulk and film forms. In particular, adjusting thin film geometry represents a practical way to tune the U/ t ( U: Coulomb interaction and t: for hopping parameter) and identify the various topological phases in the regime U ~ λ ( λ: spin–orbit interaction). However, the instability of pyrochlore iridates at high temperature and low oxygen pressure has long been a barrier to growing pyrochlore iridate thin films by conventional film growth methods. To overcome this, pyrochlore iridate films have often been grown by the solid-phase epitaxy method, which uses a metastable amorphous layer grown at low temperature. During a high temperature post-annealing process, the layer in contact with a single crystalline substrate will crystallize epitaxially in the solid state by rearranging atoms at the interface. Here, we present a perspective on the solid-phase epitaxy as a method to synthesize epitaxial pyrochlore iridate thin films and a way to search for novel correlated phenomena.

36 MATERIALS SCIENCE↗