Structural study in Highly Compressed BiFeO3 Epitaxial Thin Films on YAlO3

We report a study on the thermodynamic stability and structure analysis of the epitaxial BiFeO3 (BFO) thin films grown on YAlO3 (YAO) substrate. First we observe a phase transition of MC-MA-T occurs in thin sample (<60 nm) with an utter tetragonal-like phase (denoted as MII here) with a large c/a ratio (~1.23). Specifically, MII phase transition process refers to the structural evolution from a monoclinic MC structure at room temperature to a monoclinic MA at higher temperature (150oC) and eventually to a presence of nearly tetragonal structure above 275oC. This phase transition is further confirmed by the piezoforce microscopy measurement, which shows the rotation of polarization axis during the phase transition. A systematic study on structural evolution with thickness to elucidate the impact of strain state is performed. We note that the YAO substrate can serve as a felicitous base for growing T-like BFO because this phase stably exists in very thick film. Thick BFO films grown on YAO substrate exhibit a typical "morphotropic-phase-boundary"-like feature with coexisting multiple phases (MII, MI, and R) and a periodic stripe-like topography. A discrepancy of arrayed stripe morphology in different direction on YAO substrate due to the anisotropic strain suggests a possibility to tune the MPB-like region. Our study provides more insights to understand the strain mediated phase co-existence in multiferroic BFO system.Comment: 18 pages, 6 figures, submitted to Journal of Applied Physic

Periodic elastic nanodomains in ultrathin tetrogonal-like BiFeO3 films

We present a synchrotron grazing incidence x-ray diffraction analysis of the domain structure and polar symmetry of highly strained BiFeO3 thin films grown on LaAlO3 substrate. We revealed the existence of periodic elastic nanodomains in the pure tetragonal-like BFO ultrathin films down to a thickness of 6 nm. A unique shear strain accommodation mechanism is disclosed. We further demonstrated that the periodicity of the nanodomains increases with film thickness but deviates from the classical Kittel's square root law in ultrathin thickness regime (6 - 30 nm). Temperature-dependent experiments also reveal the disappearance of periodic modulation above 90C due to a MC-MA structural phase transition.Comment: Accepted in Phys. Rev.

Ferroelectric Control of the Conduction at the LaAlO 3 /SrTiO 3 Hetero-interface

Abstract The LaAlO 3 /SrTiO 3 (LAO/STO) interface serves as a model system in which a highly mobile quasi-twodimensional electron gas (2DEG) forms between two band insulator

Self-supervised Fine-tuning for Improved Content Representations by Speaker-invariant Clustering

Self-supervised speech representation models have succeeded in various tasks, but improving them for content-related problems using unlabeled data is challenging. We propose speaker-invariant clustering (Spin), a novel self-supervised learning method that clusters speech representations and performs swapped prediction between the original and speaker-perturbed utterances. Spin disentangles speaker information and preserves content representations with just 45 minutes of fine-tuning on a single GPU. Spin improves pre-trained networks and outperforms prior methods in speech recognition and acoustic unit discovery.Comment: Accepted to Interspeech 202

Mesocrystal-embedded functional oxide systems

Mesocrystal—a new class of crystals compared with conventional single crystals and randomly distributed nanocrystal systems—has captured significant attention in recent decades. Current studies have been focused on the advanced synthesis as well as the intriguing properties of mesocrystal. In order to create new opportunities upon functional mesocrystals, they can be regarded as a new functional entirety when integrated with unique matrix environments. The elegant combination of mesocrystals and matrices has enabled researchers to realize enthralling tunabilities and to derive new functionalities that cannot be found in individual components. Therefore, mesocrystal-embedded system forms a new playground towards multifunctionalities. This review article delivers a general roadmap that portrays the enhancement of intrinsic properties and new functionalities driven by novel mesocrystal-embedded oxide systems. An in-depth understanding and breakthroughs achieved in mesocrystal-embedded oxide systems are highlighted. This article concludes with a brief discussion on potential directions and perspectives along this research field