Tuning orbital-selective phase transitions in a two-dimensional Hund's correlated system

Hund's rule coupling ($\textit{J}$) has attracted much attention recently for its role in the description of the novel quantum phases of multi orbital materials. Depending on the orbital occupancy, $\textit{J}$ can lead to various intriguing phases. However, experimental confirmation of the orbital occupancy dependency has been difficult as controlling the orbital degrees of freedom normally accompanies chemical inhomogeneities. Here, we demonstrate a method to investigate the role of orbital occupancy in $\textit{J}$ related phenomena without inducing inhomogeneities. By growing SrRuO$_3$ monolayers on various substrates with symmetry-preserving interlayers, we gradually tune the crystal field splitting and thus the orbital degeneracy of the Ru \textit{t_2_g$}$ orbitals. It effectively varies the orbital occupancies of two-dimensional (2D) ruthenates. Via in-situ angle-resolved photoemission spectroscopy, we observe a progressive metal-insulator transition (MIT). It is found that the MIT occurs with orbital differentiation: concurrent opening of a band insulating gap in the $\textit{d$_x_y} band and a Mott gap in the \textit{d_x$$_z$$_/$$_y$$_z} bands. Our study provides an effective experimental method for investigation of orbital-selective phenomena in multi-orbital materials

New perspective on giant Rahba effect

The giant Rashba splitting on Bi/Ag(111) alloy surface which is two order of amplitude larger than Rashba on Au(111) surface has been reported from the experiment. [1] From the DFT calculations, it has been known that the amplitude of the splitting depends on the distance between Bi and Ag on surface, but the reason for that is still obscure. [2] Some proposals were made to explain the giant Rashba such as the role of in-plane potential gradient, very strong surface electric field and spin-orbit coupling. [1,3,4] However, the origin of the giant Rashba splitting has not been disclosed clearly and there must be unrevealed mechanism to explain it. In this study based on DFT calculation, we would give a new perspective on giant Rashba effect.1

Phytochemical and Antioxidant Characterization of Extracts from Unexplored Medicinal Plants <i>Salix schwerinii</i> and <i>Salix kochiana</i>

For a long time, species of the genus Salix have been widely utilized and studied as medicinal plants; however, the biological activity and phytochemical composition of Salix schwerinii (SS) and S. kochiana (SK) have not been studied at all. This study investigated the antioxidant properties of SS and SK extracts and detected phytochemical compounds in the extracts. The results showed that the antioxidant activities (IC50) of SS extract, SK extract, and ascorbic acid (reference) were as follows, respectively: 169.8, 79.8, and 71.2 μg mL−1 for ABTS cation radical scavenging and 38.4, 26.2, and 9.3 μg mL−1 for DPPH free radical scavenging. The results imply that SK has a high potential as a natural antioxidant. The phytochemical compositions of extracts (mg g−1) were analyzed as follows: SS extracts, 217.7 phenolics (1.54 catechin, 0.86 syringic acid, 0.46 luteolin, and others) and 5.06 salicin; SK extracts, 71.0 phenolics (0.54 catechin, 0.28 myricetin, 0.12 salicylic acid, and others) and 2.11 salicin. Compared to previous studies, the present findings go further to highlight that SS deserves attention as a novel source of salicin. The present study highlights the need for further studies on the aspects of medicinal functions of the extracts, bioprocess design for efficient phytochemical extraction, and applications of bioactive substances

Correlated Magnetic Weyl Semimetal State in Strained Pr 2

© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbHCorrelated topological phases (CTPs) with interplay between topology and electronic correlations have attracted tremendous interest in condensed matter physics. Therein, correlated Weyl semimetals (WSMs) are rare in nature and, thus, have so far been less investigated experimentally. In particular, the experimental realization of the interacting WSM state with logarithmic Fermi velocity renormalization has not been achieved yet. Here, experimental evidence of a correlated magnetic WSM state with logarithmic renormalization in strained pyrochlore iridate Pr2Ir2O7 (PIO) which is a paramagnetic Luttinger semimetal in bulk, is reported. Benefitting from epitaxial strain, “bulk-absent” all-in–all-out antiferromagnetic ordering can be stabilized in PIO film, which breaks time-reversal symmetry and leads to a magnetic WSM state. With further analysis of the experimental data and renormalization group calculations, an interacting Weyl liquid state with logarithmically renormalized Fermi velocity, similar to that in graphene, is found, dressed by long-range Coulomb interactions. This work highlights the interplay of strain, magnetism, and topology with electronic correlations, and paves the way for strain-engineering of CTPs in pyrochlore iridates.11Nsciescopu

Correlated Magnetic Weyl Semimetal State in Strained Pr2Ir2O7

© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbHCorrelated topological phases (CTPs) with interplay between topology and electronic correlations have attracted tremendous interest in condensed matter physics. Therein, correlated Weyl semimetals (WSMs) are rare in nature and, thus, have so far been less investigated experimentally. In particular, the experimental realization of the interacting WSM state with logarithmic Fermi velocity renormalization has not been achieved yet. Here, experimental evidence of a correlated magnetic WSM state with logarithmic renormalization in strained pyrochlore iridate Pr2Ir2O7 (PIO) which is a paramagnetic Luttinger semimetal in bulk, is reported. Benefitting from epitaxial strain, “bulk-absent” all-in–all-out antiferromagnetic ordering can be stabilized in PIO film, which breaks time-reversal symmetry and leads to a magnetic WSM state. With further analysis of the experimental data and renormalization group calculations, an interacting Weyl liquid state with logarithmically renormalized Fermi velocity, similar to that in graphene, is found, dressed by long-range Coulomb interactions. This work highlights the interplay of strain, magnetism, and topology with electronic correlations, and paves the way for strain-engineering of CTPs in pyrochlore iridates.11Nsciescopu

Heteroepitaxial Control of Fermi Liquid, Hund Metal, and Mott Insulator Phases in Single-Atomic-Layer Ruthenates

Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic-scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of correlated electronic phases in atomic-scale ruthenate-titanate heterostructures. While bulk SrRuO3 is a ferromagnetic metal, the heterointerfaces exclusively generate three distinct correlated phases in the single-atomic-layer limit. The theoretical analysis reveals that atomic-scale structural proximity effects yield Fermi liquid, Hund metal, and Mott insulator phases in the quantum-confined SrRuO3. These results highlight the extensive interfacial tunability of electronic phases, hitherto hidden in the atomically thin correlated heterostructure. Moreover, this experimental platform suggests a way to control interfacial electronic phases of various correlated materials.11Nsciescopu