Showing 1–6 of 6 results for author: Teh, S

Giant X-ray circular dichroism in a time-reversal invariant altermagnet

Authors: Jun Okamoto, Ru-Pan Wang, Yen-Yi Chu, Hung-Wei Shiu, Amol Singh, Hsiao-Yu Huang, Chung-Yu Mou, Sucitto Teh, Horng-Tay Jeng, Kai Du, Xianghan Xu, Sang-Wook Cheong, Chao-Hung Du, Chien-Te Chen, Atsushi Fujimori, Di-Jing Huang

Abstract: X-ray circular dichroism, arising from the contrast in X-ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X-ray magnetic circular dichroism because of time-reversal symmetry, yet exhibit weak X-ray n… ▽ More X-ray circular dichroism, arising from the contrast in X-ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X-ray magnetic circular dichroism because of time-reversal symmetry, yet exhibit weak X-ray natural circular dichroism. Here, we report the observation of giant natural circular dichroism in the Ni $L_3$-edge X-ray absorption of Ni$_3$TeO$_6$, a polar and chiral antiferromagnet with effective time-reversal symmetry. To unravel this intriguing phenomenon, we propose a phenomenological model that classifies the movement of photons in a chiral crystal within the same symmetry class as that of a magnetic field. The coupling of X-ray polarization with the induced magnetization yields giant X-ray natural circular dichroism, revealing the altermagnetism of Ni$_3$TeO$_6$. Our findings provide evidence for the interplay between magnetism and crystal chirality in natural optical activity. Additionally, we establish the first example of a new class of magnetic materials exhibiting circular dichroism with time-reversal symmetry. △ Less

Submitted 23 February, 2024; v1 submitted 12 December, 2023; originally announced December 2023.

Comments: Accepted by Advanced Materials (2024.2.16) Revised title: Giant X-ray circular dichroism in a time-reversal invariant altermagnet Revised drafts: Main 14 pages, 4 figures, and SI 20 pages, 8 figures

Journal ref: adv. mater. 36, 2309172 (2024)

Superconducting Proximity Effect in R7xR7R19.1o Ni Nanoislands on Pb(111)

Authors: Yen-Hui Lin, Sucitto Teh, Da-You Yeh, Chin-Hsuan Chen, Deng-Sung Lin, Horng-Tay Jeng, Pin-Jui Hsu

Abstract: We have studied the proximity_induced superconductivity in R7xR7R19.1o Ni nanoislands by combing scanning tunnelling microscopy_spectroscopy (STM_STS) with density functional theory (DFT) calculation. Through depositing Ni onto Pb(111) substrate at 80 K, the monolayer Ni nanoislands with the R7xR7R19.1o surface structure have been fabricated, where the termination of Ni atoms at hexagonal close pa… ▽ More We have studied the proximity_induced superconductivity in R7xR7R19.1o Ni nanoislands by combing scanning tunnelling microscopy_spectroscopy (STM_STS) with density functional theory (DFT) calculation. Through depositing Ni onto Pb(111) substrate at 80 K, the monolayer Ni nanoislands with the R7xR7R19.1o surface structure have been fabricated, where the termination of Ni atoms at hexagonal close packed (hcp) site is energetically preferred and the electron filling of 3d orbitals from the charge transfer leads to the vanishing magnetic moment of Ni atoms. The topographic R7xR7R19.1o lattice as well as the asymmetric height contrast in atomic unit cell are further corroborated by the STM simulations. With high spatial and energy resolution, tunneling conductance spectra have resolved an isotropic superconducting gap with Delta_Ni_(R7xR7R19.1o)_1.29 meV, which is slightly larger than Delta_Pb_1.25 meV. The temperature dependence of Delta_Ni_(R7xR7R19.1o) supports the substrate_induced superconducting proximity effect according to the same transition temperature Tc_7.14 K with the Pb(111). The line spectroscopy has spatially mapped out the small increase of Delta_Ni_(R7xR7R19.1o), which could be explained by an enhanced electron_phonon interaction under the framework of Bardeen_Cooper_Schrieffer (BCS) theory as a manifestation of the hole doping of Pb(111) from the surface Ni atoms. △ Less

Submitted 30 December, 2021; originally announced December 2021.

Comments: 7 pages, 5 figures

Machine-learned prediction of the electronic fields in a crystal

Authors: Ying Shi Teh, Swarnava Ghosh, Kaushik Bhattacharya

Abstract: We propose an approach for exploiting machine learning to approximate electronic fields in crystalline solids subjected to deformation. Strain engineering is emerging as a widely used method for tuning the properties of materials, and this requires repeated density functional theory calculations of the unit cell subjected to strain. Repeated unit cell calculations are also required for multi-resol… ▽ More We propose an approach for exploiting machine learning to approximate electronic fields in crystalline solids subjected to deformation. Strain engineering is emerging as a widely used method for tuning the properties of materials, and this requires repeated density functional theory calculations of the unit cell subjected to strain. Repeated unit cell calculations are also required for multi-resolution studies of defects in crystalline solids. We propose an approach that uses data from such calculations to train a carefully architected machine learning approximation. We demonstrate the approach on magnesium, a promising light-weight structural material: we show that we can predict the energy and electronic fields to the level of chemical accuracy, and even capture lattice instabilities. △ Less

Submitted 8 April, 2021; originally announced April 2021.

Collective behavior in the kinetics and equilibrium of solid-state photoreaction

Authors: Ruobing Bai, Ying Shi Teh, Kaushik Bhattacharya

Abstract: There is current interest in developing photoactive materials that deform on illumination and can thus be used for photomechanical actuation. This is attractive since it can be affected at a distance, different frequencies can be used to actuate different modes and to sense, and corrosion-free lightweight fiber optic cables can deliver significant power over long distances. The strategy for develo… ▽ More There is current interest in developing photoactive materials that deform on illumination and can thus be used for photomechanical actuation. This is attractive since it can be affected at a distance, different frequencies can be used to actuate different modes and to sense, and corrosion-free lightweight fiber optic cables can deliver significant power over long distances. The strategy for developing new photomechanical materials is to first develop photoactive molecules in solution, and then to incorporate these in the solid-state either by crystallization or by inserting them into polymers. This letter shows that the kinetics and the nature of the photo-induced phase transitions are profoundly different in single molecules (solution) and in the solid state using a lattice spin model. In solution, where the molecules act independently, the photoreaction follows first-order kinetics. However, in the solid state where the photoactive molecules interact with each other and therefore behave collectively during reaction, photoreactions follow the sigmoidal kinetics of nucleation and growth as in a first-order phase transition. Further, we find that the exact nature of the photo-induced strain has a critical effect on the kinetics, equilibrium, and microstructure formation. These predictions agree qualitatively with experimental observations, and provide insights for the development of new photoactive materials. △ Less

Submitted 21 December, 2020; v1 submitted 2 November, 2020; originally announced November 2020.

Comments: Accepted manuscript by Extreme Mechanics Letters

Journal ref: Extreme Mechanics Letters Volume 43, February 2021, 101160

Understanding the morphotropic phase boundary of perovskite solid solutions as a frustrated state

Authors: Ying Shi Teh, Jiangyu Li, Kaushik Bhattacharya

Abstract: Perovskite solid solutions that have a chemical composition A(C$_x$D$_{1-x})$O$_3$ with transition metals C and D substitutionally occupying the B site of a perovskite lattice are attractive in various applications for their dielectric, piezoelectric and other properties. A remarkable feature of these solid solutions is the \emph{morphotropic phase boundary} (MPB), the composition across which the… ▽ More Perovskite solid solutions that have a chemical composition A(C$_x$D$_{1-x})$O$_3$ with transition metals C and D substitutionally occupying the B site of a perovskite lattice are attractive in various applications for their dielectric, piezoelectric and other properties. A remarkable feature of these solid solutions is the \emph{morphotropic phase boundary} (MPB), the composition across which the crystal symmetry changes. Critically, it has long been observed that the dielectric and piezoelectric as well as the ability to pole a ceramic increases dramatically at the MPB. While this has motivated much study of perovskite MPBs, a number of important questions about the role of disorder remain unanswered. We address these questions using a new approach based on the random-field Ising model with long-range interactions that incorporates the basic elements of the physics at the meso-scale. We show that the MPB emerges naturally in this approach as a frustrated state where stability is exchanged between two well-defined phases. Specifically, long-range interactions suppress the disorder at compositions away from MPB but are unable to do so when there is an exchange of stability. Further, the approach also predicts a number of experimentally observed features like the fragmented domain patterns and superior ability to pole at the MPB. The insights from this model also suggest the possibility of entirely new materials with strong ferroelectric-ferromagnetic coupling using an MPB. △ Less

Submitted 2 November, 2020; originally announced November 2020.

Journal ref: Phys. Rev. B 103, 144201 (2021)

Photovoltaic effect in multi-domain ferroelectric perovskite oxides

Authors: Ying Shi Teh, Kaushik Bhattacharya

Abstract: We propose a device model that elucidates the role of domain walls in the photovoltaic effect in multi-domain ferroelectric perovskites. The model accounts for the intricate interplay between ferroelectric polarization, space charges, photo-generation and electronic transport. When applied to bismuth ferrite, results show a significant electric potential step across both 71-degree and 109-degree d… ▽ More We propose a device model that elucidates the role of domain walls in the photovoltaic effect in multi-domain ferroelectric perovskites. The model accounts for the intricate interplay between ferroelectric polarization, space charges, photo-generation and electronic transport. When applied to bismuth ferrite, results show a significant electric potential step across both 71-degree and 109-degree domain walls, which in turn contributes to the photovoltaic (PV) effect. We also find a strong correlation between polarization and oxygen octahedra tilts, which indicates the nontrivial role of the latter in the PV effect. The domain wall-based PV effect is further shown to be additive in nature, allowing for the possibility of generating above-bandgap voltage △ Less

Submitted 19 November, 2018; originally announced November 2018.