Article
Multidisciplinary Sciences
Takuma Makihara, Kenji Hayashida, G. Timothy Noe, Xinwei Li, Nicolas Marquez Peraca, Xiaoxuan Ma, Zuanming Jin, Wei Ren, Guohong Ma, Ikufumi Katayama, Jun Takeda, Hiroyuki Nojiri, Dmitry Turchinovich, Shixun Cao, Motoaki Bamba, Junichiro Kono
Summary: Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics systems with ultrastrong light-matter interactions, but have not been realized due to the typically negligible antiresonant interactions. This study reports an unusual matter-matter system with magnons, where the importance of resonant and antiresonant interactions can be easily tuned and the latter can be vastly dominant. The results demonstrate the potential of magnonic systems as an ideal platform for exploring predicted exotic quantum vacuum phenomena in ultrastrongly coupled light-matter systems, with up to 5.9 dB of quantum fluctuation suppression observed in the ground state.
NATURE COMMUNICATIONS
(2021)
Article
Chemistry, Multidisciplinary
Ruofan Li, Peng Li, Di Yi, Lauren J. Riddiford, Yahong Chai, Yuri Suzuki, Daniel C. Ralph, Tianxiang Nan
Summary: Magnon-mediated spin flow in magnetically ordered insulators enables long-distance spin-based information transport with low dissipation. In this study, anisotropy in magnon spin transport was observed in spinel ferrite, providing an approach for controlling magnonic devices via strain.
Article
Nanoscience & Nanotechnology
Jin Wang, Yongkang Xu, Shuanghai Wang, Xingze Dai, Pengfei Yan, Jian Zhou, Ruifeng Wang, Yongbing Xu, Liang He
Summary: This research focuses on investigating the magneto-transport properties of 2D material CrTe2 and uncovers the mechanism behind its ferromagnetism, providing a theoretical foundation for its applications.
ADVANCED ELECTRONIC MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Juan Jiang, Alex Taekyung Lee, Sangjae Lee, Claudia Lau, Min Li, Tor M. Pedersen, Chong Liu, Sergey Gorovikov, Sergey Zhdanovich, Andrea Damascelli, Ke Zou, Frederick J. Walker, Sohrab Ismail-Beigi, Charles H. Ahn
Summary: This study investigates the synthesis and electronic properties of epitaxial perovskite La1-xSrxRhO3 thin films, revealing the effect of Sr doping on the electronic phase diagram. Experimental data show an insulator-metal-insulator transition caused by Sr addition, which is explained by theoretical calculations.
Article
Chemistry, Multidisciplinary
Yuhan Liang, Dingsong Jiang, Yahong Chai, Yue Wang, Hetian Chen, Jing Ma, Pu Yu, Di Yi, Tianxiang Nan
Summary: In this study, we observed magnon spin transport through multiferroic BiFeO3 thin films in a spin pumping experiment at room temperature. The experimental results showed that the magnon spin transport efficiency is very high when the thickness of the BiFeO3 films exceeds 80 nm.
ADVANCED FUNCTIONAL MATERIALS
(2023)
Article
Chemistry, Physical
Berit H. H. Goodge, Benjamin Geisler, Kyuho Lee, Motoki Osada, Bai Yang Wang, Danfeng Li, Harold Y. Y. Hwang, Rossitza Pentcheva, Lena F. F. Kourkoutis
Summary: Nickel-based superconductors provide an experimental platform for exploring cuprate-like superconductivity. However, superconductivity in nickelates has only been observed in thin films, which raises questions about the polar interface between substrate and film. In this study, the authors investigate the interface between Nd1-xSrxNiO2 and SrTiO3 using advanced characterization techniques and theoretical calculations, revealing the formation of a single intermediate Nd(Ti,Ni)O-3 layer and its role in reducing interface charge density. Understanding the complex interface structure is important for the future synthesis of nickelate films on other substrates and in vertical heterostructures.
Article
Chemistry, Multidisciplinary
Junhyuk Ahn, Sanghyun Jeon, Ho Kun Woo, Junsung Bang, Yong Min Lee, Steven J. Neuhaus, Woo Seok Lee, Taesung Park, Sang Yeop Lee, Byung Ku Jung, Hyungmok Joh, Mingi Seong, Ji-hyuk Choi, Ho Gyu Yoon, Cherie R. Kagan, Soong Ju Oh
Summary: A one-step, ink-lithography technique has been developed to pattern and engineer thin films of colloidal nanocrystals, allowing modification of both the chemical nature of the nanocrystal surface and the physical properties of the thin films. This method has been successfully applied to engineer thin films of metals, semiconductors, and insulators for various applications.
Article
Chemistry, Multidisciplinary
Federico Mazzola, Sandeep Kumar Chaluvadi, Vincent Polewczyk, Debashis Mondal, Jun Fujii, Piu Rajak, Mahabul Islam, Regina Ciancio, Luisa Barba, Michele Fabrizio, Giorgio Rossi, Pasquale Orgiani, Ivana Vobornik
Summary: This study demonstrates a genuine Mott transition without any symmetry breaking side effects in thin films of V2O3 using material synthesis and photoelectron spectroscopy. The spectral signal evolves slowly over a wide temperature range approaching the metal-insulator transition, with the Fermi wave-vector remaining unchanged and a lower critical temperature than that reported for the bulk.
Article
Nanoscience & Nanotechnology
Sumaiya Kabir, Shruti Nirantar, Mahta Monshipouri, Mei Xian Low, Sumeet Walia, Sharath Sriram, Madhu Bhaskaran
Summary: Vanadium dioxide (VO2) is a versatile phase change material that undergoes insulator-to-metal transition triggered by various stimuli, with electrical stimuli offering greater control over specific regions. A metal-insulator-metal (MIM) structure study showed that the overlapping electrode arrangement requires the least voltage for switching, while the insulator-to-metal transition in VO2 is independent of electrode overlap and channel width. These findings are crucial for designing energy-efficient, addressable, and scalable micro/nanoscale devices and sensor applications using VO2.
ADVANCED ELECTRONIC MATERIALS
(2022)
Article
Chemistry, Physical
Shenli Zhang, I-Ting Chiu, Min-Han Lee, Brandon Gunn, Mingzhen Feng, Tae Joon Park, Padraic Shafer, Alpha T. N'Diaye, Fanny Rodolakis, Shriram Ramanathan, Alex Frano, Ivan K. Schuller, Yayoi Takamura, Giulia Galli
Summary: The oxygen vacancy concentration in cobaltites can be determined by the change in O K-edge XA spectra peak positions. The variation of Co-O bond length and Co-O-Co bond angle is also correlated with the presence of oxygen vacancies. The resistivity of the oxide material can be modified by adjusting the defect concentration, without any structural transformation.
CHEMISTRY OF MATERIALS
(2022)
Article
Chemistry, Physical
Shailesh Kalal, Mukul Gupta, Rajeev Rawat
Summary: The study focused on the effects of nitrogen concentration on the structural and superconducting properties of niobium mononitride (NbN) thin films deposited using reactive magnetron sputtering of Nb at different partial pressures of N2. It was found that at low nitrogen concentrations, N atoms occupy interstitial sites within Nb leading to lattice distortion, while at intermediate nitrogen concentrations, nearly stoichiometric NbN phase emerges, and further nitridation results in expansion and distortion of NbN. High magnetic field resistivity measurements showed that optimal nitrogen concentration at R-N2 = 16% resulted in maximized superconducting transition temperature (Tc) and upper critical field (HC2(0)). Additionally, applying a radio frequency (rf) bias during the growth of NbN thin films enhanced adatom mobility leading to improved crystalline ordering and higher Tc of 13.2 K.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Materials Science, Multidisciplinary
Bowen Ma, Gregory A. Fiete
Summary: This study investigates the magnon spin thermal transport in pyrochlore iridate trilayer thin films grown along the [111] direction, revealing a defined Nernst-type thermal spin current response due to the spin configuration induced by the Dzyaloshinskii-Moriya interaction. The research shows the presence of topologically protected chiral edge modes within a certain parameter range.
Article
Chemistry, Physical
Murtaza Bohra, Remi Arras, Jean-Francois Bobo, Vidyadhar Singh, Naresh Kumar, Hsiung Chou
Summary: The ability to combine multiple spintronic properties in the ZnxFe3-xO4 system with different variants of its chemical composition offers a new route towards homodevices. By growing ZnxFe3-xO4 thin films from a ZnFe2O4 target under a reduced atmosphere, with an appropriate choice of growth temperature, unique properties such as high saturation magnetization and low resistivity can be engineered. The phase formation in the laser-ablated ZnxFe3-xO4 thin films differs from bulk thermal equilibrium, showing a competition between the reduction of Zn content and the formation of O vacancies at different growth temperature zones.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Chemistry, Physical
Yogesh Kumar, Akhil Tayal, Wolfgang Caliebe, Mukul Gupta
Summary: This study investigates the diffusion of nitrogen in cobalt mononitride thin films and the impact of carbon doping on this process to improve thermal stability. The experimental results demonstrate changes in nitrogen concentration and sample structure with increasing carbon doping, leading to enhanced thermal stability. This research provides insights for potential applications in the energy sector utilizing cobalt mononitride in various devices such as Li-ion batteries and solar cells.
APPLIED SURFACE SCIENCE
(2021)
Article
Materials Science, Multidisciplinary
Yongchang Ma, Rui Chen, Yajun Li, Cuimin Lu, Chenguang Zhang
Summary: We propose a model to estimate the energy barrier responsible for the hysteresis of the thermally driven Mott phase transition and validate the model with experimental data. For heating, the resistance in VO2 films exhibits step-like changes, forming multiple nonvolatile states, while no significant changes occur during cooling. The memory ability is attributed to the structure of the metal and insulator domains.
Article
Physics, Applied
Tsunashi Shimizu, Toru Akiyama, Kohji Nakamura, Tomonori Ito, Hiroyuki Kageshima, Masashi Uematsu, Kenji Shiraishi
Summary: Theoretical investigation shows that on the Si-face, NO molecule reacts with the C-C single bond, while on the C-face it reacts with the C=C double bond. The annealing process of NO is crucial for reducing carbon-related defects at the 4H-SiC/SiO2 interface.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Physics, Applied
Toru Akiyama, Atsutaka Nakatani, Tsunashi Shimizu, Takumi Ohka, Tomonori Ito
Summary: A direct approach for calculating the individual energy of step edges on polar semiconductor surfaces using ab initio calculations is proposed. The study focuses on single-bilayer step edges on AlN(0001) and GaN(0001) surfaces and emphasizes the importance of evaluating step formation energies for understanding the stability of step edges on various polar group-III nitride surfaces. The results reveal that stable steps exhibit specific atomic configurations with threefold-coordinated atoms or hydrogen-terminated edge atoms on the upper terrace.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2021)
Article
Crystallography
Toru Akiyama, Kazuhiro Yonemoto, Fumiaki Hishiki, Tomonori Ito
Summary: The adsorption behavior of In adatom during the growth of InAs wetting layer on GaAs(001) substrate is affected by surface structural changes, particularly the (4 x 7) surface promotes In adatom adsorption due to an increased number of stable adsorption sites. This highlights the importance of surface structure changes in the nucleation and growth of InAs wetting layer on GaAs(001) substrate.
JOURNAL OF CRYSTAL GROWTH
(2021)
Article
Physics, Applied
Takahiro Kawamura, Toru Akiyama
Summary: This study investigates the relationship between bandgaps and lattice strains in Ga2O3, finding that the bandgap values decrease linearly with increasing hydrostatic strain.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Crystallography
Toru Akiyama, Takumi Ohka, Katsuya Nagai, Tomonori Ito
Summary: Through ab initio electronic structure calculations, a systematic investigation of the adsorption behavior of Al and N adatoms on vicinal AlN (0001) surface under metal-organic vapor phase epitaxy (MOVPE) growth conditions was conducted. It was found that the vicinal surface with hydrogen-terminated N atom and NH2 was the most stable under N-rich conditions, while the surface with hydrogen-terminated N atom and NH2 at the step edge was favorable over a wide range of Al chemical potential. The adsorption energy of Al adatoms at the step edge was much lower than that in the terrace region, indicating easier incorporation of Al adatoms into the step edge.
JOURNAL OF CRYSTAL GROWTH
(2021)
Article
Physics, Applied
Fumiaki Hishiki, Toru Akiyama, Takahiro Kawamura, Tomonori Ito
Summary: The structures and stability of the interface between GaN and Ga2O3 were investigated using first-principles calculations. The results showed that the stable structure of the interface strongly depends on the oxygen chemical potential. By considering the experimental conditions, the interface structures of GaN/Ga2O3 were further clarified. These calculations provide important theoretical frameworks for understanding the formation mechanism of oxide films by thermal oxidation of GaN substrate.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Toru Akiyama, Tsunashi Shimizu, Tomonori Ito, Hiroyuki Kageshima, Kenta Chokawa, Kenji Shiraishi
Summary: Theoretical investigations based on ab initio calculations reveal that N atoms incorporation at the 4H-SiC/SiO2 interface is significantly influenced by the plane orientation, with Si-face interface showing higher incorporation energy. The competition between N-incorporation and N-2 desorption plays a crucial role in understanding the atom-scale mechanism.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Satoshi Ohata, Takahiro Kawamura, Toru Akiyama, Shigeyoshi Usami, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori, Tomoaki Sumi, Junichi Takino
Summary: This paper analyzed the electronic structures of GaN with O-related point and complex defects through first-principles calculations, and investigated their influence on the optical properties of GaN. It was found that the defect levels caused by native point defects were compensated by O and H impurities, as well as certain metal impurities (Mg, Zn, Si, Ge, Sn).
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Applied
Katsuhide Niki, Toru Akiyama, Tomonori Ito
Summary: The formation of pyramidal inversion domain (PID) boundaries in highly Mg-doped GaN is crucial for Mg doping and the resulting hole concentrations. This study investigates the stable facets hosting Mg atoms in PID boundaries and estimates the formation energies for various PID boundaries of different sizes and concentrations.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Chemistry, Physical
Toru Akiyama, Tsunashi Shimizu, Tomonori Ito, Hiroyuki Kageshima, Kenji Shiraishi
Summary: Ab initio calculations were used to investigate the reactions of N2O and NH3 molecules at the interface between 4H-SiC and SiO2 during post oxidation annealing (POA). It was found that the reaction of N2O molecule resulted in the desorption of carbon oxide molecules in addition to Si-N bond formation, while the reaction of NH3 molecule led to various atomic configurations depending on the plane orientation. The energy barriers for the N2O and NH3 reactions were higher than that of the NO reaction due to different atomic configurations at the transition state structure.
Article
Physics, Applied
Toru Akiyama, Takahiro Kawamura, Tomonori Ito
Summary: The effects of charged oxygen vacancies and substrate lattice constraints on the structural stability of Ga2O3 polymorphs were investigated using density functional calculations. It was found that regardless of the crystal phase, the doubly positively charged state (V-O(2)+) remained stable over a wide range of electron chemical potential. Furthermore, the alpha phase, including V-O(2)+, became the most stable when the vacancy concentration exceeded 2.8%, and the stabilization of alpha and kappa phases compared to the beta phase was enhanced by the alpha-Al2O3(0001) substrate. These results propose a physical origin for the growth of metastable phases in Ga2O3.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Haruka Sokudo, Toru Akiyama, Tomonori Ito
Summary: The thickness dependence of GaN layers on an AlN(0001) surface was investigated using first-principles calculations to understand the self-limiting growth during metal-organic vapor phase epitaxy. The stability of GaN layers on the AlN(0001) surface was found to be similar to that on a GaN(0001) surface regardless of the GaN film thickness. Additionally, the adsorption of Ga adatom was easier on the AlN(0001) surface compared to the surface with GaN layers, suggesting suppressed growth of GaN layers on the AlN(0001) surface. These findings provide theoretical guidance for understanding the formation mechanism of GaN quantum wells.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Applied
Shuri Fujita, Toru Akiyama, Takahiro Kawamura, Tomonori Ito
Summary: The structural stability and miscibility of (AlxGa1-x)(2)O-3 alloys were theoretically investigated through electronic structure calculations. The effects of lattice constraint from α-Al2O3(0001) substrate and (Al0.4Ga0.6)(2)O-3 buffer layer on the stability and miscibility were evaluated. The results showed that only α-phase (AlxGa1-x)(2)O-3 alloys can be stabilized by the α-Al2O3(0001) substrate, and the lattice constraint greatly improved the miscibility.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Condensed Matter
Takahiro Kawamura, Kouhei Basaki, Akito Korei, Toru Akiyama, Yoshihiro Kangawa
Summary: In this study, the influence of uniaxial and equibiaxial strains on the bandgaps of short-period InN/AlN superlattices is examined using first-principles calculations. The results show that the bandgaps change in different manners depending on the strain direction, both for uniaxial and equibiaxial strains.
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
(2023)
Article
Engineering, Electrical & Electronic
Atsushi Kobayashi, Shunya Kihira, Toru Akiyama, Takahiro Kawamura, Takuya Maeda, Kohei Ueno, Hiroshi Fujioka
Summary: The polarity control of AlN by epitaxial growth using lattice-matched centrosymmetric NbN is reported. The surface of AlN grown on NbN/Al-polar AlN was atomically flat and highly crystalline. The proposed all-nitride epitaxial N-polar AlN/ NbN/Al-polar AlN heterostructure did not contain oxide materials, ensuring the stability of the interface and facilitating the fabrication of defect-free polar structures.
ACS APPLIED ELECTRONIC MATERIALS
(2023)
