Article
Materials Science, Multidisciplinary
Katsuhiro Arimoto, Takashi Koretsune, Kentaro Nomura
Summary: Theoretical study suggests that a three-dimensional topological insulator/thin-film ferromagnetic metal heterostructure could potentially exhibit a quantum anomalous Hall effect with a wide global band gap. By introducing magnetic exchange interaction in the thin-film layers, the heterostructure may achieve a wider gap realizing QAH effect even at room temperature, paving the way for experimental realization of exotic topological quantum phenomena.
Article
Chemistry, Multidisciplinary
Xiaodong Zhou, Wanxiang Feng, Yinwei Li, Yugui Yao
Summary: In this study, the emergence of spin-chirality-driven quantum anomalous Hall effect (QAHE) and quantum topological Hall effect (QTHE) is demonstrated by sandwiching a 2D Z(2) topological insulator between two chiral kagome antiferromagnetic single-layers. The QAHE is realized with fully compensated noncollinear antiferromagnetism instead of conventional collinear ferromagnetism. The Chern number can be regulated periodically with the interplay between vector- and scalar-spin chiralities, and the QAHE can even occur without spin-orbit coupling, indicating the rare QTHE. These findings open up a new avenue for antiferromagnetic quantum spintronics based on unconventional mechanisms from chiral spin textures.
Article
Chemistry, Multidisciplinary
Lei Jin, Lirong Wang, Xiaoming Zhang, Ying Liu, Xuefang Dai, Hongli Gao, Guodong Liu
Summary: The research demonstrates that 2D YN2 possesses both out-of-plane and tunable in-plane QAHE. The YN2 monolayer can exhibit either Weyl states or in-plane QAHE states under in-plane magnetization, and the Chern number and edge channel propagation direction can be adjusted by changing the direction of the in-plane magnetic field.
Article
Materials Science, Multidisciplinary
O. J. Clark, F. Freyse, L. Yashina, O. Rader, J. Sanchez-Barriga
Summary: An investigation was conducted on Au-dosed Bi2Se3 using spin- and angle-resolved photoemission, revealing the robustness of the Dirac cone against high Au coverage and the unchanged spin textures of the TSS and its accompanying surface resonances following Au deposition.
NPJ QUANTUM MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Song Sun, Hongming Weng, Xi Dai
Summary: This paper proposes that quantized and nearly half-quantized intrinsic anomalous Hall effect can be induced by in-plane external magnetic field through the Zeeman coupling in nonmagnetic 2D systems. The findings are supported by an analytical result from a 2D electron gas model with C3v symmetry and calculations based on a k center dot p Hamiltonian derived from first principle calculations.
Article
Materials Science, Multidisciplinary
Yadong Jiang, Zhaochen Liu, Jing Wang
Summary: The unoccupied part of the band structure in the magnetic topological insulator MnBi2Te4 has been studied using first-principles calculations. A possible second, unoccupied topological surface state is proposed, which has a similar electronic structure to the occupied topological surface state. Two optical effects are proposed to detect the unoccupied surface state if it exists.
Article
Nanoscience & Nanotechnology
Hang Chi, Jagadeesh S. Moodera
Summary: In this Perspective, an overview of the recent achievements in the quantum anomalous Hall effect as well as the material challenges and opportunities pertaining to engineering intrinsic/interfacial magnetic coupling are provided, which are expected to propel future development in this field.
Article
Nanoscience & Nanotechnology
L. K. Rodenbach, I. T. Rosen, E. J. Fox, Peng Zhang, Lei Pan, Kang L. Wang, M. A. Kastner, D. Goldhaber-Gordon
Summary: By comparing transport measurements of devices fabricated from Cr-doped (BiSb)(2)Te-3, it was found that bulk conduction is the dominant source of dissipation at all temperatures and electric field values, and the breakdown of the QAH phase is a bulk process. This methodology can be used to identify dissipative conduction mechanisms in new QAH materials for achieving the QAH effect at higher temperatures.
Article
Physics, Applied
Archit Bhardwaj, Syam P. Prasad, Karthik V. Raman, Dhavala Suri
Summary: The Planar Hall effect in topological insulators is mainly attributed to conduction from topologically protected surface states, but our study on Bi2Te3 thin films highlights the importance of considering bulk conduction as well. Observations of unconventional increases in the Planar Hall effect signal with thickness and temperature suggest that bulk effects may play a significant role in topological insulators.
APPLIED PHYSICS LETTERS
(2021)
Article
Chemistry, Multidisciplinary
Yuchen Ji, Zheng Liu, Peng Zhang, Lun Li, Shifei Qi, Peng Chen, Yong Zhang, Qi Yao, Zhongkai Liu, Kang L. Wang, Zhenhua Qiao, Xufeng Kou
Summary: We report the thickness-tailored quantum anomalous Hall (QAH) effect in Cr-doped (Bi,Sb)(2)Te-3thin films and demonstrate that the induced hybridization gap plays an indispensable role in determining the ground magnetic state of magnetic topological insulators (MTIs). This finding provides useful guidance for the pursuit of other QAH-based phase diagrams and functionalities through structural engineering.
Article
Materials Science, Multidisciplinary
Yingxi Bai, Linke Cai, Ning Mao, Runhan Li, Ying Dai, Baibiao Huang, Chengwang Niu
Summary: This study presents the emergence of doubled QSHE in two dimensions characterized by a high-spin Chern number of CS = 2, utilizing β-antimonene and β-bismuthene as potential material candidates with band inversions at generic k points.
Review
Physics, Multidisciplinary
Cui-Zu Chang, Chao -Xing Liu, Allan H. MacDonald
Summary: The quantum Hall effect is the characteristic experimental fingerprint of Chern insulators, which combine quantized Hall resistance with zero longitudinal resistance. Chern insulators exhibit nontrivial bulk band topology expressed by chiral states that carry current along sample edges without dissipation. The quantum anomalous Hall effect refers to the occurrence of quantum Hall effects without external magnetic fields due to spontaneously broken time-reversal symmetry. The QAH effect has been realized in four different classes of two-dimensional materials.
REVIEWS OF MODERN PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Fangxue Luo, Xiamin Hao, Yizhen Jia, Junjie Yao, Qingling Meng, Shuwei Zhai, Jinge Wu, Wenzhen Dou, Miao Zhou
Summary: The article discusses the chemical functionalization process of jacutingaite, transitioning from a QSH state to a QAH state. Through calculations and simulations, it was found that 2D halogenated jacutingaite exhibits ferromagnetism and a QAH effect, showing promise for achieving exotic topological phases.
Article
Chemistry, Physical
Nana Shumiya, Md Shafayat Hossain, Jia-Xin Yin, Zhiwei Wang, Maksim Litskevich, Chiho Yoon, Yongkai Li, Ying Yang, Yu-Xiao Jiang, Guangming Cheng, Yen-Chuan Lin, Qi Zhang, Zi-Jia Cheng, Tyler A. Cochran, Daniel Multer, Xian P. Yang, Brian Casas, Tay-Rong Chang, Titus Neupert, Zhujun Yuan, Shuang Jia, Hsin Lin, Nan Yao, Luis Balicas, Fan Zhang, Yugui Yao, M. Zahid Hasan
Summary: This study provides micro-spectroscopic evidence for the presence of a room-temperature quantum spin Hall edge state on the surface of a higher-order topological insulator. The research reveals the microstructural features of the topological phase and suggests further exploration of high-temperature transport quantization.
Article
Materials Science, Multidisciplinary
Yong-Chang Lau, Junya Ikeda, Kohei Fujiwara, Akihiro Ozawa, Jiaxin Zheng, Takeshi Seki, Kentaro Nomura, Liang Du, Quansheng Wu, Atsushi Tsukazaki, Koki Takanashi
Summary: Magnetic Weyl semimetals exhibit chiral Weyl node pairs and large intrinsic anomalous Hall effect. This study demonstrates the potential of Dirac nodes in paramagnetic state for efficient spin current generation at room temperature via the spin Hall effect.
Article
Chemistry, Physical
Chloe Groome, Huong Ngo, Jie Li, Chen Santillan Wang, Ruqian Wu, Regina Ragan
Summary: The design of the molecular environment of single atom catalysts offers a promising way to achieve high catalytic activity without the need for expensive platinum-group metals. This study utilized a first principles approach to examine the impact of spin states on the catalytic energy barriers of V, Fe, Mo, and Ta on graphene defects. Results showed that systems with higher spin state asymmetry near the Fermi energy had relatively lower activation energy barriers, leading to significant decreases in activation barrier energies for CO oxidation on Ta and V catalysts.
Article
Physics, Multidisciplinary
Chang-Jong Kang, Jeonghoon Hong, Jeongwoo Kim
Summary: In this study, we employed the DFT + DMFT technique to investigate the electronic structure of ferromagnetic monolayer CrI3 as a function of temperature and hole-doping concentration. The results show that the ferromagnetism of monolayer CrI3 originates from localized magnetic moments of Cr atoms rather than Stoner-type itinerant ones. The calculations also reveal apparent strong spin-dependent electronic correlation effects in monolayer CrI3. Furthermore, we found that the electronic and magnetic properties of monolayer CrI3 can be easily tuned by hole-doping.
JOURNAL OF THE KOREAN PHYSICAL SOCIETY
(2022)
Article
Materials Science, Multidisciplinary
Lei Gu, Jie Li, Ruqian Wu
Summary: In this review, the importance of Raman processes driven by optical phonons in spin relaxation theory in molecular magnets is explained. The sub-barrier relaxation and anomalously low Raman exponents are emphasized as common signatures of this dominance.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Physics, Applied
Yudong Pang, Zhansheng Lu, Shamraiz Hussain Talib, Xinyuan Li, Mingyang Wang, Xilin Zhang, Zongxian Yang, Ruqian Wu
Summary: This study investigates the effects of heteroatom doping and charge variation on the ability of MoS2 substrate to capture Na ions in sodium-ion batteries using first-principles calculations. The results show that Al- or Si-doped MoS2 can serve as good electrode materials with high theoretical capacity.
PHYSICAL REVIEW APPLIED
(2022)
Article
Chemistry, Multidisciplinary
Su Kong Chong, Peng Zhang, Jie Li, Yinong Zhou, Jingyuan Wang, Huairuo Zhang, Albert. V. V. Davydov, Christopher Eckberg, Peng Deng, Lixuan Tai, Jing Xia, Ruqian Wu, Kang. L. L. Wang
Summary: A novel procedure combining thin-film deposition and 2D material stacking techniques is demonstrated to create dual-gated devices of magnetically doped topological insulators. The orthogonal control over the charge density and electric displacement field is achieved in these devices. Through electrical manipulation of the surface exchange gap, the capabilities to strengthen or suppress the quantum anomalous Hall state and drive a topological phase transition to a trivial state are demonstrated. The experimental results are explained using first principle theoretical calculations, providing a practical route for in situ control of quantum anomalous Hall states and topology.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Xingxu Yan, Jie Li, Lei Gu, Chaitanya Avinash Gadre, Samuel L. Moore, Toshihiro Aoki, Shuopei Wang, Guangyu Zhang, Zhaoli Gao, Dimitri N. Basov, Ruqian Wu, Xiaoqing Pan
Summary: This study reports the discovery of curvature-induced phonon polaritons localized at the crease of folded hexagonal boron nitrides (h-BNs) using monochromated electron energy-loss spectroscopy. The creased-localized signals undergo an abnormal blue-shift, which is found to arise from the optical phonon hardening in the curled region. The study also shows that the curvature-induced phonon polariton can be controllably achieved via an electron-beam etching approach.
Article
Materials Science, Multidisciplinary
Yipeng An, Juncai Chen, Zhengxuan Wang, Jie Li, Shijing Gong, Chunlan Ma, Tianxing Wang, Zhaoyong Jiao, Ruqian Wu, Jiangping Hu, Wuming Liu
Summary: In this study, a new kagome magnesium triboride (MgB3) superconductor is predicted, with a calculated critical temperature of about 12.2 K and 15.4 K under external stress, which is potentially the highest among the reported diverse kagome-type superconductors. Various exotic physical properties of the system, including van Hove singularity, flat-band, multiple Dirac points, and nontrivial topology, are revealed. The topological and nodal superconducting nature of MgB3 is unveiled using a recently developed symmetry indicators method. This study suggests that MgB3 can serve as a new platform to explore exotic physics in the kagome structure and search for more superconductors and topological materials with XY3-type kagome lattice.
PHYSICAL REVIEW MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Jie Li, Ruqian Wu
Summary: In this study, a van der Waals (vdW) heterostructure of ultrathin MnBi2Se4 and Bi2Se3 layers is proposed as an excellent tunable platform for the quantum anomalous Hall (QAH) effect. The band gap of this heterostructure closes and reopens as the applied electric field increases, exhibiting a novel topological phase transition. It also has other advantageous properties such as a large topological band gap, perpendicular magnetization, and strong ferromagnetic ordering.
Article
Chemistry, Multidisciplinary
Huaixun Huyan, Zhe Wang, Linze Li, Xingxu Yan, Yi Zhang, Colin Heikes, Darrell G. Schlom, Ruqian Wu, Xiaoqing Pan
Summary: Defect engineering in perovskite thin films has received extensive attention due to their atomic-level modification and the design of novel nanostructures. However, three-dimensional defect-assisted nanostructures in thin film matrices usually have large misfit strains and unstable structures. In contrast, one- or two-dimensional defect-assisted nanostructures embedded in thin films can sustain large misfit strains without relaxation, making them suitable for defect engineering in perovskite thin films.
Article
Physics, Multidisciplinary
Jeonghoon Hong, Sejoong Kim, Jeongwoo Kim
Summary: We studied the catalytic properties of Pt doped and alloyed with 3d transition metals. Our calculations show that the catalytic activity of doped Pt is not significantly affected by transition metal impurities. Particularly, Pt-Fe alloys in specific ordered structures exhibit excellent catalytic activity for the oxygen reduction reaction.
JOURNAL OF THE KOREAN PHYSICAL SOCIETY
(2023)
Article
Materials Science, Multidisciplinary
S. B. Song, Z. Wang, R. Q. Wu
Summary: In this study, we used density functional theory calculations to investigate the magnetic properties of 5d transition metal monolayers on a ferroelectric substrate. Our results showed that the easy magnetization axis of iridium and platinum monolayers can be rotated by 90 degrees by reversing the electric polarization of the substrate, while the magnetocrystalline anisotropy energy of the osmium monolayer is significantly enhanced in the upward polarization state. These findings provide valuable insights for controlling the magnetization direction of monoatomic layers and developing low-energy spintronics devices.
Article
Chemistry, Physical
Ao Lou, Hua-Hua Fu, Ruqian Wu
Summary: Using density functional theory and the Boltzmann transport equation, we have discovered a new class of high-performance thermoelectric materials, called supertetrahedral Ga4C-family materials, which exhibit an ultrahigh thermoelectric figure of merit (ZT) due to a large power factor and ultralow lattice thermal conductivity. The power factor is influenced by multiple electronic band degeneracies, flat bands, and valley anisotropy, while the low lattice thermal conductivity is attributed to strong phonon scattering and low phonon group velocity. Moreover, we found that tensile strain engineering can further decrease lattice thermal conductivity while maintaining the multi-band degeneracies, valley anisotropy, and flat bands. In addition to band degeneracy, the scattering mechanism can also greatly affect the power factor during strain implementation. As a result, we observed a novel thermoelectric phenomenon, with Ca4C exhibiting a ZT value larger than 4.4 under a small strain ratio (0.75%). Our theoretical studies not only reveal a new class of high-performance thermoelectric materials with multiple effective mechanisms but also provide a realistic platform for investigating the competitive effects of different factors on enhancing the thermoelectric figure of merit.
JOURNAL OF MATERIALS CHEMISTRY A
(2023)
Article
Materials Science, Multidisciplinary
Yinong Zhou, Ruqian Wu
Summary: In this study, the possibility of direct control of topological corner states is demonstrated by introducing spin degrees of freedom and local magnetization and electric potential in a rhombus-shaped Kekule nanostructure. By applying local magnetization on one corner, strong spin polarization can be achieved in both corners. Reversal of spin polarization at both corners is achieved by applying local electric potential at the same corner. The robustness of spin polarization control under disorder is also proven, and material realization is demonstrated in a gamma-graphyne nanostructure. Other higher-order lattices and nanostructure shapes are discussed as well. These studies provide a showcase of the remote correlation of quantum states in higher-order topological materials for spintronic and quantum applications.
Article
Materials Science, Multidisciplinary
Jeonghoon Hong, Chang-Jong Kang, Jeongwoo Kim
Summary: This study investigated the electronic structure and magnetism of a two-dimensional ferromagnetic MnSe2 monolayer using density functional theory, revealing the important role of electronic correlations in the system. The primary exchange mechanism responsible for the high TC of MnSe2 monolayer was clarified, and methods to enhance TC were suggested through charge doping and heterostructure engineering.
Article
Materials Science, Multidisciplinary
S. B. Song, Z. Wang, J. Li, R. Q. Wu
Summary: Through density-functional calculations, the exchange bias effect of the antiferromagnetic Cr(001) substrate on a single magnetic molecule CoCp2 has been systematically studied. The magnetic moment and magnetic anisotropy of CoCp2 can be greatly tuned by the charge transfer between the molecule and substrate. A large exchange energy of approximately 94 meV has been found, which essentially pins the spin orientation of CoCp2. This makes CoCp2/Cr(001) an ideal combination for quantum sensing with well-decoupled quantum spin states from the target magnetic entities.
