Article
Materials Science, Multidisciplinary
Xun-Jiang Luo, Xiao-Hong Pan, Xin Liu
Summary: The study demonstrates that the interplay between superconductors and magnetic fields based on the surface states of a weak topological insulator can lead to various helical or chiral Majorana hinge modes and even corner modes. The obtained higher-order topological superconductors can naturally behave as a TSC in DIII or D symmetry class due to their certain boundaries, surfaces, or hinges. These higher-order TSCs can be characterized by boundary topological invariants, such as surface Chern numbers or surface Z(2) topological invariants for surface TSCs.
Article
Materials Science, Multidisciplinary
Yen-Ta Huang, Dung-Hai Lee
Summary: Applying the method of bosonization, we derive the bosonized theory for free fermion topological insulators and superconductors with time reversal, charge conjugation, and flavor symmetries. We also present the theory of a class of bosonic symmetry-protected topological states.
Review
Physics, Applied
M. M. Sharma, Prince Sharma, N. K. Karn, V. P. S. Awana
Summary: This review systematically studies recent advances in topological superconductivity, including both bulk systems and heterostructures. The relationship between Majorana fermions and topological superconductors and heterostructures is described, along with key experimental techniques for characterizing candidates for topological superconductivity. The potential materials that may demonstrate topological superconductivity are summarized, as well as the effects of pressure and muon spin rotation studies.
SUPERCONDUCTOR SCIENCE & TECHNOLOGY
(2022)
Article
Physics, Multidisciplinary
Aniceto B. Maghirang, Gennevieve Macam, Ali Sufyan, Zhi-Quan Huang, Chia-Hsiu Hsu, Feng-Chuan Chuang
Summary: This study systematically investigates the properties of M2C (M = Mo or W) with different surface functionalizations in 1T and 2H structures using first-principles and hybrid functional calculations. The results show that M2CO2 can be used as size-controllable 2D topological insulators, which have promising potential applications.
CHINESE JOURNAL OF PHYSICS
(2022)
Article
Multidisciplinary Sciences
Fabian R. Geisenhof, Felix Winterer, Anna M. Seiler, Jakob Lenz, Ivar Martin, R. Thomas Weitz
Summary: In electrostatically-gapped bilayer graphene, topologically protected states can emerge at stacking domain walls even without a magnetic field. This study focuses on the interplay between these domain wall states and quantum Hall edge transport, finding that low magnetic fields maintain a constant conductance while high magnetic fields exhibit transport suppression.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
A. V. Kapranov, R. S. Akzyanov, A. L. Rakhmanov
Summary: We study different types of vortices in a topological superconductor with nematic superconductivity in the Eu representation, including the Abrikosov vortex associated with vorticity in the particle-hole space and the spin vortex associated with vorticity in the spin space. By deriving the free energy using the Ginzburg-Landau approach, we calculate the critical strain at which the spin vortex is formed and show that the spin vortex and the Abrikosov vortex attract each other, resulting in a common core. We also apply Bogoliubov-de Gennes equations to study electronic states in a combined vortex structure and find no zero-energy states localized near the common vortex core of any type of vortex.
Article
Chemistry, Multidisciplinary
Peng Li, Jinjun Ding, Steven S-L Zhang, James Kally, Timothy Pillsbury, Olle G. Heinonen, Gaurab Rimal, Chong Bi, August DeMann, Stuart B. Field, Weigang Wang, Jinke Tang, Jidong Samuel Jiang, Axel Hoffmann, Nitin Samarth, Mingzhong Wu
Summary: This study reports a genuine topological Hall effect in a TI/MI structure, where the contribution of skyrmions to the Hall effect outweighs the coexistence of magnetic phases.
Article
Engineering, Mechanical
Keita Funayama, Kenichi Yatsugi, Atsushi Miura, Hideo Iizuka
Summary: In this study, the tunability of coupling phenomena between topological waveguides was experimentally investigated using MEMS technology. Wide and fine tuning of the coupling strength was achieved by adjusting the distance between waveguides and the localization length. This is crucial for large-scale integrated topological circuits and systems.
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
(2022)
Article
Physics, Multidisciplinary
Ruochen Ma, Chong Wang
Summary: In this study, we demonstrate that symmetry-protected topological (SPT) phases can also be applied to average symmetries, where local quenched disorders break the symmetries but restore them upon disorder averaging. We classify and characterize a large class of average SPT phases using a decorated domain wall approach, and show that the boundary states of such phases will almost certainly be long-range entangled. We also develop a theory for generalized average SPT phases based on density matrices and quantum channels, indicating that topological quantum phenomena associated with average symmetries can be as rich as those with exact symmetries.
Article
Multidisciplinary Sciences
Qinghua Guo, Tianshu Jiang, Ruo-Yang Zhang, Lei Zhang, Zhao-Qing Zhang, Biao Yang, Shuang Zhang, C. T. Chan
Summary: Experimental observation of non-Abelian topological charges and edge states in a PT-symmetric transmission line network, along with the discovery of a non-Abelian quotient relation for the bulk-edge correspondence. This new topological property opens up possibilities for intriguing observable phenomena in the field of material science.
Article
Physics, Multidisciplinary
Y. X. Zhao, Cong Chen, Xian-Lei Sheng, Shengyuan A. Yang
Summary: The study reveals the possibility of switching the two fundamental classes via Z(2) projective representations, allowing for unique topological phases to be achieved in different classes. For PT symmetry, the occurrence of this switching mechanism is demonstrated when P inverses the gauge transformation required to recover the original Z(2) gauge connections under P.
PHYSICAL REVIEW LETTERS
(2021)
Article
Physics, Multidisciplinary
Yafei Ren, Cong Xiao, Daniyar Saparov, Qian Niu
Summary: The study investigates the adiabatic evolution of electronic states induced by the lattice vibration of a chiral phonon, obtaining electronic orbital magnetization in the form of a topological second Chern form. The traditional theory needs refinement by introducing a k-resolved Born effective charge and accounting for the phonon-modified electronic energy and momentum-space Berry curvature contribution. The second Chern form may diverge when a Yang's monopole is near the parameter space of interest, as demonstrated in a gapped graphene model at the Brillouin zone corner.
PHYSICAL REVIEW LETTERS
(2021)
Article
Materials Science, Multidisciplinary
Wei Chen
Summary: We propose a universal topological marker that can map the topological order to lattice sites for topological insulators and superconductors with Dirac models in any dimension and symmetry class. By introducing a topological operator derived from a momentum-space universal topological invariant, we construct the topological marker by alternating projectors, position operators, and Dirac matrices. The off-diagonal elements of the topological operator yield a non-local topological marker, representing a Wannier state correlation function, which decays with a diverging correlation length at topological phase transitions. Various prototype examples are employed to demonstrate the universality of our formalism.
Article
Chemistry, Multidisciplinary
Subhajit Roychowdhury, Kartik Samanta, Premakumar Yanda, Bernard Malaman, Mengyu Yao, Walter Schnelle, Emmanuel Guilmeau, Procopios Constantinou, Sushmita Chandra, Horst Borrmann, Maia G. G. Vergniory, Vladimir Strocov, Chandra Shekhar, Claudia Felser
Summary: Magnetic interactions and nontrivial band structures can lead to exotic physical properties such as the anomalous Hall effect and topological Hall effect. EuCuAs, an antiferromagnetic material, exhibits a large topological Hall resistivity due to nontrivial spin structures. Neutron diffraction experiments reveal that the spin configuration during the metamagnetic transition results in the large topological Hall effect. The ability to control the magnetic ordering structure of EuCuAs opens up possibilities for spintronic devices based on antiferromagnets.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2023)
Article
Physics, Multidisciplinary
Ari M. Turner, Erez Berg, Ady Stern
Summary: In this study, the stability of fragile topological bands protected by space-time inversion symmetry under strong electron-electron interactions is investigated. It is found that when these fragile bands are half filled, interactions can open a gap in the many-body spectrum without breaking any symmetry or mixing degrees of freedom from remote bands. The resulting ground state is not topologically ordered. The formation of fermionic bound states known as trions is crucial for this result, which may be relevant to recent experiments in magic angle twisted bilayer graphene at charge neutrality.
PHYSICAL REVIEW LETTERS
(2022)
Article
Materials Science, Multidisciplinary
Run Xiao, Jacob T. Held, Jeffrey Rable, Supriya Ghosh, Ke Wang, K. Andre Mkhoyan, Nitin Samarth
Summary: Magnetic doping of topological quantum materials provides an attractive method for studying the effects of time reversal symmetry breaking. The introduction of transition metal Mn into Cd3As2 films shows the formation of a Mn-rich phase at the top surface, indicating that Mn acts as a surfactant during epitaxial growth of Cd3As2.
PHYSICAL REVIEW MATERIALS
(2022)
Article
Physics, Multidisciplinary
Yi-Fan Zhao, Ruoxi Zhang, Ling-Jie Zhou, Ruobing Mei, Zi-Jie Yan, Moses H. W. Chan, Chao-Xing Liu, Cui-Zu Chan
Summary: The plateau-to-plateau transition in the quantum Hall effect is a quantum phase transition between two topological states. Recent advancements in the development of quantum anomalous Hall (QAH) insulators have allowed for the study of this transition under zero magnetic field. By synthesizing magnetic topological insulator (TI)/TI pentalayer heterostructures, the researchers observed a potential plateau phase transition between C = 1 and C = 2 QAH states.
PHYSICAL REVIEW LETTERS
(2022)
Article
Multidisciplinary Sciences
Jiaqi Cai, Dmitry Ovchinnikov, Zaiyao Fei, Minhao He, Tiancheng Song, Zhong Lin, Chong Wang, David Cobden, Jiun-Haw Chu, Yong-Tao Cui, Cui-Zu Chang, Di Xiao, Jiaqiang Yan, Xiaodong Xu
Summary: The authors realize a canted-antiferromagnetic Chern insulator in atomically-thin MnBi2Te4 with electrical control of chiral-edge state transport.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Physical
Hemian Yi, Lun-Hui Hu, Yuanxi Wang, Run Xiao, Jiaqi Cai, Danielle Reifsnyder Hickey, Chengye Dong, Yi-Fan Zhao, Ling-Jie Zhou, Ruoxi Zhang, Anthony R. Richardella, Nasim Alem, Joshua A. Robinson, Moses H. W. Chan, Xiaodong Xu, Nitin Samarth, Chao-Xing Liu, Cui-Zu Chang
Summary: The change in film thickness of Bi2Se3 can induce a transition from Ising to Rashba-type superconducting pairings, providing a new approach for studying topological superconductivity.
Article
Multidisciplinary Sciences
Dmitry Ovchinnikov, Jiaqi Cai, Zhong Lin, Zaiyao Fei, Zhaoyu Liu, Yong-Tao Cui, David H. Cobden, Jiun-Haw Chu, Cui-Zu Chang, Di Xiao, Jiaqiang Yan, Xiaodong Xu
Summary: The authors of this study have created Chern insulator junctions between domains with different Chern numbers in MnBi2Te4, enabling the basic operation of a topological circuit. By controlling the Chern numbers of the individual domains, the chiral edge current can be split, rerouted, or switched off, offering potential applications in energy-efficient information transmission.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Applied
Wilson Yanez, Yongxi Ou, Run Xiao, Supriya Ghosh, Jyotirmay Dwivedi, Emma Steinebronn, Anthony Richardella, K. Andre Mkhoyan, Nitin Samarth
Summary: This study reports on the measurement of efficient charge-to-spin conversion at room temperature in Weyl semimetal-ferromagnet heterostructures with both oxidized and pristine interfaces, and compares the impact of these two different interfaces.
PHYSICAL REVIEW APPLIED
(2022)
Article
Chemistry, Multidisciplinary
Han Tay, Yi-Fan Zhao, Ling-Jie Zhou, Ruoxi Zhang, Zi-Jie Yan, Deyi Zhuo, Moses H. W. Chan, Cui-Zu Chang
Summary: The quantum anomalous Hall (QAH) insulator, which carries dissipation-free chiral edge current, has the potential for energy-efficient transformative information technology. However, practical applications of QAH insulators have been elusive due to their low working temperature and degradation in ambient conditions. In this study, we investigated the degradation of QAH devices stored in different environments and found that the use of a protective layer or an argon glovebox can minimize degradation and preserve the stable QAH properties. Our findings provide a route towards preserving the dissipation-free chiral edge state for potential applications in quantum information technology.
Article
Physics, Applied
Jeffrey Rable, Benjamin Piazza, Jyotirmay Dwivedi, Nitin Samarth
Summary: Nitrogen-vacancy centers in diamond have been proven effective in sensing the magnetization dynamics in nearby ferromagnetic materials. Researchers have demonstrated high placement accuracy of nitrogen-vacancy-containing nanodiamonds and used them as local sensors to detect optically detected ferromagnetic resonance in mesoscopically patterned Permalloy islands. The measurements revealed variations in the ferromagnetic resonance signal at different sites, showing distinct behavior at the edge and bulk of the patterned features.
PHYSICAL REVIEW APPLIED
(2022)
Article
Chemistry, Multidisciplinary
Run Xiao, Saurav Islam, Wilson Yanez, Yongxi Ou, Haiwen Liu, Xincheng Xie, Juan Chamorro, Tyrel M. McQueen, Nitin Samarth
Summary: Time-reversal invariance and inversion symmetry are responsible for the topological band structure in Dirac semimetals. Applying an external magnetic or electric field can break these symmetries and cause fundamental changes to the ground state Hamiltonian and a topological phase transition. We use universal conductance fluctuations in Cd3As2 to probe these changes. The magnitude of the fluctuations decreases with increasing magnetic field, consistent with the effect of broken time-reversal invariance. However, the magnitude increases monotonically when the chemical potential is gated away from the charge neutrality point, attributed to Fermi surface anisotropy rather than broken inversion symmetry. The agreement between experimental data and theory provides unequivocal evidence that universal conductance fluctuations are the dominant source of fluctuations and offers a general methodology for probing broken-symmetry effects in topological quantum materials.
Article
Chemistry, Multidisciplinary
Fei Wang, Yi-Fan Zhao, Zi-Jie Yan, Deyi Zhuo, Hemian Yi, Wei Yuan, Lingjie Zhou, Weiwei Zhao, Moses H. W. Chan, Cui-Zu Chang
Summary: In this study, we synthesized doped Bi2Te3 thin films with controlled doping concentrations using molecular beam epitaxy. By conducting magneto-transport measurements, we observed an unusual ferromagnetic response in both chromium (Cr)- and vanadium (V)-doped films, where the Curie temperature shows a local maximum at a critical doping concentration. We attribute this behavior to the dopant-concentration-induced magnetic exchange interaction, which transforms the ferromagnetism from van Vleck-type in a nontrivial magnetic topological insulator to Ruderman-Kittel-Kasuya-Yosida (RKKY)-type in a trivial diluted magnetic semiconductor. This work provides insights into the ferromagnetic properties of magnetically doped topological insulator thin films and facilitates the exploration of high-temperature quantum anomalous Hall effect.
Article
Materials Science, Multidisciplinary
Fan Zhang, Asmaul Smitha Rashid, Mostafa Tanhayi Ahari, Wei Zhang, Krishnan Mekkanamkulam Ananthanarayanan, Run Xiao, George J. de Coster, Matthew J. Gilbert, Nitin Samarth, Morteza Kayyalha
Summary: There is a growing interest in using multiterminal Josephson junctions to emulate topological phases and investigate superconducting mechanisms. However, the interpretation of experimental signatures in MTJJs has been conflicting. In this study, graphene-based four-terminal Josephson junctions were investigated experimentally and theoretically. Resonant features in the differential resistance maps were observed and successfully reproduced using a circuit network model. The study suggests that differential resistance measurements alone cannot distinguish resonant Andreev reflection processes from semiclassical circuit-network effects.
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
Materials Science, Multidisciplinary
Run Xiao, Junyi Zhang, Juan Chamorro, Jinwoong Kim, Tyrel M. McQueen, David Vanderbilt, Morteza Kayyalha, Yi Li, Nitin Samarth
Summary: We investigated the integer quantum Hall effect in Cd3As2 thin films with strong to moderate quantum confinement. We observed the effect not only in the spin-polarized lowest Landau level (filling factor v = 1), but also in the spin-degenerate higher index Landau levels with even filling factors (v = 2, 4, 6). As the quantum confinement increased, we also observed a lifting of the Landau-level spin degeneracy at v = 3, which manifested as an anomaly in the longitudinal and Hall resistivities.
Article
Physics, Multidisciplinary
Jue Jiang, Weiwei Zhao, Fei Wang, Renzhong Du, Ludi Miao, Ke Wang, Qi Li, Cui-Zu Chang, Moses H. W. Chan
Summary: When a ferromagnet is in contact with a superconductor, the Cooper pairs from the superconductor cannot survive inside the ferromagnet. However, when a copper oxide buffer layer is inserted between the electrodes, the proximity range of superconductivity is significantly increased. The buffer layer facilitates the conversion of singlet superconductivity into triplet supercurrent.
PHYSICAL REVIEW RESEARCH
(2022)
