scholarly journals Observation and control of the weak topological insulator state in ZrTe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Peng Zhang ◽  
Ryo Noguchi ◽  
Kenta Kuroda ◽  
Chun Lin ◽  
Kaishu Kawaguchi ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Spin Current ◽  
Side Surface ◽  
Quantum Spin ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Dirac Semimetal ◽  
Topological States ◽  
The One ◽  
And Control

AbstractA quantum spin Hall (QSH) insulator hosts topological states at the one-dimensional (1D) edge, along which backscattering by nonmagnetic impurities is strictly prohibited. Its 3D analogue, a weak topological insulator (WTI), possesses similar quasi-1D topological states confined at side surfaces. The enhanced confinement could provide a route for dissipationless current and better advantages for applications relative to strong topological insulators (STIs). However, the topological side surface is usually not cleavable and is thus hard to observe. Here, we visualize the topological states of the WTI candidate ZrTe5 by spin and angle-resolved photoemission spectroscopy (ARPES): a quasi-1D band with spin-momentum locking was revealed on the side surface. We further demonstrate that the bulk band gap is controlled by external strain, realizing a more stable WTI state or an ideal Dirac semimetal (DS) state. The highly directional spin-current and the tunable band gap in ZrTe5 will provide an excellent platform for applications.

scholarly journals Symmetry-protected hierarchy of anomalous multipole topological band gaps in nonsymmorphic metacrystals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Xiujuan Zhang ◽  
Zhi-Kang Lin ◽  
Hai-Xiao Wang ◽  
Zhan Xiong ◽  
Yuan Tian ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological States Of Matter ◽  
Quantum Spin ◽  
Band Gaps ◽  
Quantum Spin Hall Effect ◽  
Classical Systems ◽  
Topological Materials ◽  
And Topology ◽  
Topological States ◽  
Symmetry Protected

AbstractSymmetry and topology are two fundamental aspects of many quantum states of matter. Recently new topological materials, higher-order topological insulators, were discovered, featuring bulk–edge–corner correspondence that goes beyond the conventional topological paradigms. Here we discover experimentally that the nonsymmorphic p4g acoustic metacrystals host a symmetry-protected hierarchy of topological multipoles: the lowest band gap has a quantized Wannier dipole and can mimic the quantum spin Hall effect, whereas the second band gap exhibits quadrupole topology with anomalous Wannier bands. Such a topological hierarchy allows us to observe experimentally distinct, multiplexed topological phenomena and to reveal a topological transition triggered by the geometry transition from the p4g group to the C4v group, which demonstrates elegantly the fundamental interplay between symmetry and topology. Our study demonstrates that classical systems with controllable geometry can serve as powerful simulators for the discovery of novel topological states of matter and their phase transitions.

scholarly journals Generation of Spin Currents by Magnetic Field in 𝒯- and 𝒫-Broken Materials

SPIN ◽  
2019 ◽  
Vol 09 (04) ◽  
pp. 1940013 ◽  
Author(s):  
Jing Wang ◽  
Biao Lian ◽  
Shou-Cheng Zhang
Keyword(s):  
Magnetic Field ◽  
Spin Current ◽  
Quantum Spin ◽  
Pure Spin ◽  
Heusler Compounds ◽  
Spin Currents ◽  
Dirac Semimetal ◽  
Low Energy Consumption ◽  
And Inversion ◽  
The Magnetic Field

Pure spin currents carry information in quantum spintronics and could play an essential role in the next generation low-energy-consumption electronics. Here, we theoretically predict that the magnetic field can induce a quantum spin current without a concomitant charge current in metals without time reversal symmetry [Formula: see text] and inversion symmetry [Formula: see text] but respect the combined [Formula: see text] symmetry. It is governed by the magnetic moment of the Bloch states on the Fermi surface, and can be regarded as a spinful generalization of the gyrotropic magnetic effect in [Formula: see text]-broken metals. The effect is explicitly studied for a minimal model of an antiferromagnetic Dirac semimetal, where the experimental signature is proposed. We further propose candidate materials, including topological antiferromagnetic Dirac semimetals, Weyl semimetals and tenary Heusler compounds.

scholarly journals Topological phases in pyrochlore thallium niobate Tl2Nb2O6+x

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Wei Zhang ◽  
Kaifa Luo ◽  
Zhendong Chen ◽  
Ziming Zhu ◽  
Rui Yu ◽  
...  
Keyword(s):  
Solid Solution ◽  
Phase Transitions ◽  
Topological Insulator ◽  
Continuous Solid Solution ◽  
Nodal Point ◽  
New Physics ◽  
Topological Phase ◽  
Dirac Semimetal ◽  
Topological States ◽  
Topological Phase Transitions

Abstract The discovery of new topological electronic materials brings a chance to uncover new physics. Up to now, many materials have been theoretically proposed and experimentally proved to host different kinds of topological states. Unfortunately, there is little convincing experimental evidence for the existence of topological oxides. The reason is that oxidation of oxygen leads to ionic crystal in general and makes band inversion unlikely. In addition, the realization of different topological states in a single material is quite difficult, but strongly needed for exploring topological phase transitions. In this work, using first-principles calculations and symmetry analysis, we propose that the experimentally tunable continuous solid solution of oxygen in pyrochlore Tl2Nb2O6+x (0 ≤ x ≤ 1.0) leads to various topological states. Topological insulator, Dirac semimetal, and triply degenerate nodal point semimetal can be realized in it via changing the oxygen content and/or tuning the crystalline symmetries. When x = 1, it is a semimetal with quadratic band touching point at Fermi level. It transits into a Dirac semimetal or a topological insulator depending on the in-plane strain. When x = 0.5, the inversion symmetry is spontaneously broken in Tl2Nb2O6.5, leading to triply degenerate nodal points. When x = 0, Tl2Nb2O6 becomes a trivial insulator with a narrow band gap. These topological phase transitions driven by solid solution of oxygen are unique and physically plausible due to the variation of valence state of Tl+ and Tl3+. This topological oxide will be promising for studying correlation induced topological states and potential applications.

scholarly journals Manipulation of Topological States and the Bulk Band Gap Using Natural Heterostructures of a Topological Insulator

2012 ◽  
Vol 109 (23) ◽  
Author(s):  
K. Nakayama ◽  
K. Eto ◽  
Y. Tanaka ◽  
T. Sato ◽  
S. Souma ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Topological States ◽  
Bulk Band

Surfing the Quantum World

2017 ◽  
Author(s):  
Frank S. Levin
Keyword(s):  
Quantum Mechanics ◽  
Quantum Theory ◽  
Musical Instrument ◽  
Popular Science ◽  
Quantum Spin ◽  
Exclusion Principle ◽  
Maximum Height ◽  
Core Concepts ◽  
The Many ◽  
The One

Surfing the Quantum World bridges the gap between in-depth textbooks and typical popular science books on quantum ideas and phenomena. Among its significant features is the description of a host of mind-bending phenomena, such as a quantum object being in two places at once or a certain minus sign being the most consequential in the universe. Much of its first part is historical, starting with the ancient Greeks and their concepts of light, and ending with the creation of quantum mechanics. The second part begins by applying quantum mechanics and its probability nature to a pedagogical system, the one-dimensional box, an analog of which is a musical-instrument string. This is followed by a gentle introduction to the fundamental principles of quantum theory, whose core concepts and symbolic representations are the foundation for most of the subsequent chapters. For instance, it is shown how quantum theory explains the properties of the hydrogen atom and, via quantum spin and Pauli’s Exclusion Principle, how it accounts for the structure of the periodic table. White dwarf and neutron stars are seen to be gigantic quantum objects, while the maximum height of mountains is shown to have a quantum basis. Among the many other topics considered are a variety of interference phenomena, those that display the wave properties of particles like electrons and photons, and even of large molecules. The book concludes with a wide-ranging discussion of interpretational and philosophic issues, introduced in Chapters 14 by entanglement and 15 by Schrödinger’s cat.

An LQ Approach to Active Control of Vibrations in Helicopters

1996 ◽  
Vol 118 (3) ◽  
pp. 482-488 ◽  
Author(s):  
Sergio Bittanti ◽  
Fabrizio Lorito ◽  
Silvia Strada
Keyword(s):  
Optimal Control ◽  
Active Control ◽  
Linear Quadratic ◽  
Control Effort ◽  
Vibration Effect ◽  
Suitable Definition ◽  
Lq Optimal Control ◽  
The One ◽  
Definition Of ◽  
And Control

In this paper, Linear Quadratic (LQ) optimal control concepts are applied for the active control of vibrations in helicopters. The study is based on an identified dynamic model of the rotor. The vibration effect is captured by suitably augmenting the state vector of the rotor model. Then, Kalman filtering concepts can be used to obtain a real-time estimate of the vibration, which is then fed back to form a suitable compensation signal. This design rationale is derived here starting from a rigorous problem position in an optimal control context. Among other things, this calls for a suitable definition of the performance index, of nonstandard type. The application of these ideas to a test helicopter, by means of computer simulations, shows good performances both in terms of disturbance rejection effectiveness and control effort limitation. The performance of the obtained controller is compared with the one achievable by the so called Higher Harmonic Control (HHC) approach, well known within the helicopter community.

scholarly journals Structural comparison of CD163 SRCR5 from different species sheds some light on its involvement in porcine reproductive and respiratory syndrome virus-2 infection in vitro

2021 ◽  
Vol 52 (1) ◽  
Author(s):  
Hongfang Ma ◽  
Rui Li ◽  
Longguang Jiang ◽  
Songlin Qiao ◽  
Xin-xin Chen ◽  
...  
Keyword(s):  
Scavenger Receptor ◽  
Host Cells ◽  
Respiratory Syndrome Virus ◽  
Swine Industry ◽  
Prrs Virus ◽  
Rich Domain ◽  
Serious Disease ◽  
The One ◽  
And Control

AbstractPorcine reproductive and respiratory syndrome (PRRS) is a serious disease burdening global swine industry. Infection by its etiological agent, PRRS virus (PRRSV), shows a highly restricted tropism of host cells and has been demonstrated to be mediated by an essential scavenger receptor (SR) CD163. CD163 fifth SR cysteine-rich domain (SRCR5) is further proven to play a crucial role during viral infection. Despite intense research, the involvement of CD163 SRCR5 in PRRSV infection remains to be elucidated. In the current study, we prepared recombinant monkey CD163 (moCD163) SRCR5 and human CD163-like homolog (hCD163L1) SRCR8, and determined their crystal structures. After comparison with the previously reported crystal structure of porcine CD163 (pCD163) SRCR5, these structures showed almost identical structural folds but significantly different surface electrostatic potentials. Based on these differences, we carried out mutational research to identify that the charged residue at position 534 in association with the one at position 561 were important for PRRSV-2 infection in vitro. Altogether the current work sheds some light on CD163-mediated PRRSV-2 infection and deepens our understanding of the viral pathogenesis, which will provide clues for prevention and control of PRRS.

Tolerance and Control. Developing a language policy for an EMI university in Uzbekistan

2020 ◽  
Vol 34 (1) ◽  
pp. 217-237
Author(s):  
Andrew Linn ◽  
Anastasiya Bezborodova ◽  
Saida Radjabzade
Keyword(s):  
Higher Education ◽  
Language Policy ◽  
Control Measures ◽  
The Other ◽  
Language Policies ◽  
Language Ecology ◽  
English Only ◽  
English Medium Instruction ◽  
The One ◽  
And Control

AbstractThis article presents a practical project to develop a language policy for an English-Medium-Instruction university in Uzbekistan. Although the university is de facto English-only, it presents a complex language ecology, which in turn has led to confusion and disagreement about language use on campus. The project team investigated the experience, views and attitudes of over a thousand people, including faculty, students, administrative and maintenance staff, in order to arrive at a proposed policy which would serve the whole community, based on the principle of tolerance and pragmatism. After outlining the relevant language and educational context and setting out the methods and approach of the underpinning research project, the article goes on to present the key findings. One of the striking findings was an appetite for control and regulation of language behaviours. Language policies in Higher Education invariably fall down at the implementation stage because of a lack of will to follow through on their principles and their specific guidelines. Language policy in international business on the other hand is characterised by a control stage invariably lacking in language planning in education. Uzbekistan is a polity used to control measures following from policy implementation. The article concludes by suggesting that Higher Education in Central Asia may stand a better chance of seeing through language policies around English-Medium Instruction than, for example, in northern Europe, based on the tension between tolerance on the one hand and control on the other.

scholarly journals Enhanced surface state protection and band gap in the topological insulator PbBi4Te4S3

2018 ◽  
Vol 2 (10) ◽  
Author(s):  
K. Sumida ◽  
T. Natsumeda ◽  
K. Miyamoto ◽  
I. V. Silkin ◽  
K. Kuroda ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological Insulator ◽  
Surface State ◽  
Enhanced Surface ◽  
State Protection

scholarly journals Practices of sustainability and the enactment of their natures/cultures: Ecosystem services, rights of nature, and geoengineering

2021 ◽  
pp. 053901842199894
Author(s):  
Frank Adloff ◽  
Iris Hilbrich
Keyword(s):  
Ecosystem Services ◽  
Latin American ◽  
Social Systems ◽  
The Earth ◽  
Starting Point ◽  
Knowledge Cultures ◽  
Rights Of Nature ◽  
Value Of Nature ◽  
The One ◽  
And Control

Possible trajectories of sustainability are based on different concepts of nature. The article starts out from three trajectories of sustainability (modernization, transformation and control) and reconstructs one characteristic practice for each path with its specific conceptions of nature. The notion that nature provides human societies with relevant ecosystem services is typical of the path of modernization. Nature is reified and monetarized here, with regard to its utility for human societies. Practices of transformation, in contrast, emphasize the intrinsic ethical value of nature. This becomes particularly apparent in discourses on the rights of nature, whose starting point can be found in Latin American indigenous discourses, among others. Control practices such as geoengineering are based on earth-systemic conceptions of nature, in which no distinction is made between natural and social systems. The aim is to control the earth system as a whole in order for human societies to remain viable. Practices of sustainability thus show different ontological understandings of nature (dualistic or monistic) on the one hand and (implicit) ethics and sacralizations (anthropocentric or biocentric) on the other. The three reconstructed natures/cultures have different ontological and ethical affinities and conflict with each other. They are linked to very different knowledge cultures and life-worlds, which answer very differently to the question of what is of value in a society and in nature and how these values ought to be protected.

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