scholarly journals Random-Gate-Voltage Induced Al’tshuler–Aronov–Spivak Effect in Topological Edge States

2021 ◽  
Vol 38 (11) ◽  
pp. 110302
Author(s):  
Kun Luo ◽  
Wei Chen ◽  
Li Sheng ◽  
D. Y. Xing
Keyword(s):  
Gate Voltage ◽  
Berry Phase ◽  
Weak Localization ◽  
Quantum Spin ◽  
Edge States ◽  
Weak Antilocalization ◽  
Return Probability ◽  
Spin Texture ◽  
Aharonov Bohm ◽  
Fine Adjustment

Helical edge states are the hallmark of the quantum spin Hall insulator. Recently, several experiments have observed transport signatures contributed by trivial edge states, making it difficult to distinguish between the topologically trivial and nontrivial phases. Here, we show that helical edge states can be identified by the random-gate-voltage induced Φ 0/2-period oscillation of the averaged electron return probability in the interferometer constructed by the edge states. The random gate voltage can highlight the Φ 0/2-period Al’tshuler–Aronov–Spivak oscillation proportional to sin2(2πΦ/Φ 0) by quenching theΦ 0-period Aharonov–Bohm oscillation. It is found that the helical spin texture induced π Berry phase is key to such weak antilocalization behavior with zero return probability at Φ = 0. In contrast, the oscillation for the trivial edge states may exhibit either weak localization or antilocalization depending on the strength of the spin-orbit coupling, which has finite return probability at Φ = 0. Our results provide an effective way for the identification of the helical edge states. The predicted signature is stabilized by the time-reversal symmetry so that it is robust against disorder and does not require any fine adjustment of system.

scholarly journals πSpin Berry Phase in a Quantum-Spin-Hall-Insulator-Based Interferometer: Evidence for the Helical Spin Texture of the Edge States

2016 ◽  
Vol 117 (7) ◽  
Author(s):  
Wei Chen ◽  
Wei-Yin Deng ◽  
Jing-Min Hou ◽  
D. N. Shi ◽  
L. Sheng ◽  
...  
Keyword(s):  
Berry Phase ◽  
Quantum Spin ◽  
Edge States ◽  
Spin Texture ◽  
Quantum Spin Hall

scholarly journals Imaging quantum spin Hall edges in monolayer WTe2

2019 ◽  
Vol 5 (2) ◽  
pp. eaat8799 ◽  
Author(s):  
Yanmeng Shi ◽  
Joshua Kahn ◽  
Ben Niu ◽  
Zaiyao Fei ◽  
Bosong Sun ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Topological Insulator ◽  
Gate Voltage ◽  
Quantum Spin ◽  
Two Dimensional ◽  
Edge States ◽  
Local Conductivity ◽  
Quantum Spin Hall

A two-dimensional (2D) topological insulator exhibits the quantum spin Hall (QSH) effect, in which topologically protected conducting channels exist at the sample edges. Experimental signatures of the QSH effect have recently been reported in an atomically thin material, monolayer WTe2. Here, we directly image the local conductivity of monolayer WTe2 using microwave impedance microscopy, establishing beyond doubt that conduction is indeed strongly localized to the physical edges at temperatures up to 77 K and above. The edge conductivity shows no gap as a function of gate voltage, and is suppressed by magnetic field as expected. We observe additional conducting features which can be explained by edge states following boundaries between topologically trivial and nontrivial regions. These observations will be critical for interpreting and improving the properties of devices incorporating WTe2. Meanwhile, they reveal the robustness of the QSH channels and the potential to engineer them in the monolayer material platform.

scholarly journals Entanglement signatures of emergent Dirac fermions: Kagome spin liquid and quantum criticality

2018 ◽  
Vol 4 (11) ◽  
pp. eaat5535 ◽  
Author(s):  
Wei Zhu ◽  
Xiao Chen ◽  
Yin-Chen He ◽  
William Witczak-Krempa
Keyword(s):  
Entanglement Entropy ◽  
Quantum Critical Point ◽  
Quantum Spin ◽  
Spin Liquid ◽  
Dirac Fermions ◽  
Spin Liquids ◽  
Density Matrix Renormalization ◽  
Dirac Semimetal ◽  
A Charge ◽  
Aharonov Bohm

Quantum spin liquids (QSLs) are exotic phases of matter that host fractionalized excitations. It is difficult for local probes to characterize QSL, whereas quantum entanglement can serve as a powerful diagnostic tool due to its nonlocality. The kagome antiferromagnetic Heisenberg model is one of the most studied and experimentally relevant models for QSL, but its solution remains under debate. Here, we perform a numerical Aharonov-Bohm experiment on this model and uncover universal features of the entanglement entropy. By means of the density matrix renormalization group, we reveal the entanglement signatures of emergent Dirac spinons, which are the fractionalized excitations of the QSL. This scheme provides qualitative insights into the nature of kagome QSL and can be used to study other quantum states of matter. As a concrete example, we also benchmark our methods on an interacting quantum critical point between a Dirac semimetal and a charge-ordered phase.

scholarly journals Giant magnetic field from moiré induced Berry phase in homobilayer semiconductors

2019 ◽  
Vol 7 (1) ◽  
pp. 12-20 ◽  
Author(s):  
Hongyi Yu ◽  
Mingxing Chen ◽  
Wang Yao
Keyword(s):  
Magnetic Field ◽  
Berry Phase ◽  
Transition Metal Dichalcogenides ◽  
Real Space ◽  
Quantum Spin ◽  
Moire Patterns ◽  
Metal Dichalcogenides ◽  
Berry Phases ◽  
Different Origins ◽  
Moiré Patterns

Abstract When quasiparticles move in condensed matters, the texture of their internal quantum structure as a function of position and momentum can give rise to Berry phases that have profound effects on the material’s properties. Seminal examples include the anomalous Hall and spin Hall effects from the momentum-space Berry phases in homogeneous crystals. Here, we explore a conjugate form of the electron Berry phase arising from the moiré pattern: the texture of atomic configurations in real space. In homobilayer transition metal dichalcogenides, we show that the real-space Berry phase from moiré patterns manifests as a periodic magnetic field with magnitudes of up to hundreds of Tesla. This quantity distinguishes moiré patterns from different origins, which can have an identical potential landscape, but opposite quantized magnetic flux per supercell. For low-energy carriers, the homobilayer moirés realize topological flux lattices for the quantum-spin Hall effect. An interlayer bias can continuously tune the spatial profile of the moiré magnetic field, whereas the flux per supercell is a topological quantity that can only have a quantized jump observable at a moderate bias. We also reveal the important role of the non-Abelian Berry phase in shaping the energy landscape in small moiré patterns. Our work points to new possibilities to access ultra-high magnetic fields that can be tailored to the nanoscale by electrical and mechanical controls.

scholarly journals Testing topological protection of edge states in hexagonal quantum spin Hall candidate materials

2018 ◽  
Vol 98 (16) ◽  
Author(s):  
Fernando Dominguez ◽  
Benedikt Scharf ◽  
Gang Li ◽  
Jörg Schäfer ◽  
Ralph Claessen ◽  
...  
Keyword(s):  
Quantum Spin ◽  
Edge States ◽  
Quantum Spin Hall

scholarly journals Tunneling Aharonov-Bohm interferometer on helical edge states

2018 ◽  
Vol 98 (4) ◽  
Author(s):  
R. A. Niyazov ◽  
D. N. Aristov ◽  
V. Yu. Kachorovskii
Keyword(s):  
Edge States ◽  
Aharonov Bohm

scholarly journals Quantum Structured Light: Non-classical Spin Texture of Twisted Single-photon Pulses

2021 ◽  
Author(s):  
Li-Ping Yang ◽  
Zubin Jacob
Keyword(s):  
Spin Density ◽  
Electromagnetic Waves ◽  
Single Photon ◽  
Structured Light ◽  
Three Dimensional ◽  
Quantum Spin ◽  
Single Photons ◽  
Spin Order ◽  
Spin Noise ◽  
Spin Texture

Abstract Classical structured light with controlled polarization and orbital angular momentum (OAM) of electromagnetic waves has varied applications in optical trapping, bio-sensing, optical communications and quantum simulations. The classical electromagnetic theory of such structured light beams and pulses have advanced significantly over the last two decades. However, a framework for the quantum density of spin and OAM for single-photons remains elusive. Here, we develop a theoretical framework and put forth the concept of quantum structured light for space-time wavepackets at the single-photon level. Our work marks a paradigm shift beyond scalar-field theory as well as the paraxial approximation and can be utilized to study the quantum properties of the spin and OAM of all classes of twisted quantum light pulses. We capture the uncertainty in full three-dimensional (3D) projections of vector spin demonstrating their quantum behavior beyond the conventional concept of classical polarization. Even in laser beams with high OAM along the propagation direction, we predict the existence of large OAM quantum fluctuations in the transverse plane which can be verified experimentally. We show that the spin density generates modulated helical texture beyond the paraxial limit and exhibits distinct statistics for Fock-state vs. coherent-state twisted pulses. We introduce the quantum correlator of photon spin density to characterize the nonlocal spin noise providing a rigorous parallel with fermionic spin noise operators. Our work paves the way for quantum spin-OAM physics in twisted single photon pulses and also opens explorations for new phases of light with long-range spin order.

scholarly journals Skyrmions in Multiferroic Insulator

2014 ◽  
Vol 70 (a1) ◽  
pp. C1547-C1547
Author(s):  
Shinichiro Seki
Keyword(s):  
Present Finding ◽  
Berry Phase ◽  
High Energy ◽  
Electric Polarization ◽  
Orbit Interaction ◽  
Nanometer Scale ◽  
Metallic Materials ◽  
Device Applications ◽  
High Energy Efficiency ◽  
Spin Texture

Magnetic skyrmion is a topologically stable particle-like object, which appears as nanometer-scale vortex-like spin texture in a chiral-lattice magnet [1]. In metallic materials (MnSi, FeGe, Fe1-xCoxSi etc), electrons moving through skyrmion spin texture gain a nontrivial quantum Berry phase, which provides topological force to the underlying spin texture and enables the current-induced manipulation of magnetic skyrmion [2]. Such electric controllability, in addition to the particle-like nature, is a promising advantage for potential spintronic device applications. Recently, we newly discovered that skyrmions appear also in an insulating chiral-lattice magnet Cu2OSeO3 [3]. We find that the skyrmions in insulator can magnetically induce electric polarization through the relativistic spin-orbit interaction, which implies possible manipulation of the skyrmion by external electric field without loss of joule heating. The present finding of multiferroic skyrmion may pave a new route toward the engineering of novel magnetoelectric devices with high energy efficiency. In this talk, our recent attempts to drive skyrmions by external field are also introduced.

scholarly journals Квантовая когерентность и эффект Кондо в двумерном электронном газе магнитно-нелегированных гетероструктур AlGaN/GaN

2020 ◽  
Vol 54 (9) ◽  
pp. 962
Author(s):  
Н.К. Чумаков ◽  
И.А. Черных ◽  
A.Б. Давыдов ◽  
И.С. Езубченко ◽  
Ю.В. Грищенко ◽  
...  
Keyword(s):  
Kondo Effect ◽  
Electron Gas ◽  
Weak Localization ◽  
Zero Field ◽  
Dimensional Electron ◽  
Weak Antilocalization ◽  
Temperature Dependent ◽  
Localization Theory ◽  
Magnetic Transport ◽  
Dimensional Electron Gas

Abstract The unusual observation of the Kondo effect in the two-dimensional electron gas (2DEG) of magnetically undoped AlGaN/GaN heterostructures is reported. The temperature-dependent zero-field resistivity data exhibits an upturn below 120 K, while the standard low-temperature weak localization and then weak antilocalization behaviour is revealed at T → 0. Magnetic transport investigations of the system are performed in the temperature range of 0.1–300 K and at magnetic fields up to 8 T, applied perpendicularly to the 2DEG plane. The experimental data are analyzed in terms of the multichannel Kondo model for d _0 magnetic materials and weak localization theory taking into account the spin-orbit interaction.

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