- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Nuclear spin dynamics in [001] AlAs quantum well in the regime of integer and fractional quantum Hall effect
摘要： Relaxation of nuclear spins located in the vicinity of 2D electron system confined in a 16 nm [001] AlAs/AlGaAs quantum well was studied with the aid of electron spin resonance (ESR) in the regime of integer and fractional quantum Hall effect. Nuclear spin-lattice relaxation time τ was measured from the time decay of the Overhauser shift near different filling factors of the electron system. The resultant dependence of τ on filling factor turned out to be nontrivial. At the temperature 1.5 K τ reached its maximal value at the exact filling ν = 1 and decreased when ν was altered, yet this maximum vanished when the system was cooled down to 0.5 K. The fractional quantum Hall effect state at the filling of 2/3 was formed at the temperature of 0.5 K, and the development of this state was accompanied by the slowing of the nuclear spin relaxation. This observation suggests the enhancement of energy gap in the spin excitation spectrum of two-dimensional electrons at 2/3 state.
关键词： quantum wells,quantum Hall effect,spin dynamics,electron paramagnetic resonance
更新于2025-09-23 15:23:52
-
Electromagnetic and gravitational responses of photonic Landau levels
摘要： Topology has recently become a focus in condensed matter physics, arising in the context of the quantum Hall effect and topological insulators. In both of these cases, the topology of the system is defined through bulk properties (‘topological invariants’) but detected through surface properties. Here we measure three topological invariants of a quantum Hall material—photonic Landau levels in curved space—through local electromagnetic and gravitational responses of the bulk material. Viewing the material as a many-port circulator, the Chern number (a topological invariant) manifests as spatial winding of the phase of the circulator. The accumulation of particles near points of high spatial curvature and the moment of inertia of the resultant particle density distribution quantify two additional topological invariants—the mean orbital spin and the chiral central charge. We find that these invariants converge to their global values when probed over increasing length scales (several magnetic lengths), consistent with the intuition that the bulk and edges of a system are distinguishable only for sufficiently large samples (larger than roughly one magnetic length). Our experiments are enabled by applying quantum optics tools to synthetic topological matter (here twisted optical resonators). Combined with advances in Rydberg-mediated photon collisions, our work will enable precision characterization of topological matter in photon fluids.
关键词： photonic Landau levels,quantum Hall effect,chiral central charge,Chern number,mean orbital spin,topological invariants
更新于2025-09-23 15:23:52
-
High-frequency breakdown of the integer quantum Hall effect in GaAs/AlGaAs heterojunctions
摘要： The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but the behavior at higher frequencies has remained largely unexplored. Using continuous-wave terahertz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the range of 69–1100 GHz. Above 100 GHz, the quantum plateaus are strongly smeared out and replaced by weak quantum oscillations in the real part of the conductivity. The amplitude of the oscillations decreases with increasing frequency. Near 1 THz, the Hall conductivity does not reveal any features related to the filling of Landau levels. Similar oscillations are observed in the imaginary part as well; this effect has no analogy at zero frequency. This experimental picture is in disagreement with existing theoretical considerations of the high-frequency quantum Hall effect.
关键词： integer quantum Hall effect,GaAs/AlGaAs heterojunctions,terahertz spectroscopy,high-frequency Hall conductivity,quantum oscillations
更新于2025-09-23 15:22:29
-
Topological Insulator-Based van der Waals Heterostructures for Effective Control of Massless and Massive Dirac Fermions
摘要： Three dimensional (3D) topological insulators (TIs) are an important class of materials with applications in electronics, spintronics and quantum computing. With the recent development of truly bulk insulating 3D TIs, it has become possible to realize surface dominated phenomena in electrical transport measurements e.g. the quantum Hall (QH) effect of massless Dirac fermions in topological surface states (TSS). However, to realize more advanced devices and phenomena, there is a need for a platform to tune the TSS or modify them e.g. gap them by proximity with magnetic insulators, in a clean manner. Here we introduce van der Waals (vdW) heterostructures in the form of topological insulator/insulator/graphite to effectively control chemical potential of the TSS. Two types of gate dielectrics, normal insulator hexagonal boron nitride (hBN) and ferromagnetic insulator Cr2Ge2Te6 (CGT) are utilized to tune charge density of TSS in the quaternary TI BiSbTeSe2. hBN/graphite gating in the QH regime shows improved quantization of TSS by suppression of magnetoconductivity of massless Dirac fermions. CGT/graphite gating of massive Dirac fermions in the QH regime yields half-quantized Hall conductance steps and a measure of the Dirac gap. Our work shows the promise of the vdW platform in creating advanced high-quality TI-based devices.
关键词： quantum Hall effect,van der Waals heterostructures,Topological insulators,ferromagnetic insulators
更新于2025-09-23 15:21:21
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Exploring Topological Photonics in Synthetic Dimensions
摘要： In recent years, topological photonics has emerged as an exciting research ?eld in which topological concepts, originally introduced to understand the behaviour of electrons in solid-state materials, are instead exploited to design and control the behaviour of light [1]. In this direction, the development of so-called “synthetic dimensions” offers a particularly powerful approach to exploring topological photonics. The central idea of this method is to identify and couple together a set of internal degrees of freedom so as to simulate the motion of a quantum particle along an extra spatial direction [2]. In this framework, a system with D-real dimensions can be made to behave like a D + d-dimensional system, when d synthetic dimensions are added to the system. This approach, therefore, both raises the prospect of simulating exotic systems with four or more spatial dimensions, but also provides, through the external control of couplings, a straightforward way to design topological lattices in different dimensions [3]. The combination of synthetic dimensions and topological physics has lead to a very rapid expansion of re- search, starting from ultracold atomic gases [2-4] and then spreading also to photonics systems [1]. Very recently, the ?rst topological photonics model with a synthetic dimension has been realised experimentally using the spatial modes of a waveguide array by the Segev group [5], where they were able to observe the edge states associated with an effective 2D quantum Hall system.
关键词： quantum Hall effect,synthetic dimensions,photonics systems,topological photonics
更新于2025-09-23 15:19:57
-
[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - A Quantum Hall Effect Kelvin Bridge for Resistance Calibration
摘要： We describe a resistance ratio bridge suitable for calibrating a four-terminal resistor of value close to the quantum Hall resistance. The bridge includes three quantum Hall elements, wired with multiple connections. The unique properties of the quantum Hall effect provide a Kelvin-like combining network and the rejection of wiring stray resistances. The bridge has a simple schematic and does not include any adjustable element: its reading is the deviation from equilibrium, measured as a small voltage ratio. Circuit network analysis predicts that a basic implementation of the bridge can reach a calibration accuracy in the 10?8 range.
关键词： calibration,Quantum Hall effect,resistance standards,resistance bridge
更新于2025-09-23 15:19:57
-
Two-Dimensional Quantum Transport in Free-Standing InSb Nanosheets
摘要： Low-dimensional narrow band gap III?V compound semiconductors, such as InAs and InSb, have attracted much attention as one of promising platforms for studying Majorana zero modes and non-Abelian statistics relevant for topological quantum computation. So far, most of experimental studies were performed on hybrid devices based on one-dimensional semiconductor nanowires. In order to build complex topological circuits toward scalable quantum computing, exploring high-mobility two-dimensional (2D) III?V compound electron system with strong spin?orbit coupling is highly desirable. Here, we study quantum transport in high-mobility InSb nanosheet grown by molecular-beam epitaxy. The observations of Shubnikov-de Hass oscillations and quantum Hall states, together with the angular dependence of magnetotransport measurements, provide the evidence for the 2D nature of electronic states in InSb nanosheet. The presence of strong spin?orbit coupling in the InSb nanosheet is veri?ed by the low-?eld magnetotransport measurements, characterized by weak antilocalization e?ect. Finally, we demonstrate the realization of high-quality InSb nanosheet?superconductor junctions with transparent interface. Our results not only advance the study of 2D quantum transport but also open up opportunities for developing hybrid topological devices based on 2D semiconducting nanosheets with strong spin?orbit coupling.
关键词： spin?orbit interaction,quantum Hall effect,InSb nanosheet,two-dimensional transport,Josephson junction
更新于2025-09-23 15:19:57
-
van der Waals heterostructures combining graphene and hexagonal boron nitride
摘要： As the first in a large family of 2D van der Waals (vdW) materials, graphene has attracted enormous attention owing to its remarkable properties. The recent development of simple experimental techniques for combining graphene with other atomically thin vdW crystals to form heterostructures has enabled the exploration of the properties of these so-called vdW heterostructures. Hexagonal boron nitride is the second most popular vdW material after graphene, owing to the new physics and device properties of vdW heterostructures combining the two. Hexagonal boron nitride can act as a featureless dielectric substrate for graphene, enabling devices with ultralow disorder that allow access to the intrinsic physics of graphene, such as the integer and fractional quantum Hall effects. Additionally, under certain circumstances, hexagonal boron nitride can modify the optical and electronic properties of graphene in new ways, inducing the appearance of secondary Dirac points or driving new plasmonic states. Integrating other vdW materials into these heterostructures and tuning their new degrees of freedom, such as the relative rotation between crystals and their interlayer spacing, provide a path for engineering and manipulating nearly limitless new physics and device properties.
关键词： quantum Hall effect,graphene,moiré superlattices,polaritons,hexagonal boron nitride,van der Waals heterostructures
更新于2025-09-19 17:15:36
-
Optical properties of fluidic defect states in one-dimensional graphene-based photonic crystal biosensors: visible and infrared Hall regime sensing
摘要： Advances in biotechnology are outpacing studies into the use of graphene in photonic biosensors due to its peculiar optical properties and the successful progress in the nanoscale integration of photonic crystals. Moreover, going beyond the usual Dirac cone approximation for graphene introduces nonlinear effects in graphene’s optics. In this work, by the use of the transfer matrix method, we investigate the effect of hopping parameter on the chemical and biosensing performance of a 1D defective photonic biosensor with a micro/nano?uidic channel as a central defect cavity for biological ?uids and gas molecules to ?ow while interacting with two graphene sheet deposited on silicon dioxide layers of the device. As low-weight molecules absorption on graphene’s surface could affect hopping energy of graphene which plays a signi?cant role in its optical conductivity obtained from the tight-binding model for the visible range, it will serve as a promising tool for the detection of gas and other analytes. We also examine the sensitivity of the defect modes to the changes of the refractive index of the biological ?uids under the in?uence of quantum Hall situation for graphene in terahertz (THz) regime. It is revealed that two defective modes with relatively different sensing properties are emerged within the band stop of the device. The results of this study are not reported elsewhere to the best of our knowledge.
关键词： photonic crystal,hopping parameter,terahertz,biosensor,optical conductivity,visible light,graphene,quantum Hall effect
更新于2025-09-16 10:30:52
-
[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Zero-Field Quantized Anomalous Hall Resistance of (Bi,Sb)2 Te3
摘要： In the quantum anomalous Hall effect, the edge states of a ferromagnetically doped topological insulator exhibit quantized Hall resistance and dissipationless transport at zero magnetic field. Here, we present a measurement of the resistance quantization of V-doped (Bi,Sb)2Te3 devices in zero external magnetic field. For the deviation of the quantized anomalous Hall resistance from RK we determined a value of 0.17 ± 0.25 μΩ/Ω. This is a step towards realization of a practical zero-field quantum resistance standard which in combination with the Josephson effect could provide the universal quantum units standard in the future.
关键词： quantum anomalous Hall effect,quantum resistance standards,Quantum Hall effect
更新于2025-09-10 09:29:36