arXiv subjects

Gang Xiang

Publications and source records attributed to Gang Xiang.

12 recordsLinked to original sources

arXiv2025

Detection and manipulation of surface electric field noise of hexagonal boron nitride

Hexagonal boron nitride (hBN) spin defects off er transformative potential for quantum sensing through atomic-scale proximity to target samples, yet their performance is fundamentally limited by rapid coherence loss. While magnetic noise mechanisms have been extensively studied, another critical infl uence from surface electric fi eld noise remains unexplored in hBN systems. Here,we address this challenge and systematically investigate surface electric fi eld noise in hBN using shallow boron vacancy defects. The double-quantum spin relaxation behavior in response to magnetic fi elds and defect depths is examined, revealing that the relaxation rate follows a distinctive depth-related power-law dependence of ODMR splitting frequency. The relaxation is also demonstrated to be independent of the defect concentrations. Furthermore, the temperature dependence of the relaxation rate is investigated, showing a noticeable rise as the temperature increases from 296 K to 453 K, thus highlighting the infl uence of thermal eff ects on spin relaxation. To further suppress surface electric fi eld noise, we explore the eff ectiveness of passivation materials, including glycerol and PMMA. Notably, PMMA is more effi cient in mitigating surface electric fi eld noise. These experiments enhance the understanding of surface electric fi eld noise in hBN and provide a foundation for developing noise mitigation strategies in future research.

quant-ph↗

arXiv2024

Lattice dynamics and phonon dispersion of van der Waals layered ferromagnet Fe3GaTe2

Despite the tremendous progress in spintronic studies of van der Waals (vdW) room-temperature ferromagnet Fe3GaTe2, much less effort has been spent on its lattice dynamics and possible interaction with spintronic degrees of freedom. In this work, by combining Raman spectroscopy in a wide range of pressure (atmospheric pressure~19.5 GPa) and temperature (80~690 K) with first-principles calculation, we systematically studied the lattice dynamics and phonon dispersion of Fe3GaTe2. Our results show that the phonon energies of Fe3GaTe2 located at 126.0 cm-1 and 143.5 cm-1 originate from the anharmonic and harmonic vibration modes, respectively. Furthermore, the first room-temperature spin-phonon coupling in vdW ferromagnet is observed with strength of ~0.81 cm-1 at 300 K, by identifying Raman anomalies in both phonon energy and full width at half maximum (FWHM) of below Curie temperature of Fe3GaTe2. Our findings are valuable for fundamental and applied studies of vdW materials under variable conditions.

cond-mat.mtrl-sci↗

arXiv2024

Noninvasive magnetic detection of 2D van der Waals room-temperature ferromagnet Fe3GaTe2 using divacancy spins in SiC

Room-temperature (RT) two-dimensional (2D) van der Waals (vdW) ferromagnets hold immense promise for next-generation spintronic devices for information storage and processing. To achieve high-density energy-efficient spintronic devices, it is essential to understand local magnetic properties of RT 2D vdW magnets. In this work, we realize noninvasive in situ magnetic detection in vdW-layered ferromagnet Fe3GaTe2 using divacancy spins quantum sensor in silicon carbide (SiC) at RT. The structural features and magnetic properties of the Fe3GaTe2 are characterized utilizing Raman spectrum, magnetization and magneto-transport measurements. Further detailed analysis of temperature- and magnetic field-dependent optically detected magnetic resonances of the PL6 divacancy near the Fe3GaTe2 reveal that, the Curie temperature (Tc) of Fe3GaTe2 is ~360K, and the magnetization increases with external magnetic fields. Additionally, spin relaxometry technology is employed to probe the magnetic fluctuations of Fe3GaTe2, revealing a peak in the spin relaxation rate around Tc. These experiments give insights into the intriguing local magnetic properties of 2D vdW RT ferromagnet Fe3GaTe2 and pave the way for the application of SiC quantum sensors in noninvasive in situ magnetic detection of related 2D vdW magnets.

quant-ph↗

arXiv2022

Mechanism-based Tuning of Room-temperature Ferromagnetism in Mn-doped \b{eta}-Ga2O3 by Annealing Atmospher

Mn-doped \b{eta}-Ga2O3 (GMO) films with room-temperature ferromagnetism (RTFM) are synthesized by polymer-assisted deposition and the effects of annealing atmosphere (air or pure O2 gas) on their structures and physical properties are investigated. The characterizations show that the concentrations of vacancy defects and Mn dopants in various valence states and lattice constants of the samples are all modulated by the annealing atmosphere. Notably, the samples annealed in air (GMO-air) exhibit a saturation magnetization as strong as 170% times that of the samples annealed in pure O2 gas (GMO-O2), which can be quantitatively explained by oxygen vacancy (VO) controlled ferromagnetism due to bound magnetic polarons established between delocalized hydrogenic electrons of VOs and local magnetic moments of Mn2+, Mn3+, and Mn4+ ions in the samples. Our results provide insights into mechanism-based tuning of RTFM in Ga2O3 and may be useful for design, fabrication, and application of related spintronic materials.

cond-mat.mtrl-sci↗

arXiv2021

Noise Robust Named Entity Understanding for Voice Assistants

Named Entity Recognition (NER) and Entity Linking (EL) play an essential role in voice assistant interaction, but are challenging due to the special difficulties associated with spoken user queries. In this paper, we propose a novel architecture that jointly solves the NER and EL tasks by combining them in a joint reranking module. We show that our proposed framework improves NER accuracy by up to 3.13% and EL accuracy by up to 3.6% in F1 score. The features used also lead to better accuracies in other natural language understanding tasks, such as domain classification and semantic parsing.

cs.CL↗

arXiv2020

Investigating student understanding of heat engine: a case study of Stirling engine

We report on the study of student difficulties regarding heat engine in the context of Stirling cycle within upper-division undergraduate thermal physics course. An in-class test about a Stirling engine with a regenerator was taken by three classes, and the students were asked to perform one of the most basic activities---calculate the efficiency of the heat engine. Our data suggest that quite a few students have not developed a robust conceptual understanding of basic engineering knowledge of the heat engine, including the function of the regenerator and the influence of piston movements on the heat and work involved in the engine. Most notably, although the science error ratios of the three classes were similar ($\sim$10\%), the engineering error ratios of the three classes were high (above 50\%), and the class that was given a simple tutorial of engineering knowledge of heat engine exhibited significantly smaller engineering error ratio by about 20\% than the other two classes. In addition, both the written answers and post-test interviews show that most of the students can only associate Carnot's theorem with Carnot cycle, but not with other reversible cycles working between two heat reservoirs, probably because no enough cycles except Carnot cycle were covered in the traditional Thermodynamics textbook. Our results suggest that both scientific and engineering knowledge are important and should be included in instructional approaches, especially in the Thermodynamics course taught in the countries and regions with a tradition of not paying much attention to experimental education or engineering training.

physics.ed-ph↗

arXiv2020

High Curie Temperature Ferromagnetism and High Hole Mobility in Tensile Strained Mn-doped SiGe Thin Films

Diluted magnetic semiconductors (DMSs) based on group-IV materials are desirable for spintronic devices compatible with current silicon technology. In this work, amorphous Mn-doped SiGe thin films were first fabricated on Ge substrates by radio frequency magnetron sputtering and then crystallized by rapid thermal annealing (RTA). After the RTA, the samples became ferromagnetic (FM) semiconductors, in which the Curie temperature increased with increasing Mn doping concentration and reached 280 K with 5% Mn concentration. The data suggest that the ferromagnetism came from the hole-mediated process and was enhanced by the tensile strain in the SiGe crystals. Meanwhile, the Hall effect measurement up to 33 T to eliminate the influence of anomalous Hall effect (AHE) reveals that the hole mobility of the annealed samples was greatly enhanced and the maximal value was ~1000 cm2/Vs, owing to the tensile strain-induced band structure modulation. The Mn-doped SiGe thin films with high Curie temperature ferromagnetism and high hole mobility may provide a promising platform for semiconductor spintronics.

cond-mat.mtrl-sci↗

arXiv2020

Two-Dimensional Si-Ge Monolayers: Stabilities, Structures and Electronic Properties

Si-Ge monolayers (SiGeM) with different elementary proportion x (0<x<1) were systematically studied for the first-time using ab initio calculations in this work. The structural stabilities of the Si1-xGexM with different symmetries were investigated using phonon spectra, and an infinite miscibility between Si and Ge elements were revealed in the 2D honeycomb structures. The simulated scanning tunneling microscope images and Raman and infrared active modes of the Si1-xGexM were then obtained for structural characterizations. Interestingly, the study of electronic properties revealed not previously reported oscillatory nonlinear dependence of band gap values on the elementary proportion x in the Si1-xGexM, which suggests an alternative way for tuning the band gaps of 2D materials. Additionally, low effective masses (0.008m0 ~ 0.021m0) of the carriers in the semiconducting Si1-xGexM were found, which has potentials for high-speed applications. Considering the advantage of their compatibility with current Si-based technology and the trend of miniature of electronic devices, the Si1-xGexM with stable structures and excellent properties would be important for 2D applications based on group IV materials.

cond-mat.mtrl-sci↗

arXiv2020

Enhanced Valley Zeeman Splitting in Fe-Doped Monolayer MoS2

The Zeeman effect offers unique opportunities for magnetic manipulation of the spin degree of freedom (DOF). Recently, valley Zeeman splitting, referring to the lifting of valley degeneracy, has been demonstrated in two-dimensional transition metal dichalcogenides (TMDs) at liquid helium temperature. However, to realize the practical applications of valley pseudospins, the valley DOF must be controllable by a magnetic field at room temperature, which remains a significant challenge. Magnetic doping in TMDs can enhance the Zeeman splitting, however, to achieve this experimentally is not easy. Here, we report unambiguous magnetic manipulation of valley Zeeman splitting at 300 K (g = -6.4) and 10 K (g = -11) in a CVD-grown Fe-doped MoS2 monolayer; the effective g factor can be tuned to -20.7 by increasing the Fe dopant concentration, which represents an approximately fivefold enhancement as compared to undoped MoS2. Our measurements and calculations reveal that the enhanced splitting and geff factors are due to the Heisenberg exchange interaction of the localized magnetic moments (Fe 3d electrons) with MoS2 through the d-orbital hybridization.

cond-mat.mtrl-sci↗

arXiv2020

Synthesis and temperature-dependent photoluminescence of high density GeSe triangular nanoplate arrays on Si substrates

We have grown germanium selenide (GeSe) triangular nanoplate arrays (TNAs) with a high density (3.82E+6 / mm2) on the Si (111) substrate using a simple thermal evaporation method. The thickness and trilateral lengths of a single triangular nanoplate were statistically estimated by atomic force microscopy (AFM) as 44 nm, 365 nm, 458 nm and 605 nm, respectively. Transmission electron microscopy (TEM) images and X-ray diffraction (XRD) patterns show that the TNAs were composed of single crystalline GeSe phase. The Se-related defects in the lattice were also revealed by TEM images and Raman vibration modes. Unlike previously reported GeSe compounds, the GeSe TNAs exhibited temperature-dependent photoluminescence (PL). In addition, not previously reported PL peak (1.25 eV) of the 44 nm thick TNAs at 5 K was in the gaps between those of GeSe monolayers (1.5 nm) and thin films (400 nm), revealing a close relationship between the PL peak and the thickness of GeSe. The high-density structure and temperature-dependent PL of the TNAs on the Si substrate may be useful for temperature controllable semiconductor nanodevices.

cond-mat.mes-hall↗

arXiv2020

Rapid Synthesis of Thermoelectric SnSe Thin Films by MPCVD

Microwave plasma chemical vapor deposition (MPCVD) has been traditionally used to synthesize carbon-based materials such as diamonds, carbon nanotubes and graphene. Here we report that a rapid and catalyst-free growth of SnSe thin films can be achieved by using single-mode MPCVD with appropriate source materials. The analysis combing microscope images, X-ray diffraction patterns and lattice vibration modes shows that the grown thin films were composed of orthorhombic structured SnSe polycrystals mainly along the (111) direction. Further thermoelectric (TE) characterizations reveal that the power factor of the SnSe films reached 3.98 μW cm-1K-2 at 600 K, comparable to the highest reported values of SnSe thin films. Our results may open an avenue for rapid synthesis of new types of materials such as IV-VI compounds and be useful for TE application of these materials.

cond-mat.mtrl-sci↗

arXiv2014

Anti-rumor dynamics and emergence of the timing threshold on complex network

Anti-rumor dynamics is proposed on the basis of rumor dynamics and the characteristics of anti-rumor dynamics are explored by both mean-field equations and numerical simulations on complex network. The main metrics we study are the timing effect of combating rumor and the identification of influential nodes, which are what an efficient strategy against rumor may concern about. The results indicate that, there exists robust time dependence of anti-rumor dynamics and the timing threshold emerges as a consequence of launching the anti-rumor at different delay time after the beginning of rumor spreading. The timing threshold as a critical feature is further verified on a series of Barabasi-Albert scale-free networks (BA networks), where anti-rumor dynamics arises explicitly. The timing threshold is a network-dependent quantity and its value decreases as the average degree of the BA network increases until close to zero. Meanwhile, coreness also constitutes a better topological descriptor to identify hubs. Our results will hopefully be useful for the understanding of spreading behaviors of rumor and anti-rumor and suggest a possible avenue for further study of interplays of multiple pieces of information on complex network.

physics.soc-ph↗