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N. Hu

Publications and source records attributed to N. Hu.

6 recordsLinked to original sources
arXiv2023

Simulation study of intra-beam scattering effect in the HALF storage ring with Piwinski model

The Hefei Advanced Light Facility (HALF) will be a VUV and soft X-ray diffraction-limited storage ring (DLSR), and its high density of electron bunches makes the intra-beam scattering (IBS) effect very serious. In this paper, an IBS module used in the IMPACT code is developed, where the scattering process of IBS is described by the Piwinski model in Monte Carlo sampling. For benchmarking, the IMPACT code with IBS module is compared with the ELEGANT code and a semi-analytic code using Bane's model. Then, the results of IBS effect in the HALF storage ring studied by this new code are presented. With various countermeasures, the IBS impact can be controlled to a certain extent, and the expected beam emittance is approximately 59 pm.rad.

physics.acc-ph↗
arXiv2023

Strain tuned magnetotransport of Jeff=1/2 antiferromagnetic Sr2IrO4 thin films

In this work, we report observation of strain effect on physical properties of Sr2IrO4 thin films grown on SrTiO3 (001) and LaAlO3 (001) substrates. It is found that the film on LaAlO3 with compressive strain has a lower antiferromagnetic transition temperature (TN~210 K) than the film on SrTiO3 (TN~230 K) with tensile strain, which is probably caused by modified interlayer coupling. Interestingly, magnetoresistance due to pseudospin-flip of the film on LaAlO3 is much larger than that of tensile-strained film on SrTiO3, and robust anisotropic magnetoresistance is observed in the former, but H-driven reversal behavior is seen in the latter. By performing first principles calculations, it is revealed that epitaxial strain plays an efficient role in tuning the canting angle of Jeff=1/2 moments and thus net moment at every IrO2 layer, responsible for the difference in magnetoresistance between the films. The reversal of anisotropic magnetoresistance in the thin film on SrTiO3 can be ascribed to stabilization of a metastable stable with smaller bandgap as the Jeff=1/2 moments are aligned along the diagonal of basal plane by H. However, theoretical calculations reveal much higher magnetocrystalline anisotropy energy in the film on LaAlO3. This causes difficulties to drive the Jeff=1/2 moments to reach the diagonal and thereby the metastable state, explaining the distinct anisotropic magnetoresistance between two samples in a qualitative sense. Our findings indicate that strain can be a highly efficient mean to engineer the functionalities of Jeff=1/2 antiferromagnet Sr2IrO4.

cond-mat.str-el↗
arXiv2023

Structural origin of the Jeff=1/2 antiferromagnetic phase in Ga-doped Sr2IrO4

Sr2IrO4 hosts a novel Jeff =1/2 Mott state and quasi-two-dimensional antiferromagnetic order, providing a unique avenue of exploring emergent states of matter and functions that are extraordinarily sensitive to any structural variations. While the correlation between the physical property and lattice structure in Sr2IrO4 has been a focused issue in the past decade, a common perception assumes that the magnetic ordering is essentially determined by the Ir-O-Ir bond angle. Therefore, a delicate modulation of this angle and consequently a major modulation of the magnetic ordering, by chemical doping such as Ga at Ir site, has been extensively investigated and well believed. In this work, however, we present a whole package of structure and magnetism data on a series of single crystal and polycrystalline Sr2Ir1-xGaxO4 samples, revealing the substantial difference in the N\'eel temperature TN between the two types of samples, and the TN value for the polycrystalline sample x = 0.09 is even 64 K higher than that of the single crystal sample x = 0.09 (deltaTN ~ 64 K at x = 0.09). Our systematic investigations demonstrate the crucial role of the c/a ratio in tuning the interlayer coupling and thereby the Neel point TN, i.e. a higher TN can be achieved as c/a is reduced. The notable differences in structural parameters between the two groups of samples are probably caused by additional strain due to the massive grain boundaries in polycrystalline samples. The present work suggests an additional ingredient of physics that is essential in modulating the emergent properties in Sr2IrO4 and probably other iridates.

cond-mat.str-el↗
arXiv2021

Immersive Operation of a Semi-Autonomous Aerial Platform for Detecting and Mapping Radiation

Recent advancements in radiation detection and computer vision have enabled small unmanned aerial systems (sUASs) to produce 3D nuclear radiation maps in real-time. Currently these state-of-the-art systems still require two operators: one to pilot the sUAS and another operator to monitor the detected radiation. In this work we present a system that integrates real-time 3D radiation visualization with semi-autonomous sUAS control. Our Virtual Reality interface enables a single operator to define trajectories using waypoints to abstract complex flight control and utilize the semi-autonomous maneuvering capabilities of the sUAS. The interface also displays a fused radiation visualization and environment map, thereby enabling simultaneous remote operation and radiation monitoring by a single operator. This serves as the basis for development of a single system that deploys and autonomously controls fleets of sUASs.

cs.RO↗
arXiv2015

Energy Pooling Upconversion in Organic Molecular Systems

A combination of molecular quantum electrodynamics, perturbation theory, and ab initio calculations was used to create a computational methodology capable of estimating the rate of 3-body singlet upconversion in organic molecular assemblies. The approach was applied to quantify the conditions under which such relaxation rates, known as energy pooling, become meaningful for two test systems: stilbene-fluorescein and hexabenzocoronene-oligothiophene. Both exhibit low intra-molecular conversion but inter-molecular configurations exist in which pooling efficiency is at least 90\% when placed in competition with more conventional relaxation pathways. For stilbene-fluorescein, the results are consistent with data generated in an earlier experimental investigation. Exercising these model systems facilitated the development of a set of design rules for the optimization of energy pooling.

cond-mat.mes-hall↗