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arXiv 2024年

作者： Chan, Yao-Jui Faizanuddin, Syed Mohammed Kalaivanan, Raju Raman, Sankar Lin, Hsin Kar, Uddipta Singh, Akhilesh Kr. Lee, Wei-Li Vankayala, Ranganayakulu K. Ou, Min-Nan Wen, Yu-Chieh Institute of Physics Academia Sinica Taipei11529 Taiwan Taiwan International Graduate Program Academia Sinica Taipei11529 Taiwan Department of Engineering and System Science National Tsing Hua University Hsinchu300044 Taiwan

Spectroscopic identification of distinct nonlinear photocurrents unveils quantum geometric properties of electron wavefunctions and the momentum-space topological structures. This is especially interesting, but still puzzling, for chiral topological semimetals with possibilities of hosting giant quantized circular photogalvanic effect. Here we report a comprehensive terahertz (THz) emission spectroscopic analysis of nonlinear photoconductivity of chiral multifold CoSi at 0.26 ~ 1 eV. We find a large linear shift conductivity (17 μA/V2), and confirm a giant injection conductivity (167 μA/V2) as a consequence of strongly interfered non-quantized contributions from the vicinity of multifold nodes with opposite chiralities. The bulk injection current excited by the pump field with a complex wavevector is shown to carry both longitudinal and transverse components. Symmetry analyses further unveil weak nonlocal photon drag effect in addition to the photogalvanic effect. This work not only highlights chiral transition metal monosilicides for mid-infrared photovoltaic applications via various nonlinear optical channels, but also consolidates the THz spectroscopy for quantitative photovoltaic research. Copyright © 2024, The Authors. All rights reserved.

关键词： Terahertz spectroscopy

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Ultrafast measurements of the interfacial spin Seebeck effect in Au and rare-earth iron-garnet bilayers

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Physical Review Materials 2021年第7期5卷 074401-074401页

作者： Víctor H. Ortiz Michael J. Gomez Yawen Liu Mohammed Aldosary Jing Shi Richard B. Wilson Department of Mechanical Engineering and Materials Science and Engineering Program University of California Riverside California 92521 USA Department of Physics and Astronomy Program University of California Riverside California 92521 USA

We investigate picosecond spin currents across Au/iron-garnet interfaces in response to ultrafast laser heating of the electrons in the Au film. In the picoseconds after optical heating, interfacial spin currents occur due to an interfacial temperature difference between electrons in the metal and magnons in the insulator. We report measurements of this interfacial longitudinal spin Seebeck effect between Au and rare-earth iron-garnet insulators, i.e., RE3Fe5O12, where RE is Y, Eu, Tb, Tm. By systematically varying the rare-earth element, we modify the total magnetic moment of the iron garnet. We use time-domain thermoreflectance measurements to characterize the thermal response of the bilayer to ultrafast optical heating. We use time-resolved magneto-optic Kerr effect measurements of the Au layer to measure the time evolution of spin accumulation in the Au film. Replacing Y with other rare earths enhances the electron-magnon conductance Ge−m at the Au iron-garnet interface by as much as a factor of 3. The electron-magnon conductance does not follow the trend of either the total magnetization of the iron garnet or the magnetic moment of the rare earth.

关键词： Magneto-optical Kerr effect Magnons Spin Seebeck effect Spin polarization Ultrafast magnetic effects

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Highly Compact and Scalable 100 ps CTR + 3D Positioning TOF-PET Detector Sub-Unit

Highly Compact and Scalable 100 ps CTR + 3D Positioning TOF-...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： S. Pourashraf D. Innes J. W. Cates C. S. Levin Radiology Stanford University California United States of America Lawrence Berkeley National Laboratory Applied Nuclear Physics Program Berkeley California United States of America Bioengineering Physics and Electrical Engineering Stanford University California United States of America

We have developed a highly compact design for TOF-PET detector modules employing side-readout of scintillation crystal elements to achieve 100 ps CTR and 3D positioning of 511 keV interactions. Detector modules comprise 16 layers, each containing 4 sub-units. Each detector layer sub-unit is a 2×4 array of 3×3×10 mm 3 LGSO elements side-coupled to a 6×4 array of 3×3 mm² SiPMs. To achieve high packing fraction, the electronic readout is implemented with a 4-layer rigid FR4 PCB that is only 0.4 mm thick and has a width matching the 6×4 SiPM array (13.3 mm). Among many features, the circuit multiplexes 24 SiPM timing channels into 1 to reduce the readout complexity. In new configuration reported here, all external connectors have been removed and replaced with 0.4 mm pitch fine connectors for scalable signal routing at the detector module level. The timing performance of this 24:1 multiplexed readout was measured in coincidence with a reference detector, resulting in average 107±1.3 ps FWHM CTR. Thus the proposed side-readout of scintillation crystal elements and readout electronics are now configured in a layer topology and achieve the performance that are scalable to large area detector modules for a ~100 ps CTR TOF-PET system.

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Interfacial thermal transport in spin caloritronic material systems

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Physical Review Materials 2021年第11期5卷 114403-114403页

作者： Frank Angeles Qiyang Sun Victor H. Ortiz Jing Shi Chen Li Richard B. Wilson Department of Mechanical Engineering and Materials Science and Engineering Program University of CaliforniaRiverside California 92521 USA Department of Physics and Astronomy Program University of California Riverside California 92521 USA

Interfaces often govern the thermal performance of nanoscale devices and nanostructured materials. As a result, accurate knowledge of thermal interface conductance is necessary to model the temperature response of nanoscale devices or nanostructured materials to heating. Here, we report the thermal boundary conductance between metals and insulators that are commonly used in spin-caloritronic experiments. We use time-domain thermoreflectance to measure the interface conductance between metals such as Au, Pt, Ta, Cu, and Al with garnet and oxide substrates, e.g., NiO, yttrium iron garnet (YIG), thulium iron garnet (TmIG), Cr2O3, and sapphire. We find that, at room temperature, the interface conductance in these types of material systems range from 50 to 300MWm−2K−1. We also measure the interface conductance between Pt and YIG at temperatures between 80 and 350 K. At room temperature, the interface conductance of Pt/YIG is 170MWm−2K−1 and the Kapitza length is ∼40 nm. A Kapitza length of 40 nm means that, in the presence of a steady-state heat current, the temperature drop at the Pt/YIG interface is equal to the temperature drop across a 40-nm-thick layer of YIG. At 80 K, the interface conductance of Pt/YIG is 60MWm−2K−1, corresponding to a Kapitza length of ∼300 nm.

关键词： Thermal conductivity

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Enhancing Zinc Electrode Stability Through Pre-Desolvation and Accelerated Charge Transfer via a Polyimide Interface for Zinc-Ion Batteries

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Small 2024年第35期20卷 e2401713页

作者： Lai, Chi-Yu Liao, Yin-Song Ku, Hao-Yu Jao, Wen-Yang Gull, Sanna Chen, Han-Yi Chou, Jyh-Pin Hu, Chi-Chang Department of Chemical Engineering National Tsing Hua University Hsinchu300044 Taiwan Tsing Hua Interdisciplinary Program National Tsing Hua University Hsinchu300044 Taiwan Department of Materials Science and Engineering National Tsing Hua University Hsinchu300044 Taiwan Department of Physics National Changhua University of Education Changhua50074 Taiwan

Aqueous zinc-based energy storage devices possess superior safety, cost-effectiveness, and high energy density;however, dendritic growth and side reactions on the zinc electrode curtail their widespread applications. In this study, these issues are mitigated by introducing a polyimide (PI) nanofabric interfacial layer onto the zinc substrate. Simulations reveal that the PI nanofabric promotes a pre-desolvation process, effectively desolvating hydrated zinc ions from Zn(H2O)62+ to Zn(H2O)42+ before approaching the zinc surface. The exposed zinc ion in Zn(H2O)42+ provides an accelerated charge transfer process and reduces the activation energy for zinc deposition from 40 to 21 kJ mol−1. The PI nanofabric also acts as a protective barrier, reducing side reactions at the electrode. As a result, the PI-Zn symmetric cell exhibits remarkable cycling stability over 1200 h, maintaining a dendrite-free morphology and minimal byproduct formation. Moreover, the cell exhibits high stability and low voltage hysteresis even under high current densities (20 mA cm−2, 10 mAh cm−2) thanks to the 3D porous structure of PI nanofabric. When integrated into full cells, the PI-Zn||AC hybrid zinc-ion capacitor and PI-Zn||MnVOH@SWCNT zinc-ion battery achieve impressive lifespans of 15000 and 600 cycles with outstanding capacitance retention. This approach paves a novel avenue for high-performance zinc metal electrodes. © 2024 Wiley-VCH GmbH.

关键词： Charge transfer

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Super-Mossian Dielectrics for Nanophotonics

Super-Mossian Dielectrics for Nanophotonics

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Conference on Lasers and Electro-Optics (CLEO)

作者： Xielin Wang Chloe F. Doiron Zhichao Li Jacob B. Khurgin Gururaj V. Naik Applied Physics Graduate Program Smalley-Curl Institute Rice University Houston TX Department of Electrical and Computer Engineering Johns Hopkins University Baltimore MD Department of Electrical and Computer Engineering Rice University Houston TX

Searching for high-index dielectrics, we identify materials that break the index upper bound set by Moss’ rule. We highlight the promise of such super-Mossian materials by demonstrating nanophotonic devices made of F... 详细信息

ISBN: (纸本)9781957171258

关键词： Fourier transform infrared spectroscopy Nanophotonics Optical constants Optical materials Refractive index Whispering gallery modes

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An economical single-shot pulse picker without nonlinear effect and dispersion

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Review of Scientific Instruments 2024年第1期95卷 013003-013003页

作者： Hu, Chen-Wei Lu, Chia-Yen Wen, Yu-Chieh Chen, Hung-Wen International Intercollegiate Ph.D. Program National Tsing Hua University Hsinchu30013 Taiwan Institute and Undergraduate Program of Electro-Optical Engineering National Taiwan Normal University Taipei11677 Taiwan Institute of Physics Academia Sinica Taipei City115201 Taiwan Institute of Photonics Technologies National Tsing Hua University Hsinchu30013 Taiwan

An economical and stable single-shot pulse picker design without dispersion, nonlinear effect, and limitation on wavelength is proposed. This design is composed of a periodic pulse blocker (PPB), a control unit, and a mechanical shutter. It has successfully been applied to the commercial high-fluence femtosecond laser with 11-mm beam diameter, 2-mJ pulse energy, and 1-kHz repetition rate. Significantly, by incorporating commercial optical choppers equipped with custom-designed chopper blades in the PPB, this design can accommodate lasers with fluences reaching 610 mJ/cm2 and the standard 1 kHz repetition rate typical of high-fluence lasers. Furthermore, the proposed design provides a cost-effective substitute compared to using electro-optic modulators or acousto-optic modulators. © 2024 Author(s).

关键词： Cost effectiveness

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Conformity Experiment on Inelastic Scattering Exponent of Electrons in Two Dimensions

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Physical Review Letters 2024年第9期133卷 096302页

作者： Ching-Chen Yeh Pin-Chi Liao Yanfei Yang Wei-Chen Lin Alireza R. Panna Albert F. Rigosi Randolph E. Elmquist Chi-Te Liang Gaithersburg Maryland 20899 USA Department of Physics Graphene Waves Germantown Maryland 20876 USA Taiwan International Graduate Program Department of Engineering and System Science Center for Quantum Science and Engineering (CQSE) Taiwan Consortium of Emergent Crystalline Materials (TCECM) Taipei 106 Taiwan

The quantum Hall (QH) effect is one of the most widely studied physical phenomenon in two dimensions. The plateau-plateau transition within this effect can be comprehensively described by the scaling theory, which encompasses three pivotal exponents: the critical exponent κ, the inelastic scattering exponent p, and the universal exponent γ. Prior studies have focused on measuring κ and estimating γ, assuming a constant p value of 2 across magnetic fields. Here, our work marks a significant advancement by measuring all three exponents within a single graphene device and a conventional two-dimensional electron system. This study uniquely determines p at low magnetic fields (weak localization region and well outside the QH regime) and high magnetic fields (in the vicinity of the QH regime). Employing a comprehensive analytical approach that includes weak localization, plateau-plateau transitions, and variable range hopping, we have directly determined κ, p, and γ. Our findings reveal a distinct variation in p, shifting from 1 in the low magnetic field regime to 2 in the QH regime in graphene.

关键词： Electrical properties Fermions Landau levels Quantum interference effects Quantum phase transitions

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Evaluation of Maternal and Fetal S-Values from Iodine Isotopes in Nuclear Medicine Using the Monte Carlo Method

SSRN

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SSRN 2025年

作者： Coelho, Nathalia B.M. Alves, Arthur de Souza Borges Zuchet Santos, Carla J. Neves, Lúcio P. Perini, Ana P. Belinato, Walmir Ferreira, José Rafael S. Santos, William S. Postgraduate Program in Biomedical Engineering Faculty of Electrical Engineering Federal University of Uberlândia Uberlândia Brazil Institute of Physics Federal University of Uberlândia Uberlândia Brazil Federal Institute of Bahia - IFBA BA Vitória da Conquista Brazil Department of Physics Federal University of Sergipe São Cristóvão Brazil Universidade Federal da Bahia Brazil

The use of radionuclides for therapeutic and diagnostic purposes is the primary function of nuclear medicine. Among these radionuclides, the iodine family stands out as isotopes that can serve various purposes, including brachytherapy, scintigraphy, and research. The internal dosimetry of these nuclides becomes even more important when considering high-risk groups such as pregnant patients, as it involves concerns for both the mother and the fetus. This study aims to use Monte Carlo simulations to calculate S-values for a set of target organs in both the pregnant woman and the fetus, considering different source organs in the mother and three iodine isotopes: 131I, 125I, and 123I. The results indicated that 131I, with the highest emission energy, presented a high dose deposition pattern in target organs farther from the source organs, while 125I, with the lowest energy, showed a localized dose absorption pattern in adjacent organs. The highest S-values (all in mGy/MBq.s) were obtained for the pregnant woman, with values of 5.8E-05 in the thyroid using 123I and 125I, and 3.7E-04 in the bladder using 131I. For fetal organs, the most irradiated were the brain and skull using 131I, with values of 6.3E-06 and 5.6E-06, respectively, while the lowest values were associated with the use of 125I in source organs distant from the target organ, with contributions as low as 1E-12 for the thyroid as a source. This work presents a qualitative and quantitative study of the internal dosimetry of a pregnant patient and her fetus, addressing variables such as radioactive isotope and source and target organs, serving as a reference for dosimetric calculations deemed necessary in clinical practices to minimize the dose received by this critical group. © 2025, The Authors. All rights reserved.

关键词： Nuclear medicine

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Topological wave phenomena in photonic time quasicrystals

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Physical Review B 2025年第12期111卷 125421-125421页

作者： Xiang Ni Shixiong Yin Huanan Li Andrea Alù School of Physics Central South University Changsha 410083 China Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Department of Electrical Engineering City College of The City University of New York New York 10031 USA MOE Key Laboratory of Weak-Light Nonlinear Photonics School of Physics Nankai University Tianjin 300071 China Physics Program Graduate Center City University of New York New York New York 10016 USA

Time interfaces consist of abrupt and spatially uniform changes in the optical properties of a medium. Their periodic occurrence forms photonic time crystals, which offer opportunities to tailor classical and quantum light-matter interactions. Here we explore one-dimensional photonic time quasicrystals, formed when time interfaces occur in a quasiperiodic fashion featuring long-range order. We unveil the emergence of topological phases and Hofstadter butterfly spectra in these systems, and demonstrate that their temporal response emulates the localization of topological edge states, enabling the temporal analog of topological Thouless pumping. Our findings open avenues for topological photonics leveraging time as a synthetic dimension, with functionalities that go beyond their spatial counterparts.

关键词： Quasicrystals

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