Lv, Bing

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    Low-Temperature Microstructural Studies on Superconducting CaFe₂As₂
    (Nature Publishing Group, 2019-04-23) Huyan, S.; Deng, L. Z.; Wu, Z.; Zhao, K.; Sun, J. Y.; Wu, L. J.; Zhao, Y. Y.; Yuan, H. M.; Gooch, M.; Lv, Bing; Zhu, Y.; Chen, S.; Chu, C. W.; 0000-0002-9491-5177 (Lv, B); Lv, Bing
    Undoped CaFe₂As₂ (Ca122) can be stabilized in two slightly different non-superconducting tetragonal phases, PI and PII, through thermal treatments. Upon proper annealing, superconductivity with a T_{c} up to 25 K emerges in the samples with an admixture of PI and PII phases. Systematic low-temperature X-ray diffraction studies were conducted on undoped Ca122 samples annealed at 350 °C over different time periods. In addition to the diffraction peaks associated with the single-phase aggregation of PI and PII, a broad intermediate peak that shifts with annealing time was observed in the superconducting samples only. Our simulation of phase distribution suggests that the extra peak is associated with the admixture of PI and PII on the nanometer scale. High-resolution transmission electron microscopy confirms the existence of these nano-scale phase admixtures in the superconducting samples. These experimental results and simulation analyses lend further support for our conclusion that interfacial inducement is the most reasonable explanation for the emergence of superconductivity in undoped Ca122 single crystals. ©2019, The Author(s).
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    High Thermal Conductivity in Isotopically Enriched Cubic Boron Phosphide
    (WILEY-VCH Verlag GmbH & Co.) Zheng, Q.; Li, S.; Li, C.; Lv, Y.; Liu, X.; Huang, P. Y.; Broido, D. A.; Lv, Bing; Cahill, D. G.; Li, S.; Liu, X.; Lv, Bing
    Zinc blende boron arsenide (BAs), boron phosphide (BP), and boron nitride (BN) have attracted significant interest in recent years due to their high thermal conductivity (Λ) predicted by first-principles calculations. This research reports the study of the temperature dependence of Λ (120 K < T < 600 K) for natural isotope-abundance BP and isotopically enriched 11BP crystals grown from modified flux reactions. Time-domain thermoreflectance is used to measure Λ of sub-millimeter-sized crystals. At room temperature, Λ for BP and 11BP is 490 and 540 W m−1 K−1, respectively, surpassing the values of conventional high Λ materials such as Ag, Cu, BeO, and SiC. The Λ of BP is smaller than only cubic BN, diamond, graphite, and BAs among single-phase materials. The measured Λ for BP and 11BP is in good agreement with the first-principles calculations above 250 K. The quality of the crystals is verified by Raman spectroscopy, X-ray diffraction, and scanning transmission electron microscopy. By combining the first-principles calculations and Raman measurements, a previously misinterpreted Raman mode is reassigned. Thus, BP is a promising material not only for heat spreader applications in high-power microelectronic devices but also as an electronic material for use in harsh environments. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    High Thermal Conductivity in Cubic Boron Arsenide Crystals
    (American Association for the Advancement of Science) Li, Sheng; Zheng, Q.; Lv, Y.; Liu, Xiaoyuan; Wang, X.; Huang, P. Y.; Cahill, D. G.; Lv, Bing; Li, Sheng; Liu, Xiaoyuan; Lv, Bing
    The high density of heat generated in power electronics and optoelectronic devices is a critical bottleneck in their application. New, high thermally-conducting materials are needed to effectively dissipate heat and thereby enable enhanced performance of power controls, solid-state lighting, communication, and security systems. We report our experimental discovery of high thermal conductivity of 1000 ± 90 W/m/K at room temperature in cubic boron arsenide (BAs) grown through modified chemical vapor transport technique. Such thermal conductivity is a factor of 3 higher than that of silicon carbide and surpassed only by diamond and the basal plane value of graphite. This work establishes BAs as the first realization of a new class of ultrahigh thermal conductivity materials predicted by a recent theory, and a potential revolutionary thermal management material.
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    Laser Post-Processing of Halide Perovskites for Enhanced Photoluminescence and Absorbance
    (IOP Publishing Ltd, 2018-11-05) Tiguntseva, E. Y.; Saraeva, I. N.; Kudryashov, S. I.; Ushakova, E. V.; Komissarenko, F. E.; Ishteev, A. R.; Tsypkin, A. N.; Haroldson, Ross; Milichko, V. A.; Zuev, D. A.; Makarov, S. V.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Haroldson, Ross; Zakhidov, Anvar A.
    Hybrid halide perovskites have emerged as one of the most promising type of materials for thin-film photovoltaic and light-emitting devices. Further boosting their performance is critically important for commercialization. Here we use femtosecond laser for post-processing of organo-metalic perovskite (MAPbI3) films. The high throughput laser approaches include both ablative silicon nanoparticles integration and laser-induced annealing. By using these techniques, we achieve strong enhancement of photoluminescence as well as useful light absorption. As a result, we observed experimentally 10-fold enhancement of absorbance in a perovskite layer with the silicon nanoparticles. Direct laser annealing allows for increasing of photoluminescence over 130%, and increase absorbance over 300% in near-IR range. We believe that the developed approaches pave the way to novel scalable and highly effective designs of perovskite based devices.
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    Seeded Growth of Boron Arsenide Single Crystals with High Thermal Conductivity
    (Amer Inst Physics, 2018-11-05) Tian, Fei; Song, Bai; Lv, Bing; Sun, Jingying; Huyan, Shuyuan; Wu, Qi; Mao, Jun; Ni, Yizhou; Ding, Zhiwei; Huberman, Samuel; Liu, Te-Huan; Chen, Gang; Chen, Shuo; Chu, Ching-Wu; Ren, Zhifeng; Lv, Bing
    Materials with high thermal conductivities are crucial to effectively cooling high-power-density electronic and optoelectronic devices. Recently, zinc-blende boron arsenide (BAs) has been predicted to have a very high thermal conductivity of over 2000W m⁻¹ K⁻¹ at room temperature by first-principles calculations, rendering it a close competitor for diamond which holds the highest thermal conductivity among bulk materials. Experimental demonstration, however, has proved extremely challenging, especially in the preparation of large high quality single crystals. Although BAs crystals have been previously grown by chemical vapor transport (CVT), the growth process relies on spontaneous nucleation and results in small crystals with multiple grains and various defects. Here, we report a controllable CVT synthesis of large single BAs crystals (400-600 μm) by using carefully selected tiny BAs single crystals as seeds. We have obtained BAs single crystals with a thermal conductivity of 351 ± 21 W m⁻¹ K⁻¹ at room temperature, which is almost twice as conductive as previously reported BAs crystals. Further improvement along this direction is very likely.
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    Superconductivity from Site-Selective Ru Doping Studies in Zr₅Ge₃ Compound
    (IOP Publishing Ltd, 2018-10-22) Li, Sheng; Liu, Xiaoyuan; Anand, Varun; Lv, Bing; Li, Sheng; Liu, Xiaoyuan; Anand, Varun; Lv, Bing
    Systematical doping studies have been carried out to search for the possible superconductivity in the transition metal doped Zr₅Ge₃ system. Superconductivity up to 5.7 K is discovered in the Ru doped Zr₅Ge₂․₅Ru₀․₅ sample. Interestingly, with the same Ru doping, superconductivity is only induced with doping at the Ge site, but remains absent down to 1.8 K with doping at the Zr site or interstitial site. Both magnetic and transport studies have revealed the bulk superconductivity nature for Ru doped Zr₅Ge₂․₅Ru₀․₅ sample. The high upper critical field, enhanced electron correlation, and extremely small electron-phonon coupling, have indicated possible unconventional superconductivity in this system, which warrants further detailed theoretical and experimental studies.
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    Ultrafast Dynamics of Quasiparticles and Coherent Acoustic Phonons in Slightly Underdoped (BaK)Fe₂As₂
    (Nature Publishing Group, 2016-05-16) Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen; Lv, Bing
    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.
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    Evidence for Defect-Induced Superconductivity up to 49 K in (Ca₁₋ₓ)Fe₂As₂
    (Amer Physical Soc, 2016-02-12) Deng, L. Z.; Lv, Bing; Zhao, K.; Wei, F. Y.; Xue, Y. Y.; Wu, Z.; Chu, C. W.; Lv, Bing
    To explore the origin of the unusual nonbulk superconductivity with a T_c up to 49 K reported in the rare-earth-doped CaFe₂As₂, the chemical composition, magnetization, specific heat, resistivity, and annealing effect are systematically investigated on nominal Ca₁₋ₓ Rₓ)Fe₂As₂ single crystals with different x and R = La, Ce, Pr, and Nd. All display a doping-independent T_c once superconductivity is induced, a doping-dependent low field superconducting volume fraction ʄ, and a large magnetic anisotropy η the superconducting state, suggesting a rather inhomogeneous superconducting state in an otherwise microscale homogenous superconductor. The wavelength dispersive spectroscopy and specific heat show the presence of defects that are closely related to ʄ, regardless of the R involved. The magnetism further reveals that the defects are mainly superparamagnetic clusters for R = Ce, Pr, and Nd with strong intercluster interactions, implying that defects are locally self-organized. Annealing at 500 ⁰C, without varying the doping level x, suppresses ʄ profoundly but not the T_c. The above observations provide evidence for the crucial role of defects in the occurrence of the unusually high T_c ~ to 49K in Ca₁₋ₓ Rₓ Fe₂As₂ and are consistent with the interface-enhanced superconductivity recently proposed.
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    Chemical Doping and High-Pressure Studies of Layered β-PdBi₂ Single Crystals
    (American Physical Society, 2015-11-04) Zhao, K.; Lv, Bing; Xue, Y. -Y; Zhu, X. -Y; Deng, L. Z.; Wu, Z.; Chu, C. W.; Lv, Bing
    We have systematically grown large single crystals of the layered compounds β-PdBi₂, and both the hole-doped PdBi₂₋ₓPb₂ and the electron-doped NaₓPdBi₂, and studied their magnetic and transport properties. Hall effect measurements on PdBi₂, PdBi₁₈Pb₀₂, and Na₀.₀₅₇PdBi₂ show that the charge transport is dominated by electrons in all of the samples. The electron concentration is substantially reduced upon Pb doping in PdBi₂₋ₓPbₓ and increased upon Na intercalation in NaₓPdBi₂, indicating effective hole doping by Pb and electron doping by Na. We observed a monotonic decrease of the superconducting transition temperature (T_c) from 5.4 K in undoped PdBi₂ to less than 2 K for x > 0.35 in hole-doped PdBi₂₋ₓPbₓ. Meanwhile, a rapid decrease of T_c with Na intercalation is also observed in the electron-doped NaₓPdBi₂, which is in disagreement with the theoretical expectation. In addition, both the magnetoresistance and Hall resistance further reveal evidence for a possible spin excitation associated with Fermi surface reconstruction at ∼50 K in the Na-intercalated PdBi₂ sample. The complete phase diagram is thus established from hole doping to electron doping. Meanwhile, a high-pressure study of the undoped PdBi₂ shows that the T_c is linearly suppressed under pressure with a dT_c/dP coefficient of -0.28 K/GPa.