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H D Yang - One of the best experts on this subject based on the ideXlab platform.
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coexistence of isotropic and extended s wave order parameters in fese as revealed by low Temperature Specific Heat
Physical Review B, 2011Co-Authors: J Y Lin, Y S Hsieh, D A Chareev, A N Vasiliev, Y Parsons, H D YangAbstract:The comprehensive low-Temperature Specific Heat C(T) data identify both an isotropic s-wave and an extended s-wave order parameters coexisting in a superconducting single crystal FeSe with Tc=8.11 K. The isotropic gap {\Delta}0=1.33 meV on the hole Fermi sheets and the extended s-wave gap {\Delta}={\Delta}e(1+\alpha*cos2_theta) with {\Delta}e=1.13 meV and \alpha=0.78 on the electron Fermi sheets. The extended s-wave is rather anisotropic but the low energy quasiparticle excitations demonstrate no sign of the accidental nodes. The coefficient \gamma(H) manifesting the quasiparticle contribution to C is a non-linear function of the applied magnetic field H in the mixed state in accord with the anisotropic multi-order parameters.
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a low Temperature Specific Heat study of giant dielectric constant materials
Journal of Physics: Condensed Matter, 2008Co-Authors: C P Sun, Jianjun Liu, Jiunnyuan Lin, Chungang Duan, Waining Mei, H D YangAbstract:A low-Temperature Specific Heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the Specific Heat data in a very low-Temperature range, 0.6–1.5 K, and moderately low-Temperature range, 1.5–5 K, in addition to the expected Debye terms, we observed significant contributions originating from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurring at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behavior in both low and high frequency regions.
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a low Temperature Specific Heat study of the giant dielectric constant materials
Bulletin of the American Physical Society, 2008Co-Authors: C P Sun, Jianjun Liu, Jiunnyuan Lin, Chungang Duan, H D Yang, Waining MeiAbstract:Department of Physics, National Sun Yat-Sen University, Kaoshiung 804, Taiwan, Republic of China Department of Physics, University of Nebraska at Omaha, Nebraska, 68182-0266, USA Institute of Physics, National Chiao-Tung University, Hsinchu 300, Taiwan, Republic of China Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, USA Center for Material Research and Analysis, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, USA
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a low Temperature Specific Heat study of the giant dielectric constant materials
arXiv: Materials Science, 2007Co-Authors: C P Sun, Jianjun Liu, Chungang Duan, Waining Mei, J Y Lin, H D YangAbstract:Low-Temperature Specific-Heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the Specific Heat data at very low-Temperature range, 0.6 to 1.5 K, and moderately low-Temperature range, 1.5 to 5 K, in addition to the expected Debye terms, we noticed significant contributions originated from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behaviors at both low and high frequency regions.
Shahid Husain - One of the best experts on this subject based on the ideXlab platform.
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analysis of zn substitution on structure optical absorption magnetization and high Temperature Specific Heat anomaly of the nano crystalline lafeo3
Journal of Applied Physics, 2018Co-Authors: Samiya Manzoor, Shahid HusainAbstract:Nano-crystalline LaFe1−xZnxO3 (0 ≤ x ≤ 0.3) samples synthesized through the sol-gel auto-combustion technique have been studied. X-ray diffraction patterns reveal that all the samples have an orthorhombic crystal structure and exist in a single phase. Bond lengths and bond angles determined using Rietveld refinement change with the concentration, leading to the modification of the parent structure. The change in the structure is reflected in the thermal measurements too. The morphological studies reveal a wide-range of particle size distribution, consisting of nanometer-sized particles to macro-agglomerations. FTIR spectra show two strong active vibrational bands present at 564 cm−1 and 410 cm−1, which are related to the functional groups present in the material. The optical bandgap has been determined and is found to decrease with the increase in the concentration of Zn. Raman spectroscopy rules out the symmetry breaking or any other structural phase transition in the system. The Raman spectra reveal the strain present in the samples on increasing the concentration of Zn doping. The doping of Zn in place of Fe produces distortion mainly in the oxygen bending and stretching vibrations. Specific Heat as a function of Temperature has been studied and found to be sensitive to magnetic ordering. The Neel Temperature decreases from 411 °C to 377 °C with the increase in the Zn concentration, which is concomitant with the Rietveld analysis. The density of our system decreases with Zn doping and leads to the increased value of Specific Heat. Hysteresis loops indicate that Zn doping increases the magnetic moment and decreases the coercivity.Nano-crystalline LaFe1−xZnxO3 (0 ≤ x ≤ 0.3) samples synthesized through the sol-gel auto-combustion technique have been studied. X-ray diffraction patterns reveal that all the samples have an orthorhombic crystal structure and exist in a single phase. Bond lengths and bond angles determined using Rietveld refinement change with the concentration, leading to the modification of the parent structure. The change in the structure is reflected in the thermal measurements too. The morphological studies reveal a wide-range of particle size distribution, consisting of nanometer-sized particles to macro-agglomerations. FTIR spectra show two strong active vibrational bands present at 564 cm−1 and 410 cm−1, which are related to the functional groups present in the material. The optical bandgap has been determined and is found to decrease with the increase in the concentration of Zn. Raman spectroscopy rules out the symmetry breaking or any other structural phase transition in the system. The Raman spectra reveal the...
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analysis of zn substitution on structure optical absorption magnetization and high Temperature Specific Heat anomaly of the nano crystalline lafeo3
Journal of Applied Physics, 2018Co-Authors: Samiya Manzoor, Shahid HusainAbstract:Nano-crystalline LaFe1−xZnxO3 (0 ≤ x ≤ 0.3) samples synthesized through the sol-gel auto-combustion technique have been studied. X-ray diffraction patterns reveal that all the samples have an orthorhombic crystal structure and exist in a single phase. Bond lengths and bond angles determined using Rietveld refinement change with the concentration, leading to the modification of the parent structure. The change in the structure is reflected in the thermal measurements too. The morphological studies reveal a wide-range of particle size distribution, consisting of nanometer-sized particles to macro-agglomerations. FTIR spectra show two strong active vibrational bands present at 564 cm−1 and 410 cm−1, which are related to the functional groups present in the material. The optical bandgap has been determined and is found to decrease with the increase in the concentration of Zn. Raman spectroscopy rules out the symmetry breaking or any other structural phase transition in the system. The Raman spectra reveal the strain present in the samples on increasing the concentration of Zn doping. The doping of Zn in place of Fe produces distortion mainly in the oxygen bending and stretching vibrations. Specific Heat as a function of Temperature has been studied and found to be sensitive to magnetic ordering. The Neel Temperature decreases from 411 °C to 377 °C with the increase in the Zn concentration, which is concomitant with the Rietveld analysis. The density of our system decreases with Zn doping and leads to the increased value of Specific Heat. Hysteresis loops indicate that Zn doping increases the magnetic moment and decreases the coercivity.
K Samwer - One of the best experts on this subject based on the ideXlab platform.
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low Temperature Specific Heat anomalies associated with the boson peak in cuzr based bulk metallic glasses
Physical Review B, 2006Co-Authors: Yong Li, W H Wang, K SamwerAbstract:We report the pronounced low-Temperature Specific-Heat C-p anomalies associated with the boson peak in the new CuZr-based bulk metallic glasses. The origin of the C-p anomalies in the atomic glasses is interpreted with the harmonic localized mode based on the dense-packed atomic clusters structural model of metallic glass. The results might have important implications for understanding the origin of the boson peak and the structural features of metallic glasses.
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structural changes of the metallic glass zr65al7 5cu27 5 during glass transition and in the undercooled liquid region
Journal of Applied Physics, 1997Co-Authors: H Schumacher, U Herr, D Oelgeschlaeger, A Traverse, K SamwerAbstract:The metallic glass Zr65Al7.5Cu27.5 exhibits a wide Temperature range in the undercooled liquid region. This offers the possibility of examining the phenomena that occur during glass transition. We investigated this glass by x-ray diffraction and x-ray absorption spectroscopy (XAS) at room Temperature and at elevated Temperatures below and above the glass transition Temperature. The total number of nearest neighbors determined by x-ray diffraction remained unchanged. Using XAS irreversible changes in the short range order (SRO) towards the SRO of crystalline Zr2Cu is observed in the nearest neighbor shell which is consistent with the x-ray diffraction results. The long range order was not affected by these changes. From the Temperature dependence of the atomic mean-square relative displacements σ2, Debye Temperatures were determined and they compare well with low Temperature Specific Heat measurements. Above Tg the slope of σ2 increases drastically and is attributed to anharmonic effects.
Chungang Duan - One of the best experts on this subject based on the ideXlab platform.
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nodeless superconductivity in the presence of spin density wave in pnictide superconductors the case of bafe2 xnixas2
Physical Review B, 2015Co-Authors: M Abdelhafiez, Chungang Duan, Yuanyuan Zhang, Zheng He, Jun Zhao, Christoph Bergmann, C Krellner, Xingye Lu, Xiaojia ChenAbstract:The characteristics of Fe-based superconductors are manifested in their electronic, magnetic properties, and pairing symmetry of the Cooper pair, but the latter remain to be explored. Usually in these materials, superconductivity coexists and competes with magnetic order, giving unconventional pairing mechanisms. We report on the results of the bulk magnetization measurements in the superconducting state and the low-Temperature Specific Heat down to 0.4 K for BaFe$_{2-x}$Ni$_{x}$As$_{2}$ single crystals. The {electronic} Specific Heat displays a pronounced anomaly at the superconducting transition Temperature and a small residual part {at low Temperatures in the superconducting state}. The normal-state Sommerfeld coefficient increases with Ni doping for $x$ = 0.092, 0.096, and 0.10, which illustrates the competition between magnetism and superconductivity. Our analysis of the Temperature dependence of the superconducting-state Specific Heat and the London penetration depth provides strong evidence for a two-band $s$-wave order parameter. Further, the data of the London penetration depth calculated from the lower critical field follow an exponential Temperature dependence, characteristic of a fully gapped superconductor. These observations clearly show that the superconducting gap in the nearly optimally doped compounds is nodeless.
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nodeless superconductivity in the presence of spin density wave in pnictide superconductors the case of bafe2 xnixas2
Physical Review B, 2015Co-Authors: M Abdelhafiez, Chungang Duan, Huiqian Luo, Yuanyuan Zhang, Jun Zhao, Christoph Bergmann, C Krellner, Pengcheng Dai, Xiaojia ChenAbstract:The characteristics of Fe-based superconductors are manifested in their electronic, magnetic properties, and pairing symmetry of the Cooper pair, but the latter remain to be explored. Usually in these materials, superconductivity coexists and competes with magnetic order, giving unconventional pairing mechanisms. We report on the results of the bulk magnetization measurements in the superconducting state and the low-Temperature Specific Heat down to 0.4 K for ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Ni}}_{x}{\text{As}}_{2}$ single crystals. The electronic Specific Heat displays a pronounced anomaly at the superconducting transition Temperature and a small residual part at low Temperatures in the superconducting state. The normal-state Sommerfeld coefficient increases with Ni doping for $x=0.092$, 0.096, and 0.10, which illustrates the competition between magnetism and superconductivity. Our analysis of the Temperature dependence of the superconducting-state Specific Heat and the London penetration depth provides strong evidence for a two-band $s$-wave order parameter. Further, the data of the London penetration depth calculated from the lower critical field follow an exponential Temperature dependence, characteristic of a fully gapped superconductor. These observations clearly show that the superconducting gap in the nearly optimally doped compounds is nodeless.
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a low Temperature Specific Heat study of giant dielectric constant materials
Journal of Physics: Condensed Matter, 2008Co-Authors: C P Sun, Jianjun Liu, Jiunnyuan Lin, Chungang Duan, Waining Mei, H D YangAbstract:A low-Temperature Specific Heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the Specific Heat data in a very low-Temperature range, 0.6–1.5 K, and moderately low-Temperature range, 1.5–5 K, in addition to the expected Debye terms, we observed significant contributions originating from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurring at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behavior in both low and high frequency regions.
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a low Temperature Specific Heat study of the giant dielectric constant materials
Bulletin of the American Physical Society, 2008Co-Authors: C P Sun, Jianjun Liu, Jiunnyuan Lin, Chungang Duan, H D Yang, Waining MeiAbstract:Department of Physics, National Sun Yat-Sen University, Kaoshiung 804, Taiwan, Republic of China Department of Physics, University of Nebraska at Omaha, Nebraska, 68182-0266, USA Institute of Physics, National Chiao-Tung University, Hsinchu 300, Taiwan, Republic of China Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, USA Center for Material Research and Analysis, University of Nebraska-Lincoln, Lincoln, Nebraska, 68588, USA
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a low Temperature Specific Heat study of the giant dielectric constant materials
arXiv: Materials Science, 2007Co-Authors: C P Sun, Jianjun Liu, Chungang Duan, Waining Mei, J Y Lin, H D YangAbstract:Low-Temperature Specific-Heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the Specific Heat data at very low-Temperature range, 0.6 to 1.5 K, and moderately low-Temperature range, 1.5 to 5 K, in addition to the expected Debye terms, we noticed significant contributions originated from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behaviors at both low and high frequency regions.
Christophe Candolfi - One of the best experts on this subject based on the ideXlab platform.
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vibrational dynamics of the type i clathrates a8sn44 2 a cs rb k from lattice dynamics calculations inelastic neutron scattering and Specific Heat measurements
Journal of Applied Physics, 2020Co-Authors: F. Steglich, Christophe Candolfi, M M Koza, Umut Aydemir, Wilder Carrillocabrera, Yu Grin, Michael BaitingerAbstract:We report on a joint theoretical and experimental study of the vibrational dynamics of the type-I clathrates A8Sn44□2 (A = K, Rb, Cs, and □ stands for a vacancy) by high-resolution inelastic neutron scattering experiments combined with low-Temperature Specific Heat measurements (2–300 K). Ab initio lattice dynamics calculations were performed on hypothetical vacancy-free A8Sn46 clathrates in order to determine the phonon dispersions and vibrational density of states Z ( ω ). The Temperature dependence of the generalized vibrational density of states (GVDOS) was traced from 420 K down to 50 K, paying particular attention to the low-energy region of the GVDOS spectra. In the Cs and Rb compounds, the inelastic signal at low energies is dominated by several peaks mainly associated with the dynamics of the alkali metal atoms A in the polyhedral cages of the clathrate structure. In contrast, the low-energy spectrum of the K compound features a more pronounced contribution of the weighed modes of the framework S...
