The temperature dependence of the anisotropy parameter of upper critical field γHe2 （T） = Hc2^‖ （T） /Hc2^⊥ （T） and London penetration depth γλ （T） = λ‖（T）/λ⊥ （T） are calculated using two-band Ginz...The temperature dependence of the anisotropy parameter of upper critical field γHe2 （T） = Hc2^‖ （T） /Hc2^⊥ （T） and London penetration depth γλ （T） = λ‖（T）/λ⊥ （T） are calculated using two-band Ginzburg-Landau theory for layered superconductors. It is shown that, with decreasing temperature the anisotropy parameter γHc2 （T） is increased, while the London penetration depth anisotropy γλ（T） reveals an opposite behavior. Results of our calculations are in agreement with experimental data for single crystal MgB2 and with other calculations..Results of an analysis of magnetic field Hc1 in a single vortex between superconducting layers are also presented.展开更多
We consider a Ginzburg-Landau modified model of layered high-temperature superconductor under pressure. We have theoretically studied the relation between the pressure and the temperature of layered high-temperature s...We consider a Ginzburg-Landau modified model of layered high-temperature superconductor under pressure. We have theoretically studied the relation between the pressure and the temperature of layered high-temperature superconductor. If the pressure is not a constant, we have a relation of quadratic equation between the pressure and the temperature of layered high-temperature superconductor. In a special case, we find the critical temperature decreases with further increasing pressure. In another special ease, the critical temperature increases with further increasing pressure.展开更多
We report the epitaxial growth of YBCO （YBa2Cu3O7） films on YSZ （Yttria-stabilized Zirconia） （100） substrates by chemical solution deposition. The precursor solution was prepared by dissolving stoichiometric amo...We report the epitaxial growth of YBCO （YBa2Cu3O7） films on YSZ （Yttria-stabilized Zirconia） （100） substrates by chemical solution deposition. The precursor solution was prepared by dissolving stoichiometric amounts of acetates of Y（OOCCH3）3·4H2O, Ba（OOCCH3）2 and Cu（OOCCH3）·2H2O in an aqueous solution of oxalic acid （H2C2O4） and following the sol-gel route. This solution was directly dripped onto YSZ （100） substrates with the help of a Fisher pipette. To form the YBCO film, the sample was crystallized by annealing at 860 ℃ for 12 h in an oxidizing atmosphere. The characterization was performed by XRD （X-ray diffraction） analysis which revealed high intensity （001） reflections and denoted that most of the grains were c-axis oriented. Randomly oriented grains and other phases such as Y2BaCuO5 and CuO were also detected. The superconducting YBCO phase is demonstrated from the susceptibility versus temperature measurements which indicate a superconducting critical temperature ≈ 90 K. In addition, a surface morphology analysis was performed by optical microscopy and atomic force microscopy which revealed an average roughness of 0.2197 μm.展开更多
Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultima...Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultimate'understanding of iron-based superconductivity.The tetragonal binary iron selenide(β-Fe1+δSe)is the structurally simplest iron-based superconductor with a superconducting critical temperature(Tc)of 8.5 K at ambient pressure[2].By intercalation of alkali metal ions into展开更多
Deposition of clean and defect-free atomically thin two-dimensional crystalline flakes on surfaces by mechanical exfoliation of layered bulk materials has proven to be a powerful technique, but it requires a fast, rel...Deposition of clean and defect-free atomically thin two-dimensional crystalline flakes on surfaces by mechanical exfoliation of layered bulk materials has proven to be a powerful technique, but it requires a fast, reliable and non-destructive way to identify the atomically thin flakes among a crowd of thick flakes. In this work, we provide general guidelines to identify ultrathin flakes of TaSe2 by means of optical microscopy and Raman spectroscopy. Additionally, we determine the optimal substrates to facilitate the optical identification of atomically thin TaSe2 crystals. Experimental realization and isolation of ultrathin layers of TaSe2 enables future studies on the role of the dimensionality in interesting phenomena such as superconductivity and charge density waves.展开更多
文摘The temperature dependence of the anisotropy parameter of upper critical field γHe2 （T） = Hc2^‖ （T） /Hc2^⊥ （T） and London penetration depth γλ （T） = λ‖（T）/λ⊥ （T） are calculated using two-band Ginzburg-Landau theory for layered superconductors. It is shown that, with decreasing temperature the anisotropy parameter γHc2 （T） is increased, while the London penetration depth anisotropy γλ（T） reveals an opposite behavior. Results of our calculations are in agreement with experimental data for single crystal MgB2 and with other calculations..Results of an analysis of magnetic field Hc1 in a single vortex between superconducting layers are also presented.
文摘We consider a Ginzburg-Landau modified model of layered high-temperature superconductor under pressure. We have theoretically studied the relation between the pressure and the temperature of layered high-temperature superconductor. If the pressure is not a constant, we have a relation of quadratic equation between the pressure and the temperature of layered high-temperature superconductor. In a special case, we find the critical temperature decreases with further increasing pressure. In another special ease, the critical temperature increases with further increasing pressure.
文摘We report the epitaxial growth of YBCO （YBa2Cu3O7） films on YSZ （Yttria-stabilized Zirconia） （100） substrates by chemical solution deposition. The precursor solution was prepared by dissolving stoichiometric amounts of acetates of Y（OOCCH3）3·4H2O, Ba（OOCCH3）2 and Cu（OOCCH3）·2H2O in an aqueous solution of oxalic acid （H2C2O4） and following the sol-gel route. This solution was directly dripped onto YSZ （100） substrates with the help of a Fisher pipette. To form the YBCO film, the sample was crystallized by annealing at 860 ℃ for 12 h in an oxidizing atmosphere. The characterization was performed by XRD （X-ray diffraction） analysis which revealed high intensity （001） reflections and denoted that most of the grains were c-axis oriented. Randomly oriented grains and other phases such as Y2BaCuO5 and CuO were also detected. The superconducting YBCO phase is demonstrated from the susceptibility versus temperature measurements which indicate a superconducting critical temperature ≈ 90 K. In addition, a surface morphology analysis was performed by optical microscopy and atomic force microscopy which revealed an average roughness of 0.2197 μm.
文摘Iron-based superconductors include pnictides and chalcogenides.So far,the chalcogenides are much fewer in number[1],thus it is particularly valuable to find new superconductors in iron chalcogenides,for the'ultimate'understanding of iron-based superconductivity.The tetragonal binary iron selenide(β-Fe1+δSe)is the structurally simplest iron-based superconductor with a superconducting critical temperature(Tc)of 8.5 K at ambient pressure[2].By intercalation of alkali metal ions into
文摘Deposition of clean and defect-free atomically thin two-dimensional crystalline flakes on surfaces by mechanical exfoliation of layered bulk materials has proven to be a powerful technique, but it requires a fast, reliable and non-destructive way to identify the atomically thin flakes among a crowd of thick flakes. In this work, we provide general guidelines to identify ultrathin flakes of TaSe2 by means of optical microscopy and Raman spectroscopy. Additionally, we determine the optimal substrates to facilitate the optical identification of atomically thin TaSe2 crystals. Experimental realization and isolation of ultrathin layers of TaSe2 enables future studies on the role of the dimensionality in interesting phenomena such as superconductivity and charge density waves.
