分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： In this note we remark that the butterfly effect can be used to diagnose the phase transition of superconductivity in a holographic framework. Speci cally, we compute the butterfly velocity in a charged black hole background as well as anisotropic backgrounds with Q-lattice structure. In both cases we nd its derivative to the temperature is discontinuous at critical points. We also ropose that the butterfly velocity can signalize the occurrence of thermal phase transition in general holographic models.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-08
摘要： We study in detail the phase structure of a holographic p-wave superconductor model in a five dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. To construct complete phase diagrams of the model, we consider both the soliton and black hole backgrounds. In both two cases, there exist second order, first order and zeroth order phase transitions, and the so-called "retrograde condensation" also happens. In particular, in the soliton case with the mass of the vector field being beyond a certain critical value, we find a series of phase transitions happen such as "insulator/superconductor/insulator/superconductor", as the chemical potential continuously increases. We construct complete phase diagrams in terms of temperature and chemical potential and find some new phase boundaries.
分类： 物理学 >> 核物理学 提交时间： 2016-09-02
摘要： We investigate the effect of the inverse magnetic catalysis (IMC) on the charged ρ meson condensation at finite temperature in the framework of the Nambu--Jona-Lasinio model, where mesons are calculated to the leading order of 1/Nc expansion by summing up infinity quark-loops. IMC for chiral condensate has been considered in three different ways, i.e. fitting Lattice data, using the running coupling constant and introducing the chiral chemical potential, respectively. It is observed that, with no IMC effect included, the critical magnetic field eBc for charged ρ condensation increases monotonically with the temperature. However, including IMC substantially affects the polarized charged ρ condensation around the critical temperature Tc of chiral phase transition, the critical magnetic field eBc for charged ρ condensation decreases with the temperature firstly, reaches to a minimum value around Tc, then increases with the temperature. Our calculation indicates that the charged ρ condensation can exist in the temperature region of 1−1.5Tc with critical magnetic field eBc∼0.15−0.3GeV2, which suggests that high temperature superconductor might be created through non-central heavy ion collisions at LHC energies. We also show that a growing electric conductivity in early stage of non-central heavy-ion collisions substantially delays the decay of strong magnetic field, which is helpful for the formation of the high temperature superconductor.
分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2019-04-24
摘要： The electron-pairing mechanism in unconventional high temperature superconductors (HTS) has not been resolved. The author proposed that the electron-pairing medium of unconventional HTS is the change of the electron clouds of transition metal ions, which is analogous to the lattice vibration in conventional superconductors. Real-time evolution of the electron clouds of transition metal ions under excitations in La2Fe2As2O2, FeSe sheet, Fe2KSe2, CaCuO2, and HgBa2Ca2Cu3O8 was calculated by the time-dependent density functional theory (TDDFT). The characteristic frequency is about 90-250 meV, which is equivalent to the lattice vibration frequencies, showing that the change of the electron clouds of the transition metal ions can be the electron-pairing medium in unconventional HTS.
分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2019-06-13
摘要： It is proposed that the electron-pairing medium of the iron-based superconductors may be the orbital fluctuation of the transition metal ions. But the characteristic frequency of the orbital fluctuation has not been given. For the first time, the author has calculated the real-time evolution of the electron clouds of transition metal ions in BaFe2As2 under excitations by the time-dependent density functional theory (TDDFT). There are different modes of fluctuations. The characteristic frequencies are 150 meV, 160 meV, 250 meV, and 200 meV, respectively, for the modes the author observed. The results are unexpected, because the general view is that the change of the electron density is very quick, and the frequency is much higher than the lattice vibration. The frequencies the author obtained are close to that of the lattice vibration in conventional superconductors at normal and high pressures, indicating the orbital (or electron cloud) fluctuation can by the electron pairing medium. Based on the calculation results, the author proposed a new electron pairing mechanism.
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