Nonlinear uniaxial pressure dependence of the resistivity in Sr_(1-x)Ba_xFe_(1.97)Ni_(0.03)As_2

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr_(1-x)Ba_xFe_(1.97)Ni_(0.03)As_2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr_(1-x)Ba_xFe_2As_2 is determined by the strength of the magnetic-elastic coupling.     

Anharmonic Vibrational Signatures of DNA Bases and Watson-Crick Base Pairs

在密度泛函理论水平上研究了从DNA碱基单体到Watson-Crick碱基对的结构、电荷分布、以及非谐性振动参数的变化. 通过研究参与碱基对中多重氢键的NH₂、N-H和C=O的伸缩振动模式，预测了这些模式的对角非谐性常数、非对角非谐性常数、以及非谐性振动耦合对碱基结构变化的敏感性. 研究结果揭示了DNA碱基中非谐性振动势、分子间氢键和静电相互作用之间的内在联系.