Superconducting fluctuations and anomalous phonon renormalization much above superconducting transition temperature in Ca4Al2O5.7Fe2As2

Abstract

Raman studies on Ca 4 Al 2 O 5.7 Fe 2 As 2 superconductor in the temperature range of 5 K to 300 K, covering the superconducting transition temperature T c ~ 28.3 K, reveal that the Raman mode at ~ 230 cm -1 shows a sharp jump in frequency by ~ 2 % and linewidth increases by ~ 175 % at T o ~ 60 K. Below T o, anomalous softening of the mode frequency and a large decrease by ~ 10 cm -1 in the linewidth is observed. These precursor effects at T 0 ( ~ 2T c ) are attributed to significant superconducting fluctuations, possibly enhanced due to reduced dimensionality arising from weaked coupling between the well separated (~ 15 Å ) Fe-As layers in the unit cell. A large blue-shift of the mode frequency between 300 K to 60 K ( ~ 7 % ) indicates strong spin-phonon coupling in this superconductor.

Electron-phonon coupling, thermal expansion coefficient, resonance effect, and phonon dynamics in high-quality CVD-grown monolayer and bilayer MoSe2

“…Raman spectroscopic technique has been proved to be very useful for probing 2D as well bulk systems and their various aspects such as layer stacking geometry, strain effect, thermal properties, defects, number of layers, and so on [5,7,[12][13][14][15][16][17][18][19][20]. Several authors have employed temperaturedependent Raman scattering to estimate thermal properties like TEC and thermal conductivity via monitoring the behaviour of the phonon modes as a function of temperature [14][15][16].…”

Magnetoplasmon resonance technique to monitor two-dimensional Dirac superconductors in fluctuating regime

“…Yet, let us not jump to conclusions. Owing to the presence of SC fluctuations, a lot of intriguing physics occurs in superconductors above T c [18][19][20] , and this is of great interest specially in low-dimensional 21,22 and high T c superconductors 23,24 .…”

Phonon anomalies, orbital-ordering and electronic raman scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: temperature-dependent Raman study

“…Towards understanding the elementary excitations in FeBS, a few temperature-dependent Raman studies have been reported on these iron-based superconductors "1111" [22][23], "122" [24][25][26][27][28][29][30][31], "11" [32][33][34], "42622" [35] systems. The phonon anomalies observed in these systems have been attributed to mechanism such as strong spin-phonon coupling, opening of the spin density wave (SDW) gap, first-order structural phase transition and change of the charge distribution within the Fe-As plane.…”