Superconductivity-induced transverse plasma mode and phonon anomaly in the c-axis response of the bilayer compound RbCa2Fe4As4F2

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Authors

XU B. MUNZAR Dominik DUBROKA Adam SHEVELEVA E. LYZWA F. MARSIK P. WANG C. N. WANG Z. C. CAO G. H. BERNHARD C.

Year of publication 2020
Type Article in Periodical
Magazine / Source Physical Review B
MU Faculty or unit

Faculty of Science

Citation
Web https://doi.org/10.1103/PhysRevB.101.214512
Doi http://dx.doi.org/10.1103/PhysRevB.101.214512
Keywords HIGH-TEMPERATURE SUPERCONDUCTORS; INFRARED CONDUCTIVITY; OPTICAL PHONONS; CHARGE DYNAMICS; PSEUDOGAP; YBA2CU3OY; STATE; GAP
Description We studied the infrared response of polycrystalline samples of the iron arsenide superconductor (Rb, Cs)Ca2Fe4As4F2 (Rb,Cs-12442), which has a bilayer structure similar to the high-T-c cuprates YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8. The c-axis reflectivity spectra R-c have been derived from the reflectivity spectra of the polycrystalline samples R-poly and the in-plane spectrum of a corresponding Cs-12442 crystal R-ab using a geometrical averaging approach with R-c = 3R(poly) - 2R(ab). In analogy to the c-axis response of the cuprates, we observe a superconductivity-induced transverse plasma mode and a phonon anomaly that are both signatures of local electric field effects that arise from a large difference between the local conductivities in the intra- and interbilayer regions. Using a multilayer model developed for the cuprates, we obtain a good description of the c-axis response and derive the local conductivities at T similar or equal to T-c of sigma(bl)(1) (omega -> 0) similar or equal to 1000 Omega(-1)cm(-1) and sigma(int)(1) (omega -> 0) similar or equal to 15 Omega(-1)cm(-1), respectively, that are similar to the ones previously found in underdoped YBCO. Different from the cuprates, we find no evidence of a normal-state pseudogap in terms of a partial suppression of the low-energy electronic states that sets in already well above T-c. There is also no clear sign of an onset of precursor superconducting pairing correlations well above T-c similar or equal to 30 K. This highlights that the pseudogap and the precursor superconducting pairing well above T-c are unique features of the cuprates with their strong electronic correlations and, for example, not just the result of a strongly anisotropic electronic response due to the layered crystal structure.
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