CNR ExploRA

Articolo in rivista, 2021, ENG, 10.1103/PhysRevB.104.094508

Emergence of well-screened states in a superconducting material of the CaFe2As2 family

Pandeya, Ram Prakash; Sakhya, Anup Pradhan; Datta, Sawani; Saha, Tanusree; De Ninno, Giovanni; Mondal, Rajib; Schlueter, C.; Gloskovskii, A.; Moras, Paolo; Jugovac, Matteo; Carbone, Carlo; Thamizhavel, A.; Maiti, Kalobaran

Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research,Homi Bhabha Road, Colaba, Mumbai 400005, India Laboratory of Quantum Optics, University of Nova Gorica, 5001 Nova Gorica, Slovenia Elettra-Sincrotrone Trieste, Area Science Park, 34149 Trieste, Italy Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Area Science Park, I-34149 Trieste, Italy

Coupling among conduction electrons (e.g., Zhang-Rice singlet) are often manifested in the core level spectra of exotic materials such as cuprate superconductors, manganites, etc. These states are believed to play key roles in the ground state properties and appear as low binding energy features. To explore such possibilities in the Fe-based systems, we study the core level spectra of a superconductor CaFe1.9Co0.1As2 (CaCo122) in the CaFe2As2 (Ca122) family employing high-resolution hard x-ray photoemission spectroscopy. While As core levels show almost no change with doping and cooling, the Ca 2p peak of CaCo122 shows reduced surface contribution relative to Ca122 and a gradual shift of the peak position towards lower binding energies with cooling. In addition, we discover the emergence of a feature at the lower binding energy side of the well-screened Fe 2p signal in CaCo122. The intensity of this feature grows with cooling and indicates additional channels to screen the core holes. The evolution of this feature in the superconducting composition and its absence in the parent compound suggests relevance of the underlying interactions in the ground state properties of this class of materials. These results reveal another dimension in the studies of Fe-based superconductors and the importance of such states in the unconventional superconductivity in general.

Physical Review B 104 (9)