title: New superconductor LixFe1+δSe (x ≤ 0.07, Tc up to 44 K) by an electrochemical route.
abstract: The superconducting transition temperature (Tc) of tetragonal Fe1+δSe was enhanced from 8.5 K to 44 K by chemical structure modification. While insertion of large alkaline cations like K or solvated lithium and iron cations in the interlayer space, the [Fe2Se2] interlayer separation increases significantly from 5.5 Å in native Fe1+δSe to >7 Å in KxFe1-ySe and to >9 Å in Li1-xFex(OH)Fe1-ySe, we report on an electrochemical route to modify the superconducting properties of Fe1+δSe. In contrast to conventional chemical (solution) techniques, the electrochemical approach allows to insert non-solvated Li(+) into the Fe1+δSe structure which preserves the native arrangement of [Fe2Se2] layers and their small separation. The amount of intercalated lithium is extremely small (about 0.07 Li(+) per f.u.), however, its incorporation results in the enhancement of Tc up to ∼44 K. The quantum-mechanical calculations show that Li occupies the octahedrally coordinated position, while the [Fe2Se2] layers remain basically unmodified. The obtained enhancement of the electronic density of states at the Fermi level clearly exceeds the effect expected on basis of rigid band behavior.
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.|MPG-MSU Partner Group, Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Anastasia M
authors.initials: AM
authors.lastname: Alekseeva
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.|MPG-MSU Partner Group, Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Drozhzhin
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.|MPG-MSU Partner Group, Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Dosaev
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Antipov
authors.affiliation: Department of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Konstantin V
authors.initials: KV
authors.lastname: Zakharov
authors.affiliation: Department of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Olga S
authors.initials: OS
authors.lastname: Volkova
authors.affiliation: Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Russia.
authors.forename: Dmitriy A
authors.initials: DA
authors.lastname: Chareev
authors.affiliation: Department of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Vasiliev
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany.
authors.forename: Cevriye
authors.initials: C
authors.lastname: Koz
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schwarz
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany.
authors.forename: Helge
authors.initials: H
authors.lastname: Rosner
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Grin