Temperature dependent local atomic displacements in ammonia intercalated iron selenide superconductor.
Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.
Dipartimento di Fisica, Sapienza Universitá di Roma, P. le Aldo Moro 2, 00185 Roma, Italy.|Center for Life NanoScience@Sapienza, Istituto Italiano di Tecnologia, V. le Regina Elena 291, 00185 Rome, Italy.
E
E
Paris
ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallés, Barcelona, Spain.
L
L
Simonelli
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.
T
T
Wakita
ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallés, Barcelona, Spain.
C
C
Marini
Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
J-H
JH
Lee
ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallés, Barcelona, Spain.|Faculty of Physics, University of Bialystok, 1L K. Ciokowskiego Str., 15-245 Bialystok, Poland.
W
W
Olszewski
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.
K
K
Terashima
Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
T
T
Kakuto
Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
N
N
Nishimoto
Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
T
T
Kimura
Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.|Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
K
K
Kudo
Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
T
T
Kambe
Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.|Department of Physics, Okayama University, Kita-ku, Okayama 700-8530, Japan.
M
M
Nohara
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.
T
T
Yokoya
Dipartimento di Fisica, Sapienza Universitá di Roma, P. le Aldo Moro 2, 00185 Roma, Italy.
N L
NL
Saini