% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@ARTICLE{Lappas:641876,
      author       = {Lappas, Alexandros and Kaitatzi, Myrsini and Deltsidis,
                      Alexandros and Capel Berdiell, Izar and Simonelli, Laura and
                      Missyul, Alexander and Etter, Martin and Bozin, Emil S.},
      title        = {{O}rbital-{S}elective {I}nstabilities and {S}pin
                      {F}luctuations at the {V}erge of {S}uperconductivity in
                      {I}nterlayer-{E}xpanded {I}ron {S}elenide},
      journal      = {Chemistry of materials},
      volume       = {37},
      number       = {21},
      issn         = {0897-4756},
      address      = {Washington, DC},
      publisher    = {American Chemical Society},
      reportid     = {PUBDB-2025-05228},
      pages        = {8581 - 8594},
      year         = {2025},
      abstract     = {Understanding electron correlation-driven instabilities and
                      their coupling to structural phases is essential for
                      deciphering multiorbital pairing in unconventional
                      superconductors. We investigate Lix(C5H5N)yFe2Se2 (x ∼
                      0.6; y ∼ 0.7–0.9), a tetragonal β-FeSe intercalate with
                      a superconducting transition temperature (Tc = 39 K) closely
                      tied to an expanded Fe-layer spacing (∼11.4 Å).
                      High-resolution synchrotron X-ray diffraction and core-level
                      absorption spectroscopy reveal subtle lattice distortions on
                      cooling without a symmetry-breaking transition. Instead, the
                      material exhibits negative thermal expansion (NTE) in the
                      two-dimensional Fe network below TS ∼ 70 K, and stiffening
                      of local Se–Fe–Se bond dynamics near Tc. The spatially
                      incoherent rearrangement of FeSe4 tetrahedra and the
                      site-local fluctuations, signal reduced electron
                      correlations compared to those of parent β-FeSe (Tc = 8 K).
                      Complementary X-ray emission spectroscopy, a fast local
                      probe of Fe 3d valence states, detects persistent local Fe
                      spin moments below TS, unlike quenching in related systems.
                      These findings indicate that decoupling of Fe planes leads
                      to an electronically driven lattice instability. The latter
                      emerges as NTE induced from weak, orbital-selective
                      localization of in-plane Fe 3d states rather than
                      conventional transverse vibrations. Governed by Hund’s
                      coupling, this selectivity permits coexistence of local spin
                      fluctuations with itinerant d-electrons─critical for
                      enhancing Tc. These results suggest that
                      intercalation-driven d-orbital differentiation moderates
                      electron correlations, providing a pathway to optimize the
                      superconductivity in low-dimensional quantum materials.},
      cin          = {DOOR ; HAS-User / FS-PET-D},
      ddc          = {540},
      cid          = {I:(DE-H253)HAS-User-20120731 /
                      I:(DE-H253)FS-PET-D-20190712},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G3 - PETRA III (DESY) (POF4-6G3)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G3},
      experiment   = {EXP:(DE-H253)P-P02.1-20150101},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.1021/acs.chemmater.5c01488},
      url          = {https://bib-pubdb1.desy.de/record/641876},
}