Understanding interlayer interaction in layered supercoducting materials. Eugenio Paris University La Sapienza of Rome

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Ralph Dixon
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1 Understanding interlayer interaction in layered supercoducting materials Eugenio Paris University La Sapienza of Rome

2 My PhD Thesis project Study of local structure, local disorder and interlayer interaction in layered superconductors Fe-based superconductors BiS 2 -based superconductors Compounds: Ca 10 M 4 (Fe 2 As 2 ) 5 Compounds: REOBiCh 2 Li x (NH 3 ) y Fe 2 EuFBiS 2 - Eu 3 F 4 Bi 2 S 4 Technique: EXAFS, XANES Technique: EXAFS, XANES, μxanes High Pressure XAS, XRD ARPES, μarpes

3 My PhD Thesis project Study of local structure, local disorder and interlayer interaction in layered superconductors Fe-based superconductors BiS 2 -based superconductors Compounds: Ca 10 M 4 (Fe 2 As 2 ) 5 Compounds: REOBiCh 2 Li x (NH 3 ) y Fe 2 EuFBiS 2 - Eu 3 F 4 Bi 2 S 4 Technique: EXAFS, XANES Technique: EXAFS, XANES, μxanes High Pressure XAS, XRD Outline ARPES, μarpes 1. Local structural optimization in Fe-based superconductors 2. Short overview on my results on BiS 2 -based superconductors

4 The Fe-based superconductors Se Fe As Li Ba O La Ir/Pt Ca FeSe LiFeAs BaFe 2 As 2 LaFeAsO Ca 10 M 4 Fe 10 As 18 The active layer Pn/Ch Fe Pn/Ch Same building block: Fe(Pn/Ch) 4 tetrahedron

5 The Fe-based superconductors Doping Element substitution/strain Pressure Multiband materials Disconnected Fermi surface Disorder and defects control the low-energy electronic properties

Higher T c by local structural optimization Anion height Bond angle Interlayer spacing h Fe Fe Se Se α d Li Nd Dy Pr Er Ba Ce La Na T c (K) 50 40 30 20 10 FeSe 0.5 Te 0.

6 Higher T c by local structural optimization Anion height Bond angle Interlayer spacing h Fe Fe Se Se α d Li Nd Dy Pr Er Ba Ce La Na T c (K) FeSe 0.5 Te 0.5 K x Fe 2 A x (C-H-N)Fe 2 FeSe FeSe Distance between FeSe layers (Å) Y. Mizuguchi et al, SUST 23, C.H. Lee et al, Solid State Comm 152, 644 Noji et al, Physica C 504, 8

7 X-ray absorption fine structure spectroscopy (XAFS) Observable: modulation of the X-ray absorption cofficient due to the scattering of photoelectron within a cluster of neighboring atoms µ Isolated atom Photon Energy µ Embedded atom Photon Energy Why XAFS? Local (< 10 Å) and fast (10-15 s) probe Atomic site selective Does not require long range order

8 X-ray absorption fine structure spectroscopy (XAFS) Observable: modulation of the X-ray absorption cofficient due to the scattering of photoelectron within a cluster of neighboring atoms Isolated atom Embedded atom Why XAFS? µ µ Local (< 10 Å) and fast (10-15 s) probe Atomic site selective Photon Energy Photon Energy Does not require long range order Real space local information EXAFS signal Fourier transform Site projected pair distribution function Information on: Bond distance Local order/disorder Bond fluctuations - Local dynamics Wave vector (Å -1 ) Radial distance (Å)

9 Ammonia-intercalated Li x (NH 3 ) y Fe 2 High-Tc route in Fe-chalcogenide Start Pressure FeSe (T c = 8 K) Hsu et al, PNAS 105, (2008) FeSe (T c = 27 K) Mizuguchi et al, APL 93, 10 (2008) Strain FeSe 1-x Te x (T c = 15 K) Mizuguchi et al, JPSJ 78, 1 (2009) Intercalation A x Fe 2-y (T c = 32 K) Guo et al, PRB 82, (2010) 1-layer on STO FeSe (T c = 100 K)! Ge et al, Nat. Mat. 14 (2015) Local structural optimization!

Ammonia-intercalated Li x (NH 3 ) y Fe 2 High-Tc route in Fe-chalcogenide Intercalation with ammonia molecules Start FeSe (T c = 8 K) Hsu et al, PNAS 105, 14262 (2008) 50 Pressure FeSe (T c = 27 K)

10 Ammonia-intercalated Li x (NH 3 ) y Fe 2 High-Tc route in Fe-chalcogenide Intercalation with ammonia molecules Start FeSe (T c = 8 K) Hsu et al, PNAS 105, (2008) 50 Pressure FeSe (T c = 27 K) 40 A x (C-H-N)Fe 2 Mizuguchi et al, APL 93, 10 (2008) Strain FeSe 1-x Te x (T c = 15 K) T c (K) K x Fe 2 d Mizuguchi et al, JPSJ 78, 1 (2009) Intercalation A x Fe 2-y (T c = 32 K) Guo et al, PRB 82, (2010) 1-layer on STO FeSe (T c = 100 K)! Ge et al, Nat. Mat. 14 (2015) 10 0 FeSe 0.5 Te 0.5 FeSe Distance between FeSe layers (Å) Li x (NH 3 ) y Fe 2 (T c = 45 K) Burrard-Lucas et al, Nat. Mat. 12, 15 (2013) Local structural optimization! Effect of intercalation on local atomic structure?

11 Ammonia-intercalated Li x (NH 3 ) y Fe 2 Experiment ALBA synchrotron radiation facility CLÆSS beamline Fe K-edge EXAFS Single crystal of Li x (NH 3 ) y Fe 2 esfoliated under Ar atmosphere χ(k) k 2 c-axis 18 I t Measurement on high vacuum Wave vector (Å -1 ) 16 I 0 ε (a,b) plane Normal incidence T-dependence with He cryostat ε // (a,b) geometry enhances cross section of Fe-Fe scattering Se Fe FT(χ(k) k 2 ), modulus Temperature (K) Fe-Fe Fe-Se 2 Fe-Fe Fe-Se 3 4 Radial distance (Å) Fe-Se-Fe 5

12 Ammonia-intercalated Li x (NH 3 ) y Fe 2 2-shell model (Fe-Se + Fe-Fe scattering) Anion height (Å) h z Se Fe FeSe K x Fe 2-y The FeSe 4 tetrahedron is locally compressed Bond angle ( ) Temperature (K) α Fe Se E. Paris et al, Scientific Reports 6, (2016)

13 The EXAFS Debye-Waller factor Fit to the Einstein model Mean Square Relative Displacement (MSRD) R 10 χ(k) χ(r) MSRD (Å ) T c Fe-Fe θ E = 248 ± 10 K θ E Fe-Se = 313 ± 10 K E. Paris et al, Scientific Reports 6, (2016) Temperature (K) 300

14 The EXAFS Debye-Waller factor Mean Square Relative Displacement (MSRD) R 10 Fit to the Einstein model Fe-Fe bond stiffness FeSe θ E = 268 K χ(k) χ(r) MSRD (Å ) T c Fe-Fe θ E = 248 ± 10 K θ E Fe-Se = 313 ± 10 K Fe-Fe MSRD (a.u.) K x Fe 2-y θ E = 208 K Li x (NH 3 ) y Fe 2 θ E = 248 K Temperature (K) Temperature (K) 300 E. Paris et al, Scientific Reports 6, (2016)

15 Hardening of the local lattice mode at T = T c MSRD (Å ) M/H (emu/mol) Temperature (K) 120 E. Paris et al, Scientific Reports 6, (2016)

16 Hardening of the local lattice mode at T = T c Cuprates Ba122 pnictide MSRD (Å ) σ T c La 2 CuO 4.1 T c T co T co LCO Bi2212 M. Hacisalihoglu, E. Paris et al, PCCP 18 (2016) Nb 3 Ge M/H (emu/mol) T c Bi 2 Sr 2 CaCu 2 O 8+ δ Hg1201 HgBa 2 CuO 4+ δ Temperature (K) T (K) N.L. Saini et al, JPSJ 90 (2000) N.L. Saini et al, Phys. Rev. B 68 (2003) E. Paris et al, Scientific Reports 6, (2016)

17 Summary - so far... Local structural effect of NH 3 -intercalation in Li x Fe 2 Compressed FeSe layer due molecular to intercalation Bond force constant (local Fe-Fe bond dynamics) similar to binary FeSe Clear drop in Debye-Waller factor at Tc - Local lattice plays a central role Work published in E. Paris et al, Scientific Reports 6, (2016).

The skutterudite-type iron pnictide Ir-related SPT! Metallic spacer layer! Ca Ir/Pt 10.39 Å ρ ab (mωcm) As Fe 0 100 200 300 Temperature (K) K.

18 The skutterudite-type iron pnictide Ir-related SPT! Metallic spacer layer! Ca Ir/Pt Å ρ ab (mωcm) As Fe Temperature (K) K. Kudo et al, Scientific Reports 3, 3101 (2013) Ca 10 M 4 (Fe 2 As 2 ) 5 M = Ir,Pt No magnetism! Tc without doping Local structure and disorder in spacer layer? Role of M spin-orbit coupling? Response of the FeAs 4 local structure on intercalation?

Why T c in is higher when Pt is in place of Ir?

F ascribed to Ir-As disorder Sawada et al, Phys. Rev.

structure similar to other FeSC Sunagawa et al, J. Phys. Soc. Jpn.

As 2 ) 5 Ca 10 Pt 4 (Fe 2 As 2 ) 5 The difference in T c seems not

19 Why T c in is higher when Pt is in place of Ir? Ca 10 Ir 4 (Fe 2 As 2 ) 5 T c = 16 K ARPES : Non-dispersing band at E F ascribed to Ir-As disorder Sawada et al, Phys. Rev. B 89 (2014) Ca 10 Pt 4 (Fe 2 As 2 ) 5 T c = 38 K ARPES : Electronic structure similar to other FeSC Sunagawa et al, J. Phys. Soc. Jpn. 84 (2015) Different transport properties ρ ab (mωcm) Ca 10 Ir 4 (Fe 2 As 2 ) 5 Ca 10 Pt 4 (Fe 2 As 2 ) 5 The difference in T c seems not follow the anion height/angle rule (from XRD) Ni et al, PNAS 108 (2011) Temperature (K) Temperature (K)

T-dependent XAS on Ca 10 Ir 4 (Fe 2 As 2 ) 5 Spacer layer: Ir L 3 -edge EXAFS Disordered IrAs layer Filtered χ(k) k 2 4 6 8 10 Wave vector (Å -1 ) 12 FT [χ(k) k 2 ] 0 1 2 3 4 5 Distance (Å) 6 Data

20 T-dependent XAS on Ca 10 Ir 4 (Fe 2 As 2 ) 5 Spacer layer: Ir L 3 -edge EXAFS Disordered IrAs layer Filtered χ(k) k Wave vector (Å -1 ) 12 FT [χ(k) k 2 ] Distance (Å) 6 Data Fit Ir L 3 -edge ( KeV) 45 K 7 Ir L 3 /L 2 -edge XANES Marginal role of SO coupling Distribution of Ir valence - disorder! Active layer: Fe K-edge EXAFS Filtered χ(k) k Wave vector (Å -1 ) ESRF 14 FT [χ(k) k 2 ] E. Paris et al, Phys. Rev. B 90, (2014) Distance (Å) Relaxed Fe-Fe network Local disorder 6 Data Fit Fe K-edge (7.112 KeV) 35 K 7 Distorted FeAs 4 tetrahedra Fe As As height 1.5 Å As-Fe-As angle Fe-Fe stiffness 224 K Fe Static disorder Å 2

21 Why Tc in is higher when Pt is in place of Ir? Lower local disorder when Ca 10 Pt 4 (Fe 2 As 2 ) 5 with respect to Ca 10 Ir 4 (Fe 2 As 2 ) 5 FT(χ(k) k 2 ), modulus 0 Sample c Pt 4 Ir 4 (a,b) plane 80 X-ray To PFY detector Distance (Å) 8 k(å -1 ) MSRD (Å ) Fe-Fe M = Pt Fe-As M = Pt Temperature (K) ESRF

22 Why Tc in is higher when Pt is in place of Ir? Lower local disorder when Ca 10 Pt 4 (Fe 2 As 2 ) 5 with respect to Ca 10 Ir 4 (Fe 2 As 2 ) 5 FT(χ(k) k 2 ), modulus 0 Sample c Pt 4 Ir 4 (a,b) plane 80 X-ray To PFY detector 1 5 As height 2 As-Fe-As angle Fe-Fe stiffness Fe Static disorder k(å -1 ) Distance (Å) M = Ir M = Pt 1.53 Å 1.43 Å MSRD (Å ) 224 K 224 K Optimized local Fe-As bond distance/angle Å Å 2 Same peculiar Fe-Fe dynamics ESRF M = Ir Fe-Fe M = Pt 6 M = Ir Fe-As 4 2 M = Pt Temperature (K)

23 Summary - so far... Local structural effect of NH 3 -intercalation in Li x Fe 2 Compressed FeSe layer due molecular to intercalation Bond force constant (local Fe-Fe bond dynamics) similar to binary FeSe Clear drop in Debye-Waller factor at Tc - Local lattice plays a central role Work published in E. Paris et al, Scientific Reports 6, (2016). Local structure of Ca 10 M 4 (Fe 2 As 2 ) 5 Ca 10 Ir 4 (Fe 2 As 2 ) 5 Marginal role of Ir spin-orbit coupling Disordered Ir-As layer Why T c is higher when M = Pt? Relaxed Fe-Fe dynamics, distorted FeAs 4 tetrahedron resulting from strong interlayer interaction Different degree of local disorder Lower distortion of FeAs 4 tetrahedron Part of the work in E. Paris et al, Phys. Rev. B 90, (2014).

24 The BiS 2 -based superconducting family Same crystal structure of Fe-based, multiband materials Active layer Active layer Doping Chemical pressure Pressure

25 Local effect of F-doping in CeOBiS 2 Bi L 3 -edge EXAFS Ce L 3 -edge EXAFS + XANES Local structure affects: Absorption Intensity (arb. units) 4f 1 4f 0 Valence fluctuation 2.8 Coexistence of SC and FM x = 0.0 x = 0.2 x = 0.4 x = 0.6 x = 0.8 x = 1.0 Background CR Ce L 3 -edge XANES CeO1-xFxBiS Photon Energy (ev) T. Sugimoto, E. Paris et al, Phys. Rev. B 89, (2014) E. Paris et al, J. Phys.: Cond. Mat. 26, (2014) Bond distance (Å) F-content (x) Bi-S1 Bi-S Ce-S-Bi channel Bond distance (Å) x < 0.4 x > F-content (x) Ce-S-Ce channel Ce-S2 Ce-O Crossover from valence fluctuation regime to Kondo-like regime

26 Large static distortion in the Bi-S plane We observed anomalously large Debye-Waller factor for the in-plane Bi-S1 bond How does it change in other compounds? 0.03 Bi-S Ce 100% σ 2 (Å 2 ) Bi-S2 CeO 1-x F x BiS 2 σ 2 (Å 2 ) Nd 100% Bi-S1 Bi-S1(a) F-content (x) Bi-S Mean RE ionic radius (pm) Seems to be a common feature of BiS 2 -based... Bondlength splitting? Y. Mizuguchi, E. Paris et al, Phys. Chem. Chem. Phys. 17, (2015)

27 Locally distorted ground state in LaOBiS 2 Symmetric square lattice Bi-S Bi S1 Expected to be unstable towards ferroelectric distortion! a-axis b-axis Q. Liu, X. Zhang, A. Zunger, Phys. Rev. B 93, (2016) PhD ending seminar - Eugenio Paris - 27.Oct.2016

28 Locally distorted ground state in LaOBiS 2 Symmetric square lattice Bi-S Bi S1 Expected to be unstable towards ferroelectric distortion! Locally distorted a-axis b-axis a-axis b-axis Q. Liu, X. Zhang, A. Zunger, Phys. Rev. B 93, (2016) T-dependent Bi L 3 -edge EXAFS Quantification of local distortion in LaOBiS 2 In-plane displacement parameter measured PhD ending seminar - Eugenio Paris - 27.Oct.2016

29 Locally distorted ground state in LaOBiS 2 Symmetric square lattice Bi-S Bi S1 Expected to be unstable towards ferroelectric distortion! Locally distorted a-axis b-axis a-axis b-axis Q. Liu, X. Zhang, A. Zunger, Phys. Rev. B 93, (2016) T-dependent Bi L 3 -edge EXAFS Bi L 1 -edge and Se K- EXAFS Quantification of local distortion in LaOBiS 2 In-plane displacement parameter measured Removal of distortion by Se-substitution σ 2 (10-3 Å 2 ) Bi-S1 Bi-Se Confirmed theoretical prediction Bi-S x in LaOBiS 2-x Se x PhD ending seminar - Eugenio Paris - 27.Oct.2016

XAS and μarpes on self-doped Eu 3 F 4 Bi 2 S 4 system

X-ray 33 66 Sample Eu 3+ PFY c Indication of Eu 2+/3+

3 e - /Bi However...Insulating behavior!

30 XAS and μarpes on self-doped Eu 3 F 4 Bi 2 S 4 system Eu(1) Eu(2) Normalized Absorption Data Best Fit Eu 2+ X-ray Sample Eu 3+ PFY c Indication of Eu 2+/3+ valence fluctuation From XAS self-doping of 0.3 e - /Bi However...Insulating behavior! Where are the electrons? Photon Energy (KeV) M Γ X E. Paris et al, manuscript submitted

Pressure-dependent carrier concentration in Eu 3 F 4 Bi 2 S 4 Source White beam Higher energy Sample Lower energy Position-Sensitive Detector Lower energy Higher energy PSD Normalized Intensity 4f 1

31 Pressure-dependent carrier concentration in Eu 3 F 4 Bi 2 S 4 Source White beam Higher energy Sample Lower energy Position-Sensitive Detector Lower energy Higher energy PSD Normalized Intensity 4f 1 2 4f Pressure (GPa) 10 Normalized Intensity Eu valence Eu 2+ Eu GPa 11.6 GPa Photon Energy (KeV) Photon Energy (KeV) Pressure (GPa) 12 By measuring the Eu valence state we have provided the first observation of the pressure-dependent carrier doping in self-doped BiS 2 -based SC

32 Summary REOBiS 2 - family Clear evolution in the local structure of the active layer upon doping in the spacer layer Very large value of the Debye-Waller factor, indicating large local distortion In CeOFBiS2 we provided explanation for coexistence of FM and SC in terms of local displacements The BiS4 square is locally distorted into short and long Bi-S bond As predicted by theory, we observed removal of the local distortion by Se-substitution Part of the work in T. Sugimoto et al, Phys. Rev. B 89, (R) (2014). E. Paris et al, JPCM 26, (2014). T. Sugimoto et al, JPCS 592, (2015). Y. Mizuguchi et al, PCCP 17, (2015). T. Sugimoto et al, Phys. Rev. B 94, (R)(2016). Self-doped EuFBiS 2 and Eu 3 F 4 Bi 2 S 4 First observation of the electronic structure - Indication of self-doped conduction band First observation of the pressure-dependent carrier doping E. Paris et al, manuscript submitted

33 Publications 1) Role of the Ce valence in the coexistence of superconductivity and ferromagnetism of CeO 1-x F x BiS 2 revealed by Ce L 3 -edge x-ray absorption spectroscopy, Phys. Rev. B 89, (2014) 2) Determination of local atomic displacements in CeO 1-x F x BiS 2 system, J. Phys.: Cond. Mat. 26, (2014) 3) Electronic structure of LaO 1-x F x Bi (x = 0.18) revealed by photoelectron spectromicroscopy, Phys. Rev. B. 90, (2014) 4) Anderson s impurity model analysis on CeO 1-x F x BiS 2, J. Phys.: Conf. Series 592, (2015) BiS 2 -based superconductors 5) The effect of RE substitution in layered REO 0.5 F 0.5 BiS 2 : chemical pressure, local disorder and superconductivity, Phys. Chem. Chem. Phys. 17, (2015) 6) Localized and mixed valence state of Ce 4f in superconducting and ferromagnetic CeO 1-x F x BiS 2 revaled by x-ray absorption and photoemission spectroscopy, Phys. Rev. B 94, (R) (2016) 7) Electronic structure of self-doped BiS2-based superconductor Eu3Bi2F4S4 revealed by combined x-ray absorption and photoelectron spectromicroscopy, Manuscript submitted 8) Determination of temperature-dependent atomic displacements in the Ca 10 Ir 4 (Fe 2 As 2 ) 5 superconductor with a metallic spacer layer, Phys. Rev. B 90, (2014) 9) Effect of chemical pressure in the local structure of La 1-x Sm x FeAsO, Sup. Sci. Tech. 28, (2015) 10) The nanoscale structure and unoccupied valence electronic states in FeSe 1-x Te x chalcogenides probed by x-ray absorption measurements, Phys. Chem. Chem. Phys. 17, (2015) 11) Temperature dependent local atomic displacements in ammonia intercalated iron selenide superconductor, Scientific Reports 6, (2016) 12) A study of temperature dependent local atomic displacements in Ba(Fe 1-x Co x ) 2 As 2 superconductor, Phys. Chem. Chem. Phys. 18, 9029 (2016) 13) Pressure dependence of the local structure of iridium ditelluride across the structural phase transition, Phys. Rev. B 93, (2016) Fe-based superconductors Other collaborations PhD ending seminar - Eugenio Paris - 27.Oct.2016

34 Acknowledgements Gruppo G4, Sapienza Sample preparation N.L. Saini, M.Y. Hacisalihoglu Waseda University (Tokyo) T. Mizokawa Y. Mizuguchi, M. Nohara, Y. Takano, Y. Aoki,... Experiments University of Tokyo T. Sugimoto, D. Ootsuki Okayama University T. Wakita, K. Terashima, T. Yokoya C. Marini, L. Simonelli, B. Joseph A. Iadecola, P. Postorino, S. Caramazza,... PhD student support Thank you for your attention!

Superconductivity in Fe-based ladder compound BaFe 2 S 3

02/24/16 QMS2016 @ Incheon Superconductivity in Fe-based ladder compound BaFe 2 S 3 Tohoku University Kenya OHGUSHI Outline Introduction Fe-based ladder material BaFe 2 S 3 Basic physical properties High-pressure