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 effect Substitution effect Other possible parent materials BaFe 2 Se 3, CsFe 2 Se 3 Summary
Collaborators Synthesis and Characterization: Y. Hirata, F. Du, Y. Ueda (ISSP) High-pressure (DAC): H. Takahashi (Nihon Univ.) High-pressure (Cubic): Y. Uwatoko, T. Yamauchi (ISSP) Neutron: T.J. Sato, Y. Nambu (Tohoku Univ.), M. Avdeev (ANSTO) Mossbauer: T. Kawakami (Nihon Univ.) NMR: M. Ito (Nagoya Univ.) PES: T. Mizokawa (Waseda Univ.) XRD: J. Yamaura (Tokyo Tech. ) Optics: H. Okamura (Tokushima Univ.) Theory: R. Arita (Riken)
T c (K) Superconducting transition temperature H 2 S 150 Cuprates HgBa 2 Ca 2 Cu 3 O x 100 50 0 1900 Phonon Magnon Intermetallics Hg Pb NbC NbN BiSrCaCu 2 O x YBa 2 Cu 3 O 7 La 2-x Ba x CuO 4 Nb 3 Sn Nb 3 Ge 1950 Organics Year SmFeAsO MgB 2 LaFeAsO LaFePO 2000 Fe-based
Cuprates and organics superconductors Cuprates Organics Keimer, et al. Nature (2015). Kurosaki, et al. PRL (2005). Insulator Metal Insulator Metal Filling Bandwidth SC appears in the vicinity of Mott transition. Strong electron correlation effect. U ~ 1eV.
Fe-based superconductors Hosono, JACS (2008), Paglione,and Greene, Nat. Phys. (2010). Square lattice of Fe atoms. Fe 2+ coordinated by As or Se tetrahedrally.
Fe-based superconductors Dai,Hu, Dagotto, Nat. Phys. (2012). Paglione,and Greene, Nat. Phys. (2010). Stripe order, ~0.8 m B s+- symmetry Spin or orbital fluctuations T c,max ~ 60 K Mechanisms? Nesting electron hole Q xy xz, yz Orbital ordering yz (xz) Pressure Chemical substitution Ba 1-x K x Fe 2 As 2 BaFe 2-y Co y As 2 All phases are metal.
Electron correlation in Fe-based SCs Material dependence Orbital dependence electron hole Q xy xz, yz Covalent Ionic Low T c High T c T. Miyake, et al., JPSJ 79, 044705 (2010). Renormalization factor z LaFeAsO FeSe z 2 0.61 0.38 x 2 -y 2 0.66 0.47 xy 0.61 0.20 yz/zx 0.60 0.28 M. Aichhorn, et al., PRB 80, 085101 (2009). PRB 82, 064504 (2010).
Fe-based ladder compound BaFe 2 S 3 What happens if we lower the dimensionality and reduce the bandwidth? We can see the strong correlation effect. BaFe 2 S 3 Fe 2+ : (3d) 6 Orthorhombic, Cmcm Earlier works: McQueen, Petrovic, Sefat, Dagotto
Basic physical properties
cm 10 6 10 4 10 2 Resistivity BaFe 2 S 3 j // leg T N T* 10 0 10-2 0 100 200 300 T (K) Mott insulator induced by strong correlation effect.
-1 cm -1 ) Optical conductivity 2000 1000 20 K 60 120 180 240 300 Mott BaFe 2 S 3 CT Leg 0 0.0 1.0 2.0 Rung Layer Photon energy (ev) 3.0 Layer Leg Rung Quasi-one dimensional electronic state. Coherent Fe 3d bands below 0.2 ev even in Mott insulator.
c emu/mol 3x10-3 2 1 Magnetic susceptibility Leg Layer BaFe 2 S 3 H = 5 T T N T* 0 0 Rung 100 T (K) 200 300 Layer Decrease in c on cooling due to quantum fluctuations in 1 D or itinerant nature close to Mott transition. Antiferromagnetic order with the rung direction as the easy axis. Leg Rung
Neutron diffraction BaFe 2 S 3
Magnetic structure of BaFe 2 S 3 b b c a c a Stripe-type magnetic ordering. Ordered moment is 1.3 m B. Much smaller than the highspin value, 4 m B. Inter-ladder coupling is ferromagnetic along one direction, and antiferromagnetic to the perpendicular direction.
High-pressure effect
BaFe 2 S 3 under high pressure Bandwidth-control type Mott transition around 11 GPa. Superconductivity with T c = 24 K. BaFe 2 S 3 0 GPa 13.4 GPa 0 GPa 1.5 4.4 7.3 8.7 9.4 10.1 10.9 11.6 12.7 13.4
BaFe 2 S 3 under high pressure T N T* On applying pressure, T N increases and merge to T*at 3 GPa. Afterwards, T N decreases monotonically and vanishes at 11 GPa. BaFe 2 S 3
BaFe 2 S 3 under high pressure BaFe 2 S 3 Fermi liquid behavior T 2 above Mott transition. Volume fraction, 80 % => Bulkness of superconductivity.
BaFe 2 S 3 under high pressure T* T N Similar to the organic superconductors.
Substitution effect
Hole doping: Ba 1-x K x Fe 2 S 3 Robust insulating state. Magnetic order is gradually destroyed. However, glassy state is present at large x value.
Electron doping: BaFe 2-y Co y S 3 Robust insulating state. Magnetic order is also robust.
Phase diagram Electron-hole asymmetry. Opposite to 2 D Fe-based SCs. Robust insulating state due to small volume change, ~ 1%.
Charge: > Localized near MIT(, ) > Quasi 1D ( ) BaFe 2 S 3 MIT Charge: > Fermi liquid > Quasi 2D ( ) Orbital: > Ordered? ( ) Spin: > Stripe order (ND) > Reduced m, 1.3 m B (ND) > Quasi 1D (k) Questions Charge: >SC at 24 K Mott transition: Mott or Peierls? Magnetism: Localized or itinerant pictures? Role of orbitals? SC: Spin, orbital, and charge fluctuations? s+- or d wave? Substitution effect: Carrier dopant or scatter?
First principle calculation by Arita P = 0 a, b: electron xz, strong correlation g: hole z x Spin fluctuations => s+- between a and b xy and yz, irrelevant Arita, Ikeda, Sakai, Suzuki, PRB (2015); Suzuki, Arita, Ikeda, PRB (2015).
Outline Introduction Fe-based ladder material BaFe 2 S 3 Basic physical properties High-pressure effect Substitution effect Other possible parent materials BaFe 2 Se 3, CsFe 2 Se 3 Summary
cm Resistivity 10 6 10 5 10 4 CsFe 2 Se 3 10 3 10 2 BaFe 2 Se 3 10 1 10 0 10-1 BaFe 2 S 3 10-2 0 100 T (K) 200 300 Ba-S < Ba-Se. Unusual chemical trend. Mixed valence materials (Cs) > Integer valence material (Ba).
Electronic structures BaFe 2 X 3 : (3d) 6 Ionic radius: Se > S Bandwidth: S > Se CsFe 2 Se 3 : (3d) 5.5 Localized ligand holes S, Se Fe u h leg nm Ba-S Ba-Se Rb-Se Cs-Se u 0.264 0.271 0.281 0.284 w 0.269 0.270 0.276 0.275 u/w 0.98 1.00 1.02 1.03 w Ootsuki, PRB (2014). u Resistivity: BaFe 2 S 3 < BaFe 2 Se 3 < CsFe 2 Se 3.
c emu/mol c emu/mol Magnetic susceptibility Leg Layer Rung 4x10-3 4x10-3 3 2 1 0 0 Leg Layer 100 Leg Rung Layer T (K) 200 BaFe 2 Se 3 BaFe 2 S 3 Rung H = 5 T 300 Antiferromagnetic transition with variety of the easy axis. Decrease in c on cooling in A = Ba due to 1D or itinerant origin. Weak ferromagnetism in CsFe 2 Se 3. 3 2 1 0 0 Rung + Layer Leg 100 T (K) CsFe 2 Se 3 H = 5 T 200 300
Magnetic structure Moment (m B ) BaFe 2 S 3 BaFe 2 Se 3 CsFe 2 Se 3 Stripe Block Stripe Cmcm y 1 Pnma Y 4, 10, 16, 22 1.3 m B 2.8 m B 1.8 m B 110 K 255 K 175 K Wide variety of magnetic order. 3 2 Cmcm y 9 + y 7, 8 Magnetic moment scales with T N. 1 0 0 100 200 T N (K) 300
Global phase diagram by Dagotto First-principle calculation for BaFe 2 Se 3 5-fold Hubbard model on the ladder Hartree-Fock approximation (moment of 4 m B ) (3d) 6 Ba-Se Luo, PRB (2013). (3d) 5.75 Ferro. Block Stripe G-type + Para Cs-Se Ba-S Intermediate coupling, U/W ~ 0.5. Parent materials for new high-t c superconductors.
Summary: BaFe 2 S 3 Mott physics 1 D ladder lattice Stripe magnetic order Orbital order? Mott transition with dimensional crossover Superconductivity with T c = 24 K Relevance to cuprates and organic SC Non-toxic Fe-based superconductors Nambu, KO, PRB (2012). Du, KO, PRB (2012). Du, KO, PRB (2014). Ootsuki, Mizokawa, KO, PRB (2015). Hawai, Sato, KO, PRB (2015). Takahashi, KO, Nat. Mater. (2015). Hirata, KO, PRB (2015). Yamauchi, KO, PRL (2015).