1 / 29

NMR studies in Iron-based superconductor NaFeAs under pressure

NMR studies in Iron-based superconductor NaFeAs under pressure. Kitaoka Lab. Masashi Miyamoto. K.Kitagawa et.al. JPSJ 80 , 033705 (2011) L. Ma et.al. PRB 83 , 132501 (2011) G. F. Ji et.al. PRL 111 , 107004 (2013 ). Contents. 1. Introduction

alea-avila
Download Presentation

NMR studies in Iron-based superconductor NaFeAs under pressure

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NMR studies in Iron-based superconductor NaFeAsunder pressure Kitaoka Lab. Masashi Miyamoto K.Kitagawa et.al. JPSJ 80, 033705 (2011) L. Ma et.al. PRB 83, 132501 (2011) G. F. Ji et.al.PRL 111, 107004 (2013)

  2. Contents 1. Introduction ・Iron-based Superconductors ・111 system 2. Sample (NaFe1-xCoxAs) 3. Experiments 4. Results 5. Summary

  3. Iron-based superconductors Introduction 1 1900 1920 1940 1960 1980 2000 2020 Year 200 metal Pairing glue heavy fermion system high-Tccuprate Electron-phonon interaction 163 Hg-Ba-Ca-Cu-O iron-based system under high pressure （ ） 150 Hg-Ba-Ca-Cu-O Spin or valence fluctuation Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O 100 Transition temperature (K) Y-Ba-Cu-O Spin fluctuation 77 Spin fluctuation or/and Orbital fluctuation ? SmO F FeAs 50 0.9 0.11 MgB2 La-Ba-Cu-O LaO F FeAs PuCoGa5 Nb Ge 0.11 0.89 Nb Pb CeCu2Si2 NbN LaOFeP Hg NbC 0

  4. Iron-based superconductors Introduction 2 111 As 42622 1111 122 11 Fe Ln= lanthanoid Ae=Ba, Sr, Ca, Eu A =Li,Na 2D like electronic state 3D like electronic state Ln A Ae Short Ca4Al2O6-yFe2As2 FeSe LaFeAsO1-y BaFe2As2 LiFeAs Tcmax= 38 K Tcmax= 13 K Tcmax= 56 K Tcmax= 31K Tcmax= 46 K Distance between FePn-planes Distance between Fe-planes Long Long

  5. Fe-As tetrahedral structure and Tc Introduction 3 Regular tetrahedron (109.5°) hpn Fe As α As–Fe–As angle α(deg.) hpn:Pnictogen height from Fe layer (Å)

  6. Iron-based superconductors Introduction 4 111 42622 1111 122 11 Diversity of Crystal Structure Ln= lanthanoid Ae=Ba, Sr, Ca, Eu A =Li,Na 2D like electronic state Ln 3D like electronic state A Ae Ca4Al2O6-yFe2As2 FeSe LaFeAsO1-y BaFe2As2 LiFeAs Tcmax= 38K Tcmax= 13 K Tcmax= 56 K Tcmax= 31K Tcmax= 40 K ・ Superconducting state appear without doping orapplication pressure

  7. NaFe1-xCoxAs Sample 1 Electron-dope Low SC volume fraction

  8. NaFe1-xCoxAs phase diagram Sample 2 Down side Structural transition temperature (tetragonal to orthorhombic) Magnetic phase transition temperature TC AFM Upper side Stripe antiferromagnetic state Tcmax = 20K (x ≃ 0.028)

  9. High pressure study in NaFe1-xCoxAs Sample 3 TS TAFM A. F. Wang et.al. New Journal of Physics 14 (2012) 113043 TC AFM x = 0 x = 0.01 x = 0.028 x = 0.075 Pressure

  10. NaFe1-xCoxAs Sample 4 NaFeAs NaFeAs under pressure TS TAFM TC AFM NaFe0.94Co0.06As under pressure Pressure NMR measurement

  11. Nuclear magnetic resonance (NMR) Experiments 1 Zeemann splitting I = 1/2 m = -1/2 I = ±1/2 m = +1/2 H0＝0 H0 ≠ 0 gH0 Knight shift g(H0+ΔH) NMR Intensity [a.u.] frequency

  12. Nuclear magnetic resonance (NMR) Experiments 2 Zeemann splitting m = -3/2 I = 3/2 I = ±3/2, ±1/2 m = -1/2 m = +1/2 m = +3/2 H0＝0 H0 ≠ 0 Electric quadropoleinteraction(I ≧1) +1/2⇔-1/2 -1/2⇔-3/2 +3/2⇔+1/2 NMR Intensity [a.u.] frequency

  13. Nuclear magnetic resonance (NMR) Experiments 4 Zeemann splitting m = -3/2 I = 3/2 I = ±3/2, ±1/2 m = -1/2 m = +1/2 m = +3/2 H0＝0 H0 ≠ 0 Electric quadropoleinteraction(I ≧1) Exp. Antiferromagnetic state H0 -1/2⇔+1/2 -3/2⇔-1/2 +1/2⇔+3/2 NMR Intensity [a.u.] frequency

  14. Nuclear magnetic resonance (NMR) Experiments 4 Zeemann splitting m = -3/2 I = 3/2 I = ±3/2, ±1/2 m = -1/2 m = +1/2 m = +3/2 H0＝0 H0 ≠ 0 Electric quadropoleinteraction(I ≧1) Exp. Antiferromagnetic state H0 -1/2⇔+1/2 -3/2⇔-1/2 +1/2⇔+3/2 NMR Intensity [a.u.] ・Internal magnetic field ・Magnetic moment frequency

  15. Nuclear magnetic relaxation rate (T1) Experiments 5 t < 0 t > 0 t = 0 m=-1/2 H0 m=+1/2 Thermal equilibrium state M = M（∞） Exited state M = M(0) = 0 Relaxation M= M（t） M M(t) = M(∞)[1- exp(-t/T1)] t time

  16. Nuclear magnetic relaxation rate (T1) Experiments 5 t < 0 t > 0 t = 0 Electronic spin m=-1/2 H0 m=+1/2 Dynamic susceptibility T1 measurement Spin fluctuation

  17. Results NaFeAs TS TAFM TC AFM Pressure K.Kitagawa et.al. JPSJ 80, 033705 (2011)

  18. 75As-NMR spectrum Results H a/b H c Structural transition at To(=57K) AF transition at TAF(=45K) TS TAFM TC AFM

  19. 23Na-NMR spectrum Results AF transition at TAF(= 45K) Incommensurate modulation of the hyperfine field Incommensurate to commensurate crossover Commensurate AF Spin density wave (SDW)

  20. Nuclear lattice relaxation rate (T1) Results Development of a strong anisotropy of the AF fluctuation Spin fluctuation enhanced at TAF TAF TO

  21. Results NaFeAs under pressure TS TAFM TC AFM Pressure L. Ma et.al. PRB 83, 132501 (2011)

  22. 23Na-NMR spectrum (T = 2K) Results 0.4GPa 1.2GPa 2.0GPa 2.56GPa f (MHz) Antiferromagnetic ordering AF moment

  23. 23Na-NMR spectrum (T = 2K) Results 0.4GPa 1.2GPa 2.0GPa 2.56GPa f (MHz) TAF(K) Magnetic ordering tempereatureTAF increasewith pressure

  24. Results Avoiding both the structural and magnetic phase transition TS TAFM TC NaFe0.94Co0.06As under pressure AFM Pressure G. F. Ji et.al.PRL 111, 107004 (2013)

  25. Susceptibility Results NaFe0.94Co0.06As Tc max (@2.17 GPa) T SC SC x Dome shape phase diagram P

  26. Nuclear magnetic relaxation rate (T1) Results spin fluctuation Low-energy spin fluctuation is enhancedby pressure !

  27. 1/T1T Results 2.17GPa 2.46GPa 1/T1T (T = 30K) become max at P ≃ 2.17GPa Nonmonotonic pressure dependence of 1/T1T !

  28. 1/T1T (T = 30K) Results 1?11 Tcm 1/T1T (T = 30K) Simultaneous optimization of Spin fluctuation and Tc at 2.17GPa ! Superconductivity is mediated by spin fluctuation !

  29. Summary NaFeAs ・Structural transition occurs at To = 57K ・Below TAF = 45K, the ground state is stripe type of antiferromagnetic ordering AFM NaFeAs under pressure Pressure ・TAF and antiferromagnetic moment increase with pressure NaFe0.94Co0.06As under pressure ・As spin fluctuation developed, Tc becomes maximum 　　 ⇒Superconductivity is mediated by spin fluctuation

More Related