A DCA Study of the High Energy Kink Structure in the Hubbard Model Spectra

Transcription

1 A DCA Study of the High Energy Kink Structure in the Hubbard Model Spectra M. Jarrell, A. Macridin, Th. Maier, D.J. Scalapino Thanks to T. Devereaux, A. Lanzara, W. Meevasana, B. Moritz, G. A. Sawatzky, and F. C. Zhang Dresden, April 07

2 Outline Graf HE kink Model + DCA Results for Spectra Possible Method to Analyze Cuprates Conclusion Σ= Ū χcs Ū

3 Some High Energy Kink References J. Graf, et al., preprint, cond-mat/ W. Meevasana, et al., preprint, cond-mat/ T. Valla, et al., preprint, cond-mat/ J. Chang, et al., preprint, cond-mat/ B. P. Xie, et al., preprint, cond-mat/ Z.-H. Pan, et al., preprint, cond-mat/ Q.-H. Wang, et al., preprint, cond-mat/ C. Grober, et al., Phys. Rev. B 62, 4336 (2000). S. Odashima, et al., Phys. Rev. B 72, (2005). F. Ronning, et al., Phys. Rev. B 71, (2005). E. Manousakis, preprint, cond-mat/ K. Byczuk, et al., Nature Physics, cond-mat/ A. Macridin, et al. preprint,cond-mat/ cond-mat/ J. Graf, et al., preprint, cond-mat/ [4] W. Meevasana, et al., preprint, cond-mat/ [5] T. Valla, et al., preprint, cond-mat/ [6] J. Chang, et al., preprint, cond-mat/ [7] B. P. Xie, et al., preprint, cond-mat/ [8] Z.-H. Pan, et al., preprint, cond-mat/

4 High-Energy Kink (overdoped Bi2201) HE kink beginning at about ev High energy band (bottom) falls below LDA Meevasana et al., cond-mat/

5 Modelling The Cuprates U t (Zhang and Rice, PRB 1988, P.W. Anderson) U=W=8t 2eV for the cuprates

6 Small Parameter? BCS (conventional) SC: Small parameter: Cuprate (unconventional) SC: No small energy scale: But in Cuprates: Electron-phonon vertex: Thurston et al. (1989) Neglect classes of diagrams: Short-ranged AF correlations

7 Dynamical Cluster Approximation Periodic Lattice DCA (M. Hettler, PRB) Short length scales, within the cluster, treated explicitly. Long length scales treated within a mean field. Effective Medium For a review of quantum cluster approaches: Th. Maier et al., Rev. Mod. Phys. 77, pp (2005).

8 QMC Cluster Solver Effective Medium procs. QMC in the Infinite Dimensional Limit, M. Jarrell, QMC Methods in CM Physics, Ed. M. Suzuki, (World Scientific, 1993), p The Hubbard Model in Infinite Dimensions: A QMC Study, Mark Jarrell, Phys. Rev. Lett. 69, (July 1992). A QMC Algorithm for Non-local Corrections to the Dynamical Mean-Field Approximation, M. Jarrell, PRB 64, /1-23 (2001). ORNL/CES X1e, Xt3

9 4-site cluster DCA - 2D Hubbard model U=8t MJ, EPL, 2001 Nc=4, U=W=2, t'=0

10 Inverse d-wave pairing susceptibility (U=4t; n=0.90) Cluster 4A Superconducting Transition Th. Maier, PRL Zd 0(MF) 8A 1 12A 16B A 20A 24A 26A

11 The Mechanism: Clues from the pairing matrix P = + P = (1 - ) 1 Γ Nc=24, U=4t, N=0.9 χs((p,p), m) ((,0), n) Th. Maier, PRL T/t n, m/t

12 Nonlocal corrections in spectra A(k, =0) U=8t, t=8 ( ) (0,0) DMF DCA (Nc=16) Non-local corrections to DMF distort the Fermi surface. Act like t' (t'') Phys. Rev. B 66, (2002).

13 High-Energy Kink in the 2D Hubbard Model Ekink -t (0,0) =(,0) (0,0) n=0.8, (, )U=8t, cluster 16B, Kink at Ekink -t (0,0) Dispersion below bare band A. Macridin unpublished

14 High Energy Kink in the Self Energy Features below kink energy Ekink depend weakly on K QP Peaks in A(k, ) when Re( + - E(k) - (k, ))=0 intersection of black and blue lines -Im (k, ) large for Ekink Abrupt change in slope of Re (k, ) for Ekink signals the start of the waterfall structure in spectra. Dispersion for large falls below bare result by causality. Here, Re (k, ) ~ a/, where a= d (-1/ Im (k, ) >0

15 Bandstructure (t') changes waterfall t'=-0.3t (0,0) (, ) dive more steep for h-doped (t'<0) less steep for e-doped (t'>0, but AF) t'=0 (0,0) (, ) A. Macridin, PRL (2006)

16 Origin of the HE Kink Σ= Ū χcs Ū n=0.8, U=8t, cluster 16B, Ekink = - t Spin, charge, and pair terms (different ). Spin dominates Ū<U due to QP renormalization. Spin RSO used for cuprates and Heavy Fermions Kampf & Schrieffer, RPB 42 (1990). M. Norman, PRL. 59, 232 (1987). Berk & Schrieffer, PRL (1966). (0,0) (, ) (0,0) (,0) Valla, ibid.

17 Origin of the Kink in RSO k magnon dispersion 2J k (0,0) (, ) (, ) (0,0) RSO and DCA/QMC self energies agree for <0. HE kink comes from QP scattering from high energy spin fluctuations. A. Macridin unpublished cm

18 HE Spin Excitations and doping

19 RSO Applied to Superconductivity Σ= Ū χcs Ū where now = ( Ū(T) About the same Ū obtained from A(k, ) T Φd((π,0),ωn) pp ωn )

20 Possible method to analyze experiment Extract spin S(q, ) from neutron scat. use to calculate (k, )= χcs Compare to ARPES to determine Ū Ū Ū χcs Use interaction in a DCA extension of Migdal Eliashberg (J. Hague) to calculate superconducting properties Σ= Ū χcs Ū Test 1-band model and spin-fluctuation mediated pairingfor the cuprates.

21 Conclusion DCA-QMC simulations of 1-band model captures many cuprate features HE kink in 2D HM due to coupling to HE spin fluctuations Features <0 are well described by coupling quasiparticle to spin fluctuations. Same approximation captures superconducting properties. Contributes to the method used to analyze experiment

22 Magnons in 214