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Magnetic and Electronic Quasiparticle
Spectra of Iron Pnictides*
E.C.Marino
UFRJ
Rio de Janeiro, Brazil
*C.M.S da Conceição, M.B Silva Neto, E.C. Marino Phys. Rev. Lett. 106 , 117002 (2011)
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1) Introduction
2) Phenomenology
3) The Model
4) The Quantum Field Theory Approach
5) Magnetic Spectrum
6) Electronic Spectrum
7) Concluding Remarks and Prospects
Summary
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b) Superconductivity
1) Introduction
What are the most beautiful and interesting phenomena in Physics?
a) Quarks and the theories describing their interactions
My personal choice:
But…. There is an objective way of measuring………………………!!!!
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List of Nobel Prizes for Superconductivity (Total of 7)
2003 [1950] Alexei A. Abrikosov , Vitaly L. Ginzburg - Pioneering contributions to the theory of superconductors
1987 [1986] Georg Bednorz, Alex K. Müller - High-temperature superconductivity
1973 [1960] Leo Esaki, Ivar Giaever - Tunneling in superconductors [1962] Brian D. Josephson - Super-current through tunnel barriers
1972 [1957] John Bardeen, Leon N. Cooper and J. Robert Schrieffer - Theory of superconductivity
1913 [1911] Heike Kamerlingh Onnes - Matter at low temperature (discovery of SC in Hg)
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List of Nobel Prizes for Quarks and the Theories that describe them (Total of 8)
1969 [1964] Murray Gell-Mann - Quark model for particle classification
1976 [1974] Burton Richter, Samuel Ting -Discovery of the J/Psi particle
1979 [1961] Sheldon Glashow [1967] Steven Weinberg [1968] Abdus Salam - Electroweak theory
1984 [1983] Carlo Rubbia - Discovery of W and Z particles
1990 [1972] Jerome Friedman , Henry Kendall, Richard Taylor - Deep inelastic scattering experiments leading to the discovery of quarks
1999 [1972] Gerard 't Hooft, Martin Veltman - Development of a renormalization scheme for non-abelian gauge theories
2004 [1973] David J. Gross H, David Politzer , Frank Wilczek - Discovery of asymptotic freedom in the theory of the strong interaction.
2008 Makoto Kobayashi, Toshihide Maskawa - Discovery of the origin of symmetry breaking.
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2) Phenomenology
Superconductors of the 20th. Century
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Pnictides: High-Tc Supercondutors of the 21st Century
Y. Kamihara, T.Watanabe, M.Hirano and H. Hosono; J.Am.Chem. Soc. 130 (2008) 3296
2008
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The Pnictides
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Phase Diagram of an 122 material
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Phase Diagram of an 1111 material
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Something....
... to do with Rio de Janeiro?
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Yes…..in spite of that we can do good physics!!!
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Crystal Structure
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Comparing Structures of Pnictides and Cuprates
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Electronic Structure
Fe++ hasSpin = 1
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MagneticGround States
3) The Model
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Phys. Rev. Lett. 106, 117002 (2011) Magnetic and Quasiparticle Excitation Spectra of an Itinerant J1-J2 Model for Iron-Pnictide Superconductors
C. M. S. da Conceição, M. B. Silva Neto and E. C. Marino
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For J1 < 2 J2
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Spin-Orbit +Relativistic
Localized Spins
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Itinerant electrons
Itinerant electrons-localized spins interaction
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The Hopping Amplitudes
S. Raghu et al., Phys. Rev. B77, 220503 (2008)
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4) The Quantum Field Theory Approacah
Spin operatorof Fe++
Using Coherent Spin States
For evaluating the Partition Function
To begin with: justlocalized H, K=0
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We obtain
Decomposing in AF and F fluctuations
... and integrating on LA , LB
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Quantum Field Theory Action
Obtained after integration over the ferromagnetic fluctuations
Quantum Effects are included!!!
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Relevant Parameters
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Magnons: π-field fluctuation
5) Magnetic Spectrum
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π-field
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Magnon dispersion relations
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Solid line: ky =0 Dashed line: kx = ky
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Improved Model , K≠0Spin-Orbit +Relativistic
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J. Zhao et al., Phys. Rev. Lett. 101, 167203 (2008)
Neutron Scattering: Two Gaps!!!
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Two Steps in the Neutron Scattering Intensity
J. Zhao et al., Phys. Rev. Lett. 101, 167203 (2008).
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6) Electronic Spectrum
Take the itinerant part…
and do mean field…
Replacing for its static equilibrium value
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Fermi Surface and Dirac Cones
AF Ordering of Sublattice
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Dirac cones
P. Richard et al., Phys. Rev. Lett. 104, 137001 (2010).
ARPES Results
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7) Conclusion and Perspectives
QFT is an efficient method for describing complex materials
The magnetic excitation spectrum of pnictides contains two gapped branches – seen in neutron scattering experiments
The electronic quasiparticle spectrum presents two Dirac cones – seen in ARPES experiments
Present and future research – specific heat, conductivity,…
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Acknowledgements
Brazilian Funding Agencies