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Breakdown of the Kondo effect at an antiferromagnetic instability

Breakdown of the Kondo effect at an antiferromagnetic instability. F. Steglich MPI for Chemical Physics of Solids, 01187 Dresden, Germany. Outline HF quantum critical points (QCPs) Kondo breakdown QCP in YbRh 2 Si 2 Superconductivity in YbRh 2 Si 2 ?. Collaboration MPI CPfS:

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Breakdown of the Kondo effect at an antiferromagnetic instability

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  1. Breakdown of the Kondo effect at an antiferromagnetic instability F. Steglich MPI for Chemical Physics of Solids, 01187 Dresden, Germany • Outline • HF quantum critical points (QCPs) • Kondo breakdown QCP in YbRh2Si2 • Superconductivity in YbRh2Si2? Collaboration MPI CPfS: M. Brando, S. Ernst, C. Geibel, S. Hartmann, S. Kirchner, C. Krellner, S. Lausberg, H. Pfau, L. Steinke, O. Stockert, S. Wirth TU Braunschweig: G. Zwicknagl U. Goettingen: P. Gegenwart, TU Vienna: J. Custers, S. Paschen U. Cambridge: S. Friedemann, F.M. Grosche Rice U.: Q. Si Rutgers U.: P. Coleman Zhejiang U.: H.Q. Yuan

  2. Two types of QCPs [P. Gegenwart, Q. Si & F.S., Nature Phys. 4, 186 (2008)] SDW QCP(Hertz, Millis, Moriya…) Kondo breakdown at AF QCP(Si et al., Coleman et al., 2001) exemplary material: CeCu2Si2 TK≈ 15 K YbRh2Si2 TK ≈ 30 K cf. O. Stockert‘s talk

  3. Emerging local Kondo screening and spatial coherence in the HF metal YbRh2Si2 [S. Ernst et al., Nature 474, 362 (2011), cf. S. Wirth‘s talk] Hierarchy of energy scales from STS J = 7/2 CEF splitting 17, 25 & 43 meV [INS, O. Stockert et al., Physica B 378, 157 (’06)] single-ion TK TK,high 100 K TK,low  30 K [TEP, U. Koehler et al., Phys. Rev. B 77, 104412 (’08)] Kondo-lattice temperature TL TK,low

  4. YbRh2Si2: T – B phase diagram[J. Custers et al., Nature 424, 524 (2003);T. Westerkamp, Dissertation, TU Dresden (2008)] Seff = 1/2

  5. Crossed-field Hall-effect results[S. Friedemann et al., PNAS 107, 14547 (2010)] RH(B2) = lim ρH(B1, B2)/B1 B1→ 0 solid lines:

  6. Fermi surface collapse [S. Friedemann et al., PNAS 107, 14547 (2010)] Crossover position T*(B) Crossover width FWHM ~ T ω/T scaling (Q. Si, S. Kirchner) T*(B) agrees with data from ρ, λ, M (P. Gegenwart et al., Science 315, 969 (2007))

  7. Specific heat of YbRh2Si2under hydrostatic pressure p ≤ 1.4 GPa[R. Borth, M. Nicklas, unpublished]

  8. TN anomaly in C(T)/T in Yb(Rh1-xCox)2Si2[C. Krellner et al., Phys. Rev. Lett. 102, 196402 (2009); Phys. Stat. Solidi B 247, 734 (2010)] C±(t) = A± α-1│t│- α + b + E · t; t = (T - TN)/TN; +: t > 0; -: t < 0 x = 0.38 α = 0.38 α = -0.12 δTN/TN = 5 ·10-3

  9. Specific heat (B = 0) [J. Custers et al., Nature 424, 524 (2003)] ΔC = C – Cph – CQ = γT+βT3 γ ≈ 1.7 J/K2mole Magnon contribution Cm (~κm) = β T3

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