I ncommensurate correlations & mesoscopic spin resonance in YbRh 2 Si 2 *
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Incommensurate correlations
& mesoscopic spin resonance in YbRh2Si2*
*Supported by U.S. DoE Basic Energy Sciences,
Materials Sciences & Engineering DE-FG02-08ER46544
C. BroholmJohns Hopkins University
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OverviewIntroduction
SDW Quantum Criticality in metals The case of YbRh2Si2
Results & Discussion Incommensurate spin correlations Quasi-FM Quantum Critical Scaling Unconventional spin resonance
Conclusions
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Field Driven QCP in YbRh2Si2
Yb
Rh
Si
11 × c
Gegenwart et al PRL (2002)
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Kondo Lattice quantum criticality
Schroeder et al Nature (2003)Steglich et al J. Phys. Cond. Matter (2012)
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Fermi-surface reconstruction at TN?
Friedemann et al PNAS (2010)
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YbRh2Si2: neutrons come lately
200 x 5×5 mm2 crystals Mounted with H-free oil Total mass 3 g Mosaic FWHM 2o
Penetration depth ≈2 mm
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Field Driven QCP in YbRh2Si2
Yb
Rh
Si
11 × c
Gegenwart et al PRL (2002)
No n
eutro
n ye
tNo neutron yet
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CollaboratorsChris Stock & F. DemmelISIS Facility, Rutherford Appleton Lab
C. Petrovic & R. HuBrookhaven National
Laboratory
H. J. Kang & Y. Qiu
NIST Center for Neutron Research
SPINS DCS OSIRIS
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Four CF Kramer’s Doublets in YbRh2Si2
Kutuzov et al (2008)
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Incommensurate critical fluctuations
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Incommensurate correlations
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Spin Fluctuations & Neutrons ScatteringV2-yO3 Bao et al. PRL (1993)
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Spin fluctuations near MIT in V2O3
P I
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Spin Density Wave OrderB
ao e
t al.
PR
L (1
993)
Wol
ensk
i et a
l., P
RB
(199
8)
Experimental Qc
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Incommensurate correlations
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SDW from nesting instability?
(002)
(111)
(110)(110)
(1-(a/c)2, 0,2)
Norman PRB (2005)
Norman PRB (2005)
(1-(a/c)2, 1-(a/c)2,2)
Friedemann et al (2010)
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Apparent FM correlations upon heating
0.3 K
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Quantum critical scaling for Q≈0
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Critical Exponent Trovarelli et al PRL (2010)
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Magnetization SQUID & neutrons
2I M
C. Stock et. al., (2009)Gegenwart et al., NJP (2006)
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From SDW to FM correlations with field
-0.5 0 0.5 (hh2) [r.l.u.]
Effects of field: Upward shift of
spectral weightSharp peak at
FM positionField induced
resonance
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Field Induced Resonance
3.86 (neutron)g 3.56 (EPR)g
C. Stock et. al., PRL (2012)
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MnSi: Field induced “ferromagnons”
Tarvin et al., Phys. Rev. (1978).
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YbRh2Si2 : A spot in Q-space
C. Stock et. al., PRL (2012)
1.25 Tesla
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Form factor for chain-end spin
Kenzelmann et al. PRL (2003)
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Interpretation of the spin resonance
• Coincident g-factors indicate this is Electron Spin Resonance
• Coherent precession of spin density
• Similar to a Kondo length scale
• Kondo Screened spins for B>Bc
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Conclusions• Effective FM critical regime for T>1 K
• Lower T: Incommensurate critical fluctuations
• SDW instability may arise from nesting of hole fermi-surfaces
• B suppresses SDW favoring FM polarized metal
• Meso-scopic spin precession indicates Kondo screened 4f spin degree of freedom
• SDW correlations persist at lower energies in magnetized kondo lattice state
Stock et al PRL (2012)
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Outlook• SDW phase
– Can band-theory account for incommensurate Qc
– Qc may help to clarify nature of low field state and field driven transition
– Detect SDW Bragg peak and measure critical exponents
– Pressure or doping driven changes in Qc
• QCP– Inelastic scattering at lower T and ħw– Identify field driven QC metal with higher critical
temperatures and/or less neutron absorption