Tuson Park

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Probing Hidden Magnetism and Quantum Criticality
in Unconventional Superconductors

• Tuson Park

Extreme Physical Science Laboratory
(EPSL) Department of Physics Sungkyunkwan
Univeristy, Suwon 440-746, Korea (http//epsl.skku
.edu)
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Extreme Physical Science Laboratory
(EPSL) (http//epsl.skku.edu)
Physical Properties under Extreme Conditions
exploring new quantum phase space that has never
been charted in strongly correlated systems
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Collaborators
E. Park, D. Kim, B. Woo, S. Seo, S. Ju EPSL,
Sungkyunkwan University, Korea
H. Lee, F. Ronning, E. D. Bauer, R. Movshovich,
J. L. Sarrao, J. D. Thompson LANL
V. Sidorov HPPI, Russia
H. Q. Yuan Zhejiang University, China
M. B. Salamon UT-Dallas
Z. Fisk UC-Irvine
D. Pines UC-Davis
C. Varma UC-Riverside
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Outline

• 1) Introduction
• i) Phase transition
• ii) Superconductivity
• iii) Emerging new quantum phases near QCP
• 2) Probing magnetism veiled by superconductivity
  in CeRhIn5
• i) CeMIn5 (M Co, Rh, Ir) or M115
• ii) Field-induced state in SC state of CeRhIn5
• iii) Implication in connection to other classes
  of unconventional superconductors

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Classical phase transition - thermally driven
Boiling water (Liquid-gas transition)
hot
cold
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Superconductivity
Superconductivity is a macroscopic quantum state
where two electrons form a Cooper pair below Tc
e-
e-

• Zero resistance in carrying current
• (H. Kamerlingh Onnes, 1911)

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Superconductivity
2) Complete repulsion of magnetic field (W.
Meissner R. Ochsenfeld, 1933)
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Quantum phase transition
(H. von Lohneysen,96)
Quantum phase transition is a transition between
ordered and disordered states driven by quantum
fluctuations at T 0 K. cf) classical
phase transition thermal fluctuations
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Deviation from Landau-Fermi liquids New Physics !

• r ? T (? T2)
• C/T ? -log T (? constant)

(H. von Lohneysen, JPCM 8, 96)
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Are quantum critical effects relevant to
superconductivity?
AFM
SC
AFM
SC
Projected (or hidden) QCP have been rarely
identified and its roles are not appreciated
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115 CeMIn5 (M Co, Rh, Ir)
Heavy Fermion CeMIn5
Co 3d7 4s2
Ni 3d8 4s2
Fe 3d6 4s2
Cu 3d10 4s1
Mn 3d5 4s2
Rh 4d8 5s1
Pd 4d10 5s0
Ru 4d7 5s1
Ir 5d7 6s2
Pt 5d10 6s0
Os 5d6 6s2
MCo, Rh, Ir
In(2) site
Ce-In
M-In
Ce-In
In(1) site
Petrovic et al. JPCM 13, (2001)
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Pressure-induced superconductivity in CeRhIn5
AFM
P2
Hegger et al, PRL 84, 00 Park et al. 06
1 GPa 10 kbar
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Heat capacity measurements under pressure

• Piston-cylinder cell
• P lt 3.0 GPa (or 30 kbar)
• Manometer Sn SC transition
• Pressure medium silicone

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Heat capacity of CeRhIn5 for PgtP2
AFM SC
At P2.4 GPa i) Specific heat jump, ?C/CN ? 3
ii ) For field higher than Hc2, C/T weakly
diverges, indicating NFL behavior iii)
Strongly Pauli limited, i.e., Maki
parameter is 4.6 iv) No signature for FFLO in
mixed SC states
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Resistivity at P2 rc (T)
rc ? Tn
i) At 2.3 GPa (P2) and H ? Hc2, T gt 0 K with
sub-linear T dependence intrinsic ii) For H gt
Hc2, r ? T2 (LFL behavior) is recovered for T lt
TFLand A coefficient diverges near Hc2
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Heat capacity of CeRhIn5 at P1 lt P lt P2
AFM SC
At P1 lt P lt P2 i) Specific heat jump, ?C/CN ?
3 ii) At low fields, only SC is observed iii)
Above a critical field HM, a new anomaly
appears in the mixed state HM55, 11 kOe
for 2.1 and 1.9 GPa ref) Knebel et al. prb
74 (2007) iv) Is it a new quantum phase
similar to FFLO in CeCoIn5?
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Origin of the H-induced anomaly for P1ltPltP2?

• The H-induced transition temperature increases
  with H, indicating that it is not due to SC or
  extrinsic effects
• Broad peak anomaly in C/T suggests that it is 2nd
  order phase transition
• Entropy SM involved in the H-induced anomaly
  linearly depends on H, suggesting that the new
  phase is related to the vortices because the
  areal density of the flux lattice is proportional
  to H

H // ab
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Origin of the H-induced anomaly for P1ltPltP2?
For H // c-axis
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Origin of the H-induced anomaly for P1ltPltP2?
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Nature of the field-induced anomaly quantum
phase transiton
Theory for high-Tc cuprates
T 0 K
SDW SC
SC
Repulsive coupling between AFM and SC order
parameters leads to quantum- phase transition
(Demler et al., 01)
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Summary
First observation of long-range magnetic order
deep in the SC state other than high-Tc cuprates
Clean control parameter (pressure) and high
quality crystal (residual resistivity r0 40
nWcm) of CeRhIn5 provide undisputable evidence
for the presence of quantum critical point in the
SC phase Strongly suggests correlation between
quantum critical point and unconventional
superconductivity in the stronlgy correlated
superconductors ref) Park et al, Nature 440, 65
(2006)
(courtesy of M. Grafe his coworkers funded by
3D visualization ER)
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Courtesy of Graf et al. of 3D visualization team
at LANL
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Disorder, magnetism, and superconductivity in
CeCo(In,X)5

• Chemical substitution of CeCoIn5 with Cd (or Sn)
• Sn to Co115 electron-doping (Bauer et al., 2005)
• Tc is suppressed, but no magnetism
• 2) Cd to Co115 hole-doping (Pham et al., 2006)
• Magnetism is induced !

In 4d10 5s2p1
Sn 4d10 5s2p2
Cd 4d10 5s2p0
electron-doping
hole-doping
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Cd-doping to CeCoIn5
Replacing In by a small amount of Cd introduces
coexisting phase of magnetism and
superconductivity
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Pressure undoes Cd-doping effects
Applying pressure suppresses magnetism, but
induces superconductivity.
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Future directions
Chemical substitution of Cd (hole) and Sn
(electron) in CeCoIn5 presents striking
similarity to pressure dependence of CeRhIn5
Open a new avenue to study interplay between
magnetism and SC outside pressure cell How
disorder affects the delicate balance between
competing orders, especially near quantum
criticality? Probe these physics using various
techniques under high magnetic fields, high
pressures, low temperatures. Ex) neutron,
field-angle specific heat, etc
AFM SC
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