Grand challenges: heavy fermion physics

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Grand challenges heavy fermion physics
Stephen Julian University of Toronto

• Technology
• Materials
• Electronic structure
• Non-Fermi-liquid behaviour
• Non-linear behaviour

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Bringing low temperatures to the masses
Cryomech pulse-tube cooler 0.75 W at 4.2 K No
moving parts at low temperature
Cambridge Magnetic Refrigeration 50 mK from 2K
no moving parts at all!
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Grand challenges heavy fermion physics

• Technology
• Materials
• Electronic structure
• Non-Fermi-liquid behaviour and metamagnetism
• Non-linear behaviour
• Non-equilibrium behaviour

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New Materials

• Our field is largely driven by experimental
  results, and these depend on the flow of new
  materials with interesting properties
• How to you find interesting properties?

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www.sandia.gov/1100/XCSP/xdocs/Structure-PropertyR
elationsinTransuranicCompounds_Sarrao.pdf
www.theoryinstitute.org/its/rts/
persentation/Saturday/J20Sarrao20nd_06_05.ppt
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New Materials

• Compared to biology, materials preparation in
  quantum condensed matter is
• small-scale (research groups are much smaller
  than in chemistry and biology)
• Slow (the method used in my group produces one
  sample per student per year the Hardy-Bonn group
  has spent 15 years perfecting crystals of one
  material)
• comparatively unsophisticated (very little
  automation)
• Greater use of electronic structure calculations?
• Automation?
• Pressure?

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First possible approach

• Automated thin-film growth (Stuart Parkin lab)

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Superconducting elements under very high pressure
Shimizu et al., JPSJ 74 (2005) 1345.
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CeCu2Si2 a new superconducting mechanism
Yuan et al., Science 2003
Holmes et al., Phys Rev B 2004
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Quantum critical point

• Within the blue line classical
• statistics apply
• Outside the blue lines, quantum
• statistics apply

The quantum critical point.
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CePd2Si2 phase diagram
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Other quantum critical superconductors
UGe2
CeIn3
Saxena et al., Nature 2002
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BEC of triplons
triplet-singlet energy
M. Jaime et al., Phys. Rev. Lett. 93 (2004) 087203
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Grand challenges heavy fermion physics

• Technology micro-cooling, cryo-free systems
• Materials automation, high pressure measurement
• Quantum critical phases
• Electronic structure
• Non-Fermi-liquid behaviour and metamagnetism
• Non-linear behaviour
• Non-equilibrium behaviour

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Electronic structure
Add conduction electrons
Ionic lattice
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Filling the Fermi sea
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Corrections to LDA?
Sodium cobaltate H.-B. Yang et al, PRL 2004
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Weakly damped quasiparticle
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Landau quasiparticle with stronger damping
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MnSi, resistivity vs temperature
T2
Pfleiderer et al., PRB 55 (1997) 8330
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Overdamped quasiparticle
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Mass enhancement
Magnetic pairing
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QCP in YbRh2Si2
Custers et al, Nature 424 (2003) 525. Paschen et
al., Nature 432 (2004) 881.
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Phase diagram of MnSi
30.0
Pfleiderer et al. PRB 1999
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MnSi, resistivity vs temperature
T2
Pfleiderer et al., PRB 55 (1997) 8330
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Anomalous resistivity of MnSi
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Phase diagram revisited
Pfleiderer et al., Nature 2004
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Doiron-Leyraud et al., Nature 2003
M
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Grand challenges heavy fermion physics

• Technology micro-cooling, cryo-free systems
• Materials automation, high pressure measurement
• Quantum critical phases
• Electronic structure failure of LDA?
• Non-Fermi-liquid behaviour
• weakly first order quantum criticality
• Transport without particles?
• Non-linear behaviour

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What I didnt talk about

• Non-equilibrium physics
• Locally singular QCP
• Hidden order in URu2Si22
• The need for high-accuracy measurement of
  non-Fermi liquid exponents