Quantum complexity in condensed matter physics

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Quantum complexity in condensed matter physics

• S Julian
• University of Toronto

• Emergent properties
• Particle behaviour of fluctuating modes
• Broken symmetry and rigidity
• Indirect interaction

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Condensed Matter Physics
Fundamental Physics
Applied Physics
-Quantum properties of many body systems -Noise
(eg in electronic circuits) -Novel soft matter,
elasticity and viscosity -Modeling the universe
-memory devices for computers -processors for
computers -corrosion and catalysis -superconductin
g devices
Elementary particle physics
energy
Condensed matter physics
biology
time
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Combinatorial chemistry vs. emergent properties
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Empty boxes are more interesting than people
think!

• At 0K zero point motion

• At high T electrons and
• positrons are created

• At Low T black-body radiation

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Analogy with quantum condensed matter physics

• At 0K zero point motion
• of phonon, electron-hole pairs, etc.

• At high T electrons and
• positrons are created

• At Low T black-body radiation
• Real phonons and electronsholes

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Dispersion relations for (quasi)particles
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How to make a metal
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Conventional phase transition broken symmetry
states
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Conventional phase transition
Spontaneous symmetry breaking
The susceptibility diverges
gt rigidity
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Mass enhancement
Magnetic pairing
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Indirect interactions
- One of the central principles of physics
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Unusual particle-like excitations are possible
in condensed matter systems
Overdamped modes
Propagating modes
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The quantum critical point
Fe
Cu
At Tc, fluctuations diverge
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quantum critical superconductivity?
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CePd2Si2 phase diagram
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Methodology of condensed matter physics

• Crystal growth
• Crystals are to us what stars are to astronomers
• Scattering
• A good way to find out what is inside something
  is to throw something at it and see how it
  bounces off
• Nano-physics
• Scanning tunneling microscopy, point contact
  spectroscopy, etc.
• Low temperatures and high magnetic fields
• Dilution refrigeration

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Anvil pressure cells
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Phase diagram of Ca2RuO4
Antiferromagetic insulator
Temperature / K
Ferromagnetic metal
Pressure / kbar
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Structural transitions
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Atomic orbitals in crystals
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Orbital ordering
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Summary

• The fundamental principles of quantum condensed
  matter physics are
• Emergent properties new kinds of particles
  emerge as complexity increases
• Broken symmetry and rigidity
• Indirect interactions
• The methodology focuses on crystal growth,
  scattering and low temperatures.