This document provides an overview of Physics 4P70: Condensed Matter Physics I, taught by Christopher R. Wiebe at Brock University. It discusses key topics that will be covered, including crystal structure, experimental techniques used to study solids like scattering and resonance methods, and technological applications and discoveries that have emerged from condensed matter physics research, such as superconductivity. The goal is to develop an understanding of how the collective behavior of large numbers of particles gives rise to unexpected macroscopic properties in solids.

1. Physics 4P70
Condensed Matter Physics I
Christopher R. Wiebe
MCB201
X4294
Email: cwiebe@brocku.ca
A high-temperature superconductor,
cooled in liquid nitrogen, expels local
magnetic fields (called the Meissner
effect), and causes this magnet to
levitate above it

2. Solid State Physics
! Why study condensed matter?
! Condensed matter physics mostly concerns the
study of solids, but it has been extended to
amorphous substances, glasses, and liquids
! The largest branch of modern physics
! Most of the research is done on solids, be it in
crystalline or ceramic (multicrystalline powder)
form

3. Why study solids?
! Technological spin-offs:
superconductivity (MRI
machines, cheap power
transportation, etc), magnetic
recording media, rechargable
batteries
! New Physics!!
! What happens when we have
a large no. of particles MRI scanners use
(degrees of freedom)? superconductor
! Eg. Temperature makes no technology
sense when applied to one
molecule – it must be applied
to a collection of particles (eg.
A gas, liquid, or solid)
! How do 1023 no. of particles
give rise to macroscopic
properties?
Rechargeable
Test bits on a hard drive batteries

4. What makes solids special?
! In a solids, the consituent particles act in
unison to give properties (eg. Push on a
solid, and it will move, unlike a liquid or gas
– the atoms are held in place by chemical
bonds)
! What other ways can particles act in
unison?
! Sound waves – vibrations within a solid –
atoms move in a correlated way
! Conductivity – electrons migrating through
a solid – often out of step with one another,
but they can be in step (superconductivity)
! Superconductivity is an example of a
macroscopic state of matter arising from
many particles acting in a coordinated way e
! Sound waves + electronic motion = BCS
(Bardeen-Cooper-Schrieffer)
superconductivity

5. New properties : “More is different”
Magnetism in iron oxide
! Often, the laws of quantum mechanics come
into play and give rise to new and
unexpected phenomena
! Eg. Magnetism – collective state of electrons
lining up their moments in a coherent fashion
(this is from the overlap of atomic orbitals)
! Eg. Conductivity in materials – what makes a
material be a metal, insulator, or
semiconductor? This has to do with band
structure – because electrons follow Fermi
statistics, they cannot have the same energy
state. They “stack up” to form energy Band structure in materials
bands, and this gives rise to the electrical
behaviour
! Philip Anderson used the phrase “More is
different” to describe a new way of looking Fermi
at solids – many, many particles, acting in a
coherent way – give rise to new and energy,
unexpected behaviours (no longer have EF
particles in a box, interacting independent of
one another)

6. Experimental techniques to
measure solids
Heat capacity (low temperatures)
! Scattering: x-rays, neutrons,
electrons (information about where
the atoms are, excitations)
! Resonance methods: nuclear
magnetic resonance, muon spin
resonance (magnetism)
! Thermodynamic properties: specific
heat, thermal conductivity (what is
carrying the heat?)
! Electronic properties: resistivity, Hall
effect, photoemission (how do the Muon spin resonance (at TRIUMF)
electrons move? Metal,
semiconductor, or insulator?)
! Optical measurements : microwave,
infrared, etc. (how does EM radiation
interact with the electrons? What
can this tell us?)
Neutron scattering
(at NIST, USA)

7. Spin-offs of condensed matter
physics
The ring nebula
! The study of condensed matter
physics is often the starting
point for other disciplines:
! Astronomy (stars are dense
masses of fermions in space,
like solids – especially neutron
stars)
! Geology (what happens to
materials under pressure?) Polymer
thin
! Polymers, biophysics (“soft”
condensed matter – what films
happens in gels? What
happens in membranes? How
are these different than solids The Earth’s
(but are not liquids)?)
crust

8. Chapter One: Crystal Structure
! Solids are made of atoms – what structures are common?
! How do we describe these structures using language that makes sense?
! Ask yourself why I am doing this in this way? Develop a physical intuition
! How do we know that crystals are made of atoms?
! Scientist in the 18th century suspected this was true – crystals cleave, or could
be cut, very well in certain directions
! This suggests that they are made of some kind of regular unit (the planes of
atoms are arranged so that they can break apart easier in certain directions).
Gypsum being cleaved along a
An ionic crystal, being cleaved. crystallographic plane

9. Habits of crystals
The habit of a crystal describes its overall
Monoclinic
!
Hexagonal beryl gypsum
shape
! These offer clues to how the atoms are
arranged
! But, the growth (and shape) of crystals is also
determined by a number of factors, including:
! (1) Temperature
! (2) Pressure
! (3) pH (acid or basic environment), etc
! So, scientists need another way to see how
crystals form – the first way to do this is by x-
ray diffraction (we will discuss this more in
Chapter 2)
! Why do x-rays tell us about how the atoms
are arranged? Amorphous amber
Trigonal quartz
(no underlying
crystal symmetry)