4p70chap1lect1

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4p70chap1lect1

  1. 1. Physics 4P70 Condensed Matter Physics I Christopher R. Wiebe MCB201 X4294 Email: cwiebe@brocku.caA high-temperature superconductor,cooled in liquid nitrogen, expels localmagnetic fields (called the Meissnereffect), and causes this magnet tolevitate above it
  2. 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. 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. 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. 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. 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. 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. 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. 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)

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