The course could be structured around the Nobel prize winners in solid state physics - and the same topics would be covered: Shockley, Bardeen, and Brattain (for the transistor), Esaki (tunnel diodes), von Klitzing (quantum Hall effect), and Laughlin, Stormer, and Tsui (fractional quantum Hall effect), and Alferov, Kroemer, and Kilby for developing integrated circuits (which control our lives!) in semiconducting devices; Van Vleck, Neel, Mott, and Anderson (quantum theory of magnetism); Ohnnes (discovery of superconductivity), Bardeen, Cooper, and Schrieffer (theory of superconductivity), Abrikosov, Ginzburg, and Leggett (theory of superconductivity and superfluidity), Giaever and Josephson (quantum tunneling in SCs), and Bednorz and Muller (discovery of high Tc superconductivity); Richardson, Lee, and Oscheroff (discovery of superfluidity in He3); and, in chemistry, Curl, Kroto, and Smalley (discovery of the fullerenes), and Heeger, MacDiarmid, and Shirakawa (discovery and development of the conducting polymers).

     The course could also be strictly topical - with the goal being to understand, say, three problems. The quantum Hall effect requires understanding two dimensional electron flow in the inversion layer of a MOSFET operated at extremely low temperatures and high magnetic fields. And that will require looking carefully at semiconducting devices. The levitation and stability of magnets above superconducting discs requires understanding the underlying ideas of superconductivity - persistent currents and the Meissner effect - and the basis of the interaction that allows the effects to occur, including how the high Tc cuprate superconductors differ from conventional superconductors. And finally, the superfluid state of helium, although not a "solid" property, is closely related to superconductivity - and is amazing in its own right. The connection between superconductivity, magnetism, and superfluidity will be explored. Throughout the course, there will be many web links to current work - topics and new discoveries that would be difficult to understand without some mastery of the topics of this course. One of the goals of this course is to help you become conversant with some of the most interesting ideas of solid state physics and its applications.

     There are many common themes in solid state physics: The quantum theory underlies all of the main ideas - including the density of electron states and band theory so important to understand both semiconductors and superconductors. Long range order plays an important role in crystal structure, electrical conductivity, magnetic interactions, and superconductivity as does the effects of lattice vibrations and the subsequent phonon spectrum. Both magnetic order (ferromagnetism and antiferromagnetism) and the superconducting state have associated critical temperatures. The long range order associated with both magnetism and superconductivity and the phase transitions to those states is reflected in the heat capacity and ultimately in the entropy of those systems. The ideas of phase transitions and the temperatures at which they occur will be examined. Throughout the course, we will look for the common themes.

We will begin by reviewing the essential ideas of the description of semiconducting materials in order to distinguish between n- and p-type semiconductors and then see what happens when a pn junction is formed. Understanding the equilibrium diode is essential to understanding all semiconductor devices. We will explore the effects of applying bias voltages and thermal and optical stimulation in order to understand the basic diode characteristics. Ultimately, we want to know how various devices from rectifiers, tunnel diodes, LEDs, photovoltaics, junction and field effect transistors work.

This week, we will be dealing with the effects of bias voltages, changes in temperature, and light on the equilibrium diode. That is, we will discuss pn junction rectifiers, the IV characteristic curve, the temperature dependence of the saturation current, reverse current breakdown, tunneling effects in diodes, and optical absorption and emission (ie, photovoltaic cells, LEDs and lasers). Be reading the chapter carefully through the material on pn junction diodes. Look at the web sites that have been mentioned. Be working on the conceptual questions and the problems at the end of the chapter.

On Monday - we will look briefly at LEDs and lasers - ie, what diode characteristics are necessary for their operation. (You might look at Ch 7 on the distinction between direct and indirect band gaps in semiconductors). By Wed., we should start the discusson of transistors - with the dual goals of understanding transistor amplification and the distinctions between bipolar junction and field effect transistors (that discussion may spill over to the following Monday). On Friday, we will talk about field effect transistors and MOSFETs - and compare them with the bipolar junction transistor amplifier talked about on Friday.

Look at the web sites that have been mentioned. Be working on the conceptual questions and the problems at the end of the chapter. We will have a take-home exam following the transistor discussions - and those problems will be substantially like the text-book problems you have been working on.

The discussion about field effect transistors is intended to set up the discussion on the quantum Hall effect - the consequence of a very high magnetic field on a two-dimensional electron gas. We should talk about the quantum Hall effect - not because it is an important part of device discussions, but because it is interesting and only occurs in field effect transistors under extreme conditions. The FET is just the environment in which that experiment can be done.

We will begin the discussion of magnetism by mid-week. We will start by discussing the magnetic field and magnetic flux density - and how they are related. We need to deal with the idea of magnetization and magnetic susceptibility - and the distinctions between paramagnetic and diamagnetic materials (and the reasons for the differences).

The exam will be like problems which you have already been working on from the text. There will be some choice on the exam - including giving you the chance to write about some device or property of your choosing (which should be based on the topics of the course).

There will be a time limit on the exam - about four hours from when you open the exam. It is more than enough if you have been doing problems - but not enough if you have not spent much time in the material yet. It won't be a rigid time limit - ie, you can be a bit flexible how you count, but you should be reasonable. As a guideline, allow four hours of working time after you have completed your study for the test.

On Monday, we will begin our brief study of magnetism in earnest. Magnetism is ultimately due to the magnetic dipole moments associated with electrons. But the effects are very weak unless there are unpaired electrons in bound states within the atoms or ions that make up a solid. But that by itself does not lead to magnetic coupling - the idea that magnetic dipole moments associated with magnetic atoms can spontaneously align with each other even in the absence of an external magnetic field.

On Monday, we will examine the phenomenological idea of a molecular field that results in spontaneous alignment of the magnetic moments - the magnetic coupling that can occur between the magnetic atoms of a solid. And that still leads to two types of magnetically coupled solids - ferromagnetic and antiferromagnetic. The underlying principle for the magnetic interaction, of course, is quantum mechanical. We will examine the origin of that magnetic interaction.

On Monday, we will conclude our brief discussion of magnetic properties (admitting that we have only touched on some of the main points). Come in with questions.

Wednesday, we will start the discussion fo superconductivity. Much of the first couple of weeks will be spend on the basic ideas of conventional superconductivity - ie, the principle experiments and ideas associated with persistent currents, Meissner effect, etc., before the discovery of the high Tc cuprate superconductors in 1986. Some of the discussion will follow a historical perspective as a model for how the interplay between theory and experiment works.

We will continue our discussion of superconductivity experiments - with a continual goal of trying to view them as evidence to the theory behind the phenomenon. The important ideas will be how the electrons interact with each other through the lattice vibrations, the effects of magnetic fields - ie, both the critical field effect and the Meissner effect, the distinctions between Type I and Type II superconductors, and the evidence of electron pairing - from the optical absorption, specific heat, and flux quantization experiments.

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EXAM 2 - MAGNETISM AND SUPERCONDUCTIVITY

Take home, open books and notes, work alone

The exam will deal with magnetism and the magnetic properties of solids and the basic ideas of conventional superconductivity. You should look for areas of overlap between those two topics.

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Describing both the zero-resistance/persistent current characteristic of superconductors and the Meissner effect and critical field effects require understanding how the electric and magnetic fields behave inside superconducting solids - and how electrons respond to those fields. A question that was raised when talking about the properties of superconductors - in particular the Meissner effect - was whether that effect was due to the perfect conductivity of the superconductor as an ideal application of Faraday's law of induction. This discussion will show that it is not - and that the London equation will be required to adequately describe the superconducting magnetic state. But that will also lead to an explanation of how magnets iteract with superconductors - and leads to the explanation of the demonstration of the levitating magnetic and induction of the persistent surface currents demonstrated in class.

What are the essential ingredients of the theory that explains the experiments of superconductivity? The BCS theory - presented in 1957 - remains as the most compelling explanation of the superconducting state, although the mechanism described therein may not be sufficient to describe all of superconductivity. We will discuss the two-fluid model, which preceded the formal theory, and then discuss the essential ideas of BCS before concluding the quarter with how the discovery of high Tc superconductors have given life to the subject.

What are the primary characteristics of the superconducting cuprates - those perovskite structured copper oxide compounds with the high transition temperatures? Why have their discovery been so important? Is the BCS theory still valid - or are there other mechanisms that are necessary? Is there a real hope of a room temperature superconductor some day?

Oh, yeah - we still need to discuss what happens when you drop a magnet down a superconducting tube. What was it, exactly, that David Goodstein said in that discussion to which Richard Feynman responded "Of course!" - and why did we all agree so confidently?

It is said that there are three superfliuds - the electrons of superconductivity and the two isotopes of helium at temperatures near absolute zero. So what is this phenomenon called superfluidity? What are the characteristics of superfluid helium and why is interesting? And why is it a part of the discussion of superconductivity - how are the two forms of superfluid helium similar and how are they different from the classical superconductors? And why do we care?

One of the goals of the course has been to help you become conversant with these three broad areas of solid state physics and to see how these ideas are an integral part of current research. The oral exam is intended to test how well the course has prepared you to participate in a conversation involving the ideas discussed in the course. The exam will deal primarily with magnetic properties of solids and with superconductivity and related ideas. You should prepare by looking into one of the areas of current research (preferably in superconductivity or superfluidity) and be ready to discuss the work you researched. That discussion will be the st/arting point for the rest of the test.