Chapter 10: Q22CQ (page 467)
Describe the similarities and differences between Type-I and Type-II superconductors.
Both Type-I and Type-II superconductors relay on formation of cooper pairs and they exhibit isotopic effect.
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The accompanying diagrams represent the three lowest energy wave functions for three "atoms." As in all truly molecular states we consider, these states are shared among the atoms. At such large atomic separation, however, the energies are practically equal, so anelectron would be just as happy occupying any combination.
(a) Identify algebraic combinations of the states (for instance, 5+11/2+11/2 ) that would place the electron in each of the three atoms.
(b) Were the atoms closer together, the energies of states 1.11, and III would spread out and an electron would occupy the lowest energy one. Rank them in order of increasing energy as the atoms draw closer together. Explain your reasoning.
Question: - A semimetal (e.g., antimony, bismuth) is a material in which electrons would fill states to the top of a band the valence band--except for the fact that the top of this band overlaps very slightly with the bottom of the next higher band. Explain why such a material, unlike the "real" metal copper, will have true positive charge carriers and equal numbers of negative ones, even at zero temperature.
Question: The diagram shows the energy bands of a tunnel diode as the potential difference is increased. In this device high impurity atom density causes the occupied donor and unoccupied acceptor levels to spread into impurity bands which overlap respectively the n-type conduction- and the p-type valence bands. In all unbiased diodes, the depletion zone between the n-type and p-type bands constitutes a potential barrier (see Section 6.2) but in the tunnel diode it is so thin that significant tunnelling occurs. The current versus voltage plot shows that unlike a normal diode significant current begins to flow as soon as there is an applied voltageโbefore the bias voltage is Egap /e. It then decreases (so called negative resistance) before again increasing in the normal way. Explain this behavior.
In a buckyball, three of the bonds around each hexagon are so called double-bonds. They result from adjacent atoms sharing a state that does not participate in the sp2 bonding. Which state is it, and what is this extra bond ฯ-bond or a ฯ-bond? Explain.
It takes less energy to dissociate a diatomic fluorine molecule than a diatomic oxygen molecule (in fact, less than one-third as much). Why is it easier to dissociate fluorine?
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