Fall 2007 Qualifier – Part II 12 minute questions
... is given by ε = ε 0 1 − A ω 2 , where A is a constant and ε 0 is the permittivity of free space. a) Write down the dispersion relation for an electromagnetic wave, which expresses ω as a function of wave number k. b) Find the critical frequency below which a wave launched into the medium will not pr ...
... is given by ε = ε 0 1 − A ω 2 , where A is a constant and ε 0 is the permittivity of free space. a) Write down the dispersion relation for an electromagnetic wave, which expresses ω as a function of wave number k. b) Find the critical frequency below which a wave launched into the medium will not pr ...
Density of states
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In solid-state and condensed matter physics, the density of states (DOS) of a system describes the number of states per interval of energy at each energy level that are available to be occupied. Unlike isolated systems, like atoms or molecules in gas phase, the density distributions are not discrete like a spectral density but continuous. A high DOS at a specific energy level means that there are many states available for occupation. A DOS of zero means that no states can be occupied at that energy level. In general a DOS is an average over the space and time domains occupied by the system. Localvariations, most often due to distortions of the original system, are often called local density of states (LDOS). If the DOS of an undisturbedsystem is zero, the LDOS can locally be non-zero due to the presence of a local potential.