tailieunhanh - Basic Theoretical Physics: A Concise Overview P28

Basic Theoretical Physics: A Concise Overview P28. This concise treatment embraces, in four parts, all the main aspects of theoretical physics (I . Mechanics and Basic Relativity, II. Electrodynamics and Aspects of Optics, III. Non-relativistic Quantum Mechanics, IV. Thermodynamics and Statistical Physics). It summarizes the material that every graduate student, physicist working in industry, or physics teacher should master during his or her degree course. It thus serves both as an excellent revision and preparation tool, and as a convenient reference source, covering the whole of theoretical physics. It may also be successfully employed to deepen its readers’ insight and. | 278 35 Cooper Pairs Superconductors and Superfluids This means that below this temperature there is a component of the liquid which flows without energy dissipation. He4-atoms 2 protons 2 neutrons 2 electrons as composite particles are bosons. Thus even though there is a strong interaction between the boson particles they can condense without pairing and the transition to superfluidity consists in the formation of such a condensate. The case of He2 3 is fundamentally different. This atom consists of two protons only one neutron and again two electrons thus as a composite particle it is a fermion. Originally one did not expect superfluidity at all in He3. All the greater was the surprise when in 1972 Osheroff et al. 26 found that also a He3-liquid becomes a superfluid but admittedly at much lower temperatures . below mK. In fact at these low temperatures not yet ultralow see Part IV also in this liquid Cooper pairs of He3-atoms are formed where however this time the interaction favors triplet pairing . now the position factor of a Cooper pair is antisymmetric . with l 1 and the spin function is symmetric . a triplet function. As a consequence in the superfluid state of He3 both the expectation value of L and that of S can be different from zero at the same time which makes the theory very complex. In fact in 2003 a physics Nobel prize was awarded to Anthony Legget 2 who was involved in the theory of He3-superfluidity. iii Finally some words on high-temperature superconductors. This is a certain class of non-metallic superconductors with many CuO2-planes and values of Ts around 120 K . six times higher than usual. In these systems the electrons also seem to form pairs the elementary charge of the carriers of superconductivity is again 2e but the underlying mechanism is not yet clear although the systems have been under scrutiny since 1986 87. Perhaps one is dealing with Bose-Einstein condensation see Part IV of electron-pair aggregates3. The .