凝聚态物理导论-中科院课件-苏刚chapter2.pdf

Chapter 2 Structure Orderings and Symmetry Breaking §2.1 Preamble Solid: a macroscopic system with 1023/cm3 particles, a complex many-particle (including electrons and ions) system. Microscopic processes in condensed matter: determined by individual and collective motion of interacting electrons and ions; Macroscopic properties in condensed matter: overall reflections of interactions between particles and collective excitations. Some concepts, e.g. conductivity, ferromagnetism, specific heat, phase transitions, etc., can only be defined for a system with a collection of many particles, not for a single atom. In essence, the basic issue in condensed matter physics is to solve a complicated quantum-mechanical many-particle system. Phase diagram for water Short-range order (SRO) Long-range order (LRO) Disordered phase Ordering occurs with lowering symmetry. SRO: ordering extends to a few atoms or even just neighbors, where the correlation function decays exponentially with position; LRO: ordering may extend to a macroscopic distance, where the correlation function varies spatially to reach asymptotically a nonzero valve (below a certain temperature). LRO SRO Quasi long-range order (QLRO): between SRO and LRO, where the correlation function decays in a power law. Power-law decay of the spatial