What is Condensed Matter Physics?
The basic aim of Condensed Matter Physics is to understand the collective properties of large assemblies of atoms and molecules in terms of the interactions between their component parts. The study of matter on length scales above 1Å and energy scales smaller than 1eV reveals how collection of many interacting degrees of freedom exhibits novel, emergent phenomena, which are insensitive to details of what happens at shorter length and higher energy scales. For example, a gold atom, which is completely understood within the Schrödinger equation, is spherical and featureless  quite unlike the lustrous malleable and conducting metal prized by human societies. Furthermore, the same microscopic equations describe two different collections of 10^{23} molecules of H_{2}0: one might be water and the other ice (in crystalline or glassy phase), in which case the properties of the two systems are completely different and the similarity between their microscopic equations is of no practical consequence. Instead, lowenergy longwavelength physics emerges as a result of interactions among large number of particles.
Thus, a modern attitude toward Condensed Matter Physics is that the study of collective principles that govern matter is a frontier unto itself, complementary, yet separate to those of elementary particles physics and cosmology. This Introductory Course is focused on fundamental physical phenomena in (mostly) crystalline solids, discussed in terms of the basic principles of classical and quantum physics, where approximate picture of "quasiparticles", such as "quasielectrons" (interacting with other electrons through an average field) and phonons (quantized lattice vibrations), is sufficient to capture essential physics.


