Solid state physics delves into the fascinating world of solids, those materials that hold their shape. It's a branch of condensed matter physics, the largest and most diverse area of physics, that explores how the microscopic arrangements and behaviors of atoms within a solid dictate its macroscopic properties. In other words, it explains how the way billions of tiny atoms are organized and interact determines whether a material conducts electricity, shines brightly, or bends under pressure.
https://www.e-kitabi.com/solid-state-physics-2nd-edition-pdf-for-free/
Solid state physics draws upon a rich toolbox of scientific disciplines. Quantum mechanics, for instance, is essential for understanding how electrons behave within a solid's atomic structure. Crystallography comes into play to analyze the ordered, repeating arrangements of atoms that characterize most solids. Electromagnetism sheds light on how solids interact with electrical and magnetic fields. By weaving these disciplines together, solid state physicists build a theoretical understanding of how a solid "works".