So I'm fairly new to them and I was wondering about the reasons it is used so extensively. It'd be great to have a discussion on its significance in various applications. When exactly did people start using these diagrams? How is it used in various parts of physics. What all information can it convey? What according to you are some lesser known facts about the E-k diagrams? Are there any great references to gain insight about them apart from the standard books like Charles Kittle, Ashcroft Mermin etc?! Looking forward to your inputs.