I started Prof. Sachdev’s Havard course Physics 295b: Quantum Theory of Solids in the end of October 2021, and finished the first 30 lecture videos in the beginning of February 2022. For me, this course feels like the ideal next step after learning the usual undergraduate solid state physics course (talking about things like nearly free electron model, tight-bonding model, bond structure, X-ray or neutron scattering experiments…).

Subir Sachdev did an excellent job introducing techniques like

- Second quantization formulation
- Green’s function
- Mean field theory approach to interacting systems
- Diagrammatic perturbation theory

He used these powerful techniques to analyze systems like

- Free and interacting electron gas with a positive charge background (or the Jellium model). In the undergraduate solid state physics, the interesting things arise due to the periodic background potential interacting with the electron, but the interaction between electron them self is ignored. Here, we explore the situation where the background potential is trivial (uniform) but consider the effect of the Coulomb interaction between electrons.
- BSC theory of superconductivity. The key seems to relax the assumption of the ground state wavefunction; it doesn’t have to conserve particle number.
- Hubbard model
- The Kondo lattice, disordered metals and SYK model (I didn’t go to this far in this course)

The main textbook of this course is Bruus and Flensberg’s. The second-quantized operator formalism is used exclusively during the course. In this sense, a good companion book might be Atland and Simons’s, using the coherent-state path integration formualism a lot.

## What do I learn the most?

I got familiar with the **second-quantization formalism** and **mean-field theory** in the operator language by following this course. I’m also amazed to see so many interesting physical phenomena coming out of the interacting of many degrees of freedom and how powerful the techniques like mean-field approximation and the perturbation theory.

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Hello there, I have a request from you regarding this course. The course page is no more accessible to all. On the course page there were lecture notes with additional study material regarding that course, if you have downloaded it, may you please share it with me? I really need it as I am studying advanced condensed matter by myself.

Regards

Priyoda Kumar

email- priyodakumar@gmail.com

I only downloaded the lecture notes and problem sets, which now can be found in Sachdev’s new textbook, Quantum Phases of Matter. I guess the page is down due to the publishing of the book.

Best,

Bruce

Hey Bruce,

The book contains totally different material. It would be helpful if you kindly send me those notes over the email.

Thanking you in

Hello, Bruce! I have the same request as Souptik. I am curiosity about the notes by Prof. Sachdev. It’d be grateful if you could share the notes and my email is 1469848401@qq.com or ShihchiaYoung@outlook.com. Thank you very much!

Hello, Bruce! I am looking for the notes by Prof. Sachdev as well. And my email is 1469848401@qq.com or ShihchiaYoung@outlook.com. Thank you very much!