Books for Condensed Matter after Ashcroft/Mermin What are some good condensed matter physics books that can fill the gap between Ashcroft & Mermin and research papers? Suggestions for any specialized topics (such as superconductivity, CFT, topological insulators) are welcomed.
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General Condensed Matter


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*"Condensed Matter Physics", Marder.In some areas a successor to Ashcroft & Mermin.


Condensed matter at low temperatures


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*"Matter and Methods at Low Temperatures", Pobell.

*"Low-Temperature Physics", Enss.
Magnetism


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*"Magnetism in Condensed Matter", Blundell.

*"Magnetism and Magnetic Materials", Coey.



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*"Quantum Phase Transitions"

*"Advanced Solid State Physics"

*"Advanced Condensed Matter Physics"

*"Condensed Matter Field Theory", Altland and Simons.Has a lot of example systems to be explored.

*"Introduction to Superconductivity", Tinkham.Classic book on superconductivity.
A: May I also suggest A Guide to Feynman Diagrams in the Many Body Problem by Richard Mattuck, as a supplement to Altland and Simons, and Fetter and Walecka.
The book by Mattuck is a friendly, carefuly, and labored exposition to many-body theory. Beginning with the ideas of a random walk, the impurity problem, the author describes "dressing" of charge (renormalization) in a background, and spends time introducing momentum space and the Fourier transform. Then Feynman diagrams are introduced first as tree graphs (the ladder diagram for the impurity problem), and the book teaches  the organization of different kinds of graphs once loops are introduced. The concept of self-energy in both coordinate and momentum space are developed thereafter. Then the author switches gears to full-blown second quantized formalism with and without spin.
Later chapters include applications to superconductivity, finite temperature field theory, the Kondo problem, nuclear physics, and the renormalization group.
Many-body theory courses can often be the first time students are introduced to quantum field theory. As a graduate student in high-energy physics with background in condensed matter/solid state physics, I can say that high-energy versions of QFT courses do not usually focus on applications of QFT outside scattering cross-section calculations, and it is important (even for high-energy theorists in my opinion) to know what to do with QFT as a general tool. There aren't very many books on QFT which do not convert you completely into the high-energy or the cond-mat camp. That's why books like this one are useful in shaping your holistic understanding of QFT.
Personally, I found that after I was a bit unsure of what I studied something from Altland and Simons or Fetter and Walecka, I was clearer about it after reading the corresponding sections from Mattuck's book.
However, Mattuck does not discuss the path integral method, which is now almost ubiquitous in research; Altland and Simons is more modern in that sense.
A: As for books on QFT in condensed matter physics, besides Altland, Field Theories of Condensed Matter Physics by Fradkin is also excellent. It covers a lot of cutting-edge topics, including entanglement entropy/spectrum.
Kardar's Statistical Physics of Fields is more on the side of stats mech, but is also a good reference.
Nagaosa's another book: Quantum Field Theory in Condensed Matter Physics is a little more hard to read than Altland and Fradkin.
A: At the introductory level, I think Steve Simon's book on solid state physics is a great read. 
For beyond, there is a new book no-one else has mentioned but seems pretty promising: 
Introduction to many-body physics - Piers Coleman
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*Modern Condensed Matter Physics
by Steven M. Girvin and Kun Yang (Cambridge University Press, 2019) covers material from the level of Ashcroft and Mermin up through Anderson localization, the quantum Hall effect, spin liquids, topological insulators, superconductivity, etc.  Second quantization for fermions is avoided until about 3/4 of the way through the book in order to keep the level accessible to beginning students.

A: To cover that gap you will have to study many-body physics.
Similar level than Ashcroft-Mermin (although modern and complete)

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*"Solid State Physics", Grosso & Parravicini.


*"Condensed Matter in a Nutshell", G. D. Mahan.
Many-Body Physics (General)

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*"Fundamentals of Condensed Matter Physics", Marvin L. Cohen & Steven G. Louie. A much-needed textbook that gives credit both to the traditional view of the field and the modern view based on excitations. Thus, it is not only focused on many-body theory but serves as a first contact.


*"Basic Aspects of the Quantum Theory of Solids: Order and excitations", Daniel I. Khomskii. Fills the gap between the foundations and present-day solid state theory using as the main theme two concepts: order and excitations. Slick and more accessible than others. As stated in the preface the purpose of this book is attending exactly the needs of the OP.


*"Modern Condensed Matter Physics", Steven M. Girvin and Kun Yang.  Covers material from the level of Ashcroft and Mermin up through Anderson localization, the quantum Hall effect, spin liquids, topological insulators, superconductivity, etc. Second quantization for fermions is avoided until about 3/4 of the way through the book in order to keep the level accessible to beginning students.


*"Introduction to Many-Body Physics", P. Coleman. An amazing treatise on introductory and not so introductory many-body physics applied to condensed matter theory. In addition it provides historical facts and uses plenty of figures to illustrate concepts and experimental results. More updated than others.


*"Advanced Solid State Physics", Philip Phillips. "For an up-to-date perspective on solid state physics from a many-body physics perspective, may I refer you to this book" by P. Coleman in Introduction to Many-Body Physics.


*"Many-Particle Physics", G. D. Mahan.A good introduction, it covers lots of topics although notation is a bit old-fashioned. Some chapters are not very good (skip the quantum Hall effect chapter!).


*"Quantum Theory of Many-Particle Systems", Fetter & Wallecka. Very good and cheap, specially if you want to learn Feynman diagrams applied to condensed matter physics problem.


*"Methods of Quantum Field Theory in Statistical Physics", Abrikosov.A Russian classic by one of the masters. Also a bit old fashioned and not very easy for beginners but covers all the basics.


*"Condensed Matter Field Theory", Atland & Simons.Already mentioned in the other answer. For a path-integral approach to condensed matter physics.


*"Quantum Many-Particle Systems" , Negele and Orland.Very well-written and easy reading. Similar to the first one (Mahan).
Quantum Hall Effects

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*"Quantum Hall Effects: Field Theoretical Approach and Related Topics", Z. F. Ezawa.I don't like it very much, very sloppy with notation.


*"Composite Fermions", J. K. Jain.The first chapters are a good overview of quantum Hall effects. Also it is obviously biased towards Jain's theory of composite fermions (as its title reflects!) and so full of hand-waving arguments to try to justify it.


*"Perspectives in Quantum Hall Effects", S. Das Sarma and A. Pinczuk (eds.).Not easy to find, I like it though because it covers all the experimental stuff you need to know.
A: Well, for strongly correlated systems,
there are many other books you should read.
E.g. for quantum order beyond Landau-Ginzburg's theory, 
Xiao-gang Wen's book is good:《Quantum field theory of many-body systems》.
In this book, the path integral method is widely used and many materials not covered in other book are treated. Also, the chapter on quantum Hall effect is well written and it mainly focuses on effective chern-simons theory and edge-state. 
Then, the topological and quantum order is introduced and treated. In some sense, these chapters are from the author's research paper and it is not easy to read.
The Nagaosa's book is also good. It is easy to read and follow.
《Quantum field theory in strongly correlated electron systems》 
A: A lot of good suggestions already, but a few more to consider:
Burns Solid State Physics.  Similar level to A&M but stronger in some areas, like symmetry.  Appeals to material scientists.
Introduction to Superconductivity Rose-Innes.  more than AM, but easier than Tinkham
