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Solid-state physics studies how macroscopic properties of solids (mechanical, electrical, optical, etc.) result from their microscopic structure. It usually deals with the scale where quantum properties of the particles are substantial.

1 vote
2 answers
1k views

Precise definition of "nearest neighbours" in solid-state physics

I am reading Ashcroft and Mermin and, to define coordination number, they use the notion of nearest neighbours which they do not define. I'm sure it's a very trivial definition, but they had been so p …
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3 votes
3 answers
190 views

How is this expression for the energy of a free electron gas derived with the canonical ense...

Suppose we have some system of free electrons in a (say, 3D) box at a temperature $T$. From Ashcroft and Mermin equation (2.55), we can compute the energy of the system as $$U=2\sum E(\mathbf{k})f(E(\ …
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1 vote
1 answer
315 views

The uniqueness of primitive vectors in a Bravais lattice

I am reading Chapter 4 of Ashcroft and Mermin (A&M) in which the basic definitions of a Bravais lattice (BL) -- as considered as a purely mathematical entity -- are being laid down. One of the definit …
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0 votes
0 answers
37 views

Why can we assume there is no charge in the derivation of dispersion relations (Drude theory)?

In a derivation done by Ashcroft and Mermin (I am now doing the derivation for helicon waves as predicted by the Drude model), the authors use in deriving the condition for propagation of electromagne …
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3 votes
1 answer
456 views

What "goes wrong" in a Sommerfeld expansion?

Let $f$ be the Fermi function and $H$ be a function which which vanishes as $\epsilon \to -\infty$ and which diverges at $\infty$ no worse than some power of $\epsilon$. In the Sommerfeld expansion of …
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4 votes
1 answer
625 views

On $k$-space density of states and semiclassical transport

I am reading Chapter 12 of Ashcroft and Mermin and I have a great many questions, but one sticks out in particular. As background, we note that it can be shown quite generally (by applying Born-von Ka …
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1 vote

Semiclassical model of electron dynamics

See the footnote given by AM on that very same page. There is no band wherein all orbits are closed; thus, there is no band in which all occupied states and all unoccupied states have closed orbits. T …
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0 votes
1 answer
316 views

Expressing entropy density in terms of energy density

In some manipulations in the free electron theory, one initially has the energy density $u$ of the system as a function of temperature and it's desirable to have the entropy density $s$ (both volumetr …
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0 votes
1 answer
42 views

Why is electronic specific heat divided by $V$ rather than $M$?

In Ashcroft and Mermin Chapter 1, just above equation (1.50) and in the context of a classical ideal electron gas, it is said that the electronic specific heat at constant volume $c_v$ is defined by $ …
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2 votes
0 answers
172 views

Rigorous definition of the perfect conductor in macroscopic electrodynamics

Zangwill (in Modern Electrodynamics -- most of this discussion relates to Chapters 5.1 and 5.2 if you have access to the book) defines a perfect conductor as a macropscopic model for certain matter in …
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3 votes
2 answers
133 views

Why do we take $\langle{v^2}\rangle = \langle{v}\rangle^2$?

In Ashcroft and Mermin's Chapter 1, the equipartition theorem is often used to evaluate the mean speed of an electron in an (ideal) electron gas treated with classical statistical mechanics. That is, …
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1 vote
1 answer
126 views

Are there primitive unit cells which cannot be associated with primitive vectors?

In the theory of Bravais lattices, it is immediate to associate with each set of primitive unit vectors a primitive unit cell (see e.g. here). It is (probably) not hard to show that this map is an inj …
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0 votes
1 answer
105 views

On describing fcc and bcc planes in a Cartesian system (simple cubic system)

Ashcroft and Mermin remark, at the bottom of page 91 that As a general rule, face-centered and body-centered cubic Bravais lattice[s] are described in terms of a conventional cubic cell, i.e. as simp …
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1 vote
2 answers
184 views

Electrostatics of non-equilibrium situations

In footnote 1 of Chapter 13 of Ashcroft and Mermin, they remark that The only case we shall discuss in which the local equilibrium distribution is not the uniform equilibrium distribution (13.1) (wit …
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21 views

Equilibrium carrier distribution appropriate to local temperature

In Chapter 13 of Ashcroft and Mermin there is a general discussion about the nonequilibrium distribution function under the relaxation time/semiclassical transport assumptions. One of the key axioms g …
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