Questions tagged [solid-state-physics]

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.

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51 views

What does $H\parallel ab$ mean? [closed]

$H$ is an applied field. $\boldsymbol{a},\boldsymbol{b},\boldsymbol{c}$ are the lattice vectors.
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Unit Cell of a 1D Spin Chain

I encounter a problem in recognising the unit cell of a 1D spin chain. Suppose a 1D spin chain is composed by many electron sitting on different sites. The electrons can be either spin up or down. ...
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26 views

What is a bulk state and bulk bands?

I am a bachelor student and I started studying topology and I came across two terms I have never seen before: Bulk band structure and bulk states. Can someone explain these two terms or provide me a ...
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51 views

Why doesn't the classical model of electrical conduction work with iron, cadmium and bismuth?

My textbook says this: In most metals, the charge carriers are electrons and the charge - carrier density determined from Hall - effect measurements is in good agreement with calculated values for ...
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40 views

Nearly free electron model: How to diagonalize the perturbation Hamiltonian?

In the Nearly free electron model, we treat a weak periodic potential as a perturbation to the free electron model so $$H_{tot}=H_0+V(\vec{r})$$ where $H_0=\frac{\hat{p}^2}{2m}$ and $V(\vec{r})=V(\vec{...
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1answer
33 views

Picturing Electron scattering in periodic lattice

I'm reading Electrons in a Periodic Potential from The Oxford Solid State Basic. There is a particular point which I'm able to see mathematically but not quite able to picture. Consider electron in ...
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26 views

Existence of Metastable states

Do they (metastable states) exist naturally in atoms or they are artificially produced in them.
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If an iron crystal is fully magnetized spontaneously, estimate the resulting magnetization [closed]

If an iron crystal is fully magnetized spontaneously, estimate the resulting magnetization. I have no idea how to solve this problem. Could anyone help or give any suggestions? I think I need to ...
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29 views

X ray diffraction to determine crystal structure: Certain Fourier components must be zero?

In Phillip Hofmanns introduction to solid state physics, we derive that the intensity of the diffracted X-rays incident on a crystal will take the form $$I(\vec{K})\propto \left|\int_V \rho(\vec{r})e^{...
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1answer
79 views

Nearly free electron model and perturbation theory: How to determine matrix elements of perturbation?

In Steven Simons The oxford Sold state basics, the Nearly free electron model is tackled by treated the weak periodic potential as a perturbation to the free electron model. That is, the full ...
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Why is the effective mass of silicon anisotropic?

The effective mass is a tensor property of rank two. It may be anisotropic if the corresponding electron band is not perfectly isotropic. For silicon, this seems to be the case. However, there exists ...
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Diffusion always present?

Simply asked: Is diffusion always and everywhere present? Let's reduce the question to the macroscopic world. Anytime, when two materials touch each other (air <-> wall, tea <-> cup, chair ...
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Why in a semiconductor when temperature increases from 0 K, a very few electron acquire a sufficient kinetic energy but not all the electrons?

I have read that at O K temperature the covalent remains intact in a semiconductor making it an insulator but when we increase the temperature some of the electrons in the covalent bond acquire ...
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1answer
37 views

What makes of a current in solidstate/semiconductor physics?

If there is some incoming light that has hit electrons of a N-type doped silicon and broke loose these electrons from their covalent bounds and excited them to the conduction band and also excited the ...
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1answer
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Group velocity is zero at zone boundaries

The E-k diagram derived in Kronig Penney model looks like: As we can see that slope of this curve is zero at all zone boundaries as well as k=0, which makes group velocity zero at these points. Why ...
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2answers
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Confusion about ionised atom, free electron, conduction band, donor energy level and acceptor energy level

I have some confusion about the concept of some electronic bands and energy levels. Beyond valance band, For an atom, can having at least one electron in the conduction band mean that the atom has ...
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1answer
52 views

Symmetry in solid state

I learned that a physical system with higher symmetry lowers the overall energy. If it is true, why we don't have many/all elements crytalized in simple cubic structure?
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2answers
51 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 ...
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1answer
36 views

Heat Capacity at absolute zero

As Heat Capacity of solids has two contribution: One arising from lattice, called lattice heat capacity and another from electrons, called electronic heat capacity. At absolute zero, we say that heat ...
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1answer
49 views

Experimental proof for if a d.c. electric current inside a naked wire is being influenced by an external electrostatic field?

For example a d.c. electric current carrying naked wire inserted inside the electrostatic field between the two plates of a vacuum capacitor and with the wire not touching the two plates of the ...
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13 views

Energy diagram of Fermi surface electrons inside the potential well

The energy of surface Fermi electrons for a free electron is a sphere for Kx, Ky and Kz where E=(h^2 * K^2)/2m. But now what is the figure of the energy of the electrons inside a limit potential well ...
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2answers
28 views

Continuous value of crystal momentum in Bloch theorem

The reciprocal lattice of any Bravais lattice can be interpreted as a set of possible $k$ values representing the wave vector of a standing wave with the periodicity of the Bravais lattice. Therefore, ...
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1answer
45 views

Curie temperature and magnetism

What would happen to the magnetic property of a ferromagnetic material if it is heated above the Curie temperature, and then cooled down below it?
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1answer
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Particle number in the BCS theory

I don't really understand why the nonconserved particle number in the BCS theory isn't a problem. I read in the Tinkham book that it isn't a problem since the particle number is huge. The fluctuation ...
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1answer
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Treating acceleration of charged particle in quantum mechanics

I can't find any good resources online that explain how we can derive the effect of a uniform electric field on a free electron using the quantum mechanics Hamiltonian formalism. In our condensed ...
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1answer
59 views

What exactly causes resistance?

According to Ohm's Law, $V=IR$. Here $R$ denotes the resistance. It's the way I was introduced resistance. The definition is not convincing me. First of all I don't understand what causes resistance? ...
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3D topological insulator without $C_{n>2}$ rotational symmetry?

Is there any known/predicted 3D topological insulator without any $C_{n>2}$ rotational symmetry?
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1answer
30 views

Standing wave and optical mode in a crystal

I want to understand how when the wavelength $ \lambda$ is equal to 2a, with a being the lattice constant, two neighboring building particles of the crystal move in opposite direction. The general ...
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62 views

How to solve the following eigenvalue problem?

I'm trying to replicate results from this paper. A version on arXiv.org is here. In it we are supposed to solve the following eigenvalue problem first before we can proceed to tackle the main ...
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1answer
14 views

Can we interpret the spin wave dispersion as the allowed (or required) energy at a given momentum?

In condensed matter or solid state physics, we usually meet the dispersion which is a function $\omega(\vec{k})$, for example the spin wave of the antiferromagnetic Heisenberg model in the square ...
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Lattice periodicity and Brilliouin zone

I was reading this paper and found the following statement (top of right column, pg 3). In particular, the frequencies of the silicon 2 × 1 surface reconstruction can be identified at ($k_x$, $k_y$) = ...
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Interaction of nonpolar optical phonons with light

How optical phonons in nonpolar insulators, such as diamond, interact with light and cause absorption lines in the infrared region? An example is the picture from this book chapter, where phonon ...
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35 views

Atomic form factor

It's kittel solid state physics chapter 2 last section Atomic form factor is defined as: $f_j = \int dv n_j(r)exp(-i\bf{G}.\bf{r})$. If $\alpha$ is the angle between $G$ and $r$ such that $G.r=Gr\cos\...
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Absorption spectral broadening of molecules in solution compared to films

During an experiment we measured the absorption spectra of a compound in solution and also made a measurement for the same compound in solid film. Usually when I done this for other compounds there ...
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35 views

What determines helicity of 3D topological insulator surface state

Consider a 3D topological insulator surface state Hamiltonian with mass possibly due to magnetic doping $$\sum_{i,j=x,y}v_{ij} k_i \sigma_j + m\sigma_z.$$ What determines the helicity $X=\mathrm{sgn}[\...
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2answers
96 views

Simplification of the exchange term in the Hartree-Fock treatment of an interacting paramagnetic electron gas

In the Hartree-Fock treatment of the interacting electron gas it is assumed that solutions are planewaves of the form \begin{equation} \phi_{i}^{HF} = \phi_{{\bf{k}}\lambda} = \frac{1}{\sqrt{\Omega}}e^...
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30 views

Role of Fermi sea in the formation of Cooper pairs

I've read some of the many questions on the Cooper problem but didn't find an answer to the following: why would we expect Cooper pairs to form above the Fermi sea? As I understand it, for electrons ...
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Piezoelectric equations

I've seen two sets of equations for Piezoelectric(and converse piezoelectric) effect in different references, first set which is introduced in "Elements of Group Theory" by A.W. Joshi are: $$...
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Why does a macroscopic chrystal reflect the atomic lattice structure?

When we look at the macroscopic forms of crystals you can see how the atomic lattice is built up. The most common example is salt (sodium chloride), the visible cubic crystals reflecting the cubic ...
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1answer
151 views

Thermal averages with opposite sign in the exponential

I've recently seen an example where a thermal average was carried using a plus sign instead of the usual minus sign inside the exponential. $$\langle \mu \rangle = \frac{1}{Z} tr(e^{\beta H }\mu) \...
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1answer
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Can ice patterns form on the top of deep water?

Here is a picture of a pattern in ice: There are feathers, or flowers to be seen. The ice has grown on a solid underground. Water condenses on the solid underground and freezes. I have never seen ...
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282 views

Flat bands and localization in real space

When reading this paper I came across the following claim: From a band-theory point of view, the flat bands should have localized wavefunction profiles in real space Is there a rigorous proof of ...
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1answer
62 views

Why is it so easy to break a pencil when part of it is composed of layers of graphene, an extremely strong material?

Graphene is one of the strongest materials in the world. It's a two-dimensional structure (insofar the overall extension in three dimensions is concerned): A pencil contains graphite, which is a ...
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1answer
50 views

Why does the density of states in the valence band of an intrinsic semiconductor increase with decreasing energy?

I'm currently doing an introductory quantum mechanics and solid state physics course. I understand why the density of states in the valence band of an intrinsic semiconductor increases with increasing ...
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1answer
26 views

Using mass-action law to determine doping densities [closed]

I would like to understand the solution to part c) given below: Find the electron and hole densities in silicon at $300$ K, for each of the following impurity densities: a) Boron atoms at $5 \times ...
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2answers
64 views

Why electrons are freely moving in valence band? If they are moving why not any current? [closed]

Why electrons are freely moving in valence band? If they are moving why it does not have any current? For all the cases?
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2answers
90 views

$k$-dependence of the energy in solid state physics

In a crystal, the electrons are subject to a periodic potential due to the fact that the atoms form a periodic lattice. From this periodicity we can obtain the Bloch theorem, and get a general formula ...
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37 views

What is happening at the microscopic level so that superconductors expelled out magnetic field lines?

Superconductor shows perfect diamagnetism then what is happening at the microscopic level so they exhibit such behaviour? In other words why they repel the magnetic field? Why most of the good ...
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1answer
74 views

Why is lead soft?

As most of us know, lead, at room temperature, is quite soft. You can easily bend a lead rod. You can easily scrape a small piece off it with your nail, and you can even pull a thin long piece apart. ...
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3answers
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How many water molecules should I put together before I can tell If it's liquid, gas or Solid?

How many water molecules should I put together before I can tell If it's liquid, gas, or Solid? I know, there isn't any clear boundary that says that you have to put $50$ molecules or $100$ ...

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