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1answer
17 views

Out-of-plane electronic band structure for 2D materials?

There's been much recent interest in 2D materials since they can form monolayer-thick films. Since their crystal structure is periodic along the in-plane directions, the electronic band structure ...
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1answer
38 views

Do energy levels such as $E_c$, $E_v$ have negative values in semiconductors?

In energy band diagram of a semiconductor, do energy levels such as $E_c$, $E_v$ have negative values? Also, why electrons in semiconductor have energy? What is the formula for energy of an ...
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0answers
12 views

Energy-band diagram of forward-biased pn junction

When a p-n junction is forward biased then its energy-band diagram looks like this: What would happen if $V_a>V_{bi}$? ($V_{bi}$ is the built-in potential and $V_a$ is the externally applied ...
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0answers
18 views

The d-orbital splittings in WS2 monolayer

According to this paper (and many others), the formely degenerate $d$ orbitals of the tungsten atoms in the $WS_2$ monolayer are split into three groups: (1) $d_{z^2}$, (2) $d_{x^2-y^2}, d_{xy}$ and (...
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1answer
38 views

Bands in semiconductors: $E$ vs. $k$ diagram

I always thought that in a semiconductor there was one gap, one conduction band and one valence band. However, reading a book I came across this picture And now I'm very confused. Apparently there ...
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0answers
33 views

Tight binding Hamiltonian in the k-space

I want to find the band structure of this 2 dimensional lattice which isn't completely flat: Using a tight binding model.And take unit cells as they are shown in the figure. And assuming that each ...
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1answer
20 views

Electronic or excitonic band structure?

Usually, in the papers the electronic band structure for monolayers $WS_2$ is something like in the figure below: As you can see the direct bandgap is around ~2.0 eV. When we excite electrons at the ...
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1answer
34 views

Why are numbers not consistent? (Identifying phonon's frequency)

I am trying to connect several facts between each other to acquire a consistent picture. Fact 1. Monolayers of tungsten disulphide $WS_2$ have hexagonal crystal lattice, and the first Brillouin zone ...
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0answers
14 views

How does bilayer 2d materials break inversion symmetry and how does it lead to a bandgap?

Some (?) monolayer 2d materials have inversion symmetry, however bilayer materials don't (?). This opens up a bandgap in bilayer graphene. 1) How does bilayer break inversion symmetry? In which cases ...
0
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1answer
45 views

What is the shape of a band electron in momentum space?

Band electrons occupy adjacent sharply defined momentum states that in xyz space take the form of a spectrum of wave functions. These wave functions span the entire xyz volume of any compact unit of ...
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0answers
26 views

How Periodic Boundary Condition (PBC) is related to Band Structure of Quantum Dot?

I am reading about relationship between different lattices and their band structures.I have few questions about them: Q 1. Is is possible to find out band structure of a quantum dot (which is a ...
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0answers
54 views

How should I interpret the x-axis of an electronic band structure diagram ? Is it the direction an electron is moving?

Recently I've come in contact with electronic structure diagrams for my thesis and I have some difficulties getting an intuitive interpretation of reading these diagrams. What I think is happening: ...
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1answer
59 views

Notations for high symmetry points in the 1st Brillouin zone

I am trying to understand how I should interpret the letters like Г,K,M,T etc., that are usually there in the electronic band structure diagrams. So, let's assume we have graphene with its hexagonal ...
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0answers
33 views

Relationship between energy bands, DOS and magnetic ordering

I'm struggling to understand whether we can tell if a system will have magnetic ordering (e.g. antiferromagnetic) based on the aspect of an energy bands plot or/and the form of the DOS. My thought ...
0
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1answer
30 views

Photoemission to measure band gaps?

Photoemission works by conservation of energy: $$\bar{h}\omega = E_{kin} + E_i + \phi$$, where $\bar{h}\omega$ is the incident photon, $E_{kin}$ is the measured kinetic energy of the ejected ...
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0answers
25 views

what is the effect of temperature on the resistance of a photoconductor?

As we know, for a photo conductor resistance tends to decrease with increase in irradiance, but with greater irradiance comes greater temperature. Also we know, photo conductors are semiconductors,...
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1answer
40 views

Where can I learn about band theory?

I'm studying quantum mechanics and I want to understand perfectly where the bands of the electronic sturcture come from. I've read that it is related with the periodic potential, Bloch waves and ...
3
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1answer
46 views

Momentum operator in effective mass approximation

When we calculate the band structure of some solid then we often find that in the bottom of the conduction band the dispersion looks approximately quadratic with some new effective mass: $$E(k) = \...
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0answers
17 views

Effect symmetry on points in momentum space

I have to study some material for a condensed matter physics course and cam across a passage that I don't understand. "In momentum space time reversal symmetry and particle hole symmetry only have ...
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0answers
23 views

effect of inversion symmetry on the bandstructure

I have a very general question, but I hope that someone can answer it. Can someone describe what the effect of inversion symmetry is on the bandstructure. (Or is there not a general effect?). ...
1
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1answer
97 views

Energies in Band Alignments

There is something that I would like to confirm regarding the energy when aligning the bands of heterostructures. There seems to be a general consensus that there is no simple rule to align two ...
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0answers
12 views

How does electrical current affect electronic band density?

When sending a current through a conductor, electrons in the valence band gain energy. What does that mean concretely? Are electrons excited uniformly, i.e. all electrons in the valence band gain ...
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0answers
11 views

Why singlet and triplet states are not mentioned when dealing with inorganic semiconductors or other heavy materials?

Singlet and triplet states get attention in organic materials (fluorescence, phosphorescence, upconversion). Why singlet/triplet states are never mentioned in the context of inorganic semiconductors, ...
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0answers
9 views

Electronic Transport not covered by Bandstructure in Solid State Physics

From what I have read, most of the electronic transport phenomena in solids state physics seems to able to be determined with the bandstructure. Schottky Barriers, bandgaps, band discontinuities can ...
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0answers
27 views

Are Dirac points the norm for 2D band structure?

I've been doing simulations of band structure for 2D optical lattices, and something I've noticed is that, for sufficiently shallow lattices, there are typically points on the edge of the first ...
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0answers
54 views

Tight-binding model parameters fitting from ab-initio calculation results

Or the problem can be rephrased as: How to extract the tight-binding parameters from first principle calculations? I have searched some articles but all of them just give vague descriptions when ...
1
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1answer
38 views

Can the electron go below ground state due to the Zeeman effect?

I've read that the Zeeman effect can cause a single allowed energy level to split into two, one of which is higher in energy by some value \Delta E'. The other level is shifted down by the same amount....
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0answers
28 views

Could Hamiltonian near band touching point be non-linear?

We all know the Hamiltonian of weyl semimetal is +/- $\vec k\cdot \vec \sigma$, thus give the +/- 1 total flux of each weyl point. And in the band structure of real materials, if the perturbation ...
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0answers
21 views

Obtaining a Positive Hall Coefficient for Electrons Near the Top of a Valence Band

Using a Drude model of charge carriers with a charge $q$ and a mass $m$ (which I allow to take either sign at this stage) in a sample with an applied electric field $\mathbf{E}$ and magnetic field $\...
1
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1answer
38 views

What is invalidated when turning on many body interactions in a crystal?

I have just started to think about strongly interacting particles and Fermi liquid theory, and I have two questions. For non interacting particles moving in an potential field, we know that the ...
3
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2answers
89 views

Nearly Free Electron Model and the Reduced Zone Scheme

When for example studying the vibrational modes of a one dimensional diatomic chain we find that the dispersion relation $\omega(k)$ is periodic in the one dimensional reciprocal lattice vector $\frac{...
0
votes
1answer
65 views

electron blocking layer and hole blocking layer

What is basically an electron blocking layer and a hole blocking layer in contrast to an electron transport layer or a hole transport layer? In terms of the bandgap, I think if the case is one of a ...
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0answers
28 views

Single particle approximation for a conduction band electron?

I have a problem which on some levels appears very simple, but others quite complex so I thought I'd ask here to make sure I am on the right track before going ahead any further I have a 3D potential ...
0
votes
1answer
49 views

Basic question about valence/conduction bands

In most introductions to solid state physics that I've read, they explain the origin, basically, of the band gap as follows: By doing a superposition of the standing waves inside a BZ, one can find ...
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0answers
29 views

Why for each electron – hole recombination, an electron from the negative terminal of the battery is released

Why for each electron – hole recombination, an electron from the negative terminal of the battery enters the N-region and then drifts towards the junction?
2
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1answer
91 views

Does momentum space have a speed limit?

In ordinary $xyz$ space, the maximum velocity of propagation for mass-energy and/or information is $c$. So, my question: Is there also a maximum velocity of propagation in momentum ${p_x}{p_y}{p_z}$ ...
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2answers
680 views

Why is diamond transparent while graphite is not?

Diamond and graphite are both made of the same atom, carbon. Diamond has a tetrahedron structure while graphite has a flat hexagonal structure. Why is diamond transparent while graphite is not (at ...
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1answer
69 views

Magnitude of the band gap

In Kittels book on solid state physics (Introduction to solid state physics, p. 167, 8th ed.), he defines the band gap energy $E_g$ as $E_g = \int_0^1 U(x) [|\psi (+)|^2 - |\psi (-)|^2]$ where $U(x)$...
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0answers
101 views

Band gap origin

Many introductory books on solid state physics use images that I find confusing. For instance, one picture I see alot when reading about the band gap, is similar to this one: I understand that the ...
1
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1answer
384 views

Why do we have heavy and light hole bands in semiconductors?

On the topic of the valence band of a semiconductor (in this example GaAS), it is the case that the valence band has some structure to it. As shown in the illustration below, we see that at the $\...
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1answer
80 views

Relation between energy bands and Brillouin zones

In almost every book about solid state theory, electrons in a periodic potential are introduced and calculations for the dispersion relation $E(k)$ are presented. One obtains the usual pictures in ...
0
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1answer
36 views

What does it mean that an electron-hole pair is the fundamental unit of generation?

I wasn't certain to post this in chemistry or physics section. I was reading the wikipedia article on "Carrier generation and recombination" and in the second paragraph it says something that I ...
1
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1answer
211 views

Can a perfect insulator, i.e. matter devoid of all electrons conduct electricity?

Few weeks ago an article on Nautilus was published on Neutron stars. After reading that, a question was asked by a friend of mine. He asked if matter in neutron star would be able to transfer ...
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2answers
63 views

Translating Electronic Bands back to first Brilluoin Zone

For phonons, I understand why we can translate everything back into the first Brillouin Zone: there is a minimum wavelength defined by two lattice sites. For electrons, which are delocalized, I see ...
0
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1answer
56 views

What are the current carriers in a PN junction?

Imagine a PN junction in forward bias mode. The conventional current goes from the p-side to the n-side. However, as mobile holes move to the n-side, aren't there mobile electrons on the n-side which ...
4
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2answers
157 views

For the transition metals, how does counting the number of up-spins and down-spins still give you a non-integer magnetic moment?

The transition metals like Fe, Co and Ni have magnetic moments of 2.2, 1.7 and 0.6 Bohr magnetons, respectively. The band theory says that you get this when you calculate the density-of-states of the ...
2
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1answer
51 views

Metallic and Semiconducting Nanotubes, symmetry discussion

I'm interested in band gaps of Single-walled Carbon Nanotubes (SWNTs). I know that there are three kinds of SWNTs: Zigzag : $(n,0)$ Armchair : $(n,n)$ Chiral : $(n,m)$ Electical properties of ...
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1answer
49 views

Bandgaps of Silicon and their application in active optical elements

I know that silion has an indirect bandgap at $E = 1.12 \, eV $ or $ \lambda = 1.107 \, \mu m$ and I have read that active optical processes like absorption and emission have a decreased likelihood to ...
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2answers
182 views

Why do metals become insulators when oxidized?

I don't know the connection between how forming a new bond with oxygen then changes the density of states to transform the metal into an insulator. It seems like a very powerful transformation.
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0answers
52 views

Estimating Energy Bands For Dirac Comb Potential

With $$V = \sum_n aV_0(x-na) $$ I can solve exactly up to $$\cos(k a) = \cos(\kappa a) + \frac{2ma^2V_0}{\hbar^2}\frac{\sin(\kappa a)}{\kappa a} = f(\kappa a)$$ Where $E = \frac{\hbar^2 \kappa^2}{2m}...