Band Definition and 481 Threads

Hello! Double heterostructures are used in LEDs and lasers to provide both the confinement of the charge carriers and the confinement of the generated light. This image is a comparison between a homojunction and a heterojunction. As regards the unbiased junctions, when the n region and the p...

Hi. I've set myself a project with a couple of my classmates and despite the impracticability of it we want to do it as well as possible. Our aim is to look at using a massive elastic band in order to launch a payload at massive velocities, possibly even at escape velocity. To this end I've...

What do we mean by break points in band structure ? and what that sentence means : "if the band index were chosen in such a way that the energies are indexed in ascending order for any k then break points would appear in the εnk vs. k plot (with n fixed) wherever two lines intersect." ...

Hello, I am trying to figure out the width of bands in a 1-dimensional lattice. Here is a short derivation from the book I am reading: if we approximate the free electrons as being in a square well then the energy levels are ## \frac{\pi^2 \hbar^2 n^2}{2mL^2}##. If there are ##N## ions...

Hello PF! I have a project/competition in freshman college Aerospace that calls for a plane that can stay in the air for as long a time as possible while going as far as possible. The requirements don't explicitly say we need rubber bands as a propulsion but pretty much prohibit everything but...

Homework Statement I need to explain for a lab, why the efficiency of a rubber band slingshot constant for different stretch lengths. I don't need math, just a general explanation of why kinetic energy of projectile/elastic potential energy in rubber band is constant. Homework EquationsThe...

Homework Statement Hi, I just need some confirmation on 3 questions H(s) = 1/(s+1)^2 1. I was asked to calculate the poles and zeros. I believe zeros: none poles: 2 (or p1,2) = -1 2. I was also asked to calculate the slope of the magnitude response was w -> 0 Here is my sketched graph...

Homework Statement Homework Equations $$ Z(1) = \sum_{i=1}^{} e^{\frac{E_i}{K_bT}} $$ where ##E_i## is each of the possible energy states available to a single link (in this case the right and the left states). $$ P=\frac{\sum_{i=1}^{} e^{\frac{E_i}{K_bT}}}{Z} $$ The Attempt at a Solution...

-iation. Could the opacity of a material to one band of EM radiation (light) could be altered by irradiating the material with another band of EM radiation (X rays)? I think you are suggesting that: By raising the electrons in the atoms to higher energy bands (with the X rays), so that they will...

I am doing an experiment where we have to use the threshold voltage of LEDs to determine Planck's constant given the following relation $$ eV_0 = E_g = \frac{hc}{\lambda} $$ where ## V_0 ## is the threshold voltage, ## \lambda ## is the wavelength of emitted light and ## E_g ## is the band...

Hi there people! So my question is why you can see localized surface states within the band gap of the material with an STM. How is a tunneling circuit being established?

Hi, How can I prove direct band gap property of a Transition Metal Dichalcogenide electrically and optically through experimentation? I can use PL measurements to prove this for optical band gap. Is there any other equipment or technique to prove this? I can not use ARPES because channel length...

Hi all, I'm currently trying to investigate the edge current on a finite strip of Zigzag Haldane model (spinless, pi/2 phase) and I measure the current (in my code) by taking the expectation value of my current operator which is a function of wavevector k, for each eigenvector of the...

I'm teaching myself how to do DFT for my master's project, where I want to use it for calculating band structures for different heterostructures. Now to learn DFT I am on one hand reading a book on the basic theory, on the other hand using different freeware packages to try and calculate the...

Homework Statement Find band gaps for Dirac Comb potential $$V = \sum_n aV_0(x-na) $$ Homework Equations Bloch Theorem $$\psi(x+a) = e^{ika}\psi(x)$$ The Attempt at a Solution I can solve exactly up to $$\cos(k a) = \cos(\kappa a) + \frac{2ma^2V_0}{\hbar^2}\frac{\sin(\kappa a)}{\kappa a} =...

I have some qualitative questions about the relation between band structure, density of states, and Fermi energy (or Fermi level). 1) Say you have a given electronic band structure (energy as a function of k) obtained by any method. How do you relate this to the Fermi energy (or Fermi level) ...

Is there any method for how to choose k-points in band structure calculations for aluminium slab 5*5*4 can somebody help in this question? Thanks

Homework Statement Nobel prize for physics for blue laser diode using Gallium Nitride with band gap of 3.4 eV and a refractive index of 2.429. Explain how these parameters determine at what wavelength a Gallium Nitride semiconductor will laser at. Homework Equations E=\frac{hc}{\lambda}...

Do electrons in conduction band are only responsible for current? Don't the electrons in partially filled valence band capable of moving contribute to current? Material discussed-metals(conductors)

I almost "get" it, but not quite. Can someone help? Here is my current understanding. Say you solve the Kronig-Penny model. You find that you get bands of N closely spaced energy levels, with large gaps between them. Under normal conditions, electrons fill the band to some level (let's say we...

Consider the figure from section "Electrical conductivity":https://en.wikipedia.org/wiki/Valence_and_conduction_bands I understand that below the Fermi level, we have bands of allowed energy separated by band gaps. Then, we have the Fermi level. Then we have the conduction band. My question...

Hello, I'm trying to analyze the following system to get some idea about the forces present. The red line is supposed to represent the belt wrapped around the two drums. There is an extra part to the belt, however. Tangentially from the drum, a part of the string is attached to an unmovable...

I attached a picture. In the first figure, we see that the difference between bands is rather large. We see that electrons do not occupy all the energy levels from energy 0 to Fermi energy level. There are forbidden band gaps. But in the second figure, I see that the electrons occupy...

Hi! I'm sung dae with tensile strain, energy band structure could be changed. bang gap decrease with compressive strain, energy band structure could be changed. bang gap increase but I'm not sure why it could be changed .. Is there someone who explain in detail ? thanks. have a nice day! :)

Do any band structure (in absence of any external field) in general, is symmetric with respect to k? In other words, do we always have E(k)=E(-k).

I recently read about the recommended amount of exposure time to high sound volumes: http://www.dangerousdecibels.org/education/information-center/decibel-exposure-time-guidelines/. Since I am in the Band at school I was somewhat concerned about if the sound intensity would be too much...

What exactly is the relation between these 3 quantities? As far as I can tell the work function is the energy needed to bring an electron from the fermi level out into vacuum, while affinity is from the bottom of the conduction band. Does this then mean that they can be used to calculate the...

Homework Statement From the experiment I did my force was equal to 0.0686N +/- 0.00196N and my x (rubber band stretch) was equal to 0.003m +/-0.002. The question asks to determine the force constant k +/- ∆k. Homework Equations F = kx k = F/x ∆k = |k| ∆x/x +∆y/y The Attempt at a Solution k...

The abstract of this paper ( http://www.sciencemag.org/content/297/5588/1853 ) says "The electronic properties of the one-dimensional chains are dominated by an unoccupied electron band" I'm not sure what the paper is referring to by an unoccupied electron band. Wouldn't a metal be described...

if in a solid there arent no states with same energy then why energy band vs location diagram is flat?

Why is the conduction band state s-type and the corresponding valence band state p-type?

This was given as a problem in a calculus textbook I'm working through (apologies if this should have gone in the physics forum) 1. Homework Statement An ant crawls at 1foot/second along a rubber band whose original length is 2 feet. The band is being stretched at 1 foot/second by pulling the...

Can anybody explain my what is the origin of this forbidden gap? I mean how it was created and what is the physics behind this issue?

Dear forum people I consider four atomic orbitals of the silicon atom: s, px , py and pz , thus Hi,j is a 4*4 matrix. Hi,i is the expression of the diagonal matrix and Hi,j is the expression off-diagonal matrix where the expression for Hi,i and Hi,j is attached. But I can not calculate the...

So I know glass is transparent because the electrons have energy bands(or the energy to get it up to the next energy state) that are beyond the energy of visible light. But what I what to know is why do the electrons have energy bands because every single electron is the same and there all...

Landau level is the energy levels of free electron gas in a magnetic field. However, this term is also frequently used in solid state physics. I have the following questions: 1. what does this term exactly mean in band theory? After all, electrons are not free here. 2. why is de Haas-van Alphen...

Dear forum people, I know that electronic properties silicene is the same graphene but i can not figure out how can I plot band strcture silicene. I want to plot that in the following path: K→Γ→M→K

Homework Statement Emma and Don are playing in a band. While emma is marching toward Don, Don tunes his instrument to match the note that emma is playing. When emma stops, don immediately notices a beat frequency of 5 Hz. If the speed of the sound is 330m/s what is the relationship between...

As far as I am concerned, dielectric function can be computed by band structure. However, band structure is a global property of solids, while dielectric function is a local property. How a local property can be computed from a global property. Put it another way, if I want to calculate...

Hi all, I am currently writing a report about superconductors, and am currently reading about how the band gap shows that single electrons are not the charge carriers responsible for superconductivity. However, I was confused when I read that electrons are fermions and as such there are no band...

What's the electric field strength needed to get one of lithium's core electrons into the conduction band? How do you figure this out?

Hello all, I am anew user for Ansoft Maxwell, I am doing simulation for tubular machine in 3D, I have problem with band assignment, when I run the analysis there is a massage error after the mesh, which said [error] Error in mesh mapping on band, please check the potential problem in band...

Can you show me as explicitly as possible through equations?

I just learned how to get a tight-binding dispersion for graphene. But i can not figure out how can I plot that. I want to plot that in the following path: Γ→K→M→Γ I would be appreciated if could some one give me a hand on my problem. thanks for alot.

Short version: how do I figure out how much error I get when measuring light intensity vs wavelength for a given monochromator band pass width? Long version: I have a project where we will be passing white light through liquids, then looking at the spectrum intensity of the light with a...

Look at the diagram below, after all that doping, 2 blocks of Si have the same band structure? My understanding of band structure and fermi level is that: Given a block of solid (Please note, not a TYPE of solid, but this PARTICULAR block of solid) it will have its own unique band structure...

I didn't put this in the Education forum because I feel the level is probably too high. I have a physics degree and an education degree, but due to my inability to tolerate students who simply don't care about learning, I became an electrician instead. My colleagues and I were having a...

It's known that the number of states in a band is equal to the number of unit cells in crystal. Here is my problem (confusion with trivial concepts) Bloch function is a electronic state, or orbital. The number of orbitals in a band inside the first zone is equal to the number os units cells...

<< Mentor Note -- post separated out of a different thread to deal with a separate question >> Hi, I am looking transmit as well as receive power within close proximity. Currently I am looking at 27.255 MHz AM in the citizens band. It is listed on Wikipedia and in statues I found to be for...

For a wavefunction at the Brillouin boundary we have: \langle k|H|k\rangle = \epsilon_0 (\vec k) \langle k'|H|k'\rangle = \epsilon_0 (\vec k+\vec G) \langle k'|H|k\rangle = V_G = \frac{1}{L^3} \int e^{i(\vec k - \vec k') \cdot \vec r} V(r) d\vec r \langle k|H|k'\rangle = V_G^* Using...