Gap Definition and 267 Threads

Hi Can somebody explain what is a "gapless excitation"? If it is an excitation, why does it require no energy (gapless) to excite the system? Thanks, Mavi

http://en.wikipedia.org/wiki/File:Magnetischer_Kreis.svg The attached image shows a magnetic circuit with a small air gap. The magnetic material on each side of the gap is attracted to the other side. I've seen the magnitude of the force calculated based on principle of virtual work...

how the conduction band offset varies with Al concentration?? what is the different?

If I am not mistaken the problem of the mass gap in in QYM, is a claymath problem, if the author of the next blog has proven it, shouldn't his article make more background noise, i.e be noticed by the media? Here's the link: http://marcofrasca.wordpress.com/?s=mass+gap Or he hasn't proven...

I am somewhat distracted so this post will not be what it should, given that GAP is one of my interests. For those who don't already know: GAP is a powerful open source software package for computational algebra, especially computational group theory and allied subjects. This long running...

How does the band gap not violate the principle of least energy? Surely the most favourable states are those with minimum available energy - but there is a gap!

Interesting article... http://www.dailygalaxy.com/my_weblog/2009/11/the-billionyear-technology-gap-could-one-exist-the-weekend-feature.html?utm_source=feedburner"

hi I am new to this forum , i m really frustated regarding my career i have done masters in physics in India then started doing phd for 6 mnths (which i was not interested in) got married , came to usa, planned family . now I am 29 and want to start a career after 4 years of gap i got my...

Hello all, I'm just getting to grips with conduction in solids and am trying to find some values for the band gap between the valence and the conduction bands. All I can find anywhere are typical values for semiconductors (or about an eV). I also found that carbon in the diamond configuration...

Hello everyone: Do you know how to calculate the energy gap (the forbitten band) for a solid from the Kroning-Penney model?

How does a direct band gap (like that in GaAs) vary with its well width?

Ed Witten was essential in organizing the 1 million dollar prize for clarification of the mass gap in QCD that is offered by the Clay institute. But why is this issue so important? Wouldn't all the successes of QCD stay also if no glueballs existed? Can somebody explain why Witten wants the...

hi folks, I've gotten most of this problem but for one part. I've learned quite a bit reading about the physics involved here on the web, but for all I've learned when I apply it, it doesn't work (ie give the right answer). So, I'm missing something. Homework Statement In silicon, E_g =...

band gap arises due to lattice potential.band gap is produced at zone boundary due to bragg reflection.there it behaves like standing wave instead of traveling wave?further formation of 2 standing waves?please help

I'm a student in the UK, and have already applied, been rejected/accepted by various universities, and accepted a firm and insurance offer. I was accepted at Southampton, after rejections from Oxford and Imperial. I was happy with my decision, but after talking to my head of physics, I'm...

Hi guys i have a question about how semiconductor materials absorb photons at less than the band gap energy. Particularly in an indirect material like silicon. Looking at absorption spectra for silicon i expected for it to immediately drop off at lower than the band gap energy ~1100 nm (1.12...

Hi all, on one side we say that probability of finding electron with in the forbidden gap is zero, on other side we define fermi level as highest filled energy level(at absolute zero) lying in the mid of forbidden gap.Also for(T>0) probability of finding electron is 1/2 upto fermi level. So...

Can a semiconductor absorb a higher energy photon than its Band gap Eg and make a transition from valence band to conduction band? For a example commonly used IR detector is InAs (semiconductor) whose Eg is 0.354 eV, if a blue light falls on it, will it able to absorve that energy and make a...

In the first diagram on http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html" , the band gap in a semiconductor is shown. What is the corresponding Fermi momentum? If you plug E_F into the dispersion relation, you get no solution for k_F, right? I ask because an equation is given...

Homework Statement A Cyclotron is accelerating proton, where the applied magnetic field is 2 T, the potential gap is 100 KV, then how much turn are required for a kinetic energy of 20 MeV... (a) 300 (b) 200 (c) 150 (d) 100

My physics/electronics teacher told me some thing really interesting and confusing a wile ago and I have been trying to get my head round it. The forward voltage in a LED (voltage needed to drive the current) is proportional to the band gap energy. However Blue LEDs have a higher forward...

hello to everyone. It is normally said that in semiconductors the Fermi level is half way between the valence and the conduction band. I have the following question on that: what does it mean that the Fermi level is in the band gap? It should mean that the maximum energy of an electron in the...

i know this is a simple question, but i have been looking for a while (maybe 15 min) and i cannot find what is so special about Cu, Ag, and Au? i know there is something special about these 3 metals. something that none of the other metals have. i remember it having to do with fermi velocity /...

I've come across a question which talks about the employment gap and asks me to suggest reasons on how it would occur. I thought better qualification could improve skills. I got this correct but I have to expand. Can someone explain how I can talk about MRP? Thanks in advance. :smile:

Can anyone tell me what is the "Brus Approximation" in case of the bang gap of semiconductors?:rolleyes:

what is the definition of spin gap?I may have ever heard a conclusion that spin gap will not exist while the system present long range order(right?),but the system of XXZ model in external field could stay in ferromagnetic phase,and have a long range order with a gapped excitation.why?

Glass is transparent to visibile light under normal conditions; however, at extremely high intensities, glass will absorb most of the light incident upon it. This works through a process known as multiphoton absorption. In this process, several photons are absorbed at the same time. If very...

Homework Statement [Edit: Please also see additional posts below. I have tried to clarify my question somewhat but didn't want to edit this one just incase anyone can help with the full problem. Thanks! :) ] I did a lab on the band gap in germanium where I measured the voltage across a...

I especially like this part: & lastly, universal health care would probably reverse the trend: http://www.iht.com/articles/2008/03/23/america/health.php

[SOLVED] kittel page 166 Homework Statement In Figure 3 of Chapter 7 of Kittel's Solid-state physics book, it says that this is the key to understanding the origin of the energy gap. However I do not understand why. It seems like if you take the expectation value of either |\psi(-)|^2 or...

Hi again, first of all i want to thanks the replies to my previous posts. Second... I'm looking for a paper about the GaP band structure. Actually i only need the band structure tu compare it with mine but i need the reference to that paper, can you help me?? sorry for my bad english by the way...

What democracies existed between those of ancient Greece and the United States?

I have got a trouble with wave concept suppose wave is passing through a medium ( let it ,just started) suppose there are four points in the medium (particles) A,B,C,D as soon as A is disturbed even by an infinitesimally small distance , B experiences a forces (forces act...

Hi, I am currently working on high voltage system, where I need to create an impluse at the primary side of a potential transformer. I am trying to charge my circuit to at least 10kV using a half wave series voltage mutliper consisting of capacitors and diodes, and discharging them through...

The lasers used to "read" CDs, DVDs, and Blu-ray discs operate at 780 nm, 650 nm, and 405 nm, respectively. These are produced through semiconductors. Find the energy gap needed for each laser. (Blue-ray discs can have higher information density because of the shorter wavelength). Ok. I...

a stunt biker is jumping a 45m gap, he is traveling at 20m/s and the jump angel is 30 degrees i need to know if he will make it or not. I am not sure how to go about this problem, if somone could show me the steps taken to solve this i would aprecite it. thanks

What do you do if you have like a 10 or 20 year gap between your MS and your PhD with respect to getting letters of recommendation? I would eventually like to get my PhD, but I'm pretty sure that a good deal of my professors will be retired by the time I'd like to go for it. Are you...

Anyone have a reference or information on longevity and reliability experiments in high power spark gaps? I am looking at the reliability of a 97GW 78Kamp discharge spark gap I would like to know the erosion factor and fouling rate of different configurations.

Came across the following interesting problem : Two explosions take place at the same place in a rest frame with a time separation of 10 s in that frame. A) Find the time between explosions, as measured in a frame moving with a speed 0.9 c with respect to the rest frame according to...

Question: A light-emitting diode (LED) made of the semiconductor GaAsP gives off red light \lambda =650nm. what is the band gap for this semiconductor? I know the E=hc/ \lambda so it means the band gap is 1240/650=1.9 ev ??

Hello Everyone... This is my first post and I would like to tell you my problem seeking your help... I am studying Physics and Mathematics in my own with the help of some pure mathematics professor who offered to give his help to me in parts that I do not understand.. I am already enrolled...

what does "band gap bowing" means? Hi, i speak spanish, and I've tried to translate the term "band gap bowing", but literally it doesn't have any sense. So, can anyone explain this term to me so i can translate it correctly?? Thanks a lot.

I am looking to calculate the energy gap of for starters periodic elements and were wondering how we could get the list and calculation. Is there a table somewhere based on certain temperatures and constants of energy gap level? We would like to get a list of the energy gap energy for valance...

Would anybody be able to provide me with data concerning the band gap of colloidal CdSe quantum dots against their size?? I am currently using CdSe dots with a ZnS shell, capped with HDA. Any relevant information would be much appreciated. Many thanks, David Cunnah (studying PhD in opto...

Hello, i am looking for papers about GaN and GaP "history", i mean serious papers or sources, everything will be useful. Thanks. :smile:

in books we have read that there lies a forbidden gap between conduction band and valence band. and electrons can not exist in this gap i.e. probability of electron being found in this region should be zero. BUT the fermi level,which has 50% prabality to contain an electron is found in...

Hello All, I have another set of quick questions that may or may not have a quick answer :smile:. When a simple two-electrode spark gap discharges, what shape do the eclectic and magnetic fields take on? If I were to draw the electric and magnetic field vectors, would they be pointing...

This is a question where the answer is given but I don't understand how to derive it. The answer to the homogeneous eq. is: A cosh(x) + B sinh(x) with no explanation of how it is arrived at and the given answer then goes on to describe how the non-homogeneous part is solved. Diff. eq. ...

Hi all, We say the energy difference between the Top of Valence band and the bottom of Conduction band as the forbidden gap or Band gap. But when we see the fermi level at zero Kelvin, its exactly at the middle of the band gap. Does this mean that there is possibility for an electron to...

Are there any "prime gap" results like this ... I was just reading about "prime gaps" and noticed that most of the results are asymptotic, as in "true if n is sufficiently large". I was just wondering if there are any bounding results for prime gaps that are true for all n, p_n. For example...