Fermi Definition and 336 Threads

Hey everyone, So unfortunately I haven't taken Stat Mech yet (and my GRE is in a week), but through casual reading and forums I've gathered what the concept of fermi temperature and energy is...or thought I did. From what I understand, below the fermi energy (the fermi energy within an atom...

1. Fermi level is also defined as highest energy level at which electron can exist at 0K then it should be top of valence band but why is it in between conduction band and valence band ( in forbidden gap)? It should be in conduction band or valence band. How to explain this? 2. If density of...

Fermi level in an extrinsic semiconductor(after attaining thermal equilibrium) is said to be invariant (constant ) , and the proof uses the fact 'no current must flow thorough any cross-section'..But I don't think its true, charge will be transported due to diffusion and this is countered by...

Is it weird that at absolute zero in a metal, electrons at the fermi level still move around at the fermi velocity. Is the notion that everything stops at absolute zero incorrect? Thank you

how is the relationship between fermi level and band structure of solids can effect electrical conduction properties of a material?

A way to write Fermi golden rule is W_{fi} = \sum{\frac{d P_{fi}}{dt}} = \frac{2 \pi}{\hbar} \sum_{f} |V_{fi}|^2 \delta(\varepsilon_f - \varepsilon_i) where "i" is the initial unperturbed state and "f" is the final state of an ensemble of final states (i sum over them). But because of...

Am I right in thinking Fermi type beta decay is helicity suppressed, due to the necessity of having a right handed electron? This was implied but not explicitly stated in my lectures. And is this why Gamow-Teller type beta decay is the generally favoured mode?

I'm having a bit of trouble understanding what's going on with the energy diagram of a PN junction. For your normal undoped semiconductor at zero bias, if you're plotting the energy as a function of distance along the material then you've just got the two horizontal lines where the upper one...

I have taken several courses in semiconductors at the undergraduate level. Both the pure physics part (k vectors) and the more engineering parts (silicon processing, band diagrams) etc. So for all the junctions (Schottky, Ohmic, p-n) - I have never managed to imagine the idea of the Fermi...

To find the Fermi energy I need to find the electron density of the material and that I can do by finding the density of atoms in the material in some instances this same density. From what I gather it's not always that way Sometimes you have to multiply a certain number For example...

Homework Statement It is just a line of equation from my Stat Mech textbook, that says B = -V(dp)/(dV) = (10U)/(9V) = (2nEf)/3 where B is the bulk modulus, V is the volume, p is the pressure, U is the energy, n is the number per unit volume and Ef is the fermi energy. Homework...

Quick Fermi Energy Question..Free electrons?? A quick question on the Fermi energy. From a 3D cubic well, one can derive an expression for the Fermi energy of a solid: Ef = h^2/2m . (3.pi^2.N/V)^2/3 Now, I have come across an expression where N/V, electrons per volume, is replaced by...

Homework Statement The degeneracy of the nth level above the ground state for a three dimensional harmonic oscillator is (n+1)(n+2)/2 where n takes values n=0,1,2,... A gas of N non-interacting identical lithium atoms (mass 6amu) each having spin1/2 is confined in a 3d harmonic potential...

Si is doped with 6 x 1015 cm-3 donors and 2 x 1015 cm-3 acceptors. Find the position of the Fermi level with respect to Ei at 300 K. i know the equations are (for n-type) EF = kT ln(ND/ni) + Ei (for p-type) EF = kT ln(ni/NA) + Ei however, since the problem gives me both donors and...

Homework Statement "The numerator of this fraction: \overline{E}=\frac{\int \! E N(E)D(E)dE}{\int \! N(E)D(E)dE} (N(E) is the number of particles in an energy state, D(E) is the density of states) is the total (as opposed to the average particle) energy, which we'll call U_{total} here...

For a perturbation that is constant within a given time, we can use Fermi's Golden Rule. In developing Fermi's Golden Rule, 2 approximations are made: (1) The energy interval E (continuum) to which discrete states are scattered is small enough such that the density of states is constant...

Note: I already asked this question ion the introductory physics forums but have had no replies. The question I'm being asked is: If the Fermi level of copper is 7eV calculate the magnitude of the Fermi wavevector?The formula I'm pretty sure it goes with is Kf=(3pi^2ne)^2/3 The reason I'm...

For those not familiar with the term Fermi estimate/problem/question see here: http://www.vendian.org/envelope/dir0/fermi_questions.html http://en.wikipedia.org/wiki/Fermi_problem My question: Between the time that Riemann posed his famous question (in 1859) and now, how many hours have...

So, according to the Fermi function, the higher the temperature of a semiconductor, the higher the likelihood that the electrons can jump to the conduction band. But in superconductors, obviously the temperature is extremely low, so how does the Fermi level, band gap theory, and...

Locally, Fermi normal coordinates are designed to correspond with direct measurement of distances (born rigidity). I also discovered that Synge's book on GR establishes that very locally, radar distance must match Fermi normal distance, but not in general (obviously). What I am wondering is...

Show that the kinectic energy of a three-dimensional fermi gas of N free electrons at absolute zero is (Mathematica code used) u = 3/5 N Subscript[\[Epsilon], F] Now I know total energy of N particles is this integral u = \!\( \*SubsuperscriptBox[\(\[Integral]\), \(0\)...

Sorry if someone already posted this link but did anyone see this in the news? http://www.nasa.gov/home/hqnews/2010/nov/HQ_10-295_FERMI.html What are people's opinions on what this might be?

For next year's Physics Open House the Department is planning to set up a bungee jump from the top of the physics building. Assume that one end of an elastic band will be firmly attached to the top of the building and the other to the waist of a courageous participant. The participant...

Aasslam u alaikum to all, i have confusion in knowing that " how fermi level form in a compound semiconductors e.g GaN, GaAs, etc. Thanks to all

Fermi Level Problem, help plssss ! Find the location of the fermi level with respect to intrinsic level if the probability that a state filled at the conduction band edge is equal to the probability that a state is empty at valence band edge. I am looking forward to your help.

Studying the free electron model I found the fermi dirac distribution and the book told me that when T->0 we have that the fermi energy is equal to the chemical potential... why?

I thought I'd present some plots for the Fermi-normal coordinates (only in the r-t plane) for someone falling into a black hole "from infinity". Fermi-normal coordinates radiate a set of space-like geodesics from some point on the worldine of an object - in this case, the worldline of an...

My syllabus doesn't include them in first physics course, and I am in engineering major. Should I try to practice them for myself or are they not very important?

Homework Statement a) Calculate the Fermi energy for copper. b) Calculate the ratio of the number of occupied levels at an energy of 8.5 eV to the number occupied levels at the Fermi energy at room temperature. c) Based on your answer to a) and b) above, show that at room temperature...

Hi all, I've search for my question and found no answer. I think it should be pretty simple... Fermi energy corresponds to the last occupied energy, as I understand it. So, energy levels in the Fermi gas are all filled with two electron of opposite spins, up to the Fermi energy. Saying it...

Hi, I have come across a sentance in an article which I do not quite understand. H1 is just a perturbation Hamiltonian. Why will spin flips only occur at the Fermi level? Thank you

The almost simultaneous detection of low energy and high energy photons puts tight constraints on models predicting linear dependence of c on E. But it's very far from ruling out quadratic dependence. My question is, why do Lorentz-violating theories commonly predict linear rather than quadratic...

Hi The dispersion of Bogolyubov quasiparticles in a d-wave superconductor is E(\mathbf k) = \pm \sqrt{\varepsilon (\mathbf k)^2+\Delta (\mathbf k)^2}, where ε(k) is the normal-state dispersion and ∆(k) is the gap dispersion. My question is: The Fermi surface (FS) of the normal...

Hello, I have a question which has something to do with band structures etc: A two dimensional solid has two electrons per unit cell. The crystal potential is weak and the solid behaves like a free electron metal. Estimate the threshold for interband optical transitions in terms of the...

Homework Statement Problem 9.2(B) from Kittel Solid State Physics. A two-dimensional metal has one atom of valence one in a simple rectangular primitive cell of a1 = 2Å and a2 = 4Å. Calculate the radius of the free electron Fermi sphere and draw this sphere to scale on the drawing of the...

Hi Can somebody explain the meaning of the following sentence which is from Wikipedia: "Solids with a large density of states at the Fermi level become unstable at low temperatures and tend to form ground states where the condensation energy comes from opening a gap at the Fermi surface e.g...

Homework Statement What is the significance of Fermi Temperature? Homework Equations I know it is the ratio of the Fermi energy (or the chemical potential at the Fermi energy) to the Boltzmann constant. The Attempt at a Solution What does it MEAN? I've worked out the Fermi...

Hello, Im just an amateur physicsist and was interested in Fermi Energy. Found a page http://http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi2.html#c1" , that helped. However, I found the page and site a bit hard to understand in some places. Could someone please explain to me...

I was reading this website, and I don't understand this last statement. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html It reads: "Since only a tiny fraction of the electrons in a metal are within the thermal energy kT of the Fermi energy, they are "frozen out" of the heat...

Hi Strictly from the definition of the Fermi level as the highest energy occupied at zero temperature, it seems that in the presence of a band gap the Fermi level (Ef) could be placed fairly arbitrarily anywhere between the conduction (Ec) and valence (Ev) bands, since the density of states is...

Hi. Does anyone know how to calculate the fermi level for the conduction band in a quantum well?

I've tried to look this up online, but I can't find it anywhere. I'm just looking for the intrinsic fermi energy of silicon E_i ? Can someone maybe direct me towards a website where I could look it up? Either that, or is there a way to calculate it from the energy gap for intrinsic silicon...

Can anyone help explain how one can apply information say from an energy band diagram of an element/compound to its respective fermi surface / "sphere"? I understand there is a direct relationship, however, I can seem to physical interpret how one is able to say look at the energy band...

Why is it called degenerate ?? Is it because all levels upto fermi level are filled or all degeneracies of the energy levels that are present occupied at T = 0k . In deriving the average occupation no. for a deg fermi gas , we have used classical idea of momentum that is integrating over a...

Effect of Doping on Fermi Energy... I was wondering if anyone could give me a clear answer on why doping a semi conductor raises or lowers the fermi energy depending on n or p type semi conductors. There seem to be a few standard ways of explaining this, some to do with charge conservation or...

A question for those of you who know about the distribution of dark matter in the galaxy: Do we know how "clumpy" dark matter is? Can we tell yet whether dark matter is distributed about as densly as a gas or whether it's possible that there are the equivalent mass distributions that might...

I have a question that is puzzling me as always...The Fermi-Dirac distribution function is (at T=0): f\epsilon=\frac{1}{e^{\beta(\epsilon-\epsilon_{F})}+1} and we know that we can subsitute f\epsilon by 1 for \epsilon< \epsilon_{F} and 0 otherwise. However what is f(-\epsilon)? The answer is...

Guys, I have two questions: (1) what does a vanishing Fermi energy mean? (2) I have also calculated the phonon self energy for the electron phonon interaction in graphene. However in one of the papers, they state that one needs to subtract from this self energy the case of vanishing Fermi...

Hello, Im working on a paper on solar cells and i came across the term "Fermi level". What exactly is the Fermi level in this context: "The working voltage produced by the device is the difference between the chemical potential of the titanium dioxide (Fermi level) and the redox...

I know that when a metal is compressed its fermi energy is increased. I would attempt to explain this by saying, "as the volume has been decreased, so has the allowed number of particle in a 3D box states, thus as we have the same number of electrons and fewer allowed states, and the pauli...