http://www.physicsforums.com en Tue, 21 May 2013 15:02:53 GMT vBulletin 60 http://www.physicsforums.com/images/physicsforums/misc/rss.jpg http://www.physicsforums.com http://www.physicsforums.com/showthread.php?t=692854&goto=newpost Tue, 21 May 2013 07:12:11 GMT Has off-diagonal long range order (ODLRO) been measured directly experimentally in superconductors, i.e. in measurements of second order correlation... Has off-diagonal long range order (ODLRO) been measured directly experimentally in superconductors, i.e. in measurements of second order correlation functions of the electron gas? ]]> Atomic, Solid State, Comp. Physics DrDu http://www.physicsforums.com/showthread.php?t=692854 http://www.physicsforums.com/showthread.php?t=692696&goto=newpost Mon, 20 May 2013 13:55:34 GMT Hello!

I'm having my materialphysics exam in a few days, and looking some of the older exams I saw that there are many times questions about band structure and density of states. More specifically there might be a picture of some band structure plus the density of states, like this.

Then they ask you to analyze this kind of a picture and give as much information as possible (according to the free electron model, nearly-free electron model and tight-binding).

So what I'm asking are some basic ways for me to analyze this. Like can I see the crystal structure from this(fcc, bcc, hcp)? And for extra, what kind of chemical properties do they have? I know that fcc has good catalytic properties, but I have no clue about the others.

Can I see the electron configuration? I know some basics on this, s-band is the parabolic band in around the gamma-point and p-band is a smaller parabole around the X-band (I think). But what about d and f? Also can I see how many electrons there are in a subshell?

Then I'd like to know how to draw a very basic representation of the band structure with only the knowledge of the specific electron structure.

I'm sorry if this should've gone to the homework forum, but this isn't homework per se so I thought to post it here.

Thanks! ]]> Atomic, Solid State, Comp. Physics DemoniWaari http://www.physicsforums.com/showthread.php?t=692696 http://www.physicsforums.com/showthread.php?t=692629&goto=newpost Mon, 20 May 2013 05:16:52 GMT Assume we have a concentration of any specific material (in mg/M). Let's say for example: Ag (Z=47) with concentration 10 mg/M in water (H2O, Z=7.42).

How can I calculate the effective atomic number (Zeff.) for the silver-water mixture if the concentration of silver was 10 mg/M for example?

The only formula I know to calculate Zeff. is the following:



but it uses (fn) the fraction of the total number of electrons associated with each element, not the concentration in mg/M.

Is there any possible way to convert the concentration (in mg/M) into a fraction of total number of electrons for silver then calculate Zeff for the silver-water mixture mentioned above as an example?


Thanks in advance.

source: http://en.wikipedia.org/wiki/Effective_atomic_number (example for H2O provided)

]]> Atomic, Solid State, Comp. Physics sci_girl http://www.physicsforums.com/showthread.php?t=692629 http://www.physicsforums.com/showthread.php?t=692478&goto=newpost Sun, 19 May 2013 09:29:43 GMT Hello everybody, I registered here hoping to finally find a fundated answer about what I by myself seem not be able to figure out. Question in... Hello everybody,

I registered here hoping to finally find a fundated answer about what I by myself seem not be able to figure out.

Question in short:
We have calculated a list of wavenumbers for some molecular systems. How do you get the vibrational partition function from that?

My problem in detail:
Let's take this list of wave numbers as an example:

[cm^-1]
1602,13
3710,78
3829,60
(this is for one water molecule)

Now my collegue explained to me that it's correct to calculate the vibrational partition function as
[itex]q_{vib} = \frac{e^{{-h \nu}/{2kT}}}{1-e^{{-h \nu}/{kT}}}[/itex]
for each frequency and then multiply them all.
Which would give

[itex]q_{vib,1} = 0,020806[/itex]
[itex]q_{vib,2} = 0,000127[/itex]
[itex]q_{vib,3} = 0,000096[/itex]
[itex]q_{vib,tot} = 2,53E-10[/itex]

which seems really weird to me because the partition function becomes lower and lower with every vibrational mode. Can a partition function even be lower than 1?

One of the few things I could find about this is this one, page 5, eq. 3.21 to 3.22: http://www.chem.iitb.ac.in/~bltembe/pdfs/ch_3.pdf
But isn't the zero of energy scale kind of arbitrary?
Anyway, using
[itex]q_{vib} = \frac{1}{1-e^{{-h \nu}/{kT}}}[/itex]
gives

[itex]q_{vib,1} = 1,000433438[/itex]
[itex]q_{vib,2} = 1,000000016[/itex]
[itex]q_{vib,3} = 1,000000009[/itex]
[itex]q_{vib,tot} = 1,000433463[/itex]

which seems way more reasonable to me. (Right? :blushing:)

But it leaves open the question of the zero of energy scale for me. My collegue insists that it's arbitrary where you put it, so both solutions should be correct. But since it gives a factor into each of the single partition functions, how can it be equivalent? Also, would [itex]{h \nu}/{2kT}[/itex] be the correct zero?
Is it even correct to just plainly multiply the single vibrational partition functions?

Thanks for any help. Sorry for the long question, I'm just really confused about this.
Ciao!

Giogio ]]> Atomic, Solid State, Comp. Physics Giogio http://www.physicsforums.com/showthread.php?t=692478 http://www.physicsforums.com/showthread.php?t=692448&goto=newpost Sun, 19 May 2013 03:48:00 GMT Hi, I have a question regarding reciprocal space symmetry operations and would appreciate if somebody can answer that: Lets say I have two k... Hi,

I have a question regarding reciprocal space symmetry operations and would appreciate if somebody can answer that:

Lets say I have two k points, k1 and k2, in reciprocal space which are symmetric to each other. Since these two kpoints are symmetric to each other phonon scalar properties like frequency, lifetime, etc will be same for k1 and k2. Similarly, vectors like group velocity have same magnitude for k1 and k2. I am wondering how are vector components related at k1 and k2?

Thanks a lot in advace! ]]> Atomic, Solid State, Comp. Physics pinkuagarwal http://www.physicsforums.com/showthread.php?t=692448 http://www.physicsforums.com/showthread.php?t=692411&goto=newpost Sat, 18 May 2013 22:04:13 GMT Hello, I want to do an experiment in hydrogen gas H2 (1 bar) and I want to simulate the maximum amount of H+. What is the best way to get the largest... Hello, I want to do an experiment in hydrogen gas H2 (1 bar) and I want to simulate the maximum amount of H+. What is the best way to get the largest fraction of H+ with minimal energy input? Thanks. ]]> Atomic, Solid State, Comp. Physics edpell http://www.physicsforums.com/showthread.php?t=692411 http://www.physicsforums.com/showthread.php?t=692063&goto=newpost Thu, 16 May 2013 17:26:32 GMT Hi All! I am doing my Masters project on III-V Nitrides, my question is really a basic one. What are the localized states and what is meant by... Hi All!

I am doing my Masters project on III-V Nitrides, my question is really a basic one.

What are the localized states and what is meant by localization energy and degree of localization, also that excitons are localized to the tail state?

Could you please give me an answer and guide me to useful references.

Thanks All! ]]> Atomic, Solid State, Comp. Physics physiagy http://www.physicsforums.com/showthread.php?t=692063 http://www.physicsforums.com/showthread.php?t=691841&goto=newpost Wed, 15 May 2013 11:35:07 GMT As we know, Bragg's law is based on the path length difference between light which interfere with themselves after being scattered from atoms in the crystal.
If you google "Bragg's law", you will see numbers of pictures showing two light rays being scattered from two different atoms. Those two light rays are PARALLEL to each other.
How can those scattered light (which are parallel to each other) interfere with each other? And where does the interference happen? ]]> Atomic, Solid State, Comp. Physics tsopa http://www.physicsforums.com/showthread.php?t=691841 http://www.physicsforums.com/showthread.php?t=691834&goto=newpost Wed, 15 May 2013 10:16:11 GMT Hi, I need to find out how to plot my data with exponential binning. To better see the exponent of f(x) = x ^ \alpha, where x and f(x) are given,... Hi,

I need to find out how to plot my data with exponential binning.
To better see the exponent of f(x) = x ^ \alpha, where x and f(x) are given, I am asked to do exponential binning the data.

Would appreciate you help.

Yours
Atilla ]]> Atomic, Solid State, Comp. Physics atillaqurd http://www.physicsforums.com/showthread.php?t=691834 http://www.physicsforums.com/showthread.php?t=691677&goto=newpost Tue, 14 May 2013 15:15:39 GMT I've been introduced to ligand-field theory lately and was then wondering what roles f orbitals play in the magnetic properties of elements and alloys. Apparently f orbitals behave oddly in that they hybridize in weird ways because they're so large and that the crystal field actually affects the anisotropy of the f orbitals.

Are there any resources that I can use to read up on this? Or would a Fermi energy approach be better for a study on magnetism?

Thanks,
L ]]> Atomic, Solid State, Comp. Physics letshin http://www.physicsforums.com/showthread.php?t=691677 http://www.physicsforums.com/showthread.php?t=691601&goto=newpost Tue, 14 May 2013 02:03:05 GMT Hi everyone, Recently, a DLTS system has been set up in our institution. We would like to test the system with known-DLTS standard samples. ... Hi everyone,

Recently, a DLTS system has been set up in our institution. We would like to test the system with known-DLTS standard samples.
Could you, please, advise me the suppliers of those samples?

Many thanks in advance.

Regards, ]]> Atomic, Solid State, Comp. Physics dtgiang http://www.physicsforums.com/showthread.php?t=691601 http://www.physicsforums.com/showthread.php?t=691548&goto=newpost Mon, 13 May 2013 18:22:32 GMT Hi, I am modeling structure that takes into account Rashba effect, and I am not sure what is the mechanism that causes Rashba effect to appear. ... Hi, I am modeling structure that takes into account Rashba effect, and I am not sure what is the mechanism that causes Rashba effect to appear.

On wikipedia Rashba is described as spin-orbit interaction effect which appears because electron is orbiting around nucleus and electron see nucleus orbiting around from where we get effective magnetic field that further on interact with spin of the electron.

What confuses me is why Rashba appears after we apply external electric field on the structure? Does external field somehow polarize atoms in crystal structure and therefore electrons in conduction band "see" more clearly electric field of the nucleus from where we get Rashba effect? Or is it something else?

thanks in advance :) ]]> Atomic, Solid State, Comp. Physics Nemanja989 http://www.physicsforums.com/showthread.php?t=691548 http://www.physicsforums.com/showthread.php?t=691512&goto=newpost Mon, 13 May 2013 14:24:29 GMT Li-6 atom is a fermion gas because it has an odd number of fermion entities: 3 P, 3 N, 3 e- = 9. It also has been reported that Li-6 shows... Li-6 atom is a fermion gas because it has an odd number of fermion entities: 3 P, 3 N, 3 e- = 9. It also has been reported that Li-6 shows superfluid behavior (wee wiki for superfluidity).

My question is, would superfluidity behavior be predicted for Li-6 if the three electrons (e-) were removed, making the remaining Li-6 nucleus a boson with even number of fermion entities, e.g., 3 p + 3 N = 6. Has this experiment been conducted ? Thanks. ]]> Atomic, Solid State, Comp. Physics Salman2 http://www.physicsforums.com/showthread.php?t=691512 http://www.physicsforums.com/showthread.php?t=691500&goto=newpost Mon, 13 May 2013 12:39:35 GMT What is the relation between site-symmetry in crystals and symmetry of the atomic orbitals of atoms at these sites that form bonds with the... What is the relation between site-symmetry in crystals and symmetry of the atomic orbitals of atoms at these sites that form bonds with the neighboring atoms?

I'm looking for some references related to this topic (books or articles). ]]> Atomic, Solid State, Comp. Physics Wox http://www.physicsforums.com/showthread.php?t=691500 http://www.physicsforums.com/showthread.php?t=691373&goto=newpost Sun, 12 May 2013 19:42:29 GMT Hi just completed a chapter on Superconductivity in a solid-state physics book. I have a few remaining questions. I don't expect they can be easily answered, but I appreciate if someone happens to know. Most of the questions regard how the equations have been motivated. I guess that's kind of nitpicky but I like to understand the history of it.

(1) In the Cooper pair interaction, why is the el-el interaction ignored for all el- states with energies much greater than the typical phonon (where el- energy is measured relative to the Fermi level). I understand two el- states whose energy difference is greater than a typical phonon won't interact directly. But that doesn't make a statement about their absolute energies. Would I be right to say this is because we don't expect the bound Cooper state to contain these states in the solution and so it's mathematically simpler to just zero the potential for the interaction out at higher energies?

(2) Is there a better way to motivate the BCS variational form? This form is Prod[ uk + vk c_(-k)* c_k ]|0> in standard notation. Since a Cooper pair is actually linear superposition of c_(-k)*c_k states, this doesn't quite match as a "filling of Cooper pairs." Can the BCS form be derived from a Slater determinant of Cooper pairs? Perhaps all of them in the same eigenstate (since they colloquially behave like bosons).

(3) The most characteristic property of a superconductor is the zero resistance. The explanation of this is that "Changing the momentum of a single pair with respect to the common momentum requires a cost in energy equal to the binding energy. As soon as the number of pairs with random momenta increases, the energy penalty to sustain the situation becomes prohibitively large: any scattering process, that occasionally breaks or restores Cooper pairs, tends to restore the situation in which the pairs have common momentum." Is this supposed to be obvious? I just don't see why it becomes increasingly hard to break Cooper pairs as you continue to break them. The first one to break cost the binding energy. Why not also the last one?

(4) In Ginzburg-Lindau, is psi supposed to represent the wave-function of a Cooper pair (as in all Cooper pairs condense into the same state)? If not, where did they come up with the idea of a |(p-eA)psi|^2 term in the free energy?

(5) In the Josephson effect, why do begin with the assumption that the order parameter is constant in the superconductor and decays in the insulator? Isn't it the other way around when we consider the Meissner effect (i.e. boundary condition psi = 0 at surface and rises to bulk value in superconductor).

Thanks,
Sam ]]> Atomic, Solid State, Comp. Physics sam_bell http://www.physicsforums.com/showthread.php?t=691373