Software to analyze optical spectroscopy data

• software https://docs.google.com/open?id=0B2gCGTp-xJ00Z1pfclJZMm15ZFk 

• Manual: https://docs.google.com/open?id=0B2gCGTp-xJ00X2hjRHYzaUZhalU

Spin orbit coupling and effect on the spatial distribution of states

Symmetry of d electron in different environment

Boundary resistance between ferromagnetic metal and normal metal or semiconductors

Fermi energy, cause or effect?

Different kinds of electric current conductions

Space charge limited conduction (SCLC)

Dzialoshinski Moriya interaction

Properties of orthoferrites

Properties of alpha Fe2O3

Types of antiferromagnetism

How to make figures for papers:

XRR and XRD fringes

Spin glass or ferromagnets?

Neel temperature of RTO3

Nature of band gap in conjugate polymers

Power generation of a photo cell as a function of the electronic band gap

Following the post on

http://xiaoshanxu.blogspot.com/2010/07/blog-post.html

we calculated the power generation of a photo cell as a function of band gap, assuming the filling factor is unity.

As one can see that 1.1 eV is the optimal gap in terms of power generation.

Change of supersaturation

Systematic extinction rules

Systematic extinction rules

The structural factor in the crystallographic diffraction is:

$F=\Sigma { f_j exp(j \vec{r} \vec{k})}$,

where $j$ runs through all the atoms in the unit cell.

When the unit cell has more than one primitive cell in it, there might be some cases that $F$ can be zero. This is called systematic extinction (absence).

For example in BCC, for every atom at position $r$, there is another identical one at $\vec{r}+(1/2,1/2,1/2)$. Then the structural factor becomes:

$F=1+exp[i\pi (h+k+l)]$,

where $(h,k,l)$ are the reciprocal indices.

Obviously, $F$ is zero when $h+k+l=2n+1$.

TABLE I, Systematic absence because of lattice type

Lattice type	Symbol	Absence
a-center (100)	A	k+l=2n+1
b-center (010)	B	h+l=2n+1
c-center (001)	C	h+k=2n+1
face center	F	h,k,l not all odd and not all even
body center	I	h+k+l=2n+1
rhomohedral	R	-h+k+l=3n+1
hexagonal	H (triple unit cell)	h-k=3n+1 or h-k=3n+2
primitive	P	no absence

Above is only the systematic absence caused by typical symmetry of lattice types. There are other systematic absences coming from existence of screw axis and glide planes. In the end, for every space group the systematic absence is more complicated than the cases shown in the above table.

To get complete information or to find out the systematic absence for every space group, one can use Bilbao server : http://www.cryst.ehu.es/. Just click on " HKLCONDReflection conditions of Space Groups" and input the space group number.

Long wavelength dispersion relation in a solid

Long wavelength dispersion relation in a solid

In solid state physics, perhaps the most visited two elementary excitations are phonons (vibration) and magnons (spin wave). It is interesting to notice that the long wavelength dispersion relation are different for them, i.e.
phonon:
magnon: ,
where is the frequency and is the wave vector.

One can go back to the derivation of those two excitations and find the mathematical reason. On the other hand, the origin can be resorted to the fundamental difference between the two equation of motions.
phonon:
magnon: ,
where x is the displacement, is the angular momentum, is the spring constant and is the torque.

In solid, the restoring force for an oscillator comes from the imbalance of the interaction between neighbors. For long sinusoidal wave, it is always propotional to .

Hence, the final dispersion relation will be decided by the equation of motion. Since for phonon, it involves second derivative, one gets ; for magnon, the first derivative gives .