# Tag Info

## Hot answers tagged condensed-matter

6

Wood ash is most mineral. Opinions seem to differ about the composition, but it's things like calcium and potassium carbonates, phosphates and oxides. The minerals in wood are distributed throughout the wood, so as the organic material burns away you are left with a very fine network of aggregated particles of the minerals. Googling will find you lots of ...

4

The time reversal and chiral symmetry are special because they are antiunitary symmetries, in contrast to the other unitary symmetries like translation and rotation symmetries. Antiunitary symmetry operation involves complex conjugation of the wave function of the system, which is a non-trivial operation beyond unitary transforms. Unitary symmetries are ...

3

I have a lot of experience with CVD and sputtering, but limited experience in PLD; however, several of my colleagues did this all the time in our shared a laser lab. When they were attempting to reproduce a specific result all of the parameters had to be systematically varied, from the laser fluence to the substrate conditioning and temperature, and more. ...

3

It is not true that all superconductors are gapped. For example, d-wave superconductors in cuprates are gapless. The energy gap in the superconductor arises from the fact that breaking the Cooper pair requires finite energy. The low-lying quasi-particle excitations are all pair breaking excitations, so they are gapped from the ground state by the amount of ...

2

You can only distinguish the sublattices in this case because you've tagged them A,B. The process of inversion only exchanges identical carbon with carbon, leaving the crystal physically unchanged. If you gave me a crystal with one orientation and I then returned it to you without telling you whether or not it's been inverted, you'd have no way of knowing. ...

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I have no experience with either CVD or PLD, but it was interesting to think about this question. In a humble attempt to build on Peter Diehr's answer, here is some theory (at a very heuristic and simplified level). The deposition of each new layer can be thought of as being governed at large scales by some mixture of Laplacian and Eden growth in two ...

2

Metals are in solid state. So conductors are basically solids. (Don't take it too much. There are no solids in quantum physics). A conductor is hence characterized by tightly packed atoms with plenty of availability of valence electrons that are ready to get off from what that holds them. Also a good conductor like silver, iron etc. have very good atomic ...

2

I think the first helpful fact to clarify is that there are two different kinds of topological phases: there are so-called Symmetry Protected Topological (SPT) Phases (displaying 'symmetry protected topological order') and there are (intrinsic) Topological Phases (displaying '(intrinsic) topological order'). As some quick examples: topological insulators and ...

2

The Landau criterion is not in itself a criterion for superfluidity, but a criterion for the breakdown of superfluidity. Indeed, if applied to insulators or ordinary fluids, it would tell you that all of these are also superfluid... What the Landau criterion tells you is the velocity of the superfluid flow at which excitations are created from the ...

2

One can avoid the concept of symmetry breaking in this context, to avoid "non-conservation of the particle number". People have devised way to do that, see for example http://arxiv.org/pdf/cond-mat/0105058v1.pdf. However, all these approaches gives the same results than standard Bogoliubov-like methods in the thermodynamic limit. This is not too ...

2

You are probably aware that the underlying mechanism responsible for superconductivity in cuprates or Fe-based superconductors is still subject to intense debate and research. The usual BCS electron-phonon coupling (EPC) is too weak to account for superconductivity at temperatures of order $100$ K, and produces a gap of s-wave symmetry which is incompatible ...

2

One way to estimate electron-phonon coupling is to take a look on the hot-electron relaxation rate, which can be more or less directly probed by pump-probe spectroscopy. The values for $\lambda$ are around 0.2-0.5. There are few articles on this topic from C. Gadermaier. Here are the links http://dx.doi.org/10.1063/1.4726164 ...

2

The problem is that you are looking at the gap at the $\Gamma$ point ($k=0$) and not at the real gap at the Brillouin zone boundary. Here is the plot for the phonon dispersion relation of a diatomic linear chain. You can see that the real gap at the $k=\pi/a$ point is vanishing for $m_1=m_2$. This plot looks different as typical plots for a monoatomic ...

2

When we say that a lattice has a particular symmetry we mean that the lattice is mapped onto itself by the symmetry. So if I have a (2d) material which has inversion symmetry in the bulk and which has an atom at a point $(x,y)$ then inversion symmetry tells me that there is another, identical atom at $(-x, -y)$. At the surface, however, this is no longer ...

2

The spin orbit coupling can be derived from the nonrelativistic limit of the dirac equation and is given by $$H_{\text{s-p}} = \frac{\varepsilon_0}{2m_e^2c^2}\mathbf{\hat{s}}\cdot\left(\mathbf{E}\times\mathbf{\hat{p}} \right)$$ $\mathbf{E}$ is the total electric field acting on an electron, which consist of a microscopic electric field ...

2

The key is: Landau theory doesn't assume the order parameter is small. All it assumes is that the free energy is analytic in the order parameter. One then usually expands this free energy up to some order (which is possibly by definition of 'analytic'). It is key to realize that expanding a function in a variable to some order does not mean this variable has ...

1

Collected Papers of L.D. Landau edited by D. Ter Haar The Discovery of Super Fluidity These above books might help you. Start doing your own research, this is how we study.

1

For a gas: Density Nuclear half-life of the components Viscosity Temperature of liquefaction Specific heat Speed of sound Rayleigh scattering coefficient

1

Index of refraction and the extinction coefficient are related to real and imaginary parts of dielectric function via a simple functions. Empirical real and imaginary parts of a dielectric function (or Lorentz oscillator fits to them) are usually used when simulating macroscopic Maxwell equations. So, what is missing (assuming you do not mean the trivial, ...

1

Within projected augmented wave (PAW) method it is incorrect to use the smooth pseudo wave function directly to obtain integrals. The same applies for ultra-soft pseudo potentials, but I will proceed discussing about PAW. The results can indeed be wrong. For example, for coin-metals, the d-band smooth wave functions $\tilde{\Psi}$ can have norms of 0.2-0.4, ...

1

A compositional superlattice is a periodic layer structure of different materials. These typically have different bandgaps, effective masses, refractive indices etc. There are limitations on which materials can be stacked. They need to have the same crystal structure and lattice constant or at least negligible strain. The model system would be $GaAs$/$AlAs$ ...

1

The way mobility depends on average scattering time of the carriers is given here: A simple model gives the approximate relation between scattering time (average time between scattering events) and mobility. It is assumed that after each scattering event, the carrier's motion is randomized, so it has zero average velocity. After that, it accelerates ...

1

Yes, pairing is possible from a repulsive interaction. The reason behind this is that pairing has to occur in a certain angular momentum channel : $l=0$ for s-wave superconductivity, $l=1$ for p-wave, and so on. To see this, you can expand the repulsive $k$-dependent interaction on Legendre polynomials. Check this review that deals with the Kohn-Luttinger ...

1

There are no easy to verify criteria which will work in general. One way to see it is by noting that for every classical StatMech model, we can define a PEPS with the same correlation functions (for which the tensors can be easily constructed from the StatMech model), see http://arxiv.org/abs/quant-ph/0601075. On the other hand, for StatMech models it is ...

1

Consider the Ising antiferromagnet $$H=\sum Z_i Z_{i+1}$$ on a ring. It even has product ground states $|0101\cdots\rangle$ and $|1010\cdots\rangle$ (and only those product ground states). Thus, the lowest energy product states are not translational invariant.

1

There's not enough information to say. It looks like your model has spring-like (harmonic) potentials between neighboring atoms, but phonon scattering requires anharmonic potentials. Harmonic potentials mean that the superposition principle still holds, so the phonons just pass right through each other without scattering. Since you have harmonic ...

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