# Tag Info

1

Actually, this is an assumption of the Landau theory: the simplest field model exhibiting a phase transition is analogous to a $\phi^4$ theory, which has the lagrangian density $${\mathcal L} = \partial_\mu \phi \partial^\mu \phi - \frac{m^2}{2} \phi^2 - \frac{\lambda}{4} \phi^4\,.$$ For $m^2 > 0$ the potential in the above lagrangian has a single ...

3

There are many schemes to make topological superconductors. Some of these schemes have restrictions on the chemical potential $\mu$. You also need to know what type of topological superconductors you are dealing with. You can refer to the periodic table to determine this: In the paper from the link you provided the authors mention two types of ...

0

This formula is derived using conservation of charge principle and so it's valid for the superconductors as well. There's a critical magnetic field that above which a superconductor becomes normal conductor and it's a function of temperature. If a large current is to pass through a superconductor, a magnetic field will be produced that disrupts ...

1

Ohm's Law does not have a problem here any more than any other formula in the sciences which involves dividing by a denominator which can go to zero. Ohm's Law exhibits a singularity when there is no resistance, but a nonzero voltage. An ideal voltage source cannot be connected in parallel with a zero resistance, because that implies that infinite current ...

5

Looking at your question from the perspective of ideal circuit theory, an ideal resistor has the following I-V relationship: $V_R = I_R R$ The voltage across the resistor is proportional to the current through the resistor with constant of proportionality equal to $R$. In ideal circuit theory, an ideal conductor can be thought of as a "zero ohm resistor". ...

13

Ohm's law works for ordinary conductors for a reason: the particles carrying the current (usually, but not always electrons) scatter incoherently and inelastically from features of the conductor (in the case of an electron current these are generally the individual atoms of the conductor). As long as those conditions pertain, you can expect Ohm's law to be a ...

21

Ohm's law is generally NOT correct, it's called a law for historical reasons only!! It's a law in the same sense in which Hooke's law is a law... it holds only for certain systems under certain conditions, but it's widely known because it's simple and linear! It's not just superconductors, diodes are a neat everyday example of Ohm's law failing to hold. But ...

3

No, because the voltage drop across the device also goes to zero.

0

First question: Say you have a decent quality superconducting ring completely isolated from external magnetic fields. Then a supercurrent is supposed to flow (with no voltage applied) which can can last for years without much dissipation. Will this current just automatically set in the moment I cool my sample below Tc? Or do I have to apply an external ...

2

Symmetry of the superconducting gap First of all, a bit of theory. Superconductivity appears due to the Cooper paring of two electrons, making non-trivial correlations between them in space. The correlation is widely known as the gap parameter \$\Delta_{\alpha\beta}\left(\mathbf{k}\right)\propto\left\langle ...

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