Consider a metal-superconductor junction connected to a dc voltage $V$. At $T < T_c$, where $T_c$ is the superconductor's transition temperature, the current $I$ versus $V$ behavior of this junction is shown schematically in the figure below. If the superconducting energy gap is $D \text{ meV}$. The value of $D$ (rounded off to one decimal place) is _____
Step 1: Concept (Superconductor junction)
For a metal–superconductor junction, current starts flowing when:
$ eV_{th} = \Delta $
where $\Delta$ is the superconducting energy gap.
Step 2: Relation in eV units
Since voltage in mV directly gives energy in meV:
$ \Delta (\text{meV}) = V_{th} (\text{mV}) $
Step 3: From graph
$ V_{th} = 1.0 \text{ mV} $
So,
$ \Delta = 1.0 \text{ meV} $
Step 4: Energy gap definition in question
Given $D = 2\Delta$
So,
$ D = 2 \times 1.0 = 2.0 \text{ meV} $
Final Answer:
$\boxed{2.0}$
Important Questions from Superconductivity Meissner Effect BCS Theory
- Which of the following option(s) is/are correct for a Type I superconductor?
The figure schematically shows the $M$ (magnetization) - $H$ (magnetic field) plots for certain types of materials. Here $M$ and $H$ are plotted in the same scale and units. Which one of the following is the most appropriate combination?
- A material behaves as a superconductor below a critical temperature $T_c$ and as a normal conductor above $T_c$. A magnetic field $\vec{B} = B\hat{z}$ is applied when $T > T_c$. The material is then cooled below $T_c$ in the presence of $\vec{B}$. Which of the following figure represent the correct configuration of magnetic field lines?
- Amongst electrical resistivity ($\rho$), thermal conductivity ($\kappa$), specific heat ($C$), Young's modulus ($Y$), and magnetic susceptibility ($\chi$), which quantities show a sharp change at the superconducting transition temperature?
- At $T = 0$ K, which of the following diagram represents the occupation probability $P(E)$ of energy states of electrons in a BCS type superconductor?
