A Thin-Film Cryotron Suitable For Use as an Ultra-Low-Temperature Switch.

Low-temperature superconducting circuits have become important for many scientific applications. However, there are presently no high current-capacity switches (~1 mA) with low power dissipation for sub-Kelvin operation. One candidate for a sub-Kelvin switch is the cryotron, a device in which the superconductivity of a wire is suppressed with a magnetic field. Here, we demonstrate a cryotron switch suitable for sub-Kelvin temperatures. In the closed state, the maximum device current is about 900 µA. The device is switched to its open state with 2 mA of control current and has a leakage of approximately 500 nA. The transition between the closed and open states of the device is faster than 200 ns, where the measurement is limited by the speed of our measurement apparatus. We also discuss low-temperature applications for our cryotron such as a single-pole, double-throw switch.

Insensitivity of sub-Kelvin electron-phonon coupling to substrate properties.

We have examined the role of the substrate on electron-phonon coupling in normal-metal films of Mn-doped Al at temperatures below 1 K. Normal metal-insulator-superconductor junctions were used to measure the electron temperature in the films as a function of Joule heating power and phonon temperature. Theory suggests that the distribution of phonons available for interaction with electrons in metal films may depend on the acoustic properties of the substrate, namely, that the electron-phonon coupling constant Σ would be larger on the substrate with smaller sound speed. In contrast, our results indicate that within experimental error (typically ±10%), Σ is unchanged among the two acoustically distinct substrates used in our investigation.

Dipolar molecular rotors in the metal-organic framework crystal IRMOF-2.

Rotating polar linker groups in the cubic metal-organic framework single crystal known as IRMOF-2 were investigated for freedom of motion, response to an external electric field, and effects of dipole-dipole interactions. The crystals consist of octahedrally coordinated zinc oxide clusters linked by the bromoterephthalate group, which contains a rotatable bromo-p-phenylene moiety. We confirmed the rotation by dielectric spectroscopy and found a 7.3 kcal mol(-1) barrier. The non-polar analog, IRMOF-1, containing terephthalic acid, was used as a control system. DFT and MP2 computations of the rotational barrier yield results in agreement with the observation, with B3LYP/SDD being the best. A Monte Carlo analysis of the equilibrium polarization fluctuations was used to assess the possibility of polar ordering and the potential for electro-optic applications.