On-Chip Cooling by Heating with Superconducting Tunnel Junctions

Heat management and refrigeration are key concepts for nanoscale devices operating at cryogenic temperatures. The design of an on-chip mesoscopic refrigerator that works thanks to the input heat is presented, thus realizing a solid state implementation of the concept of cooling by heating. The system consists of a circuit featuring a thermoelectric element based on a ferromagnetic insulator-superconductor tunnel junction (N-FI-S) and a series of two normal metal-superconductor tunnel junctions (SINIS). The N-FI-S element converts the incoming heat in a thermovoltage, which is applied to the SINIS, thereby yielding cooling. The cooler's performance is investigated as a function of the input heat current for different bath temperatures. We show that this system can efficiently employ the performance of SINIS refrigeration, with a substantial cooling of the normal metal island. Its scalability and simplicity in the design makes it a promising building block for low-temperature on-chip energy management applications.Comment: 7 pages, 6 figure

Thermopower induced by a supercurrent in superconductor-normal-metal structures

We examine the thermopower Q of a mesoscopic normal-metal (N) wire in contact to superconducting (S) segments and show that even with electron-hole symmetry, Q may become finite due to the presence of supercurrents. Moreover, we show how the dominant part of Q can be directly related to the equilibrium supercurrents in the structure. In general, a finite thermopower appears both between the N reservoirs and the superconductors, and between the N reservoirs themselves. The latter, however, strongly depends on the geometrical symmetry of the structure.Comment: 4 pages, 4 figures; text compacted and material adde

High operating temperature in V-based superconducting quantum interference proximity transistors

Here we report the fabrication and characterization of fully superconducting quantum interference proximity transistors (SQUIPTs) based on the implementation of vanadium (V) in the superconducting loop. At low temperature, the devices show high flux-to-voltage (up to 0.52$\ \textrm{mV}/\Phi_0$) and flux-to-current (above 12$\ \textrm{nA}/\Phi_0$) transfer functions, with the best estimated flux sensitivity $\sim$2.6$\ \mu\Phi_0/\sqrt{\textrm{Hz}}$ reached under fixed voltage bias, where $\Phi_0$ is the flux quantum. The interferometers operate up to $T_\textrm{bath}\simeq$ 2 $\textrm{K}$, with an improvement of 70$\%$ of the maximal operating temperature with respect to early SQUIPTs design. The main features of the V-based SQUIPT are described within a simplified theoretical model. Our results open the way to the realization of SQUIPTs that take advantage of the use of higher-gap superconductors for ultra-sensitive nanoscale applications that operate at temperatures well above 1 K.Comment: Published version with Supplementary Informatio

Electron-phonon coupling in single walled carbon nanotubes determined by shot noise

We have measured shot noise in metallic single-walled carbon nanotubes of length L=1 $\mu$m and have found strong suppression of noise with increasing voltage. We conclude that the coupling of electron and phonon baths at temperatures $T_e$ and $T_{ph}$ is described at intermediate bias (20 mV $<$ \vv $\lesssim$ 200 mV) by heat flow equation $P=\Sigma L (T_e^3-T_{ph}^3)$ where $\Sigma \sim 3 \cdot 10^{-9}$ W/mK$^3$ due to electron interaction with acoustic phonons, while at higher voltages optical phonon - electron interaction leads to $P =\kappa_{op} L [N (T_e)-N(T_{ph})]$ where $N(T)= 1/(\exp(\hbar\Omega/k_BT)-1)$ with optical phonons energy $\hbar \Omega$ and $\kappa_{op}=2 \cdot 10^{2}$ W/m.Comment: 9 pages, 3 figure

Thermal, electric and spin transport in superconductor/ferromagnetic-insulator structures

A ferromagnetic insulator (FI) attached to a conventional superconductor (S) changes drastically the properties of the latter. Specifically, the exchange field at the FI/S interface leads to a splitting of the superconducting density of states. If S is a superconducting film, thinner than the superconducting coherence length, the modification of the density of states occurs over the whole sample. The co-existence of the exchange splitting and superconducting correlations in S/FI structures leads to striking transport phenomena that are of interest for applications in thermoelectricity, superconducting spintronics and radiation sensors. Here we review the most recent progress in understanding the transport properties of FI/S structures by presenting a complete theoretical framework based on the quasiclassical kinetic equations. We discuss the coupling between the electronic degrees of freedom, charge, spin and energy, under non-equilibrium conditions and its manifestation in thermoelectricity and spin-dependent transport.Comment: 117 pages, 33 figures. arXiv admin note: substantial text overlap with arXiv:1706.0824