Superconductor thermal filter
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Solution Overview
Problem
Current NIS coolers have limited temperature throw due to non-equilibrium quasi-particles and phonon heat migration, which leads to overheating in superconducting electrodes, and lack effective methods to prevent quasi-particle backflow and phonon heat return.
Innovation Solution
A superconductor thermal filter is designed with a multilayer structure of superconductors having decreasing energy band gaps and a normal metal quasiparticle trap, along with a bias voltage to remove hot electrons and prevent phonon heat flow, utilizing thermal boundary resistance mismatch to block phonons and quasi-particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a normal metal quasiparticle trap is used to remove hot electrons, then the temperature difference between hot and cold sides is improved, but phonon heat migrates back to the superconducting electrodes limiting the temperature difference
Solution Approach 1:
The superconductor is divided into multiple layers with different energy band gaps (first superconductor layer with larger band gap, second superconductor layer with smaller band gap). This segmentation creates a thermal filter that blocks phonons from migrating back to the superconducting electrodes while allowing hot electrons to be removed by the normal metal quasiparticle trap, thereby resolving the contradiction between improving temperature difference and preventing phonon heat loss.
2Temperature
If high current is run through the NIS junction to cool electrons, then electron cooling is achieved, but non-equilibrium quasi-particles accumulate in the superconducting leads causing severe overheating
Solution Approach 1:
A normal metal quasiparticle trap is introduced to extract non-equilibrium quasi-particles from the superconducting leads. The trap provides a pathway for quasi-particles to migrate and relax their energy in the normal metal region, preventing their accumulation in the superconducting electrodes and resolving the overheating problem while maintaining electron cooling functionality.
Solution Approach 2:
The normal metal quasiparticle trap acts as an intermediary between the superconducting leads and the heat sink. It mediates the removal of harmful quasi-particles by providing a transition region where quasi-particles can change from a superconducting state to a normal state, enabling energy relaxation without directly heating the superconducting electrodes.
3Device complexity
If a single layer superconductor is used in the NIS junction, then the device structure is simple, but it cannot effectively prevent quasi-particle backflow and phonon heat return
Solution Approach 1:
The superconductor is segmented into multiple layers with different energy band gaps, creating a thermal filter structure. The first layer with larger band gap blocks low-energy phonons, while the second layer with smaller band gap allows hot electron tunneling. This segmented structure effectively prevents quasi-particle backflow and phonon heat return without significantly increasing device complexity.
Solution Approach 2:
Different regions of the superconductor are given different local qualities through varying energy band gaps. The first superconductor layer has a larger band gap optimized for phonon blocking, while the second layer has a smaller band gap optimized for hot electron transport. This local quality differentiation enables the structure to simultaneously prevent quasi-particle backflow and maintain cooling functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively enhances the temperature difference between hot and cold sides by preventing quasi-particle backflow and phonon heat return, improving the cooling efficiency of NIS coolers and maintaining superconducting properties across layers.
Implementation Method 1
utilizing thermal boundary resistance mismatch to block phonons and quasi-particles
Implementation Method 2
block phonon heat return
Implementation Method 3
Solid-state electron cooling by the tunneling of 'hot' electrons across a normal metal-insulator-superconductor (NIS) junction
Implementation Method 4
remove hot electrons from the normal metal layer through each superconductor layer
Implementation Method 5
quasi-particles migrate to the normal metal and relax their energy there through electron-electron and electron-phonon interaction
Implementation Method 6
relax their energy there through electron-electron and electron-phonon interaction
Implementation Method 7
each superconductor layer having a smaller superconducting energy band gap than the preceding superconductor as the superconductor layers extend away from the normal metal layer
Data Source
AI summary
A superconductor thermal filter is disclosed that includes a normal metal layer having a first side, an insulating layer overlying the first side of the normal metal layer, and a multilayer superconductor structure having a first side overlying a side of the insulating layer opposite the side that overlies the normal metal layer. The multilayer superconductor structure is comprised of a plurality of superconductor layers with each superconductor layer having a smaller superconducting energy band gap than the preceding superconductor as the superconductor layers extend away from the normal metal layer. The thermal filter further includes a normal metal layer quasiparticle trap having a first side and a second side with the first side being disposed on a second side of the multilayer superconductor. A bias voltage is applied between the normal metal layer and the normal metal layer quasiparticle trap to remove hot electrons from the normal metal layer.