Periodic Reporting for period 1 - MOUNTAIN (Molecular Quantum Heat Engines)
Berichtszeitraum: 2022-05-01 bis 2024-10-31
Heat engines are an integral part of our daily lives. They power cars or produce electricity by converting heat into work. Increasing their efficiency is very difficult and only marginal improvements have been achieved over the last decades. Thus, to reach the ambitious climate goals, it is necessary to go beyond conventional technologies. Atom-sized systems where quantum mechanical effects come into play could enable this: theory predicts that their efficiency can be boosted beyond the classical limits imposed by thermodynamics. However, so far, this has not been tested in practice due to a lack of suitable model systems.
In this project, I propose to build a molecular heat engine of only a few atoms in size, with such high control over its structure and properties that these predictions can finally be tested. The engine’s quantum properties will be robust at experimentally accessible temperatures, its coupling to the environment will be controllable, and electrical transport through it will be quantum coherent. I seek to exploit the full gamut of their physical properties to boost efficiency, including spin entropy and vibrational coupling.
The fundamental insight obtained in MOUNTAIN will have huge impact on our understanding of heat and particle flow at the atomic limit. Furthermore, we will reveal experimentally the fundamental, quantum thermodynamic efficiency limits of a quantum heat engine, which will be highly relevant for the nanoscopic and quantum physics community and will fuel future theoretical and experimental work in the fields of non-equilibrium quantum systems, molecular electronics and thermoelectric devices. Although MOUNTAIN focusses on the fundamental aspects of molecular quantum heat engines, the obtained results will define the limits and possibilities for engineering future thermoelectric applications like energy harvesters of waste heat, highly efficient (cryogenic) nanoscale spot-cooling devices for thermal management applications, thermal rectifiers and transistors or even thermal logic gates and memory.
In this project, I propose to build a molecular heat engine of only a few atoms in size, with such high control over its structure and properties that these predictions can finally be tested. The engine’s quantum properties will be robust at experimentally accessible temperatures, its coupling to the environment will be controllable, and electrical transport through it will be quantum coherent. I seek to exploit the full gamut of their physical properties to boost efficiency, including spin entropy and vibrational coupling.
The fundamental insight obtained in MOUNTAIN will have huge impact on our understanding of heat and particle flow at the atomic limit. Furthermore, we will reveal experimentally the fundamental, quantum thermodynamic efficiency limits of a quantum heat engine, which will be highly relevant for the nanoscopic and quantum physics community and will fuel future theoretical and experimental work in the fields of non-equilibrium quantum systems, molecular electronics and thermoelectric devices. Although MOUNTAIN focusses on the fundamental aspects of molecular quantum heat engines, the obtained results will define the limits and possibilities for engineering future thermoelectric applications like energy harvesters of waste heat, highly efficient (cryogenic) nanoscale spot-cooling devices for thermal management applications, thermal rectifiers and transistors or even thermal logic gates and memory.
The key experimental objectives of this project are to develop devices capable of studying the thermal, thermoelectric and electronic properties of a single molecule at low temperatures.
To this end, we developed a superconducting thermometer capable of measuring minute temperature changes in nano-scale junctions at extremely low cryogenic temperatures (mK). After successful benchmarking, we integrated such thermometers in nano-scale junctions in which we immobilized a single molecule between two atomic-sharp gold electrodes. These junctions where further equipped with on-chip micro heaters which then allowed us to heat up one side of the single molecule with respect to the other side. When experimentally studying such single molecule heat engines at cryogenic temperatures, we revealed, for example, that bound states formed between spin-full molecules and superconducting electrodes form highly efficient energy filters which boost thermoelectric efficiency. As a next step we will perform ultra-fast read out of our thermometers to e.g. reveal how a single molecular heat engines dissipates heat or how heat is transported through such nanoscale engines.
To this end, we developed a superconducting thermometer capable of measuring minute temperature changes in nano-scale junctions at extremely low cryogenic temperatures (mK). After successful benchmarking, we integrated such thermometers in nano-scale junctions in which we immobilized a single molecule between two atomic-sharp gold electrodes. These junctions where further equipped with on-chip micro heaters which then allowed us to heat up one side of the single molecule with respect to the other side. When experimentally studying such single molecule heat engines at cryogenic temperatures, we revealed, for example, that bound states formed between spin-full molecules and superconducting electrodes form highly efficient energy filters which boost thermoelectric efficiency. As a next step we will perform ultra-fast read out of our thermometers to e.g. reveal how a single molecular heat engines dissipates heat or how heat is transported through such nanoscale engines.
We have shown that “thermo-current spectroscopy”, a method developed in our group, is a powerful tool to study fundamental physical effects like correlated phases or (quantum) thermodynamics. This method can be applied to many nano/mesoscale systems beyond single-molecule junctions. We have written a review article where we highlight our findings. As a next step, we will experimentally test the efficiency limits of single molecule heat engines with higher entropies using this method.