Heat control in mesoscopic conductors - exploiting quantum effects and size confinement
Doctoral thesis, 2020
This thesis deals with a theoretical analysis of heat currents, their exploitation and their control in nanoscale devices. The motivation for this study is twofold. (i) The development of nanoscale devices sets up the basis of many applications ranging from nanoelectronics to quantum technology. Such nanodevices, typically operated at low temperatures, are highly sensitive to heating effects. Hence the successful performance of these devices relies on controlling and managing this heat. (ii) Nanostructures provide appealing systems to study quantum and nonequilibrium thermodynamics because, at such small scales, the behavior of systems is highly affected by size confinement and quantum effects.
The central purpose of this thesis is to investigate the impact of specific characteristics of quantum systems, in particular of quantum size confinement, nonequilibrium effects and phase coherence, on heat transport quantities. A better understanding of this impact can lead to an improved control and exploitation of heat. This can be used for the evacuation of heat from the system, cooling, or producing power using waste heat. We propose different experimentally accessible setups. In these setups, we theoretically study transport quantities using a scattering formalism.
We pursue three main study lines in different setups: (i) We investigate phase-dependent heat transport in normal- and superconducting hybrid junctions. We show how disorder influences this, both in simple junctions as well as in a heat circulator. (ii) We analyze thermodynamical machines, which use nonequilibrium states as their resource instead of heat. Such devices show a "demonic behavior" since they seemingly challenge the second law of thermodynamics. (iii) We analyze how to exploit energy filtering of quantum conductors to perform thermoelectric cooling at the example of a quantum spin Hall device in the whole range from linear to nonlinear response.
The central purpose of this thesis is to investigate the impact of specific characteristics of quantum systems, in particular of quantum size confinement, nonequilibrium effects and phase coherence, on heat transport quantities. A better understanding of this impact can lead to an improved control and exploitation of heat. This can be used for the evacuation of heat from the system, cooling, or producing power using waste heat. We propose different experimentally accessible setups. In these setups, we theoretically study transport quantities using a scattering formalism.
We pursue three main study lines in different setups: (i) We investigate phase-dependent heat transport in normal- and superconducting hybrid junctions. We show how disorder influences this, both in simple junctions as well as in a heat circulator. (ii) We analyze thermodynamical machines, which use nonequilibrium states as their resource instead of heat. Such devices show a "demonic behavior" since they seemingly challenge the second law of thermodynamics. (iii) We analyze how to exploit energy filtering of quantum conductors to perform thermoelectric cooling at the example of a quantum spin Hall device in the whole range from linear to nonlinear response.
heat currents
thermoelectric devices
nonequilibrium thermodynamics.
fluctuations
phase-dependent heat transport
Kollektorn, MC2-huset, Kemivägen 9, Chalmers
Opponent: Dr María Rosa López Gonzalo, Universitat de les Illes Balears, Spain
Author
Fatemeh Hajiloo
Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics
Detailed study of nonlinear cooling with two-terminal configurations of topological edge states
Physical Review B,;Vol. 102(2020)
Journal article
Quantifying nonequilibrium thermodynamic operations in a multiterminal mesoscopic system
Physical Review B,;Vol. 102(2020)
Journal article
Mesoscopic effects in the heat conductance of superconducting-normal-superconducting and normal-superconducting junctions
Physical Review B,;Vol. 99(2019)
Journal article
Phase-coherent heat circulators with normal or superconducting contacts
Physical Review B,;Vol. 103(2021)
Journal article
Electronic devices are crucial to satisfy many needs of our everyday life. The electronics industry has responded to market expectations by offering products that are smaller and more powerful. This miniaturization led to devices at the nanometer scale. Heating of these tiny and densely packed devices during operation is a significant challenge.
Novel devices invented and researched in the context of nanoelectronics and quantum technologies exploit fundamentally different principles: they use quantum effects, and their behavior can hence not be explained by classical physics. Accordingly, such nanoscale devices need extremely low temperatures to operate. Also, in those systems, heating is hence detrimental to the performance and might even completely preclude the underlying quantum effects. Consequently, there is an essential need for controlling heat flows in nanoscale quantum devices. Simultaneously, quantum effects and size confinement also provide novel ways to control heat or implement heat engines with unprecedented functionalities.
This thesis deals with the theoretical study of heat control in nanoelectronic devices. We analyze in particular three effects that are unique to small-scale and quantum systems and propose to exploit them in concrete devices. First, due to quantum confinement, the conductance of nanoelectronic devices can have a strong energy dependence; this results in thermoelectric properties, which can be used for cooling. Second, phase coherence in quantum devices leads to opportunities to control heat flows coherently; based on this, heat valves and heat circulators can be designed. Finally, due to the absence of thermalization in small-scale devices, also the resources of engines can be non-thermal; this "non-thermal-ness" can be exploited as fuel for engines.
Novel devices invented and researched in the context of nanoelectronics and quantum technologies exploit fundamentally different principles: they use quantum effects, and their behavior can hence not be explained by classical physics. Accordingly, such nanoscale devices need extremely low temperatures to operate. Also, in those systems, heating is hence detrimental to the performance and might even completely preclude the underlying quantum effects. Consequently, there is an essential need for controlling heat flows in nanoscale quantum devices. Simultaneously, quantum effects and size confinement also provide novel ways to control heat or implement heat engines with unprecedented functionalities.
This thesis deals with the theoretical study of heat control in nanoelectronic devices. We analyze in particular three effects that are unique to small-scale and quantum systems and propose to exploit them in concrete devices. First, due to quantum confinement, the conductance of nanoelectronic devices can have a strong energy dependence; this results in thermoelectric properties, which can be used for cooling. Second, phase coherence in quantum devices leads to opportunities to control heat flows coherently; based on this, heat valves and heat circulators can be designed. Finally, due to the absence of thermalization in small-scale devices, also the resources of engines can be non-thermal; this "non-thermal-ness" can be exploited as fuel for engines.
Areas of Advance
Nanoscience and Nanotechnology
Subject Categories
Condensed Matter Physics
ISBN
978-91-7905-409-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4876
Publisher
Chalmers
Kollektorn, MC2-huset, Kemivägen 9, Chalmers
Opponent: Dr María Rosa López Gonzalo, Universitat de les Illes Balears, Spain