The Search for Induced Superconductivity Across Planar Al/EuS/InAs 2DEG Josephson Junctions
(2025) FYSM64 20242Department of Physics
Solid State Physics
- Abstract
- This thesis investigates superconductivity in novel planar Josephson junctions fabricated from a hybrid Al/EuS/2DEG (InGaAs/InAs/InGaAs) heterostructure. Using electron-beam lithography, selective etching, and atomic layer deposition, Josephson junction devices, constrictions, and SQUID geometries were fabricated and a selection of the devices were characterized at millikelvin temperatures. The measurements revealed superconducting windows exhibiting hysteretic behavior under magnetic fields, along with asymmetric and distorted Fraunhofer interference patterns. However, unexpectedly low normal-state resistances (on the order of tens of Ohms) and notably high critical currents (10–20 µA) raised significant uncertainties regarding the origin... (More)
- This thesis investigates superconductivity in novel planar Josephson junctions fabricated from a hybrid Al/EuS/2DEG (InGaAs/InAs/InGaAs) heterostructure. Using electron-beam lithography, selective etching, and atomic layer deposition, Josephson junction devices, constrictions, and SQUID geometries were fabricated and a selection of the devices were characterized at millikelvin temperatures. The measurements revealed superconducting windows exhibiting hysteretic behavior under magnetic fields, along with asymmetric and distorted Fraunhofer interference patterns. However, unexpectedly low normal-state resistances (on the order of tens of Ohms) and notably high critical currents (10–20 µA) raised significant uncertainties regarding the origin of the observed superconductivity, questioning whether it truly results from proximity-induced superconductivity or simply unintended shorted superconducting leads. Limited gate-tunability further complicated this interpretation. Observed asymmetries and anomalies may stem from flux trapping, ferromagnetic interface effects (EuS), and structural issues due to the lack of mesa isolation. These initial findings highlight critical challenges and suggest specific avenues for refining fabrication techniques and improving device architectures. Addressing these issues will be essential for conclusively understanding superconductivity in hybrid heterostructures and advancing their potential in future quantum electronic applications (Less)
- Popular Abstract
- What happens when the rules of electricity and magnetism start to break down, and something even stranger takes over? Imagine a world where electric current can flow forever without losing any energy, and where magnetic effects can be switched on and off at the flick of a quantum switch. That is the world of superconductors, materials that, when cooled to extremely low temperatures, conduct electricity with zero resistance.
In this project, I set out to build and test tiny “quantum bridges” called Josephson junctions, made by layering a superconductor (aluminum), a magnetic material (europium sulfide), and an extremely thin sheet of electrons (known as a two-dimensional electron gas). These hybrid devices are more than just scientific... (More) - What happens when the rules of electricity and magnetism start to break down, and something even stranger takes over? Imagine a world where electric current can flow forever without losing any energy, and where magnetic effects can be switched on and off at the flick of a quantum switch. That is the world of superconductors, materials that, when cooled to extremely low temperatures, conduct electricity with zero resistance.
In this project, I set out to build and test tiny “quantum bridges” called Josephson junctions, made by layering a superconductor (aluminum), a magnetic material (europium sulfide), and an extremely thin sheet of electrons (known as a two-dimensional electron gas). These hybrid devices are more than just scientific curiosities: they are miniature laboratories where we can explore the mysterious interplay between superconductivity and magnetism, and learn how to control the quantum world in ways that could power the computers of the future.
But making these devices is not easy. Building structures just a few atoms thick requires the precision of a watchmaker and the patience of a gardener. Even the tiniest error in fabrication can lead to unwanted “short circuits” or block the delicate quantum effects we want to see. During my thesis work, I learned how to design, fabricate, and test these devices at temperatures colder than deep space. I discovered that the interface between materials is crucial: a single atomic layer can determine whether a device works or fails. The most exciting moments came when I observed hints of new behavior: oscillations in the electrical current that could not be explained by classical physics alone. These patterns are fingerprints of quantum interference, where electrons behave not just as particles but as waves, weaving together in complex patterns dictated by the laws of quantum mechanics.
Why does this matter? Superconducting and magnetic hybrid devices are the building blocks of quantum computers and ultra-sensitive detectors. By understanding and mastering their behavior, we open doors to technologies that were science fiction only a decade ago, like computers that can solve problems beyond the reach of today’s machines, or medical sensors that can see inside the human brain without surgery.
My project is a small step in this direction, but it is a real contribution to a field that is rapidly reshaping our technological future. In exploring these hidden realms, we are not just pushing the boundaries of physics, we are discovering new ways of seeing and shaping our world. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9202463
- author
- Jamo Abdi, Sherwan LU
- supervisor
- organization
- course
- FYSM64 20242
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Superconductivity Ferromagnet 2DEG EuS InAs Proximity effect Josephson Junction Induced Superconductivity Hysteresis Gates Fabrication Fraunhofer
- language
- English
- id
- 9202463
- date added to LUP
- 2025-06-23 08:34:09
- date last changed
- 2025-06-23 08:34:09
@misc{9202463,
abstract = {{This thesis investigates superconductivity in novel planar Josephson junctions fabricated from a hybrid Al/EuS/2DEG (InGaAs/InAs/InGaAs) heterostructure. Using electron-beam lithography, selective etching, and atomic layer deposition, Josephson junction devices, constrictions, and SQUID geometries were fabricated and a selection of the devices were characterized at millikelvin temperatures. The measurements revealed superconducting windows exhibiting hysteretic behavior under magnetic fields, along with asymmetric and distorted Fraunhofer interference patterns. However, unexpectedly low normal-state resistances (on the order of tens of Ohms) and notably high critical currents (10–20 µA) raised significant uncertainties regarding the origin of the observed superconductivity, questioning whether it truly results from proximity-induced superconductivity or simply unintended shorted superconducting leads. Limited gate-tunability further complicated this interpretation. Observed asymmetries and anomalies may stem from flux trapping, ferromagnetic interface effects (EuS), and structural issues due to the lack of mesa isolation. These initial findings highlight critical challenges and suggest specific avenues for refining fabrication techniques and improving device architectures. Addressing these issues will be essential for conclusively understanding superconductivity in hybrid heterostructures and advancing their potential in future quantum electronic applications}},
author = {{Jamo Abdi, Sherwan}},
language = {{eng}},
note = {{Student Paper}},
title = {{The Search for Induced Superconductivity Across Planar Al/EuS/InAs 2DEG Josephson Junctions}},
year = {{2025}},
}