Exotische korrelierte Phasen in oxidischen zweidimensionalen Elektronensystem bei ultratiefen Temperaturen
Zusammenfassung der Projektergebnisse
The project “Exotic correlated phases in oxide two-dimensional electron systems at ultra-low temperature” explored the electronic and optical responses of electrons confined in two-dimensions at the heterointerface of MgZnO/ZnO. This is a unique platform as it is the cleanest among all oxides while being more strongly interacting than comparable III-V semiconductor-based electron systems. Correlated electrons continue to attract attention from the scientific community as their strongly emergent properties are difficult to predict via theory, and give insight into the fundamental nature of electron dynamics and its interplay with structural degrees of freedom. In this study, we aimed to implement a very low temperature experimental apparatus that would give insight into electronic phases when the density of electrons is very low. The small number of electrons means they are very sensitive to disorder and temperature fluctuations, hence necessitating both high quality samples and ultra-low temperatures. The project evolved in many ways; a study of electrons at high magnetic field, evaluation of thermodynamic properties of carriers such as their effective mass via resonance techniques, and ultimately their study at ultra-low temperatures in the absence of a magnetic field. Each of these approaches provided quantitative insight into the “strength” of interactions, i.e. in the form of monitoring the renormalization of carriers, which is a common outcome of correlations. We are now able to track interaction effects with a high degree of confidence from the moderately interacting metallic phase (which shows exotic fractional quantum Hall features with the application of a magnetic field), down to the spontaneous breakdown of the metal phase at very dilute carrier concentrations where interaction effects are the strongest. In particular, the dilute regime has remained elusive for some decades as it is where disorder is most problematic. The low temperature techniques implemented in this study have, for the first time, enable the painting of a phase diagram of competing phases as an interaction-induced metal insulator transition is traversed. The phase diagram includes a magnetic field axis, and agrees closely in a quantitative and qualitative manner with theory. In conclusion, the goals of the study were achieved in a timely manner and have advanced this material system as a premier platform for studying correlated electrons at very low temperatures, with high experimental accessibility. Future advances in crystal growth, combined with lower temperatures will give insight into experimental details that remain opaque at this stage, including possible many-body localization of carriers which may be decoupled from the phonon bath, translational symmetry breaking associated with Wigner crystallization, and potential spin-liquid behavior has the critical point of the metal-insulator transition is approached.
Projektbezogene Publikationen (Auswahl)
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A cascade of phase transitions in an orbitally mixed half-filled Landau level. Science Advances, 4(9).
Falson, Joseph; Tabrea, Daniela; Zhang, Ding; Sodemann, Inti; Kozuka, Yusuke; Tsukazaki, Atsushi; Kawasaki, Masashi; von Klitzing, Klaus & Smet, Jurgen H.
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Phase transitions at ν = 5∕2 in ZnO-based heterostructures. Physica E: Low-dimensional Systems and Nanostructures, 110, 49-51.
Falson, Joseph
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Microwave response of interacting oxide two-dimensional electron systems. Physical Review B, 102(11).
Tabrea, D.; Dmitriev, I. A.; Dorozhkin, S. I.; Gorshunov, B. P.; Boris, A. V.; Kozuka, Y.; Tsukazaki, A.; Kawasaki, M.; von Klitzing, K. & Falson, J.
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Competing correlated states around the zero-field Wigner crystallization transition of electrons in two dimensions. Nature Materials, 21(3), 311-316.
Falson, J.; Sodemann, I.; Skinner, B.; Tabrea, D.; Kozuka, Y.; Tsukazaki, A.; Kawasaki, M.; von Klitzing, K. & Smet, J. H.
