September 2018
Abstracts of the QSIT Lunch Seminar, Thursday, September 6, 2018
Tunneling into a finite Luttinger liquid coupled to capacitive leads
Antonio Štrkalj – Quantum Engineered Systems (Zilberberg group), ETH Zurich
Tunnel-junctions involving one-dimensional quantum wires show many unusual characteristics, since many-body interactions fundamentally alter the 1D emergent physics compared with conventional Fermi-liquid metals. Furthermore, tunneling spectroscopy of such quantum wires can be profoundly sensitive to the boundary conditions of the wire. Interestingly, the impact of the boundary noise becomes more prominent with increasing many-body interactions inside the wire.
In my talk, I will show how this interplay manifests when the wire is coupled to capacitive metallic reservoirs. The classical capacitance in the boundaries allows for a smooth crossover from a standard interaction-dominated regime into a regime where the tunneling is dominated by the fluctuations in the reservoirs. The latter regime is characterized by an elevated zero-bias tunneling alongside a universal power-law decay at high energies. Moreover, local tunneling measurements in this regime show a unique spatial-dependence and thus offer a tunable method by which to control the boundary effects and measure the interaction strength (Luttinger parameter) within the wire
Asymmetric quantum well system for dipolaritons and quantum Hall states
Mirko Lupatini – Advanced Semiconductor Quantum Materials (Wegscheider group), ETH Zurich
Exciton-polaritons in a microcavity are bosonic quasiparticles arising from the strong coupling between cavity photons and excitons. Due to their bosonic nature and their low effective mass – a consequence of the light-matter composition – polaritons are good candidates for the study of condensation and superfluidity of nonequilibrium quasiparticles among other phenomena. Several of these effects depend on polariton-polariton interaction, which can be enhanced by accurately engineering the structure such that electrons and holes are spatially separated, thus forming indirect excitons with a large dipole moment. This system can be achieved by delocalizing one type of carrier via tunneling between two quantum wells (QWs), whereas the other type of carrier is confined to only one of them [1]. In another type of structure, optical spectroscopy was carried out on optical excitation in the presence of a high mobility two-dimensional gas of free carriers in the strong coupling regime showing signatures of exciton-polaron-polariton resonances [2,4]. This system is suitable for further understanding of fractional quantum Hall states by optical means [3,4].
In this work, we show initial progress in combining these two structures, with the aim to form dipolaritons from excitations in a two-dimensional hole gas. In the early stage of the project, the electron tunneling was studied using a p-i-n diode structure with two asymmetric GaAs/AlGaAs QWs in the intrinsic region. In this case, there is no hole gas present in the system. An anticrossing is observed by optical spectroscopy as the electron states of the two QWs are tuned into resonance showing a tunnel coupled system. In the second stage of the project, the physics of exciton-polaron-polariton is studied in a single GaAs quantum well in the presence of a hole gas by white light reflection. An attractive and repulsive polaron feature is observed at low hole densities.
This structure can be extended by forming a hole gas in the wider QW and monolithically integrating the diode structure with a microcavity. The final system could be interesting for the study of quantum Hall states as well as polariton mediated superconductivity [5].
[1] P. Cristofolini, et. al, Science, vol 336, 704-707 (2012).
[2] M. Sidler, et al, Nature Physics, vol 13, 255–261 (2017)
[3] S. Smolka, et. al, Science, vol 346, 332-335 (2014).
[4] S. Ravets, et. al, Phys. Rev. Lett., vol 120, 57401 (2018)
[5] O. Cotlet, et. al, Phys. Review, B 93, 054510 (2016).
Co-authors:
Stefan Fält1,2, Partrick Knüppel2, Werner Dietsche1, Ataç Imamoğlu2 and Werner Wegscheider1
1 Solid State Physics Laboratory, Eidgenössische Technische Hochschule (ETH) Zurich, 8093 Zurich, Switzerland.
2 Institute of Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.