Topological properties of semiconductor heterostructures
Summary
Scientific domain: Physics
Doctoral school: I2S (https://edi2s.umontpellier.fr/)
Project title: Topological properties of semiconductor heterostructures
PhD supervisors: Benoit Jouault (L2C), Eric Tournié (IES)
Context
The PhD will take place at the University of Montpellier, France.
36 months duration, starting in September-December 2024.
Research group
The “Terahertz spectroscopy and Electronic Transport” team (TEST), from “Charles Coulomb Laboratory” (L2C).
Applicant
The candidate holds a MSc or equivalent degree in Physics or related fields, with knowledge of solid-state physics (condensed matter physics, applied physics, material science...). The candidate must have an interest for experimental physics. Additional affinity with numerical modeling techniques (python, tight binding, k-p calculations, nextnano…) will be an asset. PhD student will work in an international competitive context requiring high motivation and intellectual curiosity.
PhD supervision and contacts
Dr. Benoit Jouault,
benoit.jouault@umontpellier.fr
PhD project
The objective of this project is to probe unusual topological phases in III-V heterostructures via electronic transport and Terahertz magneto-optical measurements. Topological phases in solids have indeed attracted considerable attention, particularly since the award of the Nobel Prize in 2016 for topological concepts in condensed matter physics. Since then, these topological phases have been observed in a large number of materials, but only a small number of them have a sufficiently mastered growth and technological process to consider their possible use for the foundations of a new topological electronics and to contribute to the current advent of quantum technologies.
In this context, III-V semiconductor heterostructures based on antimony prove to be particularly interesting. One of the most striking topological phenomena, called the quantum spin Hall effect, has indeed been observed in there [1]. In addition, these InAs/GaSb composite quantum wells can recently be manufactured on silicon substrates, which makes it possible to imagine the bases of quantum and topological electronics that can be integrated into current nanoelectronic circuits.
This research is motivated by recent results from our team, which predicted and finally observed the existence of a wide and temperature insensitive topological gap in specific Sb-based quantum wells [2-6]. This breakthrough makes it possible to consider the observation of electronic edge states protected from backscattering by the non-trivial topology of the band structure, even at liquid nitrogen temperatures. It turns out that very recent measurements (Würzburg-Montpellier) indeed suggest the presence of these exotic electronic states in these structures at temperatures much higher than that of liquid helium [7].
One of the main goals of the proposed project is therefore to study the physical properties of these topological edge channels. Furthermore, even more complex topological phases (High Order Topological Phases) recently predicted by our team will also be at the heart of this thesis work.
Methods
Beyond the fundamental and applied interest of this thesis project, the strength of this PhD project is based on different collaborative and experimental aspects. Indeed, the L2C team works in close collaboration with the only laboratory in France carrying out the growth of these topological III-V materials, namely the Institute of Electronics and Systems (IES) and more precisely the team by Eric Tournié (co-supervisor of this thesis). In addition, a strong collaboration with the German Institute for Topological Insulators in Wurzburg, financed by a Franco-German ANR contract, will allow the candidate to carry out his thesis in the best conditions and to travel between several laboratories, also including the High Magnetic Fields Laboratory (LNCMI) of Toulouse and Grenoble. The PhD student will have access to unique measurement tools such as a Landau spectrometer unique in the world, and a certain number of cryostats allowing measurements of electronic transport and magneto-transmission at low temperatures (down to 260 mK) and strong magnetic fields (up to 16T in Montpellier, and more in Toulouse and Grenoble). The PhD student will also discuss the optimization of both band structures and fabrication of the devices with the other researchers involved in this project. He will also have opportunity to learn how to process a part of the nanostructured devices in a dedicated clean room in Montpellier.
Teams
- The “Terahertz spectroscopy and Electronic Transport” team (TEST), from L2C lab, is active in the THz research since more than 20 years. It is one of the leading French teams of THz research having almost all experimental facilities in the THz frequency domain. Since 2011, TEST is intensively involved in the study of various topological phase transitions in HgCdTe, InAs/GaSb and Cd3As2 by THz/MIR absorption, photoconductivity, and transport experiments under magnetic field. The group in L2C has also a strong expertise in theory of topology in solids, in theory of many-body effects in semiconductors, and in band-structure calculations.
- The NanoMIR team, from IES lab, is a world leader in growth and physics of antimonide III-V heterostructures and devices. Several international firsts have been realized in the past years, in the fields of InAs/AlSb quantum cascade lasers, GaSb-based laser diodes, or InAs/GaSb superlattice photodetectors. The IES facilities include MBE machines dedicated to the growth of antimonides, a clean room equipped for "basic" processing of III-Sb materials and devices, and experimental setups for characterization of materials and IR/THz devices. The role of NanoMIR in the project will be the growth of InAs/AlSb/GaSb structures, a contribution to their design, processing, and characterizations.
- The UNIWUE team from University of Würzburg realized and completed the first unambiguous gate voltage and temperature dependent transport measurements these III-V based topological insulators. UNIWUE has the expertise and facilities to grow InAs/GaSb structures, has expertise on the antimonide family processing line and TEM analysis. The PhD student involved in the project will visit the laboratories at UNIWUE to learn how to fabricate topological devices.
Related publications
1. L. Du et al., « Robust Helical Edge Transport in Gated InAs/GaSb Bilayers”, Phys. Rev. Lett. 114, 096802 (2015).
2. S. S. Krishtopenko and F. Teppe, “Quantum spin Hall insulator with a large bandgap, Dirac fermions, and bilayer graphene analog”, Sci. Adv. 4, eaap7529 (2018).
3. S. S. Krishtopenko et al., “Temperature-dependent terahertz spectroscopy of inverted-band three-layer InAs/GaSb/InAs quantum well”, Phys. Rev. B 97, 245419 (2018).
4. S. S. Krishtopenko et al., “Massless Dirac fermions in III-V semiconductor quantum wells”, Phys. Rev. B 99, 121405 (2019).
5. S. S. Krishtopenko, “Higher-order topological insulator in cubic semiconductor quantum wells”, Scientific Reports 11, 21060 (2021).
6. C. Avogadri et al., “Large Inverted Band Gap in Strained Three-Layer InAs/GaInSb Quantum Wells”, Phys. Rev. Res. 4, L042042 (2022).
7. M. Meyer et al., “Topological band structure in InAs/GaSb/InAs triple quantum wells”, Phys. Rev. B, 104, 085301 (2021).