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Home   /   Thesis   /   Topological-superconductor group IV nanomaterials

Topological-superconductor group IV nanomaterials

Condensed matter physics, chemistry & nanosciences Solid state physics, surfaces and interfaces


We are currently embracing the second quantum revolution, where major breakthroughs in solid-state technologies have been achieved by engineering materials with different electrical conductivities (metals, insulators, semiconductors (SEMI)), eventually reaching infinite conductivity in cooled superconductors (SC). This flourishing ecosystem has been enriched by the recent discovery of a new class of materials with remarkable electronic properties - topological (TOP) materials(1) - that is now driving both the theoretical and experimental work in condensed matter physics. Significant advances in understanding fundamental material properties, devising new fabrication processes, and discovering novel material systems are required to fully harvest the potential of solid-state quantum devices. Superconducting spin qubits, gate-tunable spin qubits, and topological qubits systems are commonly fabricated by combining multiple materials with fundamentally different properties - heterogeneous integration - in hybrid SC/SEMI and SC/TOP junctions. This is a significant challenge in material science since any structural defects and roughness at the interface between two materials would compromise the ability to detect and manipulate quantum states. The properties of these hybrid junctions are affected by the interface purity within the heterostructure, where the presence of oxides, impurities, or structural defects is a detrimental source of noise and dissipation in these material systems.(2)
The goal of this PhD thesis is to develop a scalable material platform where quantum properties can be engineered simply by tailoring the crystal structure of a single atomic element – Tin (Sn) – and achieve interfaces with the highest quality. Topological insulator/topological semimetal phases can be tailored in diamond cubic a-Sn by controlling strain,(3) while body-centered tetragonal ß-Sn behaves as a superconductor at temperatures below 4 K.(4) Currently, a controlled switch between a/ß-Sn phases is out of reach using a conventional thin film geometry.
The PhD student will establish the growth of one-dimensional (1D) Sn nanowires (NWs) on a Silicon wafer using a molecular beam epitaxy (MBE) system. NWs offer the ideal system to control the crystalline phase of a material without nucleating structural defects.(5) In this thesis, this crystal-phase engineering paradigm will be developed for group IV NWs to achieve a precise control over the growth of a-Sn and ß-Sn phases (i.e. TOP and SC phases). This protocol will then enable the growth of defect-free a/ß-Sn NWs with atomically-sharp interfaces and with the highest structural quality. This nanostructured material will provide a truly homogeneous integration of multiple states of matter in solid-state quantum devices, paving the way to explore the fundamental processes in topological quantum computation,(6) spintronics,(7) and quantum photonics.(8)
The student will investigate the structural properties (scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray diffraction, atom probe tomography) and optical properties (Raman) of the a/ß-Sn NWs using a variety of characterization techniques available at CEA. To demonstrate the presence of TOP or SC phases in these nanomaterials, the student will fabricate a NW field-effect transistor (FET) (single NW transfer to a SiO2/Si substrate, electron beam lithography, metals and oxides deposition). Next, magnetotransport measurements at cryogenic temperatures (1 K or less) will be performed to demonstrate the TOP behavior in a-Sn and SC state in ß-Sn. This thesis will train the student with a diverse skillset ranging from materials growth, structural and optoelectronic characterization, device fabrication, and quantum transport measurements.
(1) P. Liu et al., Nat. Rev. Mater. 4, 479–496 (2019).
(2) N. P. de Leon et al., Science 372, 1–20 (2021).
(3) A. Barfuss et al., Phys Rev Lett. 111, 157205 (2013).
(4) Y. Zhang et al., Sci Rep. 6, 32963 (2016).
(5) S. Assali et al., Nano Letters. 15 (12) (2015).
(6) A. Stern, N. H. Lindner, Science. 339, 1179-1184 (2013).
(7) J. Ding et al., Advanced Materials. 33, 2005909 (2021).
(8) E. D. Walsh et al., Science. 372, 409-412 (2021).


Institut de Recherche Interdisciplinaire de Grenoble
Université Grenoble Alpes
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