Brazilian PhD internships at the HFML: successful collaboration

In 2017 and 2018, two PhD students from Brazil came to Nijmegen to do a part of their post-graduate program at the HFML. Thanks to a collaboration between researchers from Brazil and dr. Steffen Wiedmann from the HFML, they had the opportunity to perform experiments in high magnetic fields and explore new territory as part of their PhD research. Wiedmann: “It has been a great success!”

For many decades, narrow gap semiconductors have been widely studied due to their potential application in infrared optical devices and thermoelectric generators. In addition, considerable efforts have been made recently to investigate spin-orbit coupling, the quantum Hall effect (QHE) and topological phases in different IV-VI based structures. Recently, Pb1‑xSnxTe has been identified as a topological crystalline insulator.

brazilian internships (1)Anderson Okazaki from the Brazilian Institute for Space Research (São José dos Campos) started his measurements in April 2017 on a full range of Pb1‑xSnxTe epitaxially grown films with the main goal to unravel their fundamental properties by means of magneto-transport experiments. In one of his high-field experiments, Okazaki performed a quantum oscillation study on SnTe, see Figure (a), to probe the topology of the Fermi surface. With angle- and temperature dependent measurements, he demonstrated that quantum oscillations in SnTe originate from the bulk band structure due to Rashba splitting of the longitudinal valley.

brazilian internships (2)September 2018, Fernando Pena from the University of Itajubá joined the group. His project was dedicated to investigate the integer QHE in a series of p-type PbTe/PbEuTe quantum well structures at low temperatures. He observed the integer QHE, see Figure (b), in quantum wells with different well widths indicating the high quality of the two-dimensional systems under study.

Using the high-field facility in collaboration with staff at the HFML, Okazaki and Pena could expand their experimental skills and knowledge, taking a close look at the science done in high magnetic fields. They achieved all their research goals as stated in the grant proposals. Currently, they are finishing their PhD programs at their universities and other publications are in preparation.

Steffen Wiedmann: ‘This was the first time that I organized these internships together with my collaborators from Brazil. Anderson and Fernando did a fantastic job. It was not only scientifically rewarding, they also had a pleasant time here in the Netherlands working together with our team members and learning new skills. I am proud that I could act as supervisor and thank Eduardo Abramof, Marcelos Peres, Sergio Pezzini and Paulo Rappl for this great collaboration.”

brazilian internships (1)

Figure: (a) Second derivative of longitudinal resistance Rxx as a function of 1/B measured on SnTe epitaxial films at 4.2 K and up to 30 T. (b) Quantum Hall effect in a PbTe/PbEuTe QW at 0.35 K and up to 33 T: Hall resistance Rxy (blue dashed line) and longitudinal resistance Rxx (red line).

Related publication
Shubnikov–de Haas oscillations in topological crystalline insulator SnTe(111) epitaxial films, A. K. Okazaki, S. Wiedmann, S. Pezzini, M.L. Peres, P.H.O. Rappl and E. Abramof, Physical Review B (2018).

Anderson Okazaki and Fernando Pena obtained a one-year PhD fellowship from the Federal Agency for Support and Evaluation of Graduate Education (CAPES).

Steffen Wiedmann