PI at JKU: a.Univ.-Prof. Gunther Springholz
Project duration: 01.01.2020-31.12.2023

In Cooperation with École Normale Supérieure (ENS) Paris, Laboratoire de Physique, PI: Dr. Louis-Anne de Vaulchier

Topological insulators are a novel class of materials that are electrically insulating in the bulk but conducting at the surface. This surface conduction is similar to the relativistic motion of light in vacuum and thus, exhibits peculiar properties compared to conventional conductors. Topological “crystalline” insulators are a subclass of these materials where the relativistic character of the surface electrons is governed by the symmetry of the crystal structure.  The objective of the joint research project of the Johannes Kepler University in Linz and the Ecole Normale Superiéure in Paris is to fabricate low dimensional topological crystalline insulator thin film heterostructures and to investigate the properties of the surface channel. Particular focus will be to develop control the topology character by external means to lay the grounds for practical device applications. This control will be achieved based on the fact that the ‘relativistic’ surface conduction can be manipulated by the chemical composition, mechanical strain, pressure, electric fields and magnetism. One can thus obtain functional devices such as transistors based on nanostructures of such materials that make use of the relativistic conduction properties.  

This international project brings together the expertise in fabrication of thin film heterostructures in Linz and the study of their properties using optical and electrical measurements at high magnetic fields and low temperatures in Paris. The goal is to solve the technological challenges and provide a novel platform for device applications. In particular, we will develop approaches to fabricate nanolayers and heterostructures with optimized properties using layer-by-layer growth with atomic precision. The novel physics of the obtained structures will be studied in detail by optical and electrical techniques that enable us to extract the velocity, mass and energy of surface electrons and study the evolution of their relativistic character as a function of band topology. This is essential to understand how this state of matter comes to exist and thus to understand the fundamental physics behind. In the second part, we will develop schemes to alter the crystalline symmetry of the material by introducing lattice deformations and we will explore how magnetism impacts surface conduction and suppresses its relativistic character. Overall, the project will establish that certain materials and material combinations provide an on-demand relativistic physics platform where novel exotic effects can be realized.  

G. Krizman, B. A. Assaf, T. Phuphachong, G. Bauer, G. Springholz, L. A. de Vaulchier, Y. Guldner
Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy, opens an external URL in a new window
Physical Review B 98, 245202 (2018)

G. Krizman, B.A. Assaf, M. Orlita, T. Phuphachong, G. Bauer, G. Springholz, G. Bastard, R. Ferreira, L.A. de Vaulchier, Y. Guldner
Avoided level crossing at the magnetic field induced topological phase transition due to spin-orbital mixing, opens an external URL in a new window
Physical Review B 89, 161202(2018)

G. Krizman, B. A. Assaf, T. Phuphachong, G. Bauer, G. Springholz, G. Bastard, R. Ferreira, L. A. de Vaulchier, Y. Guldner,
Tunable Dirac interface states in topological superlattices, opens an external URL in a new window
Physical Review B 98, 075303 (2018)

B. A. Assaf, T. Phuphachong, E. Kampert, V. V. Volobuev, P. S. Mandal, J. Sánchez-Barriga, O. Rader, G. Bauer, G. Springholz, L. A. de Vaulchier, Y. Guldner
Negative Longitudinal Magnetoresistance from Anomalous N=0 Landau Level in Topological Materials, opens an external URL in a new window
Physical Review Letters 119, 106602 (2017)

Badih A. Assaf , Thanyanan Phuphachong , Valentine V. Volobuev, Günther Bauer, Gunther Springholz, Louis-Anne de Vaulchier, Yves Guldner
Magnetooptical determination of a topological index
npj Quantum Materials 2, 26 (2017)

Partha S. Mandal, Gunther Springholz, Valentine V. Volobuev, Ondrej Caha, Andrei Varykhalov, Evangelos Golias, Günther Bauer, Oliver Rader & Jaime Sánchez-Barriga,
Topological quantum phase transition from mirror to time reversal symmetry protected topological insulator, opens an external URL in a new window
Nature Communications 8, 968 (2017)

Thanyanan Phuphachong, Badih A. Assaf  Valentine V. Volobuev , Günther Bauer , Gunther Springholz ,Louis-Anne de Vaulchier  Yves Guldner
Dirac Landau Level Spectroscopy in Pb1−xSnxSe and Pb1−xSnxTe across the Topological Phase Transition: A Review, opens an external URL in a new window
Crystals 7, 29 (2017)

V. V. Volobuev, P. S. Mandal, M. Galicka, O. Caha, J. Sanchez-Barriga, D. Di Sante, A. Varykhalov, A. Khiar, S. Picozzi, G. Bauer, P. Kacman, R. Buczko, O. Rader, G. Springholz
Giant Rashba Splitting in Pb1-xSnxTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk, opens an external URL in a new window
Advanced Materials 29, 1604185 (2017) 

B.A. Assaf, T. Phuphachong, V.V. Volobuev, A. Inhofer, G. Bauer, G. Springholz, L.A. de Vaulchier, Y. Guldner 
Massive and massless Dirac fermions in Pb1-xSnxTe topological crystalline insulator probed by magneto-optical absorption, opens an external URL in a new window
Scientific Reports 7, 20323 (2016)