€ 3 million grant for research on topological correlated matter

Researchers from the Radboud University and five other Dutch universities have received an NWO GROOT grant of 3 million euros for their proposal to merge two major fields of physics research, namely topological materials and correlated materials, with the aim to arrive at new materials classes where both characteristics are present and to find what new physics emerges at their intersection.

Innovative technologies that make modern digital society possible are inextricably linked to breakthroughs in controlling the electrical properties of materials. This project brings together experts in the Netherlands that want to open up a new field of research, in order to develop materials whose electrical and magnetic properties can be changed easily and very strongly with external buttons such as pressure, temperature or applied voltage. The GROOT grant will be used mainly to appoint young researchers and postdocs in the coming five years. Physicists from the Institute for Molecules and Materials (IMM) and HFML-FELIX are participating in the project.

Band structure

Atoms or ions are arranged in a periodic array in a crystalline material. Electrons within the lattice arrange themselves in bands of allowed energies separated by forbidden regions or gaps. This resulting ‘band structure’, determines whether the material in question is a metal (without a gap), an insulator (with a large gap) or a semiconductor (with a small gap).

Topology

Topology aids our understanding of the band structure and electronic properties of materials and introduces a robustness, or invariance, to observable quantum properties. The role of topology in condensed matter systems became even more ubiquitous with the discovery of topological insulators in 2004 – that were insulating in the bulk but conducting at the surface – and whose topological character was found to be an intrinsic property of its band structure. This discovery ushered in a new field of research and a whole new class of topological matter, where non-interacting band theory is key, has been found.

Correlated matter

The term ‘correlated’ matter relates to a wide class of materials in which the behavior of electrons cannot be described in terms of non-interacting particles. Conventional band theory cannot be applied to these materials since it fails to take into account, for instance, the interaction between the electrons themselves. These interactions can also lead to transitions into new phases, such as magnetism or superconductivity and the stronger the interaction, the higher the temperature at which these phenomena occur and thus the greater their potential for technological exploitation. Correlated quantum matter is a thriving field, even though the ability to predict properties of strongly correlated materials is still limited.

Topological correlated matter

The ideas of topological classification can in principle be also used to describe the ground state configurations of correlated materials, but only now are we beginning to realize genuine forms of topological correlated matter. “Topology makes otherwise subtle quantum effects robust, while electron interactions induce states with long-range order such as superconductivity and magnetism. The combination of topology and correlation thus brings robustness and order to the world of quantum materials with the potential to create transformative technologies”, says Steffen Wiedmann, Assistant Professor at HFML.

Nigel Hussey, Professor of Correlated Electron Systems at HFML: “We believe that there is an enormous untapped potential to create new paradigms in the fields of topology and correlated electron systems as well as to realize a host of entirely novel properties”.

A schematic phase diagram concerning the research of the consortium.

Research with high magnetic fields

At the HFML, Wiedmann and Hussey will explore new emergent phenomena made accessible by carefully selected material platforms and a unique combination of tunable environments such as magnetic fields up to 38 Tesla, pressure, doping or strain – in order to advance our understanding of interacting topological systems and in particular, the prospects for new physics and functionality in the vicinity of so-called topological quantum phase transitions, phase transitions that occur in the vicinity of absolute zero by purely quantum means.

Research at the IMM

At the IMM, Khajetoorians will explore the essential ingredients to creating topological correlated matter in model systems. This will be achieved by controlling interactions in bottom-up built designer lattices. In conjunction with theory performed by Katsnelson and Morais Smith (Utrecht), we will try to create recipes on how to create new and exotic states of matter. Katsnelson will also provide fundamental theory support in understanding the new and emergent phenomena observed in new material systems in this consortium.

Alexander Khajetoorians, Professor and head of the Scanning Probe Microscopy department at the IMM: “I believe there is vast potential to create new material systems, with unpredictable and exciting behavior. This would only be possible in such a synergetic and collaborative project like TOPCORE.”

Misha Katsnelson, Professor and head of the Theory of Condensed Matter department at the IMM: “Whereas topological matter is already well understood at the level of conventional, single-particle band theory, almost nothing is known on many-body effects in these materials. This is a challenge and a dream for a condensed-matter theoretician, to work in this field in collaboration with our colleague experimentalists.”

Consortium

The consortium members are: Erik van Heumen and Anne de Visser (Institute of Physics, University of Amsterdam), Alexander Brinkman and Chuan Li (MESA+ Institute for Nanotechnology, University of Twente), Andrea Caviglia (Kavli Institute of Nanoscience, Delft University of Technology), Nigel Hussey and Steffen Wiedmann (HFML-FELIX), Misha Katsnelson and Alexander Khajetoorians (IMM), Cristiane Morais Smith (Institute for Theoretical Physics, University of Utrecht) and Jianting Ye (Zernike Institute for Advanced Materials, University of Groningen).

Dr. Steffen Wiedmann,
Assistant Professor Semiconductor & Nanostructures at the HFML. His research focuses on the investigation and tunability of topological matter by means of electrical and thermal transport.

Prof. Nigel Hussey,
Professor of Correlated Electron Systems at HFML. His research focus is the electrical and thermal transport properties of low dimensional metals, strange metals, and unconventional superconductors.

Prof. Alexander Khajetoorians, 
Professor of Scanning Probe Microscopy at the IMM. His research focus is on studying magnetism, lower dimensional electronic structure, and superconductivity with scanning probe microscopy techniques.

Prof. Mikhail Katsnelson,
Professor of Theory of Condensed Matter at the IMM. His main research interests  are on two-dimensional materials, theory of magnetism, strongly correlated systems and quantum many-body theory in general.

NWO GROOT

The grants of NWO GROOT are intended for consortia in which research groups use collaboration (coordinated consolidation of strengths and areas of expertise) to create added value. An outstanding track record and the quality of the scientific results achieved by the applicant(s) are important criteria in assessing the proposals submitted. The GROOT grant gives researchers the opportunity and freedom to strengthen and/or expand excellent, challenging and innovative lines of research.

More information

Steffen Wiedmann
Nigel Hussey
Mikhail Katsnelson
Alexander Khajetoorians