News

News

Knobs control Dirac energy in topological insulators

Four knobs - bulk stoichiometry, surface decoration, temperature, and photon exposure - are shown to control the energy of Dirac surface states in topological insulators, and can be used to determine the true 'flat band' energy band alignment at the surface of binary, ternary or quaternary 3D TI's.

Four different knobs can be used to control the Dirac energy in topological insulators, in this way one can tune the surface electronic structure of 3D TI's. This work is just out in PRB.


Top: the surfaces of all five TI's are n-type after band bending. Bottom: using the illumination 'knob', flat band conditions are restored and the true Fermi level position emerges.

Top: the surfaces of all five TI's are n-type after band bending.
Bottom: using the illumination 'knob', flat band conditions are restored and the true Fermi level position emerges.

 


Interfacing 3D topological insulator BSTS with Ag, Fe and Nb published in PRB

PRB now out on the electronic structure of interfaces between the bulk insulating 3D topological insulator BSTS and a commonly used contact metal (Ag), a magnetic metal (Fe) and a superconductor (Nb) metal on the bulk TI BSTS.

Interfacing 3D topological insulator BSTS. Nick de Jong's paper is now out in PRB on the electronic structure of interfaces between the bulk insulating 3D topological insulator BSTS and a commonly used contact metal (Ag), a magnetic metal (Fe) and a superconductor (Nb) metal on the bulk TI BSTS.

Binding energy of the Dirac point in BSTS for deposition of Ag, Fe and Nb at 40K. First n-type and then p-type behaviour is seen.

Binding energy of the Dirac point in BSTS for deposition of Ag, Fe and Nb at 40K. First n-type and then p-type behaviour is seen.


Nick found that for all coverages at room temperature and <0.2 ML coverages at 40K that all three metals shift the chemical potential up, increasing the binding energy of the Dirac point. For deposition and measurement at low T, after the initial increase in Dirac point binding energy (upward shift of chemical potential, donor behaviour of the metal overlayer), the behaviour reverses and the chemical potential them moves downward, reducing the Dirac point energy (acceptor behaviour of the metals). For silver this switch goes together with formation of substitutional defects (AgTe,Se), but for the less mobile Fe and Nb it is linked to clustering of the adatoms on the surface.


Pick up the paper in the publications section of the webpage, or click here.

The experiments were carried at the 1^2 end-station at BESSY-II/HZB in Berlin.


This research is part of the FOM/NWO-N Programme 134 'Topological Insulators', which combines the forces of groups from Leiden, Delft, Amsterdam & Twente, and is led by the Mark Golden in Amsterdam.

 

 


Archive

Postdoc position: materials physics & crystal growth of 3D topological insulators

Opening for a postdoc (2 years) on materials physics & crystal growth of 3D topological insulators, working within the Dutch national research programme on TI's. For this position the focus is on the development of new topological systems, topological superconductors and related materials. Recruitment window now closing.....

TI PD MatPhys xtal


Research background

The Netherlands has a FOM-funded, national research programme on Topological Insulators, co-ordinated out of Amsterdam (programme leader, Mark Golden) with project leaders Alexander Brinkman (Twente), Leo Kouwenhoven (Delft), Carlo Beenakker (Leiden), Jan Zaanen (Leiden) and Kareljan Schoutens (Amsterdam).

The primary aims of the FOM Topological Insulators programme are to create, investigate and control the novel electronic, magnetic and superconducting properties arising from topologically protected states in 2D and in particular 3D insulating systems.

This TI field is globally one of great dynamism, with the unique properties of topological insulators seen to make these systems promising candidate materials for spintronic applications and even for topological quantum information processing.

The Amsterdam QMat group (Prof. Mark S. Golden, Dr. Anne de Visser, Dr. Erik van Heumen, Dr. Yingkai Huang) has been making excellent progress in the generation of truly bulk-insulating 3D topological insulators in the Bi,Sb,Te,Se-family of materials and a lively collaboration has been set up with the group at Twente on interfacing these materials with superconductors and building devices for nanotransport experiments. In house, the Amsterdam team is also growing potential topological superconductors based on metal-intercalated Bi2Se3 and half-Heusler systems, and is using high-resolution angle-resolved photoemission spectroscopy and low-T STM/STS to study the electronic (surface) states of all these topological materials in k- and real space, as well as conducting (magneto)transport investigations of the same systems.


Job description

This two-year postdoc research associate (PDRA) position is ideal for an experienced and ambitious physicist with clear interest and experience in materials or a materials scientist with a keen interest in physics. There are many avenues still open to explore in both the bulk synthesis/growth of these materials and in their spectroscopic and transport investigation, with - for example - potential Weyl fermion systems being a topic of current interest. Fully equipped laboratories for materials preparation and single crystal growth (Czochralski, Bridgeman, TSFZ-optical furnaces) are the main tools at the disposal of the PDRA, as are physical characterization tools such as X-ray diffraction (powder and Laue) and a new PPMS set-up for measuring key transport parameters of the crystals grown. Dr. Huang provides the day to day leadership of the crystal growth effort, and has many years experience of top-level crystal growth of intermetallics (heavy fermions, U-compounds, Fe pnictides, magnetocaloric systems, topological insulators) and oxides (cuprates, manganites, etc.).

Prior experience of (solid state) materials preparation is a precondition, and experience of crystal growth is an advantage. Given appropriate experience, inclination and speedy success in the crystal growth, participation in other activities here in Amsterdam (FT-STS, ARPES, synchrotron based work, mK and high field transport) is also possible.


Location

The QMat group is part of the Van der Waals-Zeeman Institute, itself a division of the IoP at the University of Amsterdam. The group's research focuses on the experimental investigation of the electronic structure and properties of quantum matter and emergent materials. The systems we work on are at the forefront of fundamental solid state physics research, but also possess potential for eventual application in future technologies connected to energy (superconductors), spintronics (topological insulators, magnetoresistive systems) and nanoscience (1D systems, oxide heterointerfaces).

The IoP is situated in new, purpose-built laboratories and teaching space in the building of the Faculty of Science of the University of Amsterdam in the Science Park Amsterdam. This location also plays host to numerous national research institutes such as AMOLF (nanophotonics, biomolecular systems, photovoltaics), NIKHEF (Subatomic Physics) and CWI (mathematics and Computer Science), as well as ARCNL (Advanced Research Center for Nanolithography, which combines the leading Dutch tech firm ASML with both Amsterdam universities and AMOLF).


Requirements

PhD in solid state/materials physics, material science or solid state chemistry. Prior experience of solid state materials synthesis and interest in crystal growth.


Conditions of employment

You will be employed by the FOM-foundation for a fixed period of two years.
Your salary will be up to a maximum of 3,922 euro gross per month, depending on your level of experience. The salary is supplemented with a holiday allowance of 8% and an end-of-year bonus of 8.33%.

The conditions of employment of the FOM-foundation are laid down in the Collective Labour Agreement for Research Centres (Cao-Onderzoekinstellingen), more exclusive information is available at this website under Personeelsinformatie (in Dutch) or under Personnel (in English).
General information about working at FOM can be found in the English part of this website under Personnel. The 'FOM job interview code' applies to this position.


Applications

The applications window on the FOM webpage for this position has closed. We are currently going through the applications. If you still want to try and squeeze an application in - then hurry!. Send the following to me via email:

A cv, list of publications, contact coordinates of at least three references and a motivation as to why you candidate wish to join the group to do this project (maximum one A4). Applications without this motivation statement will not be considered, but those including this will get our full attention.

All documents should be in the form of .pdf files, no .doc or .docx, please (we won't open them).


Contact
Prof.dr. Mark S. Golden
Van der Waals-Zeeman Institute
IoP
University of Amsterdam
M.S.Golden-at-uva.nl


PhD position: spectroscopy of 2-dimensional electron systems in complex oxides

Opening for a PhD researcher working within the Dutch national research programme on oxide heterointerfaces. For this position, the focus is on the experimental investigation of the electronic structure and magnetic properties of complex oxide thin films and their heterointerfaces. Recruitment window now closing.....

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Research background

In the last few years, great progress has been achieved in the creation and fundamental exploration of unconventional 2-dimensional electron systems at interfaces between complex oxides. The iconic example of this highly active and global research field is the emergence of an interacting, 2D electron gases (2-DEGs) - which are metallic and also displays both magnetism and superconductivity - at the interface between the two insulating materials SrTiO3 and LaAlO3. The inherent richness of the physics of transition metal oxides means that given tailoring and effective external control of their transport and magnetism, these systems are front runners for the development of a future oxide electronics technology.

Dutch physics plays a leading role in this field, and recently a FOM-funded, national research programme on '2-dimensional electron systems in complex oxides', co-ordinated by Hans Hilgenkamp (MESA+, University of Twente) has been launched. This programme bundles a number of globally visible Dutch groups whose research spans activities from thin film growth and generation of (nano)devices (Twente, Delft, Leiden), through transport (Twente, Nijmegen, Delft) and high-field mangetotransport (Nijmegen) to spectroscopy and microscopy (Amsterdam, Leiden). The broad coverage this consortium enables, plus the excellent track record of the groups involved, mean this Dutch programme is one of the major players in the global research scene into complex oxide 2-DEGs.

The focus of this new programme - which builds on the success of an earlier complex oxide heterointerface FOM-programme ('InterPhase') - is on tailoring the electronic and magnetic properties of complex oxide thin films, generating novel materials combinations and employing advanced device structures.

Within this national programme, the Amsterdam group:

  • Mark S. Golden, full professor
  • Hermann A. Dürr, adjunct professor in Amsterdam; HAD's main position is at the SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC (Menlo Park, California)
  • Erik van Heumen, assistant professor, leader of the optics lab

is responsible for using state-of-the-art electron and X-ray spectroscopies to investigate the electronic structure and magnetism in 2D complex oxide systems and their (hetero)interfaces. We are recruiting for a highly motivated and talented physicist to join our team as a PhD researcher, who will grow into the driver's seat of Dutch spectroscopic research into complex oxide 2-DEG systems.


Job description

This PhD researcher's work will focus on the experimental investigation of the electronic structure and magnetic properties of complex oxide thin films and their heterointerfaces. (S)he will become expert in the use of state-of-the art electron spectroscopic and soft (and hard) X-ray techniques that give a direct window on the electronic states of the 2-DEGs. Through close collaboration with the thin film synthesis team and with the other programme partners also investigating the very same samples, the research of the PhD candidate can contribute to breakthroughs in our understanding of how to tailor and tune the properties of these promising systems, and how efficient switching of heterointerface devices can pave the way to the era of oxide electronics.

The research will mainly involve angle-resolved photoemission spectroscopy (ARPES), high-resolution core level spectroscopy (using both hard and soft X-rays), as well as resonant and dichroic X-ray absorption and scattering techniques. This project calls for a young scientist with a passion for physics, a desire to be involved in cutting-edge research in a globally fast moving and competitive field and someone keen to pick up and master complex experiments, also in the context of international large-scale facilities (light sources).

Armed with a collaborative, communicative and open mind-set, the PhD researcher will be able make the most of the excellent opportunities for joint research with the other partners of the Dutch national programme on this topic, and the same characteristics will also ensure rapid crystallisation of an effective 'complex oxide team', together with a postdoc we are about to recruit for, also funded from the same FOM-programme.

The Amsterdam lab has first rate facilities for ARPES, core level photoemission, scanning tunnelling microscopy & spectroscopy, as well as optical spectroscopy, and all of these experiments are part of the plans within the complex oxide programme. Samples of the highest quality are grown in Twente and are transported to the Amsterdam (or light source) labs using a purpose-built 'UHV-suitcase', so enabling surface sensitive experiments and the determination of the true ground state properties of the thin film systems, without the distorting effects of air exposure/water adsorption, etc.. Experiments will also take place at leading light sources within Europe (e.g. BESSY-II at the Helmholtz Center Berlin or PETRA III at DESY in Hamburg), and the link to Prof. Dürr's group at SLAC will facilitate advanced X-ray imaging experiments at the SSRL (SLAC) and possibly also lead to success in gaining access to the unique X-ray laser LCLS (SLAC). All these activities bring the added advantage of hands-on experience of working at international large scale user facilities, and the huge international network this brings with it.


Location

Measured on citation impact, Dutch physics research is among the very best in the world. The FOM-PhD position will be hosted by QMat Amsterdam, the hard condensed matter research cluster within the Van der Waals-Zeeman Institute, a division of the IoP at the University of Amsterdam. The group's research focuses on the experimental investigation of the electronic structure and properties of quantum matter and emergent materials. The systems we work on are at the forefront of fundamental solid state physics research, but also possess potential for eventual application in future technologies connected to energy (superconductors), spintronics (topological insulators, magnetoresistive systems) and nanoscience (1D systems, oxide heterointerfaces).

The IoP is situated in new, purpose-built labs in the Science Park campus that houses the Faculty of Science of the University of Amsterdam. The Science Park also plays host to numerous national research institutes such as AMOLF (nanophotonics, biomolecular systems, photovoltaics), NIKHEF (Subatomic Physics) and CWI (mathematics and Computer Science), and so the day-to-day environment of the PhD researcher is a dynamic and globally extremely well connected centre for science research. Amsterdam itself is an intellectually vibrant, creative, multicultural and internationally-oriented city of great beauty, and forms an ideal and safe backdrop for a young PhD researcher's transition to become a full-blooded researcher and expert in experimental physics. As mentioned already, regular trips to synchrotron light sources in Europe (and also in the US) will be an integral part of this research job.

Once per quarter, the whole FOM-programme community ('2-dimensional electron systems in complex oxides') meets to share ideas and data, and to set the points for future collaborative research. This means the other PhD and postdoc researchers (with their supervisors) forms an important, additional community in which the PhD researcher will operate and grow.


Requirements

M.Sc. in physics (experiment or theory) or from a physics-heavy chemistry or materials programme is required. Applicants with a degree in chemistry or materials science are also requested to detail their affinity with condensed matter physics and motivation for pursuing a Ph.D in experimental physics.

Other skills/experiences/documents that would benefit the application are:

  • previous laboratory experience using a form of spectroscopy;
  • working knowledge of a programming language (python, C++ or equivalent);
  • good knowledge of theoretical condensed matter physics;
  • very good English oral and written communication skills;
  • scientific publications and/or a reference letter from MSc. thesis advisor

Conditions of employment

When fulfilling a PhD position at the FOM foundation, you will get the status of junior scientist.
You will have an employee status and can participate in all the employee benefits FOM offers. You will get a contract for 4 years. Your salary will be up to a maximum of 2,718 euro gross per month.The salary is supplemented with a holiday allowance of 8% and an end-of-year bonus of 8.33%.
You are supposed to have a thesis finished at the end of your four year term with FOM.
A training programme is part of the agreement. You and your supervisor will make up a plan for the additional education and supervising that you specifically need. This plan also defines which teaching activities you will be responsible (up to a maximum of 10% of your time). The conditions of employment of the FOM-foundation are laid down in the Collective Labour Agreement for Research Centres (Cao-Onderzoekinstellingen), more exclusive information is available at this website under Personeelsinformatie (in Dutch) or under Personnel (in English).
General information about working at FOM can be found in the English part of this website under Personnel. The 'FOM job interview code' applies to this position.


Applications

The applications window on the FOM webpage for this position has closed. We are currently going through the applications. If you still want to try and squeeze an application in - then hurry!. Send the following to me via email:

A cv, list of publications, contact coordinates of at least three references and a motivation as to why you candidate wish to join the group to do this project (maximum one A4). Applications without this motivation statement will not be considered, but those including this will get our full attention.

All documents should be in the form of .pdf files, no .doc or .docx, please (we won't open them).


Contact
Prof.dr. Mark S. Golden
Van der Waals-Zeeman Institute
IoP
University of Amsterdam
M.S.Golden-at-uva.nl