Dr. Jan Gui-Hyon Dreiser

Jan Dreiser is a staff scientist at the Swiss Light Source. After obtaining his Vordiplom in physics from the Technische Universität München (Germany) and a Diplôme d'Etudes Approfondies (MSc equivalent) in physics from the Université Joseph Fourier, Grenoble (France) he was awarded his PhD from ETH Zürich (Switzerland) in 2007 on the laser spectroscopy of single spins in individual semiconductor quantum dots. Afterwards he worked as a postdoctoral research follow at the Universität Freiburg (Germany), where he started working on molecular magnetism, and at the Paul Scherrer Institut. He was awarded a SNF Ambizione grant, which was hosted at the EPF Lausanne with PSI as a co-host. During this time he started working on the surface deposition of molecular magnets in the framework of molecular spintronics, which is still his main area of scientific activity.

The operation and the development of the X-Treme beam line, which is specialized in soft X-ray magnetic circular dichroism at high magnetic fields and low temperatures, and which includes an in-situ sample preparation chamber and a scanning tunneling microscope. Furthermore, planning and development of the beam line in view of the upcoming SLS upgrade. Local organizer of the PSI part of the European HERCULES school for PhD students and Postdocs from 2018-2020. Member of beam time proposal selection and scientific expert group panels.

Our main research activities are in the field of (molecular) spintronics and surface science employing molecular magnets, nanoparticles as well as magnetic 2D materials.  Here, we are pursuing ideas to develop suitable material stacks, nanostructures and techniques to enable quantum information processing and ultra high density data storage devices. Specifically, in this regard we are interested in what factors govern the longitudinal relaxation and transverse (coherence) times of spins in engineered nanostructures and layered molecule-inorganic stacks. Further, we are investigating optically addressable materials, in which its electronic and/or magnetic states can be manipulated and/or read out by UV/visible/NIR light irradiation.

We use a number of experimental techniques with a focus on X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and scannning tunneling microscopy (STM). Furthermore, we use or have used SQUID magnetometry, high-resolution laser spectroscopy (optical/near infrared), inelastic neutron scattering, (THz-)electron paramagnetic resonance. 

The full publication list can be downloaded HERE. Jan Dreiser's publications in the DORA-PSI repository can be found HERE.

Understanding the Superior Stability of Single-Molecule Magnets on an Oxide Film  M. Studniarek, C. Wäckerlin, A. Singha, R. Baltic, K. Diller, F. Donati, S. Rusponi, H. Brune, Y. Lan, S. Klyatskaya, M. Ruben, A.P. Seitsonen, J. Dreiser, Advanced Science 6, 1901736 (2019). Single-molecule magnets exhibit magnetic bi-stability up to a system specific blocking temperature. They are attractive candidates for ultra-high density magnetic data storage because of their nanometric size, their sublimability and the possibility of chemical functionalization and directed self-assembly on surfaces. In this publication we identify the main magnetic relaxation mechanisms of LnPc₂ single-molecule magnets adsorbed on magnesium oxide films. In relation to these results, we show in [Giant Hysteresis of Single-Molecule Magnets Adsorbed on a Nonmagnetic Insulator  C. Wäckerlin, F. Donati, A. Singha, R. Baltic, S. Rusponi, K. Diller, F. Patthey, M. Pivetta, Y. Lan, S. Klyatskaya, M. Ruben, H. Brune, J. Dreiser, Adv. Mat. 28, 5195-5199 (2016)]  that the insertion of few monolayers thick magnesium oxide films can have a tremendous stabilization effect in reducing the fluctuations of the magnetic moment. This leads to a magnetic hysteresis opening of up to 3 Tesla at 3 Kelvin which is the current record for any surface deposited single-molecule magnet. Important classes of single-molecule magnets containing a single lanthanide ion have been highlighted in the review article [Molecular Lanthanide Single-Ion Magnets: From Bulk to Submonolayers  J. Dreiser, J. Phys.: Condens. Matter 27, 183203 (2015)].

Direct Observation of Charge Transfer and Magnetism in Fe₄Co₄ Cyanide-Bridged Molecular Cubes  N. Daffé, J.-R. Jiménez, M. Studniarek, A. Benchohra, M.-A. Arrio, R. Lescouëzec, J. Dreiser, Journal of Physical Chemistry Letters 10, 1799 (2019). This optically switchable material belongs to the group of molecular Prussian blue analogues. Here a inter-metal charge transfer triggered by light gives rise to paramagnetic moment, which is present in a long-lived metastable state. Here we observe directly by X-ray absorption spectroscopy and X-ray magnetic circular dichroism the changes of the electronic and magnetic structure before and after the irradiation.

Engineering On-Surface Spin Crossover: Spin-State Switching in a Self-Assembled Film of Vacuum Sublimable Functional Molecule  K.S. Kumar, M. Studniarek, B. Heinrich, J. Arabski, G. Schmerber, M. Bowen, S. Boukari, E. Beaurepaire, J. Dreiser, M. Ruben, Advanced Materials, 30, 1705416 (2018). Spin crossover molecules exhibit a temperature dependent spin transition, which gives rise to paramagnetic and diamagnetic behavior above and below a crossover temperature, respectively. In this publication we were able to show that by suitable functionalization the molecules can be organized in a lamellar structure which keeps the spin crossover properties in few layers of the lamellar assemblies organized in double layers.

Magnetic Remanence in Single Atoms  F. Donati, S. Rusponi, S. Stepanow, C. Wäckerlin, A. Singha, L. Persichetti, R. Baltic, K. Diller, F. Patthey, E. Fernandes, J. Dreiser, Z. Sljivancanin, K. Kummer, C. Nistor, P. Gambardella, H. Brune, Science 352, 318-321 (2016). Similar to single-molecule magnets, single-atom magnets allow the storage of information in the magnetization state of a single metal ion. The challenge is to find systems that are stable, i.e., keep their magnetic moment for a sufficiently long time at room temperature. In this breakthrough experiment we could show that individual holmium atoms supported on ultrathin magnesium oxide films grown on Ag(100) substrates show long magnetic relaxation times even at temperatures up to 30 K. 

Three-Axis Anisotropic Exchange Coupling in the Single-Molecule Magnets (NEt₄)[Mn^III₂(5-Brsalen)₂(MeOH)₂M^III(CN)₆], M = Ru, Os  J. Dreiser, K. S. Pedersen, A. Schnegg, K. Holldack, J. Nehrkorn, M. Sigrist, P. Tregenna-Piggott, H. Mutka, H. Weihe, V. S. Mironov, J. Bendix, O. Waldmann, Chem. Eur. J. 19, 3693 (2013). In the trinuclear Mn(III)-M-Mn(III) single-molecule magnet incorporating M = Ru(III), Os(III) the metal ions are bridged by cyanide ligands. Our study using a combination of frequency domain Fourier transform (FD-FT) THz-EPR, inelastic neutron scattering (INS) and SQUID measurements yields deep insight into the Mn-M exchange coupling. It reveals that the exchange coupling can be described by a three-axis anisotropic J matrix with Jxx, Jyy, Jzz on its diagonal. The values of the exchange parameters depend on the bending angle of the cyanide bridged metal-metal units. These results are important for the future synthesis of single-molecule magnets containing heavy transition metal ions.

Observation of Faraday Rotation from a Single Confined Spin  M. Atatüre, J. Dreiser (Equal contribution with M. Atatüre), A. Badolato, A. Imamoğlu, Nature Physics 3, 101 (2007). The spin of a single electron trapped in a InGaAs semiconductor quantum dot can be optically addressed which enabled the controlled manipulation of the spin degrees of freedom. Here we demonstrate the feasibility of reading the single spin using the Faraday rotation effect, in which the narrow-band readout laser is far detuned from the main resonant optical transitions. This scheme is particularly useful to avoid optical spin-pumping effects, which are interesting for the spin state preparation but which are unwanted for a pure readout of the spin state.

Optical Control of Quantum Dot-Spin States (Book Chapter),  M. Atatüre, J. Dreiser, A. Badolato, A. Imamoğlu, Semiconductor Quantum Bits, Edited by O. Benson and F. Henneberger, World Scientific Publishing Co. (2008).