Dr. Urs Staub

Urs Staub

Group Leader Microscopy and Magnetism
and Scientist (RESOXS)

Paul Scherrer Institute
Forschungsstrasse 111
5232 Villigen PSI
Switzerland

Biography

Urs Staub is the leader of the Microscopy and Magnetism group that is part of the Condensed Matter Laboratory within the Photon Science division. He studied physics at the ETH in Zürich, and made his PhD in the Laboratory for Neutron Scattering at ETH/PSI in the field of rare earth magnetism in cuprate superconductors. He received a fellowship from the Swiss National Science Foundations for postdoctoral research studies in the f-electron chemistry group at the Argonne National Laboratory in the US. There he complemented is expertise in neutron scattering with synchrotron based x-ray diffraction and x-ray absorption. He then returned to PSI to the neutron group, where a after short period of time he then moved to the Swiss Light Source Project, which was later funded and realized. He obtained soon after a staff scientist position. Later he took over Microscopy and Magnetism group. At the SLS he built a resonant soft x-ray scattering endstation for which he pioneered polarization analysis and powder diffraction using resonant soft x-ray scattering. He has been a member of several proposal review panels and advised several funding agencies for funding proposals including early stage Sonderforschungsgesuche from the Deutsche Forschungsgemeinschaft. He also is a member of the Scientific Advisory Committee of the synchrotron SOLEIL and had been/is a member of several national competence center for research of the Swiss National Science Foundations as well as in the board of several scientific organization such as the Swiss Physical Society and the Swiss Society for Photon Science.

Institutional Responsibilities

Urs Staub is head of the Magnetism and Microscopy in the Laboratory of Condensed Matter in the Photon Science Division. The Group consists of three independent sub-groups which perform research in the area of condensed matter and operates the X-Treme and SIM beamline including the RESOXS endstation at the SLS. As group leader, Urs Staub is responsible for the leadership and for budget and the development strategies of the group and their members and the operated beamlines. He is also responsible for the operation of the RESOXS endstation.

Scientific Research

Urs Staub’s scientific research is currently focused on fundamental questions on the interplay of the crystal structure with the electronic and magnetic properties of advanced materials. One particular strong research area is concerned with the ultrafast dynamics of spins, electrons, orbitals and their carriers, the atoms. His particular interest is the study of mechanisms of switching domains and its fundamental speed limits, understanding novel emergent states in equilibrium and in the time domain (excited state) and how ultrafast structural electronic and magnetic phase transitions can occur. In particular, he uses ultrashort x-ray pulses created from x-ray free electron lasers for his research, looking into ultrafast dynamics that is on the forefront of the field. In addition, his interest is in coherently driving fundamental excitations in a solid, which allow him to disentangle the different couplings between the charge, spin and lattice in real time. In equilibrium physics, he mainly is interested in looking into non-standard ways to drive polarization or magnetization, e.g. drive magnetization by electric fields or polarization by magnetic fields and look into very fundamental quantum problems such as magnetic monopoles, magneto-electric quadrupoles or toroidal moments and finding ways to quantify their effects and role in advanced materials using various x-ray techniques.

Selected Publications

For an extensive overview we kindly refer you to our publication repository DORA (includes publications since joining PSI). A complete list of publications can be found on: /media/57814/edit

ORBITAL DYNAMICS DURING AN ULTRAFAST INSULATOR TO METAL
TRANSITION

Sergii Parchenko, Eugenio Paris, Daniel McNally Elsa Abreu, Markus Dantz, Elisabeth M. Bothschafter, Alexander H. Reid, William F. Schlotter, Ming-Fu Lin Scott F. Wandel, Giacomo, Coslovich, Sioan Zohar Georgi L. Dakovski, J. J. Turner, S. Moeller Yi Tseng, Milan Radovic, Conny Saathe Marcus Agaaker, Joseph E. Nordgren, Stephen L. Johnson, Thorsten Schmitt and Urs Staub, Phys. Rev. Research, 2, 023110 (2020).

This is the first soft x-ray resonant x-ray scattering study that directly accesses the changes in the orbital reconstruction of an ultrafast insulator-metal transition. It investigates the transient changes of a d-d (orbital) excitation in V2O3 after photo excitation. The experiments are based on ultrashort x-ray pulses from an XFEL.

 

FIELD-INDUCED DOUBLE SPIN SPIRAL IN A FRUSTRATED CHIRAL MAGNET

Mahesh Ramakrishnan, Evan Constable, Andres Cano, Maxim Mostovoy, Jonathan S. White, Namrata Gurung, Enrico Schierle, Sophie de Brion, Claire V. Colin, Frederic Gay, Pascal Lejay, Eric Ressouche, Eugen Weschke, Valerio Scagnoli, Rafik Ballou, Virginie Simonet and Urs Staub, NPJ Quantum Materials 4 60 (2019).

Here we combine resonant soft x-ray diffraction with neutron diffraction and small angle neutron scattering to investigate the magnetic field dependence of the magnetic order in a doubly chiral frustrated magnet that is also multiferroic. We find a phase transition that creates and additional polarization, which leads to an enhancement or reversal of the polarization depending on the choice of enantiomer of the chiral crystal. We can pin this change to the occurrence of an additional long wavelength magnetic ordering in the spin system. The theoretical considerations show that these langasite would have all the ingredients for the occurrence of Skyrmions on an antiferromagnetic background.  

 

Terahertz-driven phonon upconversion in SrTiO3

M. Kozina, M. Fechner, P. Marsik, T. van Driel, J. M. Glownia, C. Bernhard, M. Radovic,

D. Zhu, S. Bonetti, U. Staub and M. C. Hoffmann, Nature Phys. 15, 387 (2019).

In this work we drive the polar soft mode in SrTiO3 with a direct THz excitation far into the non-linear regime, which results in the excitation of higher lying phonon modes ()phonon up conversion) through non-linear phonon-phonon couplings. We use ultra-short x-ray pulses from an XFEL to study the atomic motions in real time, allowing us to quantify the atomic motions, which represents a significant time dependent polar distortion compared to the ferroelectric distortion related perovskites.

 

The ultrafast Einstein–de Haas effect

C. Dornes, Y. Acremann, M. Savoini, M. Kubli, M. J. Neugebauer, E. Abreu, L. Huber, G. Lantz, C. A. F. Vaz, H. Lemke, E. M. Bothschafter, M. Porer, V. Esposito, L. Rettig, M. Buzzi, A. Alberca, Y. W. Windsor, P. Beaud, U. Staub, Diling Zhu, Sanghoon Song, J. M. Glownia & S. L. Johnson,  Nature 565, 209 (2019).

Here, we are able to show how fast momentum from a ferromagnetic align spin system can be transferred to the lattice when the ferromagnet is excited by an ultrashort laser pulse. The momentum transfer of a laser excitation im an Fe film creates an acoustic shear wave that is followed with real time using ultrafast x-ray diffraction on an XFEL. The results show that 80% of the momentum is transfer to the lattice within 200 fs.

 

Ultrafast relaxation dynamics of the antiferrodistortive phase in Ca doped SrTiO3

M. Porer, M. Fechner, E. Bothschafter, L. Rettig, M. Savoini, V. Esposito, J. Rittmann, M. Kubli, M. J. Neugebauer, E. Abreu, T. Kubacka, T. Huber, G. Lantz, S. Parchenko, S. Grübel, A. Paarmann, Noack, P. Beaud, G. Ingold, U. Aschauer, S. L. Johnson, and U. Staub,  Phys. Rev. Lett.  121, 055701 (2018).

This work shows that the soft mode driven 2nd order octahedral-rotation transition in SrTiO3 can be induced on ultrafast time scale through an optical excitation. This effect can be described by ultrafast hole doping that relaxes the chemical potential and rotates the octahedra to a straight alignment, close to the cubic high temperature phase. The ultrafast octahedral rotation has been determined by ultrafast x-ray diffraction, performed at the FEMTO slicing source of the SLS.

 

NONLINEAR ELECTRON-PHONON COUPLING IN DOPED MANGANITES

V. Esposito, M. Fechner, R. Mankowsky, H. Lemke, M. Chollet, J.M. Glownia, M. Nakamura, M. Kawasaki, Y. Tokura, U. Staub, P. Beaud, and M. Först, Phys. Rev. Lett. 118, 247601 (2017).

Here we show that driving the phononic subsystem in half doped manganite’s does not induce the metal-insulator transition due a scheme of non-linear phononics. When driving the IR active mode by midIR excitation, the gap closes directly through a non-linear electron phonon coupling. Experiments have used ultrafast resonant hard x-ray diffraction to study the dynamics of the orbital and charge order suppression at an XFEL.

 

Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho

L. Rettig, C. Dornes, N. Thielemann-Kühn, N. Pontius, H. Zabel, D. L. Schlagel, T. A. Lograsso, M. Chollet, A. Robert, M. Sikorski, S. Song, J. M. Glownia, C. Schüßler-Langeheine, S. L. Johnson, and U. Staub, Phys. Rev. Lett. 116, 257202 (2016).

In this study, we have disentangled how fast the antiferromagnetic order in the 4f and 5d shell of elemental Ho is suppressed by an optical excitation. It is shown that the both magnetic shells, the 5d shell, which is responsible for the magnetic exchange interaction, and the localized 4f shell, have the same sublattice demagnetization timescale, indicative for a strong correlation between the two shells, which is very different compared to Gd metal. Though the suppression of the sublattice magnetization of both shells is very fast, the changes in the spiral length is rather slow.