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Welcome to the SwissFEL Bernina Group

The Bernina group works on experimental studies of beyond-equilirium ultrafast phenomena in condensed matter. It develops and operates the Bernina Instrument of SwissFEL, which is presently under commissioning and performing first experiments. The group arises from the FEMTO group at the Swiss Light Source.

Scientific Highlights

18. September 2018

Bernina status first summer shutdown

The summer shutdown was used to install more missing hardware. With the new components the Bernina instrument will be already very close to the full design capabilities when the exciting time of user experiments will begin in 2019.

5. September 2018

Figure 1 (a) Transient relative x-ray intensity of the (1.5 0.5 0.5) superlattice reflection of Sr0.97Ca0.03TiO3 upon above bandgap excitation with 40 fs pulses Inset: STO crystal structure as seen along the c-axis. phi measures the antiferrodistortive rotation of the oxygen octahedra (exaggerated) and represents the order parameter. (b) Calculated energy change per STO cubic unit cell as a function of oxygen displacement u/u0 along the in-plane cubic crystal axes resulting from the octahedral rotation at …

Moving Atoms by Photodoping

Understanding how and how fast we can drive atoms to create a structural phase transition is of fundamental interest as it directly relates to many processes in nature. Here we show that a photoexcitation can drive a purely structural phase transition before the energy is relaxed in the material that corresponds to a “warmer” equilibrated state.

20. Juni 2018

Regisseure mit Zusatzaufgaben

SwissFEL Speicher Grossforschungsanlagen

Datenspeicher aus neuartigen Materialien sollen ermöglichen, Informationen auf kleinerem Raum viel schneller und energiesparender als bisher aufzuzeichnen. Filmaufnahmen mit dem Röntgenlaser zeigen, was im Inneren möglicher neuer Speichermedien passiert und wie sich die Prozesse, bei denen das Material zwischen zwei Zuständen wechselt, optimieren lassen.

6. April 2018

A first glance at the SwissFEL x-rays wave-front

X-ray Free Electron Lasers (XFELs) combine the properties of synchrotron radiation (short wavelengths) and laser radiation (high lateral coherence, ultrashort pulse durations). These outstanding machines allow to study ultra-fast phenomena at an atomic level with unprecedented temporal resolution for answering the most intriguing open questions in biology, chemistry and physics.

31. Januar 2018

Photoinduced transitions in magnetoresistive manganites: A comprehensive view

Using the FEMTO slicing source at SLS, we have studied the structural response during the photoinduced transition in a charge-ordered Pr_1-xCa_xMnO₃ thin films. By investigating the dynamics of both superlattice reflections and regular Bragg peaks, we disentangle the different structural contributions and analyze their relevant time-scales. Comparing these results with studies of the charge order and magnetic dynamics, a comprehensive picture of the phase transition linked to a single critical fluence f_c is proposed.

30. November 2017

First time resolved Pilot Experiment by SwissFEL: Semiconductor to metal transition in Ti₃O₅ nanocrystals

On the 30th of November 2017 SwissFEL saw its first time resolved pilot experiment in the Bernina experimental station of the SwissFEL ARAMIS beamline. A team of scientists from the University of Rennes, ESRF and PSI, led by Marco Cammarata (Univ. Rennes) and Henrik Lemke (PSI), successfully started the experimental phase at SwissFEL. The goal was to study the picosecond dynamics of a light-induced phase transition from a semiconductor to metallic crystal structure in a Titanium Oxide (D).

29. November 2017

Coupling between a Charge Density Wave and Magnetism in an Heusler Material

The prototypical magnetic memory shape alloy Ni2MnGa undergoes various phase transitions as a function of the temperature, pressure, and doping. In the low-temperature phases below 260 K, an incommensurate structural modulation occurs along the [110] direction which is thought to arise from the softening of a phonon mode. It is not at present clear how this phenomenon is related, if at all, to the magnetic memory effect. Here we report time-resolved measurements which track both the structural and magnetic components of the phase transition from the modulated cubic phase as it is brought into the high-symmetry phase.

15. Juni 2017

Nonlinear electron-phonon coupling in doped manganites

We employ time-resolved resonant x-ray diffraction to study the insulator-to-metal transition that is launched via resonant excitation of an infrared-active optical phonon mode in a half doped manganite. We find that the charge order reduces promptly with a highly nonlinear (quartic) dependence on excitation fluence.

22. März 2017

Ultrafast formation of a charge density wave state in 1T-TaS₂: observation at nanometer scales using time-resolved X-ray diffraction

Femtosecond time-resolved x-ray diffraction is used to study a photoinduced phase transition between two charge density wave (CDW) states in 1T-TaS₂, namely the nearly commensurate (NC) and the incommensurate (I) CDW states. Structural modulations associated with the NC-CDW order are found to disappear within 400 fs.

Contact

Bernina Group
OVGA/320
5232 Villigen PSI
Switzerland

Henrik Lemke
Group Leader
+41 56 310 49 82
henrik.lemke@psi.ch

Welcome to the SwissFEL Bernina Group