We just finished a study demonstrating a way to use time-resolved RIXS to measure the collective exctiations of quantum materials, in this instance CDW-ordered La2-xBaxCuO4 (LBCO). The idea is to weakly perturb the system with a pump pulse and then measure the time evolution of the order parameter, which encodes the collective excitations of the system. The advantage of this technique is that the energy information comes from the time dynamics in a Fourier sense, allowing one to achieve extraordinarily high, sub-meV resolution. We found that the excitations in LBCO are overdamped and propagate diffusively, exhibiting dynamic critical scaling analogous to that observed in Oswald ripening in metal alloys in the 1980’s. The study, which was a collaboration with Nigel Goldenfeld’s group done at the new LCLS free electron laser facility at SLAC, was published in Science Advances.
These images were taken at beamline ID-6 at the Advanced Photon Source (credit: Ali Husain).
Our paper on density fluctuations in Bi2Sr2CaCu2O8+x appeared in the Proceedings of the National Academy of Sciences. This study shows that, unlike conventional metals, this so-called “strange metal” does not exhibit propagating plasmons. Instead, it shows a continuum of fluctuations exhibiting “local scale invariance”–a phase in which time and space axes become decoupled. The origin of these fluctuations is still a mystery.
Read all about it here.
After several months of HVAC renovations the M-EELS instrument is back up and running. Looking forward to a blissful summer of experiments.
The M-EELS experiment is down for six weeks as the ESCO project to rebuild the HVAC system for the entire MRL building moves to our floor. The whole instrument is now encased in a giant plywood box to protect it from dust and mishaps. We hope to be recommissioning the instrument in the middle of March. No new science will happen until early May.
We just published a paper finally demonstrating that TiSe2 contains a Bose condensate of excitons. The experimental signature is a soft plasmon that falls to zero frequency at Tc. Bert Halperin and Maurice Rice nicknamed this phase “excitonium” in their 1968 Rev. Mod. Phys. paper to emphasize the physical picture of an exciton condensate as an electronic crystal. This discovery, which we believe should be viewed as a landmark in our field, was done using our new M-EELS technique (see Sean’s paper, below).
The media frenzy over this discovery has been unreal, surpassing our wildest expectations. Some of the better written articles may be found in Newsweek, The Independent, and the The Daily Mail. Here is a polished video on YouTube.
Here’s a link to the article in Science.
Our low-temperature crystallography instrument has a new home. It now lives in a dedicated space in 117 MRL, where it will be used by many research groups for decades to come. Stella Sun and Sangjun Lee did a great job moving the equipment, and thanks go to Youli Li for helping with the alignment and calibration.
We just finished our first Free Electron Laser experiment, using the SXR endstation during Run 15 of the Linac Coherent Light Source. The goal was to study the collective modes of the stripe phase in La2-xBaxCuO4.
SLAC Facebook post here.
After 2.5 years of refereeing, Sean’s M-EELS paper was finally published in the open-access journal SciPost. This paper explains the reasons for developing the M-EELS technique and how it works.
Read it here.
We did our first experiment on qRIXS, the world’s first fully angle-resolved soft RIXS spectrometer, which is under development at the Advanced Light Source. This thing will open up a new approach to studying valence band excitations in materials.