Allison Research Group

The worst professor webpage is one that is very detailed, yet very dated, as this implies inactivity. So as the focus of our work is more and more on 2D materials and exciton physics, it was time to update to the research page again.

We all piled in to the minivan and drove to the Ultrafast Surface Dynamics Conference in Waterville Valley, NH. It was a great conference with much of the time-resolved ARPES and momentum microscopy community there.

Jianwei gave an exciting talk on exciton dynamics in WS2/WSe2 heterostructures.

Jianwei Ding presenting at USD14

In collaboration with the Qiu group at Yale, we have posted a new paper about the ARPES of trions in 2D materials, bound states of either two electrons and one hole or two holes and one electron. The paper is available here: https://arxiv.org/pdf/2511.19280

Jin Bakalis has successfully defended her dissertation and competed her Ph. D on her pioneering work in time- and angle-resolved photoemission and ultrafast electron dynamics in graphene. Many thanks to the committee members Mike White, Chris Johnson, and Matthew Bird.

Jin will take some time off to visit family in Korea before starting a job. Also shown in the picture are Jianwei, Zach, and Alex, who carry on the tr-ARPES torch.

In collaboration with the Qiu group at Yale, we have posted a new paper on excitons in TMD heterostructures. Using time-resolved ARPES in combination with ab initio theory, we determine the mixture of excitons produced in MoSe2/WS2 bilayers after above-gap excitation at different twist angles.

Our results indicate a much more complicated, and richer, story than previously reported, involving lattice strain and a mixture of inter-layer and intra-layer excitons with different binding energies.

https://doi.org/10.48550/arXiv.2502.14138

Our web server died again, of course right during proposal season. Ugh. This time it was a Raspberry Pi. From now no more DIY web servers. We have migrated to a professional solution hosted by GoDaddy, with new domain allisongroup.net. I have high hopes for you, GoDaddy.

Stay tuned for more updates to the website reflecting current research efforts soon!

We have posted a new “perspective” article on cavity-enhanced HHG for high-performance photoemission experiments. It can be found here: https://arxiv.org/abs/2410.11589

Michael Wahl has completed his M.S.I. degree in the Allison lab, developing tunable frequency combs with arbitrary (0-60.5 MHz) for the Allison lab tr-ARPES instrument. This is the last piece of the tr-ARPES laser puzzle.

Mike is off now to Boulder, CO to further work on frequency combs in the research group of Prof. Scott Diddams.

We have posted a new paper regarding imaging pseudospin dynamics in graphene. Working at the low excitation fluences enabled by our unique tr-ARPES instrument, we are able to vary the relative importance of electron-electron and electron-phonon scattering on the dynamics and also momentum-resolve the nascent photoexcited electrons before they relax. These are very challenging measurements due the very short carrier lifetimes in graphene and the need to resolve fine momentum-space features of the distributions.