Laboratory of Ultrafast Dynamics

The Laboratory of Ultrafast Dynamics at the University of Pittsburgh The Lab supports several graduate students and postdoctoral fellows.

Dr. Hrvoje Petek's Laboratory of Ultrafast Dynamics studies electronic structures and dynamics at molecule/solid interfaces using two photon photoemission spectroscopy and time-resolved two-photon photoemission techniques at the University of Pittsburgh.

08/10/2021

Poincaré engineering of light

We create a plasmonic vortex and perform vectorial imaging of its electric field components on the nanofemto scale, by interferometric time-resolved photoemission electron microscopy https://doi.org/10.1021/acs.chemrev.0c00146. The experiment is performed on a topologically trivial Ag/vacuum interface, but the vectorial surface plasmon polariton field and spin texture imposes its topology on matter, as can be described by field component Stokes parameter decomposition on a Poincarè sphere. Such vectorial plasmonic vortex fields break the time reversal symmetry, thereby imposing their topology on trivial matter. See the light at https://doi.org/10.1557/s43577-021-00152-x.

01/09/2021

How do plasmons decay into hot electrons?
Free electrons in a metal screen optical fields preventing their pe*******on, to cause their reflection; they perform a function that we use as optical mirrors. This collective response enables light to interact strongly with the electronic system, and therefore has been of interest for converting photon energy to hot electrons. This interaction was described by JJ Hopfield in 1965, but the physics and chemistry community has adopted a very different model, that is not very optimistic. By performing two-photon photoemission spectroscopy on single crystal silver surfaces, we show that in agreement with Hofield's theory, plasmons decay to excite electrons from the Fermi level, converting photon energy more effectively: https://pubs.acs.org/doi/10.1021/acsphotonics.0c01412?ref=pdf

12/24/2020

Congratulations to Yanan and the PEEM team, including visitors Robin Huang and Atsushi Kubo, for publishing their work on the nanofemto imaging of a plasmonic meron quasiparticle in Nature (https://doi.org/10.1038/s41586-020-3030-1). This was truly a a great accomplishments bringing together various expertise. If you would like to know what is a meron go to (http://ultrafast.phyast.pitt.edu/publications/significant-accomplishments.html). Consider meron a nonlinear window to nonreciprocal physics. To see the nanofemto movie of a plasmonic meron go to (http://ultrafast.phyast.pitt.edu/publications/plasmonic-vortex.html).

07/24/2020

Photoemission Horizon
What is a photoemission horizon? It is where electrons rise above the vacuum barrier. As electron parallel momentum increases, more energy above the Fermi level must be supplied by photons to induce photoemission. We have used 4 photon photoemission to excite electrons from the Y point of Ag(110) surface, via an unoccupied surface state. Multiphoton photoemission enables us to overcome the photoemission horizon without spending time and money to generate XUV pulses. By looking away from the Brillouin zone center, we can learn many new things, as will become evident. This technical accomplishment was published in New Journal of Physics.
http://dx.doi.org/10.1088/1367-2630/ab98d6

06/27/2020

they seem happy to be out in incoherent light.

06/27/2020

Group photo taken by a UFO during a moment of failed social distancing to commemorate an outing to Ohiopyle. No rafting this year, however.

06/13/2020

How do you take a snapshot of light?
Well you have to be very fast, because there is nothing faster than light. But one can do it in Petek's laboratory by interferometric time-resolved photoemission electron miscoscopy. Dąbrowski, Dai, and Petek report a review article on how they image surface plasmon field and spin textures evolving at the speed of light (300 nm/fs) on the nanofemto scale in an article that was just published in Chemical Reviews:
https://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.0c00146

05/06/2020

How to dress a metal?
Well, you need intense ultrafast light pulses, which provide a time-periodic potential acting together with the lattice ions, to define the potential experienced by electrons. The optical field transiently modifies (dresses) the electronic bands, potentially changing them from an electron to a hole type. We demonstrate that light can be used to modify electronic band structures of solids on the attosecond time scale of optical field oscillation. In other words, if you do not like the reflection you see in a metallic mirror, you can now change it with an intense coherent field. This experiment beautifully demonstrates the power of coherent multiphoton photoelectron spectroscopy to probe optical interactions in solids. Read about it in Nature Communications: https://rdcu.be/b3ZjN

03/27/2020

The research supervision team waiting to be let into Allen hall/NPL to check and maintain their equipment, armed against corona virus. We had to wait 45 min to be let in, but at least is was a nice day.

02/08/2020

To perturb or not to perturb..., that is the question. We excite metals hard enough to drive 4-7 photon transitions. One or two photons may not be enough for photoemission, but we can drive electrons harder so that they absorb more photons than necessary for photoemission, which is called above threshold photoemission. The question then is whether this occurs by a perturbative multi-quantum transition or a non-perturbative field-induced process. Well, to find out, you just have to read and form your opinion. https://journals.aps.org/prb/abstract/10.1103/PhysRevB.101.075409

02/04/2020

We examine the nanoscale distribution of plasmonic fields by TR-PEEM measurement of Ag nanocrystals on Si surface. The imaging shows that factors, like wavelength, polarization, and optical phase determine the location of plasmonic fields in complex nanoparticles. In other words, one must perform nanofemto imaging to understand how plasmonic fields transfer energy to nano materials. This is the editor's pick in the Journal of Chemical Physics:
https://aip.scitation.org/doi/10.1063/1.5139543

12/15/2019

When anomalous is not anomalous. Electron-phonon interaction defines properties in familiar materials that are derived from frontier s and p symmetry electron orbitals that color our thinking about what is normal electron-phonon interaction. Materials incorporating atoms with d frontier orbitals can behave oppositely, however, as analyzed by a joint international experiment/theory collaboration involving researchers from Germany, the USA, China, and Finland:
https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.1.033153
https://twitter.com/electrondynamix/status/1206128611817934848

We demonstrate by experiment and theory that distinct electron-phonon properties of TiO2 arise from how the crystal field of ligands lifts the atomic orbital degeneracy. Right thinking shows that anomalous is normal.

08/26/2019

What is a plasmonic spin Hall effect? Surface plasmon polaritons are chiral because of momentum-traverse spin locking: changing the sign of plasmon momentum changes the sign of its spin. This causes circularly polarized surface plasmons to focus to a different spot than linearly polarized plasmons. This is a very subtile difference to observe in a far field measurement, but is immediately evident with PEEM imaging of the focusing. It could be used to interact in enantiomeric molecules in a space specific manner. Our results were published in:
https://doi.org/10.1021/acsphotonics.9b00422

08/04/2019

How to turn lead into gold?
or better how to turn C60 molecules into a herringbone stitch pattern through intermolecular charge transport? The answer is simple-just use black phosphorus as a compressive template for aligning C60 molecules so that their electronic orbitals hybridize into a conductive band. The electronic properties of C60 solids have been disappointing as a molecular semiconductor. Min Feng and her group used black phosphorous to optimize the intermolecular hybridization so that delocalized bands could form and be imaged by STM and characterized by theory. I participated as the Luo Jia Chair at Wuhan University. See the Nature Commun. article:

https://www.nature.com/articles/s41467-019-11300-y

07/14/2019

What is a metal?

A metal gains its optical properties from large negative real part of its dielectric function. but the dielectric function must eventually pass through zero. The epsilon zero condition defines the bulk plasmon frequency from which all metal plasmonic properties derive. We have examined the nonlinear photoemission of Ag(111) surface at epsilon near zero condition (ENZ), and find plasmonic responses, which have been observed before, but not discussed as such. The attached figure shows how two-photon photoemission spectra change drastically through the ENZ region (3.9 eV). Surprisingly, we find a collective bulk plasmonic response in single particle photoemission spectra, which could have significant implications in plasmonically induced processes. The results were published recently in Physical Review Letters.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.017404

Photos from Laboratory of Ultrafast Dynamics's post 05/19/2019

Ran into a family of geese moving to the North side of Allegheny River across the Veteran's bridge.

05/14/2019

It takes time to learn what experimental data is trying to communicate. Coherent phonon modes in Si, in the first 100 fs after excitation, show strong wavelength dependence, that we found a few years ago. In a new paper Japanese theory collaborators interpret the experiments in terms of plasmon-phonon, Rosen-Zenner coupling. The results have just been published in Physical Review B.
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.174304

04/28/2019

Congratulations to Marcel and Andi for their PRX publication on coherent multidimensional spectroscopy applied to Ag(111) surface. May it become the benchmark for coherent photoemission spectroscopy.

https://link.aps.org/doi/10.1103/PhysRevX.9.011044

04/28/2019

Congratulations to Marcel and Kathatina for brith of their daughter Laura. it crowns Marcel's achievements this year.

12/04/2017

We have just published our research on plasmonic hot electron generation in Ag nanoparticle decorated TiO2 surface in Nature Photonics
https://doi.org/10.1038/s41566-017-0049-4
The hot electron generation does not happen as generally believed by transfer from Ag nanoparticles.

09/06/2017

Our mini-review on ultrafast microscopy with particular focus on photoemission electron microscopy was finally published in J. Phys. Chem. Lets. as a Perspective article. In a few days we look forward to the cover. Congratulations Maciej and Yanan.
http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.7b00904

06/19/2017

Just came back from Ultrafast Surface Dynamics 10 in Inzel Germany, where we celebrated 20 years of USD and the coming of age (Japanese style) of Uli Höfer and Martin Aeschlimann. I was fortunately spared the embarrassment.

05/07/2017

Congratulations to Shengmin, Adam and Cong. It will be lonely without you. Come back anytime to visit us.

04/21/2017

How does excitation of plasmonic modes in metallic nano clusters create excitations in a semimetal or semiconductor substrate? In case of silver clusters on graphite's ti through the direct dipole-dipole coupling whereby plasmons transfer their energy to π-π* excitation in the substrate. The coupling mechanism is important for understanding plasmonically enhanced chemistry. The details can be found in our just published article in the Journal of the American Chemical Society.
http://pubs.acs.org/doi/abs/10.1021/jacs.7b01079

01/13/2017

See the new commentary on ultrafast photoemission electron microscopy of a photovoltaic junction in action. The research was performed by Prof. Keshav Dani of Okinawa Institute of Science and Technology (OIST) in Okinawa, and his coworkers. It is another important application of ultrafast PEEM.
http://rdcu.be/op8W

Want your school to be the top-listed School/college in Pittsburgh?

Click here to claim your Sponsored Listing.

Videos (show all)

Vectorial imaging of surface plasmon polaritons

Location

Address


3941 O'Hara Street, G01 Allen Hall
Pittsburgh, PA
15260
Other Pittsburgh schools & colleges (show all)
Tepper School of Business at Carnegie Mellon Tepper School of Business at Carnegie Mellon
Pittsburgh

The Tepper School consistently ranks among the top business schools in the world. The school’s legacy

Barco Law Library Barco Law Library
3900 Forbes Avenue
Pittsburgh, 15260

The Barco Law Library

Entertainment Technology Center Entertainment Technology Center
700 Technology Drive
Pittsburgh, 15219

The ETC is the premiere professional graduate program for interactive entertainment as it’s applied across a variety of fields. The ETC balances educational goals, professional development, and engaging experiences; or Learn, Work, and Play.

Robert Morris Men's Hockey - NCAA Robert Morris Men's Hockey - NCAA
7600 Grand Avenue
Pittsburgh, 15225

Page of the Robert Morris University NCAA Division I men's hockey program.

Pitt Gymnastics Pitt Gymnastics
Fitzgerald Field House
Pittsburgh, 15213

The official page of the University of Pittsburgh Gymnastics Team | 2016 EAGL Champions | #H2P

Pace School Pace School
2432 Greensburg Pike
Pittsburgh, 15221

Pace serves kids K thru age 21 with autism and emotional challenges who have exhausted resources in their home school districts. Pace blends mental health and developmental services through all parts of the school day maximizing each students potential.

Mt. Lebanon High School Alumni Association Mt. Lebanon High School Alumni Association
7 Horsman Drive
Pittsburgh, 15228

The Mt. Lebanon High School Alumni Association serves graduates of Mt. Lebanon High School.

Carnegie Mellon Student Senate Carnegie Mellon Student Senate
5000 Forbes Avenue
Pittsburgh, 15213

The Carnegie Mellon Undergraduate Student Senate is the undergraduate component of Carnegie Mellon's

Heinz College of Information Systems and Public Policy Heinz College of Information Systems and Public Policy
4800 Forbes Avenue
Pittsburgh, 15213

The official Facebook account for Carnegie Mellon University's Heinz College of Information Systems a

Robert Morris Lacrosse Robert Morris Lacrosse
6001 University Boulevard
Pittsburgh, 15108

True success for our team comes in knowing that you and all of your teammates gave everything to become the very best that you are capable of...

The Information Networking Institute (INI) The Information Networking Institute (INI)
4616 Henry Street
Pittsburgh, 15213

The Information Networking Institute (INI) at Carnegie Mellon University offers master’s degree pr