Johannes Feist: Scientific Publications


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Theoretical Challenges in Polaritonic Chemistry (PDF)
J. Fregoni, F. J. Garcia-Vidal, and J. Feist


Reply to the Comment on “On the SN2 Reactions Modified in Vibrational Strong Coupling Experiments: Reaction Mechanisms and Vibrational Mode Assignments”
C. Climent and J. Feist
Cavity-modified Chemistry: Towards Vacuum-field Catalysis
C. Climent, F. J. Garcia-Vidal, and J. Feist
Abstract: ...In the preceding chapters, electric field effects on chemical reactivity have been extensively discussed, focusing on STM setups and enzyme catalysis among many others. Here we will focus on a rather different and only recently explored approach to manipulate chemical reactions with electric fields. With the use of resonant cavity modes hosted in Fabry–Pérot cavities for instance, as well as plasmonic modes, very recent investigations have shown modifications of chemical reactivity and dynamics, including thermal reactions and photochemistry, as well as manipulation of materials properties and non-adiabatic processes. All these works have given birth to a new field termed polaritonic chemistry due to the fact that in the so-called strong-coupling regime, polaritons become the new eigenstates of the system. These are hybrid states of light and matter that inherit properties from both constituents, providing new means to modify chemical phenomena. The aim of this chapter is two-fold: on one side, we aim to provide a general background on confined light modes and strong coupling for the non-specialised reader, and on the other, we aim to review the recent achievements of the field, paying special attention to modifications in ground-state reactivity. To this end, the chapter is organised as follows. After an introduction to settle basic concepts, we review the most relevant experimental and theoretical work in which modified chemical reactivity has been reported and conclude with the challenges faced by the field.
Photoisomerization Efficiency of a Solar Thermal Fuel in the Strong Coupling Regime (PDF)
J. Mony, C. Climent, A. U. Petersen, K. Moth-Poulsen, J. Feist, and K. Börjesson
Multi-scale dynamics simulations of molecular polaritons: The effect of multiple cavity modes on polariton relaxation (PDF)
R. H. Tichauer, J. Feist, and G. Groenhof
Abstract: ...Coupling molecules to the confined light modes of an optical cavity is showing great promise for manipulating chemical reactions. However, to fully exploit this principle and use cavities as a new tool for controlling chemistry, a complete understanding of the effects of strong light–matter coupling on molecular dynamics and reactivity is required. While quantum chemistry can provide atomistic insight into the reactivity of uncoupled molecules, the possibilities to also explore strongly coupled systems are still rather limited due to the challenges associated with an accurate description of the cavity in such calculations. Despite recent progress in introducing strong coupling effects into quantum chemistry calculations, applications are mostly restricted to single or simplified molecules in ideal lossless cavities that support a single light mode only. However, even if commonly used planar mirror micro-cavities are characterized by a fundamental mode with a frequency determined by the distance between the mirrors, the cavity energy also depends on the wave vector of the incident light rays. To account for this dependency, called cavity dispersion, in atomistic simulations of molecules in optical cavities, we have extended our multi-scale molecular dynamics model for strongly coupled molecular ensembles to include multiple confined light modes. To validate the new model, we have performed simulations of up to 512 Rhodamine molecules in red-detuned Fabry–Pérot cavities. The results of our simulations suggest that after resonant excitation into the upper polariton at a fixed wave vector, or incidence angle, the coupled cavity-molecule system rapidly decays into dark states that lack dispersion. Slower relaxation from the dark state manifold into both the upper and lower bright polaritons causes observable photo-luminescence from the molecule–cavity system along the two polariton dispersion branches that ultimately evolves toward the bottom of the lower polariton branch, in line with experimental observations. We anticipate that the more realistic cavity description in our approach will help to better understand and predict how cavities can modify molecular properties.


On the SN2 reactions modified in vibrational strong coupling experiments: reaction mechanisms and vibrational mode assignments (PDF)
C. Climent and J. Feist
Abstract: ...Recent experiments have reported modified chemical reactivity under vibrational strong coupling (VSC) in microfluidic Fabry–Pérot cavities. In particular, the reaction rate of nucleophilic substitution reactions at silicon centers (SN2@Si) has been altered when a vibrational mode of the reactant was coupled to a confined light mode in the strong coupling regime. In this situation, hybrid light–matter states known as polaritons are formed and seem to be responsible for the modified chemical kinetics. These results are very encouraging for future applications of polaritonic chemistry to catalyze chemical reactions, with the ability to manipulate chemical phenomena without any external excitation of the system. Still, there is no theory capable of explaining the mechanism behind these results. In this work we address two points that are crucial for the interpretation of these experiments. Firstly, by means of electronic structure calculations we report the reaction mechanism in normal conditions of the two recently modified SN2@Si reactions, obtaining in both cases a triple-well PES where the rate-determining step is due to the Si–C and Si–O bond cleavage. Secondly, we characterize in detail the normal modes of vibration of the reactants. In the VSC experiments, reaction rates were modified only when specific vibrations of the reactants were coupled to a cavity mode. We find that these vibrations are highly mixed among the different fragments of the reactants leading to a completely new assignment of the IR peaks coupled to cavity modes in the original experimental works. Our results are fundamental for the interpretation of the VSC experiments given that in the absence of a theory explaining these results, the current phenomenological understanding relies on the assignment of the character of the vibrational IR peaks.
Photoprotecting Uracil by Coupling with Lossy Nanocavities (PDF)
S. Felicetti, J. Fregoni, T. Schnappinger, S. Reiter, R. de Vivie-Riedle, and J. Feist
Cumulant expansion for the treatment of light-matter interactions in arbitrary material structures (PDF)
M. Sánchez-Barquilla, R. E. F. Silva, and J. Feist


Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations (PDF)
G. Groenhof, C. Climent, J. Feist, D. Morozov, and J. J. Toppari
Abstract: ...When photoactive molecules interact strongly with confined light modes in optical cavities, new hybrid light–matter states form. They are known as polaritons and correspond to coherent superpositions of excitations of the molecules and of the cavity photon. The polariton energies and thus potential energy surfaces are changed with respect to the bare molecules, such that polariton formation is considered a promising paradigm for controlling photochemical reactions. To effectively manipulate photochemistry with confined light, the molecules need to remain in the polaritonic state long enough for the reaction on the modified potential energy surface to take place. To understand what determines this lifetime, we have performed atomistic molecular dynamics simulations of room-temperature ensembles of rhodamine chromophores strongly coupled to a single confined light mode with a 15 fs lifetime. We investigated three popular experimental scenarios and followed the relaxation after optically pumping (i) the lower polariton, (ii) the upper polariton, or (iii) uncoupled molecular states. The results of the simulations suggest that the lifetimes of the optically accessible lower and upper polaritons are limited by (i) ultrafast photoemission due to the low cavity lifetime and (ii) reversible population transfer into the “dark” state manifold. Dark states are superpositions of molecular excitations but with much smaller contributions from the cavity photon, decreasing their emission rates and hence increasing their lifetimes. We find that population transfer between polaritonic modes and dark states is determined by the overlap between the polaritonic and molecular absorption spectra. Importantly, excitation can also be transferred ”upward” from the lower polariton into the dark-state reservoir due to the broad absorption spectra of the chromophores, contrary to the common conception of these processes as a ”one-way” relaxation from the dark states down to the lower polariton. Our results thus suggest that polaritonic chemistry relying on modified dynamics taking place within the lower polariton manifold requires cavities with sufficiently long lifetimes and, at the same time, strong light–matter coupling strengths to prevent the back-transfer of excitation into the dark states.
Cavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity (PDF)
J. Galego, C. Climent, F. J. Garcia-Vidal, and J. Feist
Abstract: ...Here, we present a fundamental study on how the ground-state chemical reactivity of a single molecule can be modified in a QED scenario, i.e., when it is placed inside a nanoscale cavity and there is strong coupling between the cavity field and vibrational modes within the molecule. We work with a model system for the molecule (Shin-Metiu model) in which nuclear, electronic, and photonic degrees of freedom are treated on the same footing. This simplified model allows the comparison of exact quantum reaction rate calculations with predictions emerging from transition state theory based on the cavity Born-Oppenheimer approach. We demonstrate that QED effects are indeed able to significantly modify activation barriers in chemical reactions and, as a consequence, reaction rates. The critical physical parameter controlling this effect is the permanent dipole of the molecule and how this magnitude changes along the reaction coordinate. We show that the effective coupling can lead to significant single-molecule energy shifts in an experimentally available nanoparticle-on-mirror cavity. We then apply the validated theory to a realistic case (internal rotation in the 1,2-dichloroethane molecule), showing how reactions can be inhibited or catalyzed depending on the profile of the molecular dipole. Furthermore, we discuss the absence of resonance effects in the present scenario, which can be understood through its connection to Casimir-Polder forces. Finally, we treat the case of many-molecule strong coupling and find collective modifications of reaction rates if the molecular permanent dipole moments are oriented with respect to the cavity field.


Reply to the Comment on ‘Quantum theory of collective strong coupling of molecular vibrations with a microcavity mode’ (2015 New J. Phys. 17 053040) (PDF)
J. del Pino, J. Feist, and F. J. Garcia-Vidal


Multiscale Molecular Dynamics Simulations of Polaritonic Chemistry (PDF)
H. L. Luk, J. Feist, J. J. Toppari, and G. Groenhof
Abstract: ...When photoactive molecules interact strongly with confined light modes as found in plasmonic structures or optical cavities, new hybrid light-matter states can form, the so-called polaritons. These polaritons are coherent superpositions (in the quantum mechanical sense) of excitations of the molecules and of the cavity photon or surface plasmon. Recent experimental and theoretical works suggest that access to these polaritons in cavities could provide a totally new and attractive paradigm for controlling chemical reactions that falls in between traditional chemical catalysis and coherent laser control. However, designing cavity parameters to control chemistry requires a theoretical model with which the effect of the light-matter coupling on the molecular dynamics can be predicted accurately. Here we present a multiscale quantum mechanics/molecular mechanics (QM/ MM) molecular dynamics simulation model for photoactive molecules that are strongly coupled to confined light in optical cavities or surface plasmons. Using this model we have performed simulations with up to 1600 Rhodamine molecules in a cavity. The results of these simulations reveal that the contributions of the molecules to the polariton are time-dependent due to thermal fluctuations that break symmetry. Furthermore, the simulations suggest that in addition to the cavity quality factor, also the Stokes shift and number of molecules control the lifetime of the polariton. Because large numbers of molecules interacting with confined light can now be simulated in atomic detail, we anticipate that our method will lead to a better understanding of the effects of strong coupling on chemical reactivity. Ultimately the method may even be used to systematically design cavities to control photochemistry.
Plasmon-exciton-polariton lasing (PDF)
M. Ramezani, A. Halpin, A. I. Fernández-Domínguez, J. Feist, S. R.-K. Rodriguez, F. J. Garcia-Vidal, and J. Gómez Rivas
Abstract: ...Metallic nanostructures provide a toolkit for the generation of coherent light below the diffraction limit. Plasmonic-based lasing relies on the population inversion of emitters (such as organic fluorophores) along with feedback provided by plasmonic resonances. In this regime, known as weak light–matter coupling, the radiative characteristics of the system can be described by the Purcell effect. Strong light–matter coupling between the molecular excitons and electromagnetic field generated by the plasmonic structures leads to the formation of hybrid quasi-particles known as plasmon-exciton-polaritons (PEPs). Due to the bosonic character of these quasi-particles, exciton-polariton condensation can lead to laser-like emission at much lower threshold powers than in conventional photon lasers. Here, we observe PEP lasing through a dark plasmonic mode in an array of metallic nanoparticles with a low threshold in an optically pumped organic system. Interestingly, the threshold power of the lasing is reduced by increasing the degree of light–matter coupling in spite of the degradation of the quantum efficiency of the active material, highlighting the ultrafast dynamic responsible for the lasing, i.e., stimulated scattering. These results demonstrate a unique room-temperature platform for exploring the physics of exciton-polaritons in an open-cavity architecture and pave the road toward the integration of this on-chip lasing device with the current photonics and active metamaterial planar technologies.



Radiative heat transfer in the extreme near field (PDF)
K. Kim, B. Song, V. Fernández-Hurtado, W. Lee, W. Jeong, L. Cui, D. Thompson, J. Feist, M. T. H. Reid, F. J. García-Vidal, J. C. Cuevas, E. Meyhofer, and P. Reddy
Abstract: ...Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres, quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.
Enhancement of near-field radiative heat transfer using polar dielectric thin films (PDF)
B. Song, Y. Ganjeh, S. Sadat, D. Thompson, A. Fiorino, V. Fernández-Hurtado, J. Feist, F. J. Garcia-Vidal, J. C. Cuevas, P. Reddy, and E. Meyhofer


What will it take to observe processes in 'real time'? (PDF)
S. R. Leone, C. W. McCurdy, J. Burgdörfer, L. S. Cederbaum, Z. Chang, N. Dudovich, J. Feist, C. H. Greene, M. Ivanov, R. Kienberger, U. Keller, M. F. Kling, Z.-H. Loh, T. Pfeifer, A. N. Pfeiffer, R. Santra, K. Schafer, A. Stolow, U. Thumm, and M. J. J. Vrakking


Autoionization of Molecular Hydrogen: Where do the Fano Lineshapes Go? (PDF)
A. Palacios, J. Feist, A. González-Castrillo, J. L. Sanz-Vicario, and F. Martín


Time shifts in photoemission from a fully correlated two-electron model system (PDF)
S. Nagele, R. Pazourek, J. Feist, and J. Burgdörfer



Differential cross sections for non-sequential double ionization of He by 52 eV photons from the Free Electron Laser in Hamburg, FLASH (PDF)
M. Kurka, J. Feist, D. A. Horner, A. Rudenko, Y. H. Jiang, K. U. Kühnel, L. Foucar, T. N. Rescigno, C. W. McCurdy, R. Pazourek, S. Nagele, M. Schulz, O. Herrwerth, M. Lezius, M. F. Kling, M. Schöffler, A. Belkacem, S. Düsterer, R. Treusch, B. I. Schneider, L. A. Collins, J. Burgdörfer, C. D. Schröter, R. Moshammer, and J. Ullrich





PhD thesis

Two-photon double ionization of helium (PDF)

Diploma thesis

Transport through quantum wires with surface disorder (PDF)