@article{ManassenJbaraAverbukhetal.2022, author = {Manassen, Yishay and Jbara, Moamen and Averbukh, Michael and Hazan, Zion and Henkel, Carsten and Horovitz, Baruch}, title = {Tunnel current noise spectra of spins in individual dimers of molecular radicals}, series = {Physical review : B, Condensed matter and materials physics}, volume = {105}, journal = {Physical review : B, Condensed matter and materials physics}, number = {23}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.105.235438}, pages = {9}, year = {2022}, abstract = {We report the detection of electron spin resonance (ESR) in individual dimers of the stable free radical 2,2,6,6tetramethyl-piperidine-1-oxyl (TEMPO). ESR is measured by the current fluctuations in a scanning tunneling microscope (ESR-STM method). The multipeak power spectra, distinct from macroscopic data, are assigned to dimers having exchange and Dzyaloshinskii-Moriya interactions in the presence of spin-orbit coupling. These interactions are generated in our model by interfering electronic tunneling pathways from tip to sample via the dimer???s two molecules. This is the first demonstration that tunneling via two spins is a valid mechanism of the ESR-STM method.}, language = {en} } @article{JelkenHenkelSanter2020, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Polarization controlled fine structure of diffraction spots from an optically induced grating}, series = {Applied physics letters}, volume = {116}, journal = {Applied physics letters}, number = {5}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5140067}, pages = {4}, year = {2020}, abstract = {We report on the remote control of the fine structure of a diffraction spot from optically induced dual gratings within a photosensitive polymer film. The material contains azobenzene in the polymer side chains and develops a surface relief under two-beam holographic irradiation. The diffraction of a polarized probe beam is sensitive to the orientation of the azobenzene groups forming a permanently stored birefringence grating within the film. We demonstrate that the fine structure of the probe diffraction spot switches from a Gaussian to a hollow or a hollow to a "Saturn"-like structure by a change in polarization. This makes it potentially useful in photonic devices because the beam shape can be easily inverted by an external stimulus.}, language = {en} } @article{PapkeYadavalliHenkeletal.2014, author = {Papke, Thomas and Yadavalli, Nataraja Sekhar and Henkel, Carsten and Santer, Svetlana}, title = {Mapping a plasmonic hologram with photosensitive polymer films: standing versus propagating waves}, series = {ACS applied materials \& interfaces}, volume = {6}, journal = {ACS applied materials \& interfaces}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/am503501y}, pages = {14174 -- 14180}, year = {2014}, abstract = {We use a photosensitive layer containing azobenzene moieties to map near-field intensity patterns in the vicinity of nanogrids fabricated within a thin silver layer. It is known that azobenzene containing films deform permanently during irradiation, following the pattern of the field intensity. The photosensitive material reacts only to stationary waves whose intensity patterns do not change in time. In this study, we have found a periodic deformation above the silver film outside the nanostructure, even if the latter consists of just one groove. This is in contradiction to the widely accepted viewpoint that propagating surface plasmon modes dominate outside nanogrids. We explain our observation based on an electromagnetic hologram formed by the constructive interference between a propagating surface plasmon wave and the incident light. This hologram contains a stationary intensity and polarization grating that even appears in the absence of the polymer layer.}, language = {en} } @article{JelkenHenkelSanter2019, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Solving an old puzzle: fine structure of diffraction spots from an azo-polymer surface relief grating}, series = {Applied physics : B, Lasers and optics}, volume = {125}, journal = {Applied physics : B, Lasers and optics}, number = {11}, publisher = {Springer}, address = {Heidelberg}, issn = {0946-2171}, doi = {10.1007/s00340-019-7331-8}, pages = {11}, year = {2019}, abstract = {We report on the experimental and theoretical interpretation of the diffraction of a probe beam during inscription of a surface relief grating with an interference pattern into a photo-responsive polymer film. For this, we developed a set-up allowing for the simultaneous recording of the diffraction efficiency (DE), the fine structure of the diffraction spot and the topographical changes, in situ and in real time while the film is irradiated. The time dependence of the DE, as the surface relief deepens, follows a Bessel function exhibiting maxima and minima. The size of the probe beam relative to the inscribed grating (i.e., to the size of the writing beams) matters and has to be considered for the interpretation of the DE signal. It is also at the origin of a fine structure within the diffraction spot where ring-shaped features appear once an irradiation time corresponding to the first maximum of the DE has been exceeded.}, language = {en} } @article{JelkenHenkelSanter2020, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Formation of half-period surface relief gratings in azobenzene containing polymer films}, series = {Applied physics : B, Lasers and optics}, volume = {126}, journal = {Applied physics : B, Lasers and optics}, number = {9}, publisher = {Springer}, address = {Heidelberg}, issn = {0946-2171}, doi = {10.1007/s00340-020-07500-w}, pages = {14}, year = {2020}, abstract = {We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45 degrees relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films.}, language = {en} } @article{HovhannisyanNematiHenkeletal.2023, author = {Hovhannisyan, Karen V. and Nemati, Somayyeh and Henkel, Carsten and Anders, Janet}, title = {Long-time equilibration can determine transient thermality}, series = {PRX Quantum}, volume = {4}, journal = {PRX Quantum}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {2691-3399}, doi = {10.1103/PRXQuantum.4.030321}, pages = {23}, year = {2023}, abstract = {When two initially thermal many-body systems start to interact strongly, their transient states quickly become non-Gibbsian, even if the systems eventually equilibrate. To see beyond this apparent lack of structure during the transient regime, we use a refined notion of thermality, which we call g-local. A system is g-locally thermal if the states of all its small subsystems are marginals of global thermal states. We numerically demonstrate for two harmonic lattices that whenever the total system equilibrates in the long run, each lattice remains g-locally thermal at all times, including the transient regime. This is true even when the lattices have long-range interactions within them. In all cases, we find that the equilibrium is described by the generalized Gibbs ensemble, with three-dimensional lattices requiring special treatment due to their extended set of conserved charges. We compare our findings with the well-known two-temperature model. While its standard form is not valid beyond weak coupling, we show that at strong coupling it can be partially salvaged by adopting the concept of a g-local temperature.}, language = {en} } @article{HerzogReppertPudelletal.2022, author = {Herzog, Marc and Reppert, Alexander von and Pudell, Jan-Etienne and Henkel, Carsten and Kronseder, Matthias and Back, Christian H. and Maznev, Alexei A. and Bargheer, Matias}, title = {Phonon-dominated energy transport in purely metallic heterostructures}, series = {Advanced functional materials}, volume = {32}, journal = {Advanced functional materials}, number = {41}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.202206179}, pages = {8}, year = {2022}, abstract = {Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers. Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface. Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au.}, language = {en} }