@article{BouchouleSchemmerHenkel2018, author = {Bouchoule, Isabelle and Schemmer, Max and Henkel, Carsten}, title = {Cooling phonon modes of a Bose condensate with uniform few body losses}, series = {Scipost Physics}, volume = {5}, journal = {Scipost Physics}, number = {5}, publisher = {Scipost foundation}, address = {Amsterdam}, issn = {2542-4653}, doi = {10.21468/SciPostPhys.5.5.043}, pages = {18}, year = {2018}, abstract = {We present a general analysis of the cooling produced by losses on condensates or quasi-condensates. We study how the occupations of the collective phonon modes evolve in time, assuming that the loss process is slow enough so that each mode adiabatically follows the decrease of the mean density. The theory is valid for any loss process whose rate is proportional to the jth power of the density, but otherwise spatially uniform. We cover both homogeneous gases and systems confined in a smooth potential. For a low-dimensional gas, we can take into account the modified equation of state due to the broadening of the cloud width along the tightly confined directions, which occurs for large interactions. We find that at large times, the temperature decreases proportionally to the energy scale mc(2), where m is the mass of the particles and c the sound velocity. We compute the asymptotic ratio of these two quantities for different limiting cases: a homogeneous gas in any dimension and a one-dimensional gas in a harmonic trap.}, language = {en} } @article{HenkelJacobStoppetal.2019, author = {Henkel, Carsten and Jacob, Georg and Stopp, Felix and Schmidt-Kaler, Ferdinand and Keil, Mark and Japha, Yonathan and Folman, Ron}, title = {Stern-Gerlach splitting of low-energy ion beams}, series = {New journal of physics : the open-access journal for physics}, volume = {21}, journal = {New journal of physics : the open-access journal for physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/ab36c7}, pages = {14}, year = {2019}, abstract = {We present a feasibility study with several magnetic field configurations for creating spin-dependent forces that can split a low-energy ion beam by the Stern-Gerlach (SG) effect. To the best of our knowledge, coherent spin-splittings of charged particles have yet to be realised. Our proposal is based on ion source parameters taken from a recent experiment that demonstrated single-ion implantation from a high-brightness ion source combined with a radio-frequency Paul trap. The inhomogeneous magnetic fields can be created by permanently magnetised microstructures or from current-carrying wires with sizes in the micron range, such as those recently used in a successful implementation of the SG effect with neutral atoms. All relevant forces (Lorentz force and image charges) are taken into account, and measurable splittings are found by analytical and numerical calculations.}, language = {en} } @article{HenkelSchmidt2019, author = {Henkel, Carsten and Schmidt, Paul Philip}, title = {On anomalously large nano-scale heat transfer between metals}, series = {Journal of the Optical Society of America : B, Optical physics}, volume = {36}, journal = {Journal of the Optical Society of America : B, Optical physics}, number = {4}, publisher = {Optical Society of America}, address = {Washington}, issn = {0740-3224}, doi = {10.1364/JOSAB.36.000C10}, pages = {C10 -- C14}, year = {2019}, abstract = {Non-contact heat transfer between two bodies is more efficient than the Stefan-Boltzmann law when the distances are on the nanometer scale (shorter than Wien's wavelength), due to contributions of thermally excited near fields. This is usually described in terms of the fluctuation electrodynamics due to Rytov, Levin, and co-workers. Recent experiments in the tip-plane geometry have reported "giant" heat currents between metallic (gold) objects, exceeding even the expectations of Rytov theory. We discuss a simple model that describes the distance dependence of the data and permits us to compare to a plate-plate geometry, as in the proximity (or Derjaguin) approximation. We extract an area density of active channels which is of the same order for the experiments performed by the groups of Kittel (Oldenburg) and Reddy (Ann Arbor). It is argued that mechanisms that couple phonons to an oscillating surface polarization are likely to play a role.}, language = {en} } @article{Henkel2021, author = {Henkel, Carsten}, title = {Heat transfer and entanglement}, series = {Annalen der Physik}, volume = {533}, journal = {Annalen der Physik}, number = {10}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0003-3804}, doi = {10.1002/andp.202100089}, pages = {15}, year = {2021}, abstract = {The non-equilibrium state of two oscillators with a mutual interaction and coupled to separate heat baths is discussed. Bosonic baths are considered, and an exact spectral representation for the elements of the covariance matrix is provided analytically. A wide class of spectral densities for the relevant bath modes is allowed for. The validity of the fluctuation-dissipation relation is established for global equilibrium (both baths at the same temperature) in the stationary state. Spectral measures of entanglement are suggested by comparing to the equilibrium spectrum of zero-point fluctuations. No rotating-wave approximation is applied, and anomalous heat transport from cold to hot bath, as reported in earlier work, is demonstrated not to occur.}, language = {en} } @article{Henkel2020, author = {Henkel, Carsten}, title = {Thermally excited quasiparticles in metals, dispersion forces, and the thermal anomaly}, series = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, volume = {35}, journal = {Modern physics letters : A, Particles and fields, gravitation, cosmology, nuclear physics}, number = {3}, publisher = {World Scientific}, address = {Singapore}, issn = {0217-7323}, doi = {10.1142/S021773232040009X}, pages = {9}, year = {2020}, abstract = {We provide a brief review of the contribution of thermally excited carriers to dispersion forces. In a metal, these carriers generate charge and current fluctuations whose spectral frequencies are comparable to k(B)T/(h) over bar. They are very likely responsible for the "plasma vs. Drude" anomaly.}, language = {en} } @article{Henkel2017, author = {Henkel, Carsten}, title = {Nanoscale Thermal Transfer}, series = {Zeitschrift f{\"u}r Naturforschung A}, volume = {72}, journal = {Zeitschrift f{\"u}r Naturforschung A}, number = {2}, publisher = {De Gruyter}, address = {Berlin}, issn = {0932-0784}, doi = {10.1515/zna-2016-0372}, pages = {99 -- 108}, year = {2017}, abstract = {An electromagnetic theory of thermal radiation is outlined, based on the fluctuation electrodynamics of Rytov and co-workers. We discuss the basic concepts and the status of different approximations. The physical content is illustrated with a few examples on near-field heat transfer.}, language = {en} } @article{NematiHenkelAnders2022, author = {Nemati, Somayyeh and Henkel, Carsten and Anders, Janet}, title = {Coupling function from bath density of states}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {139}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {3}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0295-5075}, doi = {10.1209/0295-5075/ac7b42}, pages = {7}, year = {2022}, abstract = {Modelling of an open quantum system requires knowledge of parameters that specify how it couples to its environment. However, beyond relaxation rates, realistic parameters for specific environments and materials are rarely known. Here we present a method of inferring the coupling between a generic system and its bosonic (e.g., phononic) environment from the experimentally measurable density of states (DOS). With it we confirm that the DOS of the well-known Debye model for three-dimensional solids is physically equivalent to choosing an Ohmic bath. We further match a real phonon DOS to a series of Lorentzian coupling functions, allowing us to determine coupling parameters for gold, yttrium iron garnet (YIG) and iron as examples. The results illustrate how to obtain material-specific dynamical properties, such as memory kernels. The proposed method opens the door to more accurate modelling of relaxation dynamics, for example for phonon-dominated spin damping in magnetic materials.}, language = {en} } @article{HorovitzHenkel2021, author = {Horovitz, Baruch and Henkel, Carsten}, title = {Spin entanglement via scanning tunneling microscope current}, series = {Physical review : B, Condensed matter and materials physics}, volume = {104}, journal = {Physical review : B, Condensed matter and materials physics}, number = {8}, publisher = {American Physical Society}, address = {Ridge, NY}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.L081405}, pages = {5}, year = {2021}, abstract = {We consider a system of two spins under a scanning tunneling microscope bias and derive its master equation. We find that the tunneling elements to the electronic contacts (tip and substrate) generate an exchange interaction between the spins as well as a Dzyaloshinskii-Moriya interaction in the presence of spin-orbit coupling. The tunnel current spectrum then shows additional lines compared to conventional spin-resonance experiments. When the spins have degenerate Larmor frequencies and equal tunneling amplitudes (without spin orbit), there is a dark state with a vanishing decay rate. The coupling to the electronic environment generates significant spin-spin entanglement via the dark state, even if the initial state is nonentangled.}, language = {en} } @article{EiznerHorovitzHenkel2012, author = {Eizner, E. and Horovitz, Baruch and Henkel, Carsten}, title = {Van der waals-casimir-polder interaction of an atom with a composite surface}, series = {The European physical journal : D, Atomic, molecular, optical and plasma physics}, volume = {66}, journal = {The European physical journal : D, Atomic, molecular, optical and plasma physics}, number = {12}, publisher = {Springer}, address = {New York}, issn = {1434-6060}, doi = {10.1140/epjd/e2012-30294-x}, pages = {11}, year = {2012}, abstract = {We study the dispersion interaction of the van der Waals and Casimir-Polder (vdW-CP) type between a neutral atom and the surface of a conductor by allowing for nonlocal electrodynamics, i.e. electron diffusion. We consider two models: (i) bulk diffusion, and (ii) diffusion in a surface charge layer. In both cases, we find that the transition to a semiconductor as a function of the conductivity is continuous, unlike the case of a local model. The relevant parameter is the electric screening length and depends on the carrier diffusion constant. We find that for distances comparable to the screening length, vdW-CP data can distinguish between bulk and surface diffusion, hence it can be a sensitive probe for surface states.}, language = {en} } @article{HorovitzHenkel2012, author = {Horovitz, Baruch and Henkel, Carsten}, title = {Surface plasmons at composite surfaces with diffusive charges}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {97}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {5}, publisher = {EDP Sciences}, address = {Mulhouse}, issn = {0295-5075}, doi = {10.1209/0295-5075/97/57010}, pages = {6}, year = {2012}, abstract = {Metal surfaces with disorder or with nanostructure modifications are studied, allowing for a localized charge layer (CL) in addition to continuous charges (CC) in the bulk, both charges having a compressional or diffusive nonlocal response. The notorious problem of "additional boundary conditions" is resolved with the help of a Boltzmann equation that involves the scattering between the two charge types. Depending on the strength of this scattering, the oscillating charges can be dominantly CC or CL; the surface plasmon (SP) resonance acquires then a relatively small linewidth, in agreement with a large set of data. With a few parameters our model describes a large variety of SP dispersions corresponding to observed data.}, language = {en} } @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} }