Publications of the SNOM group

2026

• M. Roeper, R. Buschbeck, J. Wetzel, T. Ritschel, A.-L. Hofmann, V. Kovtunovych, M.N. Pionteck, J. Taboada-Gutiérrez, A. B. Kuzmenko, M. Basini, V. Unikandanunni, I. Kiseleva, J. Geck, S.C. Kehr, M. Lederer, S. Sanna, L.M. Eng, and S.D. Seddon.
  "Uniaxial strain-driven ferroelastic domain tuning in LaAlO₃."
  Advanced Science, e78098 (2026).
  doi: 10.1002/advs.78098
• J. Wetzel, J. Taboada-Gutiérrez, M. Roeper, F.G. Kaps, G.L. Esposito, D. Marchese, R. Buschbeck, P. Lenz, J.M. Klopf, H.A. Bechtel, S.N. Gilbert Corder, J. Teyssier, S.C. Kehr, L.M. Eng, A.B. Kuzmenko, and S.D. Seddon.
  "Ultra-high THz-field-confinement at LaAlO₃ twin walls."
  Nature Communications (2026).
  doi: 10.1038/s41467-026-77689-5
• F.H. Feres, M. Bearzatto, A. Debacq, G. Nemeth, R.A. Mayer, Y.B. Marcal, M. V. de Paiva, M. Obst, F. Kaps, J. Wetzel, O. Hatem, W. Zhou, R. Jing, H. Whang, A. Cernescu, S. Winnerl, J.M. Klopf, M. Liu, F. Borondics, I.D. Barcelos, R.O. Freitas, A.I. F. Tresguerres-Mata, Y. De Wilde, L.M. Eng, M. Lobet, S.C. Kehr und F.C. B. Maia. "Infrared light scattering and emission from epsilon near-zero hyperbolic phonon-polaritons in two-dimensional crystals."
  arXiv:2608.15771 (2026).
  doi: 10.48550/arXiv.2608.15771
• R. Buschbeck, M.N. Pionteck, N. Herrmann, M. Rüsing, S.C. Kehr, S. Sanna, S., and L.M. Eng.
  "Ab initio modeling and experimental analysis of contrast in broadband coherent anti-Stokes Raman spectroscopy: A case study on ferroelectric domain walls."
  Physical Review B 114, 034104 (2026).
  doi: 10.1103/m1xq-rlft
• T.S. Arnaud, R.W. Spangler, J.D. Georgaras, J.B. Haber, D. Hirt, M. Obst, G. Álvarez-Pérez, M. Long III, F.G. Kaps, J. Wetzel, C. Ragle, J.E. Buchner, Y. Kim, A.S. Senarath, R. Niemann, M. He, G. Carini, U. Arregui-Leon, A.C. Behera, R. Bangari, N. Sahoo, N.C. Brumby, J.M. Klopf, M. Wolf, L.M. Eng, S.C. Kehr, T.G. Folland, A. Paarmann, P.E. Hopkins, F. Jornada, J.-P. Maria, and J.D. Caldwell.
  "Tailoring Phonon-Driven Responses in α-MoO₃ Through Isotopic Enrichment."
  Advanced Materials 38, e73629 (2026).
  doi: 10.1002/adma.73629
• M. Flemming, P. Zechel, R.R. Nair, E. Mahnke, M. Löffler, A. Ong, B. Rellinghaus, L.M. Eng, K. Leo, and H. Kleemann.
  "Universal material basis for biocompatible printed electrolytes in Organic Electrochemical Transistors."
  arXiv:2604.25830 (2026).
  doi: 10.48550/arXiv.2604.25830
• H. Zandipour, F. Kaps, R. Buschbeck, M. Obst, A. Senarath, R. Niemann, N.S. Mueller, G. Alvarez-Perez, K. Diaz-Granados, R.A. Kowalski, J. Wetzel, R. Balasubramanyam Iyer, M. Wortel, J.M. Klopf, T. Anderson, A. Jacobs, M. Ebrish, L.M. Eng, A. Paarman, S.C. Kehr, J.D. Caldwell, and T.G. Folland.
  "Uncovering the properties of homo-epitaxial GaN devices through cross-sectional infrared nanoscopy."
  arXiv:2603.08858 (2026).
  doi: 10.48550/arXiv.2603.08858
• G. Carini, M. Pradhan, E. Gelzinyte, A. Ardenghi, S. Dixit, M. Obst, A.S. Senarath, N.S. Mueller, G. Alvarez-Perez, K. Diaz-Granados, R.A. Kowalski, R. Niemann, F.G. Kaps, J. Wetzel, R. Balasubramanyam Iyer, P. Mazzolini, M. Schubert, J.M. Klopf, J.T. Margraf, O. Bierwagen, M. Wolf, K. Reuter, L.M. Eng, S.C. Kehr, J.D. Caldwell, C. Carbogno, T.G. Folland, M.R. Wagner, and A. Paarmann.
  "Spectral tuning of hyperbolic shear polaritons in monoclinic gallium oxide via isotopic substitution."
  Advanced Materials 0:e14561 (20256).
  doi: 10.1002/adma.202514561

2025

• F. Hempel, M. Rüsing, F. Vernuccio, K.J. Spychala, R. Buschbeck, G. Cerullo, D. Polli, and L.M. Eng. 
  "Phonon dephasing times determined with time-delayed broadband coherent anti-Stokes Raman scattering." 
  Physical Review B 112,  224106 (2025).
  doi:10.1103/1ctr-csjy
• F.H. Feres, F.C.B. Maia, S. Chen, V. Mazzotti, R.A. Mayer, M. Obst, O. Hatem, L. Wehmeier, T. Nörenberg, M.S. Queiroz, J.M. Klopf, S.C. Kehr, L.M. Eng, A.R. Cadore, R. Hillenbrand, R.O. Freitas, and I.D. Barcelos.
  "Two-dimensional talc as a natural hyperbolic material."
  Nanoscale 17, 24151 (2025).
  doi: 10.1039/d5nr02966j
• R.A. Kowalski, N.S. Mueller, G. Álvarez-Pérez, M. Obst, K. Diaz-Granados, G. Carini, A. Senarath, S. Dixit, R. Niemann, R. B. Iyer, F. G. Kaps, J. Wetzel, J.M. Klopf, I. I. Kravchenko, M. Wolf, T.G. Folland, L.M. Eng, S.C. Kehr, P. Alonso-Gonzalez, A. Paarmann, and J.D. Caldwell.
  "Ultraconfined THz Phonon Polaritons in Hafnium Dichalcogenides."
  Nature Materials 24, 1735 (2025).
  doi: 10.1038/s41563-025-02345-0
• A. Luferau, A. Pashkin, S. Winnerl, M. Obst, S.C. Kehr, E. Dimakis, T.V.A.G. de Oliveira, L.M. Eng, and Manfred Helm.  
  "Time-resolved nanospectroscopy of III–V semiconductor nanowires."
  Nanoscale Advances 7, 3692 (2025).
  doi: 10.1039/D5NA00307E
• L. Abylgazina, I. Senkovska, M. Maliuta, C. Bachetzky, M. Rauche, K. Pöschel, J. Schmidt, M. Isaaxs, D. Morgan, M. Otyepka, E. Otyepkova, M. Mendt, Y.D. More, R. Buschbeck, A. Schneemann, A. Synytska, A. Pööpl, L.M. Eng, J.-C. Tan, E. Brunner, and S. Kaskel.
  "The role of surface deformation on responsivity of the pillared layer metal–organic framework DUT-8 (Ni)." 
  Chemical Science 16, 6402  (2025).
  doi: 10.1039/d4sc08223k

2024

• C.S.J. Lee, C. Canalias, R. Buschbeck, B. Koppitz, F. Hempel, Z. Amber, L.M. Eng, and M. Rüsing.

  "Impact of ion exchange on vibrational modes in Rb-doped KTiOPO₄: A Raman spectroscopy study on the interplay between ion exchange and polarization switching"

  Phys. Rev. B 110, 214115 (2024).
  doi: 10.1103/PhysRevB.110.214115

• R.A. Mayer, L. Wehmeier, M. Torquato, X. Chen, F.H. Feres, F.C.B. Maia, M. Obst, F.G. Kaps, A. Luferau, J.M. Klopf, S.N. Gilbert Corder, H.A. Bechtel, J.C. González, E.R. Viana,
  L.M. Eng, S.C. Kehr, R.O. Freitas, and I.D. Barcelos.
  "Paratellurite Nanowires as a Versatile Material for THz Phonon Polaritons."
  ACS Photonics 11, 4323 (2024).
  doi:10.1021/acsphotonics.4c01249
• J. Álvarez-Cuervo, M. Obst, S. Dixit, G. Carini, A. I. F. Tresguerres-Mata, C. Lanza, E. Terán-García, G. Álvarez-Pérez, L. Fernández-Álvarez, K. Diaz-Granados, R. Kowalski, A. S. Senerath, N. S. Mueller, L. Herrer, J.M. De Teresa, S. Wasserroth, J. M. Klopf, T. Beechem, M. Wolf, L.M. Eng, T.G. Folland, A. Tarazaga Martín-Luengo, J. Martín-Sánchez, S.C. Kehr, A.Y. Nikitin, J.D. Caldwell, P. Alonso-González, and A. Paarmann.
  "Unidirectional Ray Polaritons in Twisted Asymmetric Stacks."
  Nature Communications 15, 9042 (2024).
  doi:10.1038/s41467-024-52750-3
• F. Bernhardt, S. Gharat, A. Kapp, F. Pfeiffer, R. Buschbeck, F. Hempel, O. Pashkin, S.C. Kehr, M. Rüsing, S. Sanna, and L.M. Eng.
  "Lattice dynamics of LiNb1-xTaxO3 solid solutions: Theory and experiment."
  Physica Status Solidi A: Applications and Materials Science 2300968 (2024). doi:10.1002/pssa.202300968
• A. Luferau, M. Obst, S. Winnerl, A. Pashkin, S.C. Kehr, E. Dimakis, F.G. Kaps, O. Hatem, K. Mavridou, L.M. Eng, and M. Helm.
  "Hot-Electron Dynamics in a Semiconductor Nanowire under Intense THz Excitation."
  ACS Photonics 11, 3123 (2024).
  doi:10.1021/acsphotonics.4c00433

2023

• F. Kaps, S.C. Kehr, and L.M. Eng.
  "Polarization Sensitivity in Scattering-Type Scanning Near-Field Optical Microscopy – Towards Nanoellipsometry."
  Applied Sciences 13, 10429 (2023).
  doi:10.3390/app131810429
• M. Obst, T. Nörenberg, G. Álvarez-Pérez, T.V.A.G. de Oliveira,  J. Taboada-Gutiérrez, F.H. Feres, F.G. Kaps, O. Hatem, A. Luferau, A.Y. Nikitin, J.M. Klopf, P. Alonso-González, S.C. Kehr, and L.M. Eng.
  "Terahertz Twistoptics – Engineering Canalized Phonon Polaritons."
  ACS Nano 17, 19313 (2023).
  doi:10.1021/acsnano.3c06477
  Preprint available at: doi:10.48550/arXiv.2308.03343

• J. Matson, S. Wasserroth, X. Ni, M. Obst, K. Diaz-Granados, G. Carini, E. Renzi, E. Galiffi, T.G. Folland, L.M. Eng, J.M. Klopf, S. Mastel, S. Armster, V. Gambin, M. Wolf, S.C. Kehr, A. Alu, A. Paarmann, and J. Caldwell.

  "Controlling the Propagation Asymmetry of Hyperbolic Shear Polaritons in Beta-Gallium Oxide."
  Nature Communications 14, 5240 (2023).
  doi:10.1038/s41467-023-40789-7
• F.H. Feres, I.D. Barcelos, A.R. Cadore, L. Wehmeier, T. Nörenberg, R.A. Mayer, R.O. Freitas, L.M. Eng, S.C. Kehr, and F.C.B. Maia.
  "Graphene Nano-Optics in the Terahertz Gap."
  Nano Letters 23, 3913 (2023).
  doi:10.1021/acs.nanolett.3c00578

2022

• T. Nörenberg, G. Álvarez-Pérez, M. Obst, L. Wehmeier, F. Hempel, J.M. Klopf, A.Y. Nikitin, S.C. Kehr, L.M. Eng, P. Alonso-González, and T.V.A.G. de Oliveira.
  "Germanium Monosulfide as Natural Platform for Highly Anisotropic THz Polaritons."
  ACS Nano 16, 20174 (2022).

  doi:10.1021/acsnano.2c05376

• M. Chen, T.V.A.G. De Oliveira, I. Ilyakov, T. Nörenberg, F. Kuschewski, J.-C. Deinert, N. Awari, A. Ponomaryov, M. Kuntzsch, S.C. Kehr, L.M. Eng, M. Gensch, and S. Kovalev.
  "Terahertz-slicing — an all-optical synchronization for 4th generation light sources."
  Optics Express 30, 26955 (2022).
  doi:10.1364/OE.454908

2021

• J. Barnett, L. Wehmeier, A. Heßler, M. Lewin, J. Pries, M. Wuttig, J.M. Klopf, S.C. Kehr, L.M. Eng, and T. Taubner.
  "Far-Infrared Near-Field Optical Imaging and Kelvin Probe Force Microscopy of Laser-Crystallized and -Amorphized Phase Change Material Ge₃Sb₂Te₆."
  Nano Letters 21, 9012 (2021).
  doi:10.1021/acs.nanolett.1c02353
• S. Kovalev, K.-J. Tielrooij, J.-C. Deinert, I. Ilyakov, N. Awari, M. Chem, A. Ponomaryov, M. Bawatna, T.V.A.G. de Oliveira, L.M. Eng, K.A. Kuznetsov, D.A. Safronenkov, G.Kh. Itaeva, P.I. Kuznetsov, H.A. Hafez, D. Turchinovich, and M. Gensch.
  "Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulators."
  npj Quantum Materials 6, 84 (2021).
  doi:10.1038/s41535-021-00384-9
• Z. Yao , X. Chen , L. Wehmeier , S. Xu , Y. Shao , Z. Zeng , F. Liu , A. McLeod , S.N. Gilbert Corder , M. Tsuneto , W. Shi , Z. Wang , W. Zheng , H.A. Bechtel , G.L. Carr , M.C. Martin , A. Zettl , D.N. Basov , X. Chen , L.M. Eng , S.C. Kehr, and M. Liu.
  "Probing subwavelength in-plane anisotropy with antenna-assisted infrared nano-spectroscopy."
  Nature Communications 12, 2649 (2021).
  doi:10.1038/s41467-021-22844-3
• F.H. Feres, R.A. Mayer, L. Wehmeier, F.C.B. Maia, E. Viana, A. Malachias, H.A. Bechtel, J.M. Klopf, L.M. Eng, S.C. Kehr, J. González, R. Freitas, and I. Barcelos.
  "Sub-diffractional cavity modes of terahertz hyperbolic phonon polaritons in tin oxide."
  Nature Communications 12, 1995 (2021).
  doi:10.1038/s41467-021-22209-w
• T. Nörenberg, L. Wehmeier, D. Lang, S.C. Kehr, and L.M. Eng.
  "Compensating for artifacts in scanning near-field optical microscopy due to electrostatics."
  APL Photonics 6, 036102 (2021).
  doi:10.1063/5.0031395
• T.V.A.G. de Oliveira, T. Nörenberg, G. Álvarez-Pérez, L. Wehmeier, J. Taboada-Gutiérrez, M. Obst, F. Hempel, E.J.H. Lee, J.M. Klopf, I. Errea, A.Y. Nikitin, S.C. Kehr, P. Alonso-González, and L.M. Eng.
  "Nanoscale-confined Terahertz Polaritons in a van der Waals Crystal."
  Advanced Materials 33, 2005777 (2021).     
  doi:10.1002/adma.202005777

2020

• H. Amin Pour, L.M. Eng, and S.C. Kehr.
  "Spatially confined vector fields at material-induced resonances in near-field- coupled systems."
  Optics Express 28, 32316 (2020).
  doi:10.1364/OE.402893
• S. Messerschmidt, A. Krampf, L. Vittadello, M. Imlau, T. Nörenberg, L.M. Eng, and David Emin.
  "Small-Polaron Hopping and Low-Temperature (45–225 K) Photo-Induced Transient Absorption in Magnesium-Doped Lithium Niobate ."    
  Crystals 10, 809 (2020).
  doi:10.3390/cryst10090809
• A. Soltani, F. Kuschewski, M. Bonmann, A. Generalov, A. Vorobiev, F. Ludwig, M.M. Wiecha, D. Čibiraitė, F. Walla, S. Winnerl, S.C. Kehr, L.M. Eng, J. Stake, and H. Roskos..
  "Direct nanoscopic observation of plasma waves in the channel of a graphene field-effect transistor."
  Light: Science & Applications 9, 97 (2020).
  doi: 10.1038/s41377-020-0321-0
• L. Wehmeier, T. Nörenberg, T.V.A.G. de Oliveira, J.M. Klopf, S.-Y. Yang, L.W. Martin, R. Ramesh, L.M. Eng, and S.C. Kehr.
  "Phonon-induced near-field resonances in multiferroic BiFeO₃ thin films at infrared and THz wavelengths."
  Applied Physics Letters 116, 071103 (2020).  
  doi: 10.1063/1.5133116

2019

• M. Chen, J.-C. Deinert, B. Green, Z. Wang, I. Ilyakov, N. Awari, M. Bawatna, S. Germanskiy, T.V.A.G. de Oliveira, G. Geloni, T. Tanikawa, M. Gensch, and S. Kovalev.
  "Pulse and field-resolved THz-diagnostics at 4th generation lightsources."
  Optics Express 27, 32360 (2019).
  doi: 10.1364/OE.27.032360
• L. Wehmeier, D. Lang, Y. Liu, X. Zhang, S. Winnerl, L.M. Eng, and S.C Kehr.
  "Polarization-dependent near-field phonon nanoscopy of oxides: SrTiO₃, LiNbO₃, and PbZr_0.2Ti_0.8O₃."
  Physical Review B 100, 035444 (2019). 
  doi: 10.1103/PhysRevB.100.035444
• D. Lang, L. Balaghi, S. Winnerl, H. Schneider, R. Hübner, S.C. Kehr, L.M. Eng, M. Helm, E. Dimakis, and A. Pashkin.
  "Nonlinear plasmonic response of doped nanowires observed by infrared nanospectroscopy."
  Nanotechnology 30, 084003 (2019). 
   doi: 10.1088/1361-6528/aaf5a7
• B. Kirbus, C. Godau, L. Wehmeier, H. Beccard, E. Beyreuther, A. Haußmann, and L. M. Eng.
  "Real-Time 3D Imaging of Nanoscale Ferroelectric Domain Wall Dynamics in Lithium Niobate Single Crystals under Electric Stimuli: Implications for Domain-Wall-Based Nanoelectronic Devices."
  ACS Applied Nano Materials 2, 5787 (2019).
  doi: 10.1021/acsanm.9b01240

2018

• J. Döring, D. Lang, L. Wehmeier, F. Kuschewski, T. Nörenberg, S.C. Kehr, and L.M. Eng.
  "Low-temperature nanospectroscopy of the structural ferroelectric phases in single-crystalline barium titanate."
  Nanoscale 10, 18074-18079 (2018).
  doi: 10.1039/C8NR04081H
• T. Firkala, F. Kuschewski, T. Nörenberg, J.M. Klopf, A. Pashkin, H. Foerstendorf, M. Rudolph, S.C. Kehr, and L.M. Eng.
  "Near-field optical examination of potassium n-butyl xanthate / chalcopyrite flotation products."
  Minerals 8 (3), 118 (2018).
  doi: 10.3390/min8030118
• S. Kovalev, Z. Wang, J.-C. Deinert, N. Awari, M. Chen, B. Green, S. Germanskiy, T.V.A.G. de Oliveira, J.S. Lee, A. Deac, D. Turchinovich, N. Stojanovic, S. Eisebitt, I. Radu, S. Bonetti, T. Kampfrath, and M. Gensch.
  "Selective THz control of magnetic order: new opportunities from superradiant undulator sources."
  Journal of Physics D: Applied Physics 51, 114007 (2018).
  doi: 10.1088/1361-6463/aaac75
• D. Lang, J. Döring, T. Nörenberg, Á. Butykai, I. Kézsmárki, H. Schneider, S. Winnerl, M. Helm, S.C. Kehr, and L.M. Eng.
  "Infrared nanoscopy down to liquid helium temperatures."
  Review of Scientific Instruments 89, 033702 (2018).
  doi: 10.1063/1.5016281
• L.M. Eng, F. Kuschewski, J. Döring, L. Wehmeier, Th. de Oliveira, H.-G.g von Ribbeck, D. Lang, B. Green, S. Kovalev, N. Awari, S. Winnerl, M. Helm, M. Gensch, and S.C. Kehr.
  "Near-field THz nanoscopy at novel accelerator-based photon sources (Conference Presentation)."
  Proceedings SPIE 10531, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XI, 105310E.
  doi: 10.1117/12.2289463.5751529139001

2017

• S.C. Kehr, J. Döring, M. Gensch, M. Helm, and L.M. Eng.
  "FEL-Based Near-Field Infrared to THz Nanoscopy."
  Synchrotron Radiation News 30 (4), 31-35 (2017). 
  doi: 10.1080/08940886.2017.1338421
• A. Butykai, S. Bordács, I. Kézsmárki, V. Tsurkan, A. Loidl, J. Döring, E. Neuber, P. Milde, S.C. Kehr, and L.M. Eng.
  "Characteristics of ferroelectric-ferroelastic domains in Néel-type skyrmion host GaV₄S₈." 
  Scientific Reports 7, 44663 (2017).
  doi: 10.1038/srep44663
• L. Wehmeier, T. Kämpfe, A. Haußmann, and L. M. Eng.
  "In Situ 3D Observation of the Domain Wall Dynamics in a Triglycine Sulfate Single Crystal upon Ferroelectric Phase Transition."
  physica status solidi (RRL) - Rapid Research Letters 11, 1700267 (2017).
  doi: 10.1002/pssr.201700267
• A. Haußmann, L. Kirsten, S. Schmidt, P. Cimalla, L. Wehmeier, E. Koch, and L. M. Eng. "Three-Dimensional, Time-Resolved Profiling of Ferroelectric Domain Wall Dynamics by Spectral-Domain Optical Coherence Tomography."
  Annalen der Physik 529, 1700139 (2017).
  doi: 10.1002/andp.201700139

2016

• J. Döring, L.M. Eng, and S.C. Kehr.
  "Low-temperature piezoresponse force microscopy on barium titanate." 
  Journal of Applied Physics 120, 84103 (2016).
  doi: 10.1063/1.4961523
• F. Kuschewski, H.-G. von Ribbeck, J. Döring, S. Winnerl, L.M. Eng, and S.C. Kehr
  "Narrow-band near-field nanoscopy in the spectral range from 1.3 to 8.5 THz."
  Applied Physics Letters 108, 113102 (2016).
  doi: 10.1063/1.4943793
• S.C. Kehr, R.G.P. McQuaid, L. Ortmann, T. Kämpfe, F. Kuschewski, D. Lang, J. Döring, J.M. Gregg, and L.M. Eng.
  "A Local Superlens." 
  ACS Photonics 3, 20-26 (2016).
  doi: 10.1021/acsphotonics.5b00365

2015

• F. Kuschewski, S.C. Kehr, B. Green, Ch. Bauer, M. Gensch, and L.M. Eng.
  "Optical nanoscopy of transient states in condensed matter." 
  Scientific reports 5 (2015).
  doi: 10.1038/srep12582
• M. Fehrenbacher, S. Winnerl, H. Schneider, J. Döring, S.C. Kehr, L.M. Eng, Y. Huo,  O.G. Schmidt, K. Yao, Y. Liu, and M. Helm.
  "Plasmonic superlensing in doped GaAs." 
  Nano letters 15, 1057-1061 (2015).
  doi: 10.1021/nl503996q

List of all publications of Prof. Eng's group

Recent theses of the SNOM group

Recent conference contributions of the SNOM group