TY - GEN A1 - Seibold, Götz T1 - On the Evaluation of Higher-Harmonic-Current Responses for High-Field Spectroscopies in Disordered Superconductors T2 - Condensed Matter N2 - We discuss a formalism that allows for the calculation of a higher-harmonic-current response to a strong applied electric field for disordered superconducting systems described on the basis of tight-binding models with on- and/or intersite interactions. The theory is based on an expansion of the density matrix in powers of the field amplitudes, where we solve the equation of motion for the individual components. This allows the evaluation of higher-order response functions on significantly larger lattices than one can achieve with a previously used approach, which is based on a direct temporal integration of the equation of motion for the complete density matrix. In the case of small lattices, where both methods can be applied by including also the contribution of collective modes, we demonstrate the agreement of the corresponding results. KW - superconductivity KW - third-harmonic generation KW - disorder Y1 - 2023 UR - https://www.mdpi.com/2410-3896/8/4/95 U6 - https://doi.org/10.3390/condmat8040095 SN - 2410-3896 VL - 8 IS - 4 SP - 1 EP - 16 ER - TY - GEN A1 - Lorenzana, Jose A1 - Seibold, Götz T1 - Long-Lived Higgs Modes in Strongly Correlated Condensates T2 - Physical Review Letters N2 - We investigate order parameter fluctuations in the Hubbard model within a time-dependent Gutzwiller approach. While in the weak coupling limit we find that the amplitude fluctuations are short-lived due to a degeneracy with the energy of the edge of the quasiparticle continua (and in agreement with Hartree-Fock+RPA theory), these are shifted below the edge upon increasing the interaction. Our calculations therefore predict undamped amplitude (Higgs) oscillations of the order parameter in strongly coupled superconductors, cold atomic fermion condensates, and strongly interacting charge- and spin-density wave systems. We propose an experimental realization for the detection of the spin-type Higgs mode in undoped cuprates and related materials where, due to the Dzyaloshinsky-Moriya interaction, it can couple to an out-of-plane ferromagnetic excitation that is visible via the Faraday effect. KW - Magnetism KW - Quasiparticles & collective excitations KW - Spin dynamics KW - Superconducting order parameter KW - Superconductivity KW - Antiferromagnets KW - Atomic gases KW - High-temperature superconductors Y1 - 2024 UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.026501 U6 - https://doi.org/10.1103/PhysRevLett.132.026501 SN - 0031-9007 VL - 132 IS - 2 SP - 026501-1 EP - 026501-8 ER - TY - GEN A1 - Wahlberg, Eric A1 - Arpaia, Riccardo A1 - Chakraborty, Debmalya A1 - Kalaboukhov, Alexei A1 - Vignolles, David A1 - Proust, Cyril A1 - Black-Schaffer, Annica M. A1 - Bauch, Thilo A1 - Seibold, Götz A1 - Lombardi, Floriana T1 - Boosting superconductivity in ultrathin YBa₂Cu₃O₇−δ films via nanofaceted substrates T2 - Nature communications N2 - In cuprate high-temperature superconductors the doping level is fixed during synthesis, hence the charge carrier density per CuO2 plane cannot be easily tuned by conventional gating, unlike in 2D materials. Strain engineering has recently emerged as a powerful tuning knob for manipulating the properties of cuprates, in particular charge and spin orders, and their delicate interplay with superconductivity. In thin films, additional tunability can be introduced by the substrate surface morphology, particularly nanofacets formed by substrate surface reconstruction. Here we show a remarkable enhancement of the superconducting onset temperature and the upper critical magnetic field Hc,2 in nanometer-thin YBa2Cu3O7−δ films grown on a substrate with a nanofaceted surface. We theoretically show that the enhancement is driven by electronic nematicity and unidirectional charge density waves, where both elements are captured by an additional effective potential at the interface between the film and the uniquely textured substrate. Our findings show a new paradigm in which substrate engineering can effectively enhance the superconducting properties of cuprates. This approach opens an exciting frontier in the design and optimization of high-performance superconducting materials. KW - Electronic properties and materials KW - Superconducting properties and materials Y1 - 2026 U6 - https://doi.org/10.1038/s41467-025-67500-2 SN - 2041-1723 VL - 17 SP - 1 EP - 8 PB - Springer Nature CY - London ER - TY - GEN A1 - Schlipf, Jon A1 - Cutolo, Maria Alessandra A1 - Manganelli, Costanza Lucia A1 - Reiter, Sebastian A1 - Seibold, Götz A1 - Skibitzki, Oliver A1 - Wenger, Christian A1 - Fischer, Inga Anita T1 - Fabrication and optical characterization of CMOS-compatible honeycomb-like large-scale lattices of near-field coupled plasmonic TiN nanotriangles T2 - Advanced optical materials N2 - Honeycomb-like plasmonic titanium nitride nanotriangle arrays defined by photolithography and fabricated in a modified silicon-germanium electronic–photonic integrated circuit process in a state-of-the-art pilot line. The nanotriangle arrays are characterized in experiments and simulations. The momentum-dependent reflectance spectra exhibit not only features that are consistent with surface lattice resonances in the honeycomb lattice but also minima governed by near-field coupling of the individual nanotriangles. The optical characterization results in combination with simulation-based predictions indicate that such nanotriangle arrays are capable of supporting collective plasmonic resonances that can be described as massless Dirac particles. The fabrication approach opens up the possibility of integrating the structures into device fabrication processes, and avenues toward near-infrared sensing and communication applications are predicted. KW - Plasmonic Nanostructures KW - Optics of Nanostructures Y1 - 2025 UR - https://advanced.onlinelibrary.wiley.com/doi/epdf/10.1002/adom.202403408 U6 - https://doi.org/10.1002/adom.202403408 SN - 2195-1071 VL - 2025 SP - 1 EP - 8 PB - Wiley-VCH CY - Weinheim ER -