@misc{GrilliDiCastroMirarchietal., author = {Grilli, Marco and Di Castro, Carlo and Mirarchi, Giovanni and Seibold, G{\"o}tz and Caprara, Sergio}, title = {Dissipative Quantum Criticality as a Source of Strange Metal Behavior}, series = {Symmetry}, volume = {15}, journal = {Symmetry}, number = {3}, issn = {2073-8994}, doi = {10.3390/sym15030569}, abstract = {The strange metal behavior, usually characterized by a linear-in-temperature (T) resistivity, is a still unsolved mystery in solid-state physics. It is often associated with the proximity to a quantum critical point (a second order transition at temperature T=0, leading to a broken symmetry phase) focusing on the related divergent order parameter correlation length. Here, we propose a paradigmatic shift, focusing on a divergent characteristic time scale due to a divergent dissipation acting on the fluctuating critical modes while their correlation length stays finite. To achieve a divergent dissipation, we propose a mechanism based on the coupling between a local order parameter fluctuation and electron density diffusive modes that accounts both for the linear-in-T resistivity and for the logarithmic specific heat versus temperature ratio CV/T∼log(1/T), down to low temperatures.}, language = {en} } @misc{HizhnyakovSeibold, author = {Hizhnyakov, Vladimir and Seibold, G{\"o}tz}, title = {Nanoscale phase separation in cuprate superconductors}, series = {Physica C: Superconductivity and its Applications}, volume = {612}, journal = {Physica C: Superconductivity and its Applications}, issn = {1873-2143}, doi = {10.1016/j.physc.2023.1354309}, pages = {1 -- 7}, abstract = {Electronic inhomogeneities are nowadays a well established feature of high-temperature superconductors, most prominently exemplified by the observation of charge-ordered states in a large number of cuprate materials. In this contribution we review the particular contribution of the Stuttgart-Tartu-Cottbus group to this field, which has been largely stimulated by intense discussion with K. Alex M{\"u}ller. The original scenario, which was based on the formation of a percolative electronic network, is substantiated by a microscopic analysis of the clustering of magnetic polarons within the one-band Hubbard model.}, language = {en} } @misc{BenfattoCastellaniSeibold, author = {Benfatto, Lara and Castellani, Claudio and Seibold, G{\"o}tz}, title = {Linear and nonlinear current response in disordered d-wave superconductors}, series = {Physical Review B}, volume = {108}, journal = {Physical Review B}, issn = {2469-9969}, doi = {10.1103/PhysRevB.108.134508}, pages = {134508-1 -- 134508-15}, abstract = {We present a detailed theoretical investigation of the linear and nonlinear optical response in a model system for a disordered d-wave superconductor. By evaluating the quasiparticle contribution (BCS response) we show that for both quantities the gap symmetry considerably changes the paradigm of the optical response as compared to the conventional s-wave case. For what concerns the linear response our findings agree with previous work showing that in strongly disordered d-wave superconductors a large fraction of uncondensed spectral weight survives below Tc, making the optical absorption around the gap-frequency scale almost unchanged with respect to the normal state. Our numerical results are in excellent quantitative agreement with experiments in overdoped cuprates. In the nonlinear regime we focus on the third-harmonic generation (THG), finding that, as already established for the s-wave case, in general a large THG is triggered by disorder-activated paramagnetic processes. However, in the d-wave case the BCS response is monotonously increasing in frequency, losing any signature of THG enhancement when the THz pump frequency ω matches the gap maximum Δ, a hallmark of previous experiments in conventional s-wave superconductors. Our findings, along with the mild polarization dependence of the response, provide an explanation for recent THG measurements in cuprates, setting the framework for the theoretical understanding of nonlinear effects in unconventional cuprates.}, language = {en} } @misc{Seibold, author = {Seibold, G{\"o}tz}, title = {On the Evaluation of Higher-Harmonic-Current Responses for High-Field Spectroscopies in Disordered Superconductors}, series = {Condensed Matter}, volume = {8}, journal = {Condensed Matter}, number = {4}, issn = {2410-3896}, doi = {10.3390/condmat8040095}, pages = {1 -- 16}, abstract = {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.}, language = {en} }