arXiv subjects

Thomas Gozlinski

Publications and source records attributed to Thomas Gozlinski.

5 recordsLinked to original sources

arXiv2025

Visualization of defect-induced interband proximity effect at the nanoscale

The vast majority of superconductors have more than one Fermi surface, on which the electrons pair below the critical temperature $T_C$, yet their superconducting behavior can be well described by a single-band Bardeen-Cooper-Schrieffer theory. This is mostly due to interband scattering, especially in superconductors in the dirty limit, rigidly linking the pairing amplitude of the different bands. This effect has severely limited experimental studies of the complex physics of multiband superconductivity. In this study, we utilize the fact that elementary Pb - as a clean limit system - has two Fermi surfaces that are only weakly coupled by interband scattering, allowing the formation of two separate condensates. By studying crystallographic defects in the form of stacking fault tetrahedra with our millikelvin scanning tunneling microscope, we show how to locally tune interband coupling ranging from weak to strong coupling and modify the superconducting order parameters from two well separated gaps to one merged gap around defects. The experiments critically test the theory of multiband superconductors and give a route to access a wide range of predicted quantum effects in these systems.

cond-mat.supr-con↗

arXiv2024

Equivalence of pseudogap and pairing energy in a cuprate high-temperature superconductor

The pseudogap stands out in the phase diagram of the cuprate high-temperature superconductors because its origin and relationship to superconductivity remain elusive. The origin of the pseudogap has been debated, with competing hypotheses attributing it to preformed electron pairs or local order, such as charge density waves. Here, we present unambiguous evidence supporting the pairing scenario, using local shot-noise spectroscopy measurements in Bi2Sr2CaCu2O8+{\delta}. Our data demonstrates that the pseudogap energy coincides with the onset of electron pairing, and is spatially heterogeneous with values reaching up to 70 meV. Our results exclude a pure local order origin of the pseudogap, link the pseudogap to Cooper pair formation, and show that the limiting factor for higher Tc in cuprates is phase coherence.

cond-mat.supr-con↗

arXiv2023

Bosonic excitation spectra of superconducting $\mathrm{Bi_2Sr_2CaCu_2O_{8+δ}}$ and $\mathrm{YBa_2Cu_3O_{6+x}}$ extracted from scanning tunneling spectra

A detailed interpretation of scanning tunneling spectra obtained on unconventional superconductors enables one to gain information on the pairing boson. Decisive for this approach are inelastic tunneling events. Due to the lack of momentum conservation in tunneling from or to the sharp tip, those are enhanced in the geometry of a scanning tunneling microscope compared to planar tunnel junctions. This work extends the method of obtaining the bosonic excitation spectrum by deconvolution from tunneling spectra to nodal $d$-wave superconductors. In particular, scanning tunneling spectra of slightly underdoped $\mathrm{Bi_2Sr_2CaCu_2O_{8+δ}}$ with a $T_c$ of $82\,\mathrm{K}$ and optimally doped $\mathrm{YBa_2Cu_3O_{6+x}}$ with a $T_c$ of $92\,\mathrm{K}$ reveal a resonance mode in their bosonic excitation spectrum at $Ω_\mathrm{res} \approx 63\,\mathrm{meV}$ and $Ω_\mathrm{res} \approx 61\,\mathrm{meV}$ respectively. In both cases, the overall shape of the bosonic excitation spectrum is indicative of predominant spin scattering with a resonant mode at $Ω_\mathrm{res}<2Δ$ and overdamped spin fluctuations for energies larger than $2Δ$. To perform the deconvolution of the experimental data, we implemented an efficient iterative algorithm that significantly enhances the reliability of our analysis.

cond-mat.supr-con↗

arXiv2023

Identification of multiple-flux-quanta vortices by core states in the two-band superconductor Pb

Superconductors are of type I or II depending on whether they form an Abrikosov vortex lattice. Although bulk lead (Pb) is classified as a prototypical type-I superconductor, we observe single-flux-quantum and multiple-flux-quanta vortices in the intermediate state using mK scanning tunneling microscopy. We show that the winding number of individual vortices can be determined from the real space wave function of its Caroli-de Gennes-Matricon bound states. This generalizes the index theorem put forward by Volovik for isotropic electronic states to realistic electronic structures. In addition, the bound states due to the two superconducting bands of Pb can be separately detected. This yields strong evidence for low inter-band coupling and an independent closure of the gaps inside vortices.

cond-mat.supr-con↗

arXiv2019

Microscopic charging and in-gap states in superconducting granular aluminum

Following the emergence of superconducting granular aluminum (grAl) as a material for high-impedance quantum circuits, future development hinges on a microscopic understanding of its phase diagram, and whether the superconductor-to-insulator transition (SIT) is driven by disorder or charging effects. Beyond fundamental relevance, these mechanisms govern noise and dissipation in microwave circuits. Although the enhancement of the critical temperature, and the SIT in granular superconductors have been studied for more than fifty years, experimental studies have so far provided incomplete information on the microscopic phenomena. Here we present scanning tunneling microscope measurements of the local electronic structure of superconducting grAl. We confirm an increased superconducting gap in individual grains both near and above the Mott resistivity $ρ_\mathrm{M} \approx 400\ μΩcm$. Above $ρ_\mathrm{M}$ we find Coulomb charging effects, a first indication for decoupling, and in-gap states on individual grains, which could contribute to flux noise and dielectric loss in quantum devices. We also observe multiple low-energy states outside the gap, which may indicate bosonic excitations of the superconducting order parameter.

cond-mat.supr-con↗