Superconductivity In Heterostructures Research Articles

Emergence of Exotic Spin Texture in Supramolecular Metal Complexes on a 2D Superconductor.

Designer heterostructures have offered a very powerful strategy to create exotic superconducting states by combining magnetism and superconductivity. In this Letter, we use a heterostructure platform combining supramolecular metal complexes (SMCs) with a quasi-2D van der Waals superconductor NbSe_{2}. Our scanning tunneling microscopy measurements demonstrate the emergence of Yu-Shiba-Rusinov bands arising from the interaction between the SMC magnetism and the NbSe_{2} superconductivity. Using x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we show the presence of antiferromagnetic coupling between the SMC units. These result in the emergence of an unconventional 3×3 reconstruction in the magnetic ground state that is directly reflected in real space modulation of the Yu-Shiba-Rusinov bands. The combination of flexible molecular building blocks, frustrated magnetic textures, and superconductivity in heterostructures establishes a fertile starting point to fabricating tunable quantum materials, including unconventional superconductors and quantum spin liquids.

A comprehensive review of superconductivity in heterostructures and superlattices comprising 2D materials

A comprehensive review of superconductivity in heterostructures and superlattices comprising 2D materials

Transition from three- to two-dimensional Ising superconductivity in few-layer NbSe2 by proximity effect from van der Waals heterostacking

We report the experimental observation of Ising superconductivity in 3-dimensional NbSe2 stacked with single-layer MoS2. The angular dependence of the upper critical magnetic field and the temperature dependence of the upper parallel critical field confirm the appearance of two-dimensional Ising superconductivity in the 3-dimensional NbSe2 with single-layer MoS2 overlay. We show that the superconducting phase has strong Ising spin-orbit correlations which make the holes spin non-degenerate. Our observation of Ising superconductivity in heterostructures of few-layer NbSe2 of thickness ~ 15 nm with single-layer MoS2 raises the interesting prospect of observing topological chiral superconductors with nontrivial Chern numbers in a momentum-space spin-split fermionic system.

Coulomb blockade effects in a topological insulator grown on a high-Tc cuprate superconductor

The evidence for proximity-induced superconductivity in heterostructures of topological insulators and high-Tc cuprates has been intensely debated. We use molecular-beam epitaxy to grow thin films of topological insulator Bi2Te3 on a cuprate Bi2Sr2CaCu2O8+x, and study the surface of Bi2Te3 using low-temperature scanning tunneling microscopy and spectroscopy. In few unit-cell thick Bi2Te3 films, we find a V-shaped gap-like feature at the Fermi energy in dI/dV spectra. By reducing the coverage of Bi2Te3 films to create nanoscale islands, we discover that this spectral feature dramatically evolves into a much larger hard gap, which can be understood as a Coulomb blockade gap. This conclusion is supported by the evolution of dI/dV spectra with the lateral size of Bi2Te3 islands, as well as by topographic measurements that show an additional barrier separating Bi2Te3 and Bi2Sr2CaCu2O8+x. We conclude that the prominent gap-like feature in dI/dV spectra in Bi2Te3 films is not a proximity-induced superconducting gap. Instead, it can be explained by Coulomb blockade effects, which take into account additional resistive and capacitive coupling at the interface. Our experiments provide a fresh insight into the tunneling measurements of complex heterostructures with buried interfaces.

Signatures of spin-triplet Cooper pairing in the density of states of spin-textured superconductor-ferromagnet bilayers

The existence of spin-triplet superconductivity in non-collinear magnetic heterostructures with superconductors is by now well established. This observation lays the foundation of superconducting spintronics with the aim to create a low-power consuming devices in order to replace the conventional electronics limited by heating. From a fundamental point of view the investigation of the structure and properties of spin-triplet Cooper pairs continues. Recently, spectroscopic evidence has shown to offer more detailed insights in the structure of triplet Cooper pairs than the supercurrent. Hence, we study here the structure of spin-triplet Cooper pairs through the density of states (DOS) in bilayers of a textured magnetic insulator in proximity to a superconductor. Using quasiclassical Green function methods, we study the local DOS, both spin-resolved and spin-independent. We show that the equal-spin and mixed-spin triplet Cooper pairs leads to different spectroscopic signatures, which can be further enhanced by spin-polarized spectroscopy. Our results show the huge potential spin-polarized tunneling methods offer in characterizing unconventional superconductivity in heterostructures.

Feshbach Shape Resonance in Multiband Superconductivity in Heterostructures

We report experimental data showing the Feshbach shape resonance in the electron doped MgB2 where the chemical potential is tuned by Al, Sc, and C substitutions. The scaling of the critical temperature Tc as a function of the Lifshitz parameter z = EΓ−EF, where EF is the chemical potential and EΓ is the energy of the Γ critical point where the σ Fermi surface changes from the 3D to a 2D topology, is reported. The resonant amplification of Tc(z) driven by the interband pairing is assigned to a Feshbach shape resonance characterized by quantum superposition of pairs in states corresponding to different spatial location and different parity. It is centered at z = 0 where the chemical potential is tuned to a Van Hove-Lifshits feature for the change of Fermi surface dimensionality in the electronic energy spectrum in one of the subbands. In this heterostructure at atomic limit the multiband superconductivity is in the clean limit because the disparity and negligible overlap between electron wavefunctions in different subbands suppresses the single electron interband impurity scattering rate. The emerging scenario from these experimental data suggests that the Feshbach shape resonance could be the mechanism for high Tc in particular nanostructured architectures.