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Devising effective platinum (Pt)-free nanomaterials for catalyzing oxygen reduction reaction (ORR) is desired, but some main drawbacks still exist for commercial implementation in fuel cell systems. Herein, we present the preparation of gold (Au)-modified palladium (Pd) thin films with various thicknesses of Au using magnetron sputtering deposition. It is found that the prepared Au-modified Pd (Au/Pd) thin films with some desirable characteristics such as large electrochemical surface area (ECSA), improved electron transfer, along with high catalytical active positions reveal markedly boosted electro-catalytic activity and stability for oxygen reduction in acidic environments compared with pure Pd catalyst. Noticeably, the as-deposited Au/Pd thin films exhibit a connection in oxygen reduction ability as a function of Au thickness, with the 0.16 nm Au/Pd thin film being the best ORR sample. Significantly, 0.16 nm Au/Pd material demonstrates superior stability after 1000 potential cycles in comparison with the 0.16 nm Pt/Pd owing to the influence of Au modification as well as its structurally stable surfaces., Comment: 26 pages, 8 figures, 2 tables

Van der Waals heterostructures are an excellent platform for studying intriguing interface phenomena, such as moir\'e and proximity effects. Surface science techniques like scanning tunneling microscopy (STM) have proven a powerful tool to study such heterostructures but have so far been hampered because of their high sensitivity to surface contamination. Here, we report a dry polymer-based assembly technique to fabricate van der Waals heterostructures with atomically clean surfaces. The key features of our suspended dry pick-up and flip-over technique are 1) the heterostructure surface never comes into contact with polymers, 2) it is entirely solvent-free, 3) it is entirely performed in a glovebox, and 4) it only requires temperatures below 130$^{\circ}$. By performing ambient atomic force microscopy and atomically-resolved scanning tunneling microscopy on example heterostructures, we demonstrate that we can fabricate air-sensitive heterostructures with ultra-clean interfaces and surfaces. Due to the lack of polymer melting, the technique is further compatible with heterostructure assembly under ultra-high vacuum conditions, which promises ultimate heterostructure quality.

One-dimensional (1D) topological superconductivity is a state of matter that is not found in nature. However, it can be realised, for example, by inducing superconductivity into the quantum spin Hall edge state of a two-dimensional topological insulator. Because topological superconductors are proposed to host Majorana zero modes, they have been suggested as a platform for topological quantum computing. Yet, conclusive proof of 1D topological superconductivity has remained elusive. Here, we employ low-temperature scanning tunnelling microscopy to show 1D topological superconductivity in a van der Waals heterostructure by directly probing its superconducting properties, instead of relying on the observation of Majorana zero modes at its boundary. We realise this by placing the two-dimensional topological insulator monolayer WTe$_2$ on the superconductor NbSe$_2$. We find that the superconducting topological edge state is robust against magnetic fields, a hallmark of its triplet pairing. Its topological protection is underpinned by a lateral self-proximity effect, which is resilient against disorder in the monolayer edge. By creating this exotic state in a van der Waals heterostructure, we provide an adaptable platform for the future realization of Majorana bound states. Finally, our results more generally demonstrate the power of Abrikosov vortices as effective experimental probes for superconductivity in nanostructures., Comment: 13 pages, 4 figures

Low-dimensional materials have remarkable properties that are distinct from their bulk counterparts. A paradigmatic example is Ising superconductivity that occurs in monolayer materials such as NbSe2 which show a strong violation of the Pauli limit. In monolayers, this occurs due to a combination of broken inversion symmetry and spin-orbit coupling that locks the spins of the electrons out-of-plane. Bulk NbSe2 is centrosymmetric and is therefore not an Ising superconductor. We show that bulk misfit compound superconductors, (LaSe)1.14(NbSe2) and (LaSe)1.14(NbSe2)2, comprised of monolayers and bilayers of NbSe2, exhibit unexpected Ising protection with a Pauli-limit violation comparable to monolayer NbSe2, despite formally having inversion symmetry. We study these misfit compounds using complementary experimental methods in combination with first-principles calculations. We propose theoretical mechanisms of how the Ising protection can survive in bulk materials. We show how some of these mechanisms operate in these bulk compounds due to a concerted effect of charge-transfer, defects, reduction of interlayer hopping, and stacking. This highlights how Ising superconductivity can, unexpectedly, arise in bulk materials, and possibly enable the design of bulk superconductors that are resilient to magnetic fields., Comment: 14 pages, 4 figures, 4 extended data items

Transition metal dichalcogenides (TMDs) display a rich variety of instabilities such as spin and charge orders, Ising superconductivity and topological properties. Their physical properties can be controlled by doping in electric double-layer field-effect transistors (FET). However, for the case of single layer NbSe$_2$, FET doping is limited to $\approx 1\times 10^{14}$ cm$^{-2}$, while a somewhat larger charge injection can be obtained via deposition of K atoms. Here, by performing ARPES, STM, quasiparticle interference measurements, and first principles calculations we show that a misfit compound formed by sandwiching NbSe$_2$ and LaSe layers behaves as a NbSe$_2$ single layer with a rigid doping of $0.55-0.6$ electrons per Nb atom or $\approx 6\times 10^{14}$ cm$^{-2}$. Due to this huge doping, the $3\times3$ charge density wave is replaced by a $2\times2$ order with very short coherence length. As a tremendous number of different misfit compounds can be obtained by sandwiching TMDs layers with rock salt or other layers, our work paves the way to the exploration of heavily doped 2D TMDs over an unprecedented wide range of doping.

The combination of different exotic properties in materials paves the way for the emergence of their new potential applications. An example is the recently found coexistence of the mutually antagonistic ferromagnetism and superconductivity in hydrogenated boron-doped diamond, which promises to be an attractive system with which to explore unconventional physics. Here, we show the emergence of Yu-Shiba-Rusinov (YSR) bands with a spatial extent of tens of nanometers in ferromagnetic superconducting diamond using scanning tunneling spectroscopy. We demonstrate theoretically how a two-dimensional (2D) spin lattice at the surface of a three-dimensional (3D) superconductor gives rise to the YSR bands, and how their density-of-states profile correlates with the spin lattice structure. The established strategy to realize new forms of the coexistence of ferromagnetism and superconductivity opens a way to engineer the unusual electronic states and also to design better performing superconducting devices., Comment: 13 pages, 5 figures

Fourier transformation of atomically resolved STM topography of $(LaSe)_{1.14}(NbSe_2)$ revealed a surface modulation along the hexagonal surface lattice of $NbSe_2$ layer, but with a two times larger period. We compare it to the modified charge density wave found on plain $NbSe_2$ under strain., Comment: Withdrawn due to data re-evaluation