Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2_2

Nonreciprocal transport refers to charge transfer processes that are sensitive to the bias polarity. Until recently, nonreciprocal transport was studied only in dissipative systems, where the nonreciprocal quantity is the resistance. Recent experiments have, however, demonstrated nonreciprocal supercurrent leading to the observation of a supercurrent diode effect in Rashba superconductors, opening the vision of dissipationless electronics. Here we report on a supercurrent diode effect in NbSe$_2$ constrictions obtained by patterning NbSe$_2$ flakes with both even and odd layer number. The observed rectification is driven by valley-Zeeman spin-orbit interaction. We demonstrate a rectification efficiency as large as 60%, considerably larger than the efficiency of devices based on Rashba superconductors. In agreement with recent theory for superconducting transition metal dichalcogenides, we show that the effect is driven by an out-of-plane magnetic field component. Remarkably, we find that the effect becomes field-asymmetric in the presence of an additional in-plane field component transverse to the current direction. Supercurrent diodes offer a further degree of freedom in designing superconducting quantum electronics with the high degree of integrability offered by van der Waals materials.Comment: 18 pages, 12 figure

Data archive of "Supercurrent and phase slips in a ballistic carbon nanotube bundle embedded into a van der Waals heterostructure"

Data archive for the article "", accepted for publication in Nano Letters

Supercurrent and Phase Slips in a Ballistic Carbon Nanotube Bundle Embedded into a van der Waals Heterostructure

We demonstrate long-range superconducting correlations in a several-micrometers-long carbon nanotube bundle encapsulated in a van der Waals stack between hBN and NbSe2. We show that a substantial supercurrent flows through the nanotube section beneath the NbSe2 crystal as well as through the 2 μm long section not in contact with it. The large in-plane critical magnetic field of this supercurrent is an indication that even inside the carbon nanotube Cooper pairs enjoy a degree of paramagnetic protection typical of the parent Ising superconductor. As expected for superconductors of nanoscopic cross section, the current-induced breakdown of superconductivity is characterized by resistance steps due to the nucleation of phase slip centers. All elements of our hybrid device are active building blocks of several recently proposed setups for realization of Majorana fermions in carbon nanotubes

Data archive for the article: Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2 nanowires

Set of raw measured data for the article: "Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2 nanowires"

Data archive for the article: Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2

Set of raw measured data for the article: "Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2 nanowires"

Air tightness of hBN encapsulation and its impact on Raman spectroscopy of van der Waals materials

Raman spectroscopy is a precious tool for the characterization of van der Waals materials, e.g. for the determination of the layer number in thin exfoliated flakes. For sensitive materials, however, this method can be dramatically invasive. In particular, the light intensity required to obtain a significant Raman signal is sufficient to immediately photo-oxidize few-layer thick metallic van der Waals materials. In this work we investigated the impact of the environment on Raman characterization of thin NbSe2 crystals. We show that in ambient conditions the flake is locally oxidized even for very low illumination intensity. Based on this extreme sensitivity to the presence of light and oxygen, we could study the air-tightness of the hBN encapsulation method, the most common passivation method for a wide range of 2D material-based devices. We find that only fully encapsulated devices are reliably air-tight. On the contrary, a simple hBN cover from the top does not prevent a slow diffusion of oxygen between the SiO2 surface and the flake itself

Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2

Nonreciprocal transport refers to charge transfer processes that are sensitive to the bias polarity. Until recently, nonreciprocal transport was studied only in dissipative systems, where the nonreciprocal quantity is the resistance. Recent experiments have, however, demonstrated nonreciprocal supercurrent leading to the observation of a supercurrent diode effect in Rashba superconductors. Here we report on a supercurrent diode effect in NbSe2 constrictions obtained by patterning NbSe2 flakes with both even and odd layer number. The observed rectification is a consequence of the valley-Zeeman spin-orbit interaction. We demonstrate a rectification efficiency as large as 60%, considerably larger than the efficiency of devices based on Rashba superconductors. In agreement with recent theory for superconducting transition metal dichalcogenides, we show that the effect is driven by the out-of-plane component of the magnetic field. Remarkably, we find that the effect becomes field-asymmetric in the presence of an additional in-plane field component transverse to the current direction. Supercurrent diodes offer a further degree of freedom in designing superconducting quantum electronics with the high degree of integrability offered by van der Waals materials