Study Observes Superconductivity Coupled With Spin Orbit Parity in Thin 2M-WS2

Study Observes Superconductivity Coupled With Spin Orbit Parity in Thin 2M-WS2

Crystal structure and characterizations of 2M-WS2a, schematic diagram of two bands of opposite parity inverting at Γ with color indicating different orbitals (represented by dark blue and red, respectively). The spectrum after projection is plotted to show such topological band inversion that edge states can be given. SOPC superconductivity appears when copper pairs with the states close to the topological band crossing (such as near the Fermi EF level), where SOPC is strong and crucial. b, Top and side views of the crystal structure of 2M-WS2, where the a-axis (purple dashed line), b-axis (pink dashed line), c-axis (light blue dashed line), and c*-axis (pink dashed line) dashed dark blue oriented perpendicular to the {001} planes) are marked. The tungsten atoms are displaced from their octahedral sites due to strong intermetallic bonds, forming the zigzag metal-metal chains visible along the a-axis. c, Density functional theory calculated the d-states for tungsten atoms and p-states for sulfur atoms projected into the monolayer (left) and bilayer (right) electronic bands of the 2M-WS2, where one can achieve a clear band inversion between the W and S bands. Observed around the Γ point. d, Optical images of few layered flakes of 2M-WS2 cleaved on a SiO2/Si substrate. The number of layers (L) is labeled in the left image and the a-axis of each crystal is marked with cyan dashed lines in the left and right images. Scale bars, 4 µm. e, Brightfield TEM image taken from a section of an exfoliated 2M-WS2 ribbon-like flake, with the inset being the electron diffraction pattern of the selected area. Show that the long axis of the codend is along the direction <100> (one axis, as marked by the cyan dashed line). Scale bar, 500 nm. f, Experimental annular darkfield scanning transmission electron microscopy image taken from 2M-WS2 flake viewed along the c* axis. The inset shows the simulated image. Scale bar, 0.5 nm. Credit: physics of nature (2022). DOI: 10.1038/s41567-022-01812-8

In recent years, many physicists and materials scientists have been studying superconductors, materials that can conduct direct current electricity without loss of energy when cooled to a given temperature. These materials could have many valuable applications, including generating power for imaging machines (eg, MRI scanners), trains, and other technological systems.

Researchers from Fudan University, Shanghai Qi Zhi Institute, Hong Kong University of Science and Technology and other institutes in China have recently discovered a new mechanism for generating an anisotropically enhanced in-plane upper critical field in atomically thin centrosymmetric superconductors with topological band inversions. His work, published in physics of naturespecifically demonstrated this mechanism in a thin layer of 2M-WS2a material that has recently attracted much research attention.

“In 2020, an article by our theoretical collaborator Prof. KT Law proposed that 2D centrosymmetric superconductors with a topological band inversion, such as 1T′-WTe2 exhibit a different type of superconductivity, called spin-orbit parity-coupled superconductivity (SOPC),” Enze Zhang, one of the researchers who conducted the study, told Phys.org.

“SOPC is predicted to produce a novel superconductivity near the topological band junction with anisotropic and greatly enhanced spin susceptibility with respect to the plane magnetic field addresses. At that time, we were conducting research on the superconducting properties atomically thin 2M-WS2so after speaking with Prof. KT Law, we feel that the emerging van der Waals superconductor 2M-WS2 would probably be a promising candidate for spin-orbit parity-coupled superconductivity.”

The structure of the monolayer 2M-WS2 is identical to that of 1T′-WTe2, material previously investigated by Prof. Law and his team. 2M-WS2however, it has a unique stacking mode, which distinguishes it from other transition metal dichalcogenides.

The researchers previously found that in its bulk form, this material exhibits a high superconducting transition temperature. youC. of 8.8 K. In addition, theoretical calculations suggested that atomically thin layers of 2M-WS2 maintain topological edge states with band inversion.

In their experiments, Zhang and his colleagues measured the in-plane upper critical field in a high magnetic field and confirmed the violation of Pauli’s limit law. They also observed a strongly anisotropic double symmetry in the material, in response to the direction of the in-plane magnetic field.

“Tunneling experiments performed under high in-plane magnetic fields also showed that the superconducting gap in atomically thin 2M-WS2 possesses an anisotropic magnetic response along different in-plane magnetic field directions, and it persists well above the Pauli limit,” Zhang explained. “Using self-consistent mean field calculations, our theoretical collaborators conclude that these unusual behaviors originate from in the strong -orbit-parity coupling arising from topological band inversion in 2M-WS2.”

The researchers’ experiments spanned several steps. First, the team made magnetic transport measurements in the atomically thin 2M-WS.2 and found that its upper in-plane critical field is not only well beyond the paramagnetic Pauli limit, but also exhibits strongly anisotropic twofold symmetry in response to the direction of the in-plane magnetic field.

Subsequently, they used tunneling spectroscopy to collect measurements under high in-plane magnetic fields. These measurements revealed that the superconducting gap in atomically thin 2M-WS2 it possesses an anisotropic magnetic response along different in-plane magnetic field directions, which persists well above the Pauli limit.

Finally, the researchers performed a series of self-consistent mean field calculations to better understand the origin of the unusual behaviors they observed in their sample. Based on their results, they concluded that these behaviors originate from the strong spin-orbit parity coupling that arises from topological band inversion in 2M-WS.2which effectively fixes the spin of the states near the topological band junction and re-normalizes the effect of external Zeeman fields in an anisotropic fashion.

“We discovered a new mechanism for generating an anisotropically enhanced in-plane upper critical field in atomically thin centrosymmetric superconductors with topological band inversions, highlighting 2D 2M-WS2 as a wonderful platform for the study of exotic superconducting phenomena, such as higher-order topological superconductivity and other device applications,” Zhang said.

“The novel properties found here are highly non-trivial, as they directly reflect strong SOPC inherited from topological band inversion in the normal state of 2M-WS.2that had been ignored for many years in previous studies of centrosymmetric superconductors”.

In recent years, more research teams around the world have been exploring the properties and mechanisms of centrosymmetric superconductors. transition metal dichalcogenides (TMD), as a 1T′-MoS superconducting monolayer2and 1T′-WTe2due to the characteristic coexistence of the structure of topological bands and the superconductivity within them.

The recent paper by Zhang and colleagues could pave the way toward exploring strongly anisotropic and enhanced in-plane large critical upper fields, which could further improve the current understanding of the exotic physics of these materials.

“We now plan to explore the usual superconducting properties (such as the in-plane upper critical field and the behavior of tunneling spectroscopy in a high magnetic field) of more atomically thin centrosymmetric superconductors with topological band reversals,” Zhang added.

More information:
Enze Zhang et al, Superconductivity coupled with spin-orbit parity in atomically thin 2M-WS2, physics of nature (2022). DOI: 10.1038/s41567-022-01812-8

Ying-Ming Xie et al, Spin-Orbit-Parity-Coupled Superconductivity in Topological Monolayer WTe2, Physical Review Letters (2020). DOI: 10.1103/PhysRevLett.125.107001

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Citation: Study Observes Superconductivity Coupled with Spin Orbit Parity in Thin 2M-WS2 (21 Dec 2022) Retrieved 21 Dec 2022 from https://phys.org/news/2022-12-spin-orbit- parity-coupled-superconductivity-thin-2m-ws2.html

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