Universality of Upper Critical Field in the TMD Superconductor Family

Seminar
Condensed Matter Resnick seminar
QUEST Center event
No
Speaker
Hadar Steinberg
Date
25/01/2024 - 13:30 - 12:30Add to Calendar 2024-01-25 12:30:00 2024-01-25 13:30:00 Universality of Upper Critical Field in the TMD Superconductor Family In transition metal dichalcogenides (TMDs) such as H-NbSe2 an H-TaS2 , superconducting properties are retained down to a single layer, making them useful platforms for studying thickness-dependent effects. Specifically, NbSe2 exhibits a reduction in its TC from 7.2 K in the bulk to approximately 3 K in the single-layer limit. In TaS2 , conversely, TC increases from 0.8 K in the bulk to approximately 3 K in the single layer limit. This contradicting behavior, which long puzzled researchers, could be related to a thickness-dependent suppression of superconductivity by the competing charge density wave (CDW) phase. I will present measurements of device-based high-resolution tunneling spectra in TaS2 , where we track the gap structure from the bulk all the way to a single layer. Our devices allow for simultaneous evaluation of the gap ∆, TC , and the upper critical field HC2 . Although TaS2 is considered as a dirty superconductor, we find that HC2 is proportional to ∆ 2 , a relation expected for clean superconductors. Even more curiously, we find that the same ratio between HC2 and ∆2 holds for other TMDs: NbSe2 of all thicknesses, and bulk TaSe2 ,  covering 4 orders of magnitude in HC2 and covering both clean and dirty limits. Conference room on the 0th floor of Resnick building Department of Physics physics.dept@mail.biu.ac.il Asia/Jerusalem public
Place
Conference room on the 0th floor of Resnick building
Abstract

In transition metal dichalcogenides (TMDs) such as H-NbSe2 an H-TaS2 , superconducting properties are retained down to a single layer, making them useful platforms for studying thickness-dependent effects. Specifically, NbSe2 exhibits a reduction in its TC from 7.2 K in the bulk to approximately 3 K in the single-layer limit. In TaS2 , conversely, TC increases from 0.8 K in the bulk to approximately 3 K in the single layer limit. This contradicting behavior, which long puzzled researchers, could be related to a thickness-dependent suppression of superconductivity by the competing charge density wave (CDW) phase. I will present measurements of device-based high-resolution tunneling spectra in TaS2 , where we track the gap structure from the bulk all the way to a single layer. Our devices allow for simultaneous evaluation of the gap ∆, TC , and the upper critical field HC2 . Although TaS2 is considered as a dirty superconductor, we find that HC2 is proportional to ∆ 2 , a relation expected for clean superconductors. Even more curiously, we find that the same ratio between HC2 and ∆2 holds for other TMDs: NbSe2 of all thicknesses, and bulk TaSe2 ,  covering 4 orders of magnitude in HC2 and covering both clean and dirty limits.

Last Updated Date : 20/01/2024