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- Cho, Chang-woo, et al.
(author)
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Competition between orbital effects, Pauli limiting, and Fulde-Ferrell-Larkin-Ovchinnikov states in 2D transition metal dichalcogenide superconductors
- 2022
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In: New Journal of Physics. - : IOP Publishing Ltd. - 1367-2630. ; 24:8
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Journal article (peer-reviewed)abstract
- We compare the upper critical field of bulk single-crystalline samples of the two intrinsic transition metal dichalcogenide superconductors, 2H-NbSe2 and 2H-NbS2, in high magnetic fields where their layer structure is aligned strictly parallel and perpendicular to the field, using magnetic torque experiments and a high-precision piezo-rotary positioner. While both superconductors show that orbital effects still have a significant impact when the layer structure is aligned parallel to the field, the upper critical field of NbS2 rises above the Pauli limiting field and forms a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, while orbital effects suppress superconductivity in NbSe2 just below the Pauli limit, which excludes the formation of the FFLO state. From the out-of-plane anisotropies, the coherence length perpendicular to the layers of 31 angstrom in NbSe2 is much larger than the interlayer distance, leading to a significant orbital effect suppressing superconductivity before the Pauli limit is reached, in contrast to the more 2D NbS2.
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| 3. |
- Cho, Chang-woo, et al.
(author)
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Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov state in bulk NbS2
- 2021
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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 12
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Journal article (peer-reviewed)abstract
- We present measurements of the magnetic torque, specific heat and thermal expansion of the bulk transition metal dichalcogenide (TMD) superconductor NbS2 in high magnetic fields, with its layer structure aligned strictly parallel to the field using a piezo rotary positioner. The upper critical field of superconducting TMDs in the 2D form is known to be dramatically enhanced by a special form of Ising spin orbit coupling. This Ising superconductivity is very robust to the Pauli paramagnetic effect and can therefore exist beyond the Pauli limit for superconductivity. We find that superconductivity beyond the Pauli limit still exists in bulk single crystals of NbS2 for a precisely parallel field alignment. However, the comparison of our upper critical field transition line with numerical simulations rather points to the development of a Fulde-Ferrell-Larkin-Ovchinnikov state above the Pauli limit as a cause. This is also consistent with the observation of a magnetic field driven phase transition in the thermodynamic quantities within the superconducting state near the Pauli limit. Superconductivity is often destroyed under magnetic field larger than a critical value called Pauli limit. Here, the authors report superconductivity beyond the Pauli limit in bulk single crystals of NbS2, suggesting the development of a Fulde-Ferrell-Larkin-Ovchinnikov state.
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