Superconductors in SQUID-Based Ultralow Field NMR—Flux-Trapping in Type-II Wires

Hwang, Sung Ho; Körber, Rainer; Kim, Ki Woong; Hung, Kam; Lee, Seong-Joo; Shim, Jeong-Hyun; Burghoff, M.

doi:10.1109/tasc.2014.2363623

Cited by 4 publications

(2 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Figure b shows the magnetization variation with respect to temperature ( M – T profile) for our synthesized LK-99 with Field Cool (FC) and Zero Field Cool (ZFC) protocols. The M – H curve at 280 K and M – T curve at 500 Oe for LK-99 are similar to those of NbAs 2 , which is a diamagnetic material, and the similar behavior in the M – T profile of recently synthesized single crystals of LK-99 by Puphal et al The linear diamagnetic hysteresis in the M – H plot is also observed in superconducting Pb wires, which is expected for a perfect superconducting sample with no pining centers and without demagnetization corrections in magnetization loop. However, here the linear loop is very unlikely to be attributable to the presence of a superconducting phase, as LK-99 is highly resistive and polycrystalline with some minor impurities.…”

Section: Resultssupporting

confidence: 76%

Absence of Superconductivity in LK-99 at Ambient Conditions

Kumar,

Kumar Karn,

Kumar

et al. 2023

ACS Omega

View full text Add to dashboard Cite

The report of the synthesis of modified lead apatite (LK-99), with evidence of superconductivity at more than boiling water temperature, has steered the scientific community. There have been several failures to reproduce superconductivity in LK-99, despite partial successes. Here, we have continued our efforts to synthesize phase-pure LK-99 with improved precursors. The synthesis process being followed is the same as suggested by Sukbae Lee et al. The phase purity of each precursor is evidenced by powder X-ray diffraction (PXRD) and is well-fitted by Rietveld refinement. The PXRD confirms the synthesis of phase-pure polycrystalline LK-99 with a lead apatite structure. The sample is highly resistive, showing insulator-like behavior in resistivity measurement in the temperature range from 215 to 325 K, which confirms the absence of superconductivity in synthesized LK-99 at room temperature. The magnetization measurements of LK-99 on the SQUID magnetometer resemble the behavior of a resistive diamagnetic material at 280 K. Moreover, we have also performed first principle calculations to investigate the electronic band structure of LK-99 in the vicinity of the Fermi level. Our study verifies that the copper (Cu)-doped lead apatite (LK-99) exhibits band crossing at the Fermi level, indicating the generation of strong correlation in the presently studied system. Our experimental results do not approve the appearance of superconductivity in LK-99, i.e., Pb 9 CuP 6 O 25 .

show abstract

Section: Resultssupporting

confidence: 76%

Absence of Superconductivity in LK-99 at Ambient Conditions

Kumar,

Kumar Karn,

Kumar

et al. 2023

ACS Omega

View full text Add to dashboard Cite

show abstract

“…The use of type-I superconductors as a possible material for pick-up coils in SQUID-based ULF MR was also investigated, however with some conflicting results concerning trapped flux. Hwang et al [5] did not observe line-broadening in NMR-signals from water using lead (Pb) pick-up coils after applying pulsed fields up to 160 mT, well above the critical field of the wire of 50 mT at 4.2 K [8]. This leads to the conclusion that Pb does not trap flux and therefore renders it a potential alternative.…”

Section: Introductionmentioning

confidence: 99%

Ultra-sensitive SQUID Systems for Pulsed Fields—Degaussing Superconducting Pick-Up Coils

Al-Dabbagh

Storm

2018

IEEE Trans. Appl. Supercond.

Self Cite

View full text Add to dashboard Cite

SQUID systems for ultra-low-field magnetic resonance (ULF MR) feature superconducting pick-up coils which must tolerate exposure to pulsed fields of up to 100 mT. Using type-II superconductor niobium (Nb) field distortions due to trapped vortices in the wire result. In addition, their rearrangement after quick removal of the pulsed field leads to excess low frequency noise which limits the signal-to-noise ratio. In contrast, type I superconductors, such as lead (Pb), do not exhibit vortices but form an intermediate state with the coexistence of normal and superconducting domains.We measured the magnetization loops of superconducting wire samples of Nb and Pb together with their noise behavior after pulsed fields. Pb also exhibits significant excess low frequency noise once the wire has been driven into the intermediate state.To avoid this problem, we removed the field not abruptly but in a linearly decaying sinusoidal manner thereby degaussing the wire. After application of 57 mT, we found that Nb can be degaussed within at least 50 ms, the shortest time used in this study. Pb can also be degaussed, albeit within 100 ms and a more complex dependency on the degaussing parameters. After successful degaussing, negligible excess low frequency noise is observed.

show abstract