Abstract
The flux quantization is a key indication of electron pairing in superconductors. For example, the well-known flux quantization is considered strong evidence for the existence of charge-, two-electron Cooper pairs. Here we report evidence for multicharge flux quantization in mesoscopic ring devices fabricated using the transition-metal kagome superconductor . We perform systematic magnetotransport measurements and observe unprecedented quantization of magnetic flux in units of and in magnetoresistance oscillations. Specifically, at low temperatures, magnetoresistance oscillations with period are detected, as expected from the flux quantization for charge- superconductivity. We find that the oscillations are suppressed and replaced by resistance oscillations with periodicity when the temperature is increased. Increasing the temperature further suppresses the oscillations, and robust resistance oscillations with periodicity emerge as evidence for charge- flux quantization. Our observations provide the first experimental evidence for the existence of multicharge flux quanta and emergent quantum matter exhibiting higher-charge superconductivity in the strongly fluctuating region above the charge- Cooper pair condensate, revealing new insights into the intertwined and vestigial electronic order in kagome superconductors.
- Received 7 September 2023
- Revised 16 January 2024
- Accepted 12 March 2024
DOI:https://doi.org/10.1103/PhysRevX.14.021025
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
ViewpointCooper Pairs Pair Up in a Kagome Metal
Published 13 May 2024
In its superconducting state, an exotic metal harbors charge carriers that appear to have 4 and 6 times the charge of a single electron, suggesting the formation of Cooper-pair “molecules.”
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Popular Summary
Superconductivity originates from the pairing up of electrons in what are called Cooper pairs. But theory also hints at fundamentally new types of superconducting states that could emerge from electron quartets (two Cooper pairs) or sextets (three Cooper pairs). Despite intensive theoretical studies, the basic properties of such states—and even the question of whether they exist—remain mysterious due to a lack of experimental evidence. Here, we provide the first evidence of four- and six-electron superconducting states.
A key indication of electron pairing in superconductors is the quantization of magnetic flux. That is, when a magnetic flux is applied, it can take only integer multiples of some fundamental value. In our experiments, we find evidence for multicharge flux quantization in mesoscopic ring devices fabricated using the superconductor . Specifically, at low temperatures, we detect magnetoresistance oscillations with periods consistent with two-electron superconductivity. As the temperature increases, we find that the two-electron oscillations are suppressed and replaced by ones matching four-electron groupings. Further temperature increases show the four-electron oscillations giving way to six-electron oscillations indicating six-electron superconductivity.
Our observations provide the first experimental evidence for the existence of multicharge flux quanta and emergent quantum matter exhibiting higher-charge superconductivity, revealing new insights into superconductivity phenomena beyond the condensation of two-electron Cooper pairs.
