We report on the first observation of a pronounced reentrant superconductivity phenomenon in a superconductor/ferromagnet layered system. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T(c) drops sharply with increasing thickness dCuNi) of the ferromagnetic layer, until complete suppression of superconductivity is observed at d(CuNi) approximately equal to 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d(CuNi) > or =13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov-like state in the ferromagnetic layer.
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http://dx.doi.org/10.1103/PhysRevLett.97.057004 | DOI Listing |
Rev Sci Instrum
September 2024
Laboratoire de Physique des Plasmas, Ecole Polytechnique-CNRS-Univ Paris-Sud-UPMC, Rte de Saclay, 91128 Palaiseau, France.
A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the "Gas-Puff Imaging" (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system's plasma-facing components. The system features a pair of "converging-diverging" nozzles for partially collimating the gas puffed locally ≈135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera.
View Article and Find Full Text PDFSmall
November 2024
School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
Transition metal dichalcogenide TiSe exhibits a superconducting dome within a low pressure range of 2-4 GPa, which peaks with the maximal transition temperature T of ≈1.8 K. Here it is reported that applying high pressure induces a new superconducting state in TiSe, which starts at ≈16 GPa with a substantially higher T that reaches 5.
View Article and Find Full Text PDFJ Phys Condens Matter
May 2024
Department of Physics, Kent State University, Kent, OH 44242, United States of America.
We apply the Migdal-Eliashberg theory of superconductivity to heavy-fermion and mixed valence materials. Specifically, we extend the Anderson lattice model to a case when there exists a strong coupling between itinerant electrons and lattice vibrations. Using the saddle-point approximation, we derive a set of coupled nonlinear equations which describe competition between the crossover to a heavy-fermion or mixed-valence regimes and conventional superconductivity.
View Article and Find Full Text PDFNat Commun
April 2024
NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA.
Reentrant superconductivity is an uncommon phenomenon in which the destructive effects of magnetic field on superconductivity are mitigated, allowing a zero-resistance state to survive under conditions that would otherwise destroy it. Typically, the reentrant superconducting region derives from a zero-field parent superconducting phase. Here, we show that in UTe crystals extreme applied magnetic fields give rise to an unprecedented high-field superconductor that lacks a zero-field antecedent.
View Article and Find Full Text PDFPNAS Nexus
January 2024
MPA-MAGLAB, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
There has been a recent surge of interest in UTe due to its unconventional magnetic field ()-reinforced spin-triplet superconducting phases persisting at fields far above the simple Pauli limit for . Magnetic fields in excess of 35 T then induce a field-polarized magnetic state via a first-order-like phase transition. More controversially, for field orientations close to and above 40 T, electrical resistivity measurements suggest that a further superconducting state may exist.
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