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تسجيل مستخدم جديدInterfacial superconductivity above Pauli limit in homogeneously disordered tungsten carbide - Ga composite
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A directed narrow jet of an organo-metallic gas containing a heavy metal can be decomposed by an accelerated beam of gallium ions, leaving behind a track made up of a complex residue of gallium, heavy metal and carbon. The process is highly controllable and in certain cases, the residue has remarkable superconducting properties, like an upper critical field ($H_{c2} sim 10~{rm T} $) that is higher than the paramagnetic limit. Werthamer-Helfand-Hohenberg (WHH) analysis shows the presence of moderate spin-orbit (SO) scattering and a Maki parameter compatible with unconventional (e.g., FFLO-like) superconducting states. Using a spatially resolved mass spectrometric technique (Atomic probe tomography), we show that the possible origin of the SO effects lies in the formation of nano-crystalline tungsten carbide (WC) with a possible non-centrosymmetric crystal structure. We also show that when Ga is distributed on the surface of nano-crystallite WC, the sp-orbitals of Ga give rise to bands with a significant density of states near the Fermi energy. The superconductor is in the dirty limit where the mean free path ($l$) is much smaller than the zero temperature coherence length, i.e., $lllxi_{0}~{approx}~5{~rm nm}$. Low-temperature magnetotransport with {em in-situ} rotation of the sample in a magnetic field shows clear anisotropic effects that weaken as the width of the tracks are increased from $sim~100{~rm nm}$ to $sim~1{~ {mu}rm m}$ [Phys. Rev. B 103, L020504, 2021]. The combination of the transition temperature ($T_c~{approx}~5~ {rm K}$), the critical field $H_{c2} geq 10~ {rm T}$ and nanometer-scale patternability of these tracks make them an attractive component for engineered mesoscopic structures.
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