Study on the High-Frequency Conversion Characteristics of Quench and Recovery States Under Thermal Modulation of a Superconducting Flux Transformation Amplifier
Guilong LiQiaochu DingShiyi ZhangQingfa DuMengchun PanPeisen LiJunping PengWeicheng QiuJiafei HuYueguo Hu
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To tackle the challenge posed by 1/f noise which significantly hinders the practical application of superconductor/tunnel magnetoresistance (TMR) composite magnetic sensors in low-frequency detection, this paper proposes a magnetic field thermal modulation method specifically tailored for the superconductor/TMR composite sensor. The method employs alternating joule heating via a resistance wire to induce partial quenching and recovery states conversion in the superconducting flux transformation amplifier (SFTA). Firstly, a thermo-electric-magnetic comprehensive finite element simulation model was developed to obtain the temperature and magnetic field distributions during the quenching and recovery state conversion process, and then to realize the size optimization of the thermal modulated structure. Final experimental tests conducted in the liquid nitrogen environment demonstrated a high modulation frequency of 5 kHz was achieved. Meanwhile, the interlayer capacitor-coupling effect was introduced to explain the phenomenon of resistance deviation from zero for the thermal modulated superconducting constriction under the higher modulation frequency. The breakthrough in this article holds promise for the low-frequency application of superconductor/TMR composite sensors.Keywords:
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Over the past six years, superconductivity at high temperatures has been reported in a variety of hydrogen-rich compounds under high pressure. That high temperature superconductivity should exist in these materials is expected according to the conventional theory of superconductivity, as shown by detailed calculations. However, here we argue that experimental observations rule out conventional superconductivity in these materials. Our results indicate that either these materials are unconventional superconductors of a novel kind, which we term ``nonstandard superconductors,'' or alternatively, that they are not superconductors. If the first is true, we point out that the critical current in these materials should be several orders of magnitude larger than in standard superconductors, potentially opening up the way to important technological applications. If the second is the case, which we believe is more likely, we suggest that the signals interpreted as superconductivity are either experimental artifacts or they signal other interesting physics but not superconductivity.
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Within the framework of the linearized Ginzburg-Landau theory, we study the phase boundary of thin superconducting films. These films are nanostructured such that there is a one-dimensional periodic enhancement of the surface superconductivity which can be realized, e.g., by placing superconducting stripes with a higher critical temperature on top of the film, leading to a one-dimensional modulation of the superconducting boundary condition. We study the influence of this one-dimensional modulation on the enhancement of the critical temperature of the film. In a second step we also place stripes at the bottom of the film and we study both in-phase and out-of-phase modulation.
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Abstract Using heterostructures that combine a two superconductor (Nb-Pb). We demonstrate the modulation of the superconducting condensate at the nanoscale via variation of mean-free path. The modulation of superconductivity can be obtained not only for chosing smaller superconducting lengths comparing with bulk superconducting length or considering several geometric shapes, but also whether strong local dopping effect can be produced over the superficial area of the superconductor. Through this mechanism, a nanoscale pattern of two condensates regions can be created in the superconductor. This yields a magenetization curves that has no counterpart in the literature. We show that this form of modulation based on the possibity of change mean-free path represent a groundbreaking prospects in the study of the effects that might exploit unique superconducting properties, due to allows the manipulation of magnetic flux quanta.
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UTe2 is a newly-discovered unconventional superconductor wherein multicomponent topological superconductivity is anticipated based on the presence of two superconducting transitions and time-reversal symmetry breaking in the superconducting state. The observation of two superconducting transitions, however, remains controversial. Here we demonstrate that UTe2 single crystals displaying an optimal superconducting transition temperature at 2 K exhibit a single transition and remarkably high quality supported by their small residual heat capacity in the superconducting state and large residual resistance ratio. Our results shed light on the intrinsic superconducting properties of UTe2 and bring into question whether UTe2 is a multicomponent superconductor at ambient pressure.
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A unique platform for investigating the correlation between the antiferromagnetic (AFM) and superconducting (SC) states in high temperature superconductors is created by the discovery of alkaline iron selenide superconductors which are composed of an AFM insulating phase and a SC phase separated spatially. Our previous studies showed that pressure can fully suppress the superconductivity of ambient-pressure superconducting phase (SC-I) and AFM order simultaneously, then induce another superconducting phase (SC-II) at higher pressure. Consequently, the connection between the two superconducting phases becomes an intriguing issue. In this study, on the basis of observing pressure-induced reemergence of superconductivity in Rb0.8Fe2-ySe2-xTex (x=0, 0.19 and 0.28) superconductors, we find that the superconductivity of the SC-I and SC-II phases as well as the AFM ordered state can be synchronously tuned by Te doping and disappear together at the doping level of x=0.4. We propose that the two superconducting phases are connected by the AFM phase, in other words, the state of long-ranged AFM order plays a role in giving rise to superconductivity of the SC-I phase, while the fluctuation state of the suppressed AFM phase drives the emergence of SC-II phase. These results comprehensively demonstrate the versatile roles of AFM states in stabilizing and developing superconductivity in the alkaline iron selenide superconductors.
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