critical field
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Author(s):  
Yixin Liu ◽  
Han Zhang ◽  
Xiaowen Han ◽  
Teng Wang ◽  
Lingling Wang ◽  
...  

Abstract High quality superconducting thin films are the basis for the application of superconducting devices. Here we report the fllm growth and superconducting properties of the Ta films. The films were grown by the pulsed laser deposition technique on the α-Al2O3 substrates. It is found that, with the increase of the fllm thickness from 20 nm to 61 nm, both the superconducting transition temperature Tc and residual resistance ratio RRR display an upward trend, while the upper critical field decreases monotonously in a wide temperature region. A clear anisotropic behavior is revealed by comparing the upper critical fields with two difierent orientations (H ⊥ film and H // film). The anisotropy parameter Γ is found to be as high as 20 for the sample with the thickness of 20 nm. The systematical evolution from two- to three-dimensional features for the superconductivity with the increase of fllm thickness is observed in the temperature dependent upper critical fleld data. Moreover, the vortex liquid region tends to expand with the increase of the fllm thickness.


2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Kazuhisa Hoshi ◽  
Ryosuke Kurihara ◽  
Yosuke Goto ◽  
Masashi Tokunaga ◽  
Yoshikazu Mizuguchi

AbstractCentrosymmetric compounds with local inversion symmetry breaking have tremendously interesting and intriguing physical properties. In this study, we focus on a BiCh2-based (Ch: S, Se) layered superconductor, as a system with local inversion asymmetry, because spin polarisation based on the Rashba–Dresselhaus-type spin–orbit coupling has been observed in centrosymmetric BiCh2-based LaOBiS2 systems, while the BiCh2 layer lacks local inversion symmetry. Herein, we report the existence of extremely high in-plane upper critical fields in the BiCh2-based system LaO0.5F0.5BiS2−xSex (x = 0.22 and 0.69). The superconducting states are not completely suppressed by the applied magnetic fields with strengths up to 55 T. Thus, we consider that the in-plane upper critical field is enhanced by the local inversion symmetry breaking and its layered structure. Our study will open a new pathway for the discovery of superconductors that exhibit a high upper critical field by focusing on the local inversion symmetry breaking.


2021 ◽  
Vol 5 (11) ◽  
Author(s):  
D. A. Mayoh ◽  
S. J. R. Holt ◽  
T. Takabatake ◽  
G. Balakrishnan ◽  
M. R. Lees

2021 ◽  
Vol 5 (11) ◽  
Author(s):  
H. Su ◽  
T. Shang ◽  
F. Du ◽  
C. F. Chen ◽  
H. Q. Ye ◽  
...  

Author(s):  
A.D. Alekhin

A brief review of the results of studies of the effect of gravity in inhomogeneous substance near a critical state of a critical fluid (CF) has been presented in paper, based on the data of light scattering, refractometry, and slow neutron transmission methods.Based on these data, the field-altitude asymmetry of various properties of an inhomogeneous substance has been analyzed, namely order parameter Dr(z), scattered light intensity I(z), density gradient dr(z)/dz of the substance. It had been shown that the field-altitude asymmetries of the scattered light intensity I(z)~dr/dm(h) and the density gradient dr(z)/dz~dr/dh(h) of the substance are diametrically opposite. The different altitudinal asymmetry of these quantities dr/dh(h) and dr/dm(h) is explained in paper by the altitude asymmetry of the derivative of the chemical potential dm/dh, and hence with the altitude asymmetry of the chemical potential Dm(h)>>h in the external field h.To the present time, the physical mechanism of the altitude asymmetry of the gravity effect has not been studied. In this regard the mechanism of the formation of the vertical asymmetry of the internal critical field Dm(h) has proposed in paper to be associated with the kinetic characteristics of the inhomogeneous critical fluid: the diffusion coefficients D (h) and viscosity coefficients h(h), when the system passes from a homogeneous state to an inhomogeneous one under the action of an internal asymmetric fields |DU(z)|= |Dm(z)|>>|h=rcgz/Pc|. For this purpose, a high-pressure cell with a height L, with a critical filling density of the substance is considered in paper.It has been shown that when the system is under critical density filling by substance =rc  the critical level of substance z = 0 with the critical density rc  at the critical temperature Tc is realized above the middle of the sample with an inhomogeneous substance. Based on the literature data of P-V-T-measurements and the gravity effect in benzene and ethane, the values of the altitudinal change in the internal critical field have been found. It has been shown that the value of the critical internal inhomogeneous field in the inhomogeneous critical fluid significantly exceeds the variable of the Earth's gravity |DU(h,Tc)|= |Dm(h,Tc)>>|h|  It has been also shown that the magnitude of this field according to the cubic law depends on the critical temperature Tc of the substance: |Dm(z,Tc1)/|Dm(z,Tc2) » (Tc1/Tc2)3.


2021 ◽  
Author(s):  
Daniel Andrew Turner ◽  
Graeme Burt ◽  
Tobias Junginger

Abstract Superconducting Radio-Frequency cavities are currently made out of niobium. Niobium cavities are limited by the magnetic field on the cavity walls due to the entry of vortices at the field of first vortex penetration, Hvp. Low temperature baking in vacuum or low pressure gas atmosphere removes the strong decrease of the quality factor with accelerating gradient (high field Q-slope). Some cavities reach surface magnetic field above the lower critical field, Hc1. One hypothesis for this performance increase is that the outer layer affected by the treatments acts as a barrier for vortex penetration (effective bilayer). Using a vibrating sample magnetometer the field of first flux penetration (Hvp) was measured for Nb ellipsoids with various low temperature treatments. All Hvp values were found to be consistent with the lower critical field, Hc1 , as predicted for clean niobium. This led to the conclusion that a metastable flux free state above Hc1 cannot be observed in DC magnetometry for low temperature baked niobium unlike for bilayers consisting of two superconductors as previously published. The effect of flux pinning differed significantly between treatments, suggesting that the high field Q-slope mitigation might be related to vortex pinning in the surface of the cavities.


2021 ◽  
pp. 162454
Author(s):  
Yuxian Wu ◽  
Zhiwei Wen ◽  
Yong Li ◽  
Yajing Cui ◽  
Yongliang Chen ◽  
...  

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