meissner effect
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2022 ◽  
Author(s):  
J. E. Hirsch ◽  
F. Marsiglio

Abstract The Meissner effect, magnetic field expulsion, is a hallmark of superconductivity. Associated with it, superconductors exclude applied magnetic fields. Recently Minkov et al. presented experimental results reportedly showing “definitive evidence of the Meissner effect” in sulfur hydride and lan-thanum hydride under high pressure1. Instead, we show here that the evidence presented in that paper does not support the case for superconductivity in these materials. Together with experimental evidence discussed in earlier papers, we argue that this clearly indicates that hydrides under pressure are not high temperature superconductors.


2022 ◽  
Author(s):  
S. Y. Wang ◽  
Yijun Yu ◽  
Jinxiang Hao ◽  
Yang Feng ◽  
Jinjiang Zhu ◽  
...  

Abstract Monolayers of a prototypical cuprate high transition-temperature (TC) superconductor Bi2Sr2CaCu2O8+δ (Bi2212) was recently found to show TC and other electronic properties similar to those of the bulk. The robustness of superconductivity in an ideal two-dimensional (2D) system was an intriguing fact that defied the Mermin-Wagner theorem. Here, we took advantage of the high sensitivity of scanning SQUID susceptometry to image the phase stiffness throughout the phase transition of Bi2212 in the 2D limit. We found susceptibility oscillated with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up till TC. The temperature and sample size-dependence of the modulation period agreed well with our Coulomb gas analogy of a finite 2D system based on Berezinskii–Kosterlitz–Thouless (BKT) transition. In the multilayers, the susceptibility oscillation differed in a small temperature regime below TC in consistent with a dimensional-crossover led by interlayer coupling. Serving as strong evidence of BKT transition in the bulk, there appeared a sharp superfluid density jump at zero-field and paramagnetism at small fields just below TC. These results unified the phase transitions from the monolayer Bi2212 to the bulk as BKT transition with finite interlayer coupling. This elucidating picture favored the pre-formed pairs scenario for the underdoped cuprates regardless of lattice dimensionality.


Entropy ◽  
2022 ◽  
Vol 24 (1) ◽  
pp. 83
Author(s):  
Alexey Nikulov

The law of entropy increase postulates the existence of irreversible processes in physics: the total entropy of an isolated system can increase, but cannot decrease. The annihilation of an electric current in normal metal with the generation of Joule heat because of a non-zero resistance is a well-known example of an irreversible process. The persistent current, an undamped electric current observed in a superconductor, annihilates after the transition into the normal state. Therefore, this transition was considered as an irreversible thermodynamic process before 1933. However, if this transition is irreversible, then the Meissner effect discovered in 1933 is experimental evidence of a process reverse to the irreversible process. Belief in the law of entropy increase forced physicists to change their understanding of the superconducting transition, which is considered a phase transition after 1933. This change has resulted to the internal inconsistency of the conventional theory of superconductivity, which is created within the framework of reversible thermodynamics, but predicts Joule heating. The persistent current annihilates after the transition into the normal state with the generation of Joule heat and reappears during the return to the superconducting state according to this theory and contrary to the law of entropy increase. The success of the conventional theory of superconductivity forces us to consider the validity of belief in the law of entropy increase.


2022 ◽  
Vol 258 ◽  
pp. 02006
Author(s):  
Atsuki Hiraguchi ◽  
Katsuya Ishiguro ◽  
Tsuneo Suzuki

We investigate the Abelian dual Meissner effect due to violation of the non-Abelian Bianchi identity in SU (3) gauge thoery without gauge fixing. To decide the vacuum type, we evaluate the Ginzburg-Landau parameter from the spatial distribution of color electric fields and squared monopole density. Although the study is done only on 24 (40)3 × 4 lattice at β = 5.6, the SU (3) vacuum is found to be of the type 1 near the border of type 1 and type 2. We also confirm the dual Ampere’s law directly.


2021 ◽  
Author(s):  
Mahir Al-ani

Abstract This paper presents a superconducting thermo-magnetic-mechanical (STMM) energy conversion process. This energy conversion concept revolves around of utilizing a cryogenic coolant, e.g., liquid nitrogen, as a thermal energy facilitator to cool down the superconductor to below the critical temperature. Then, utilizing the mixed state, i.e., Meissner effect and weak vertex - which leads to partially shielding the magnetic field - an external magnetic field is used to apply force on the superconductor and create motion. The concept proposed is demonstrated using thorough Multiphysics understanding i.e., thermal, magnetic, and mechanical. The proof of concept is completed by using a combination of analytical and numerical simulations and calculations, and measurements. Using this concept, a practical automotive drive has been theoretically designed and compared with a counterpart electric drive. The proposed technology has a potential to provide a step change for the sustainable cleaner cost-effective transportation.


2021 ◽  
Author(s):  
Atindra Pal ◽  
Arnab Bera ◽  
Sirshendu Gayen ◽  
Suchanda Mondal ◽  
Riju Pal ◽  
...  

Abstract Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5 K in the quasione dimensional crystals of non-centrosymmetric (TaSe4)3I (space group: P¯421c). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: P4/mnc) where it behaves like a non-magnetic insulator[1–4]. The coexistence here upfront contradicts the popular belief that superconductivity and ferromagnetism are two apparently antagonistic phenomena. Notably, here, for the first time, we have clearly detected Meissner effect in the superconducting state despite the coexisting ferromagnetic order. The coexistence of superconductivity and ferromagnetism projects non-centrosymmetric (TaSe4)3I as a host for complex ground states of quantum matter including possible unconventional superconductivity with elusive spin-triplet pairing[5–8].


Author(s):  
M.R. Koblischka ◽  
A. Koblischka-Veneva ◽  
A.L. Pessoa ◽  
C.L. Carvalho ◽  
R. Zadorosny

2021 ◽  
Author(s):  
Jorge Hirsch ◽  
Frank Marsiglio

Abstract The Meissner effect, magnetic field expulsion, is a hallmark of superconductivity. Associated with it, superconductors exclude applied magnetic fields. Recently Minkov et al. presented experimental results reportedly showing ``definitive evidence of the Meissner effect'' in sulfur hydride and lanthanum hydride under high pressure [1]. Instead, we show here that the evidence presented in that paper does not support the case for superconductivity in these materials. Together with experimental evidence discussed in earlier papers, we argue that this clearly indicates that hydrides under pressure are not high temperature superconductors.


2021 ◽  
Author(s):  
Vasily Minkov ◽  
Sergey Bud'ko ◽  
Fedor Balakirev ◽  
Vitali Prakapenka ◽  
Stella Chariton ◽  
...  

Abstract In the last few years, the superconducting transition temperature, Tc, of hydrogen-rich compounds has increased dramatically, and is now approaching room temperature. However, the pressures at which these materials are stable exceed one million atmospheres and limit the number of available experimental probes - superconductivity has been primarily identified based on electrical transport measurements. Here, we report definitive evidence of the Meissner effect – a key feature of superconductivity – in H3S and LaH10. Furthermore, we have determined characteristic superconducting parameters: a lower critical field Hc1 of ∼1.9 and ∼1.0 T, and a London penetration depth λL of ∼13 and ∼21 nm in Im-3m-H3S and Fm-3m-LaH10, respectively. These compounds have low values of the Ginzburg-Landau parameter κ ∼7–14 and belong to the group of “moderate” type II superconductors.


Author(s):  
Serguei S Komissarov

Abstract Recently, it was claimed by King & Pringle that accretion of electric charge by a black hole rotating in an aligned external magnetic field results in a “dead” vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford-Znajek mechanism cannot operate. Here we study in details the properties of the Wald solution for electrically charged black holes discussed in their paper. Our results show that the claim is erroneous as in the solution with the critical charge q0 = 2aB0 there exists a drop of electrostatic potential along all magnetic field lines except the one coinciding with the symmetry axis. It is also found that while uncharged rotating black holes expel external vacuum magnetic field from their event horizon (the Meissner effect), electric charging of black holes pulls the magnetic field lines back on it, resembling what has been observed in some previous force-free, RMHD and PIC simulations of black hole magnetospheres. This suggests that accretion of electric charge may indeed be a feature of the black hole electrodynamics. However, our analysis shows that the value q0 of the BH charge given by Wald is likely to be only an upper limit, and that the actual value depends of the details of the magnetospheric physics.


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