A New Microscopic Approach To Deal with the Temperature- and Applied Magnetic Field–Dependent Critical Current Densities of Superconductors

Excellent fits were obtained by Talantsev (MPLB 33, 1950195, 2019) to the temperature (T)-dependent upper critical field (H c2 (T)) data of H 3 S reported by Mozaffari et al. [Nature Communications 10, 2522] by employing four alternative phenomenological models, each of which invoked two or more properties from its sample-specific set S 1 = {T c , gap, coherence length, penetration depth, jump in sp.ht.} and a single value of the effective mass (m*) of an electron. Based on the premise that the variation of H c2 (T) is due to the variation of the chemical potential μ(T), we report here fits to the same data by employing a T-, μand m*-dependent equation for H c2 (T) and three models of μ(T), viz. the linear, the parabolic and the concave-upward model.For temperatures up to which the data are available, each of these provides a good fit. However, for lower values of T, their predictions differ. Notably, the predicted values of H c2 (0) are much higher than in any of the models dealt with by Talantsev. In sum, we show here that the addressed data are explicable in a framework comprising the set S 2 = {μ, m*, interaction parameter λ m , Landau index N L }, which is altogether different from S 1 .

Section: Discussionmentioning

confidence: 99%

“…Incorporating temperature, chemical potential and an applied field, the generalized BCS equation derived in [9] and employed here is…”

Section: The Pairing Equation Incorporating Chemical Potential Temper...mentioning

confidence: 99%

A Dynamical Approach to the Explanation of the Upper Critical Field Data of Compressed H3S

Malik¹,

Varma²

2023

“…The framework of Paper I comprised three core equations: (i) a μ-, Tand H-dependent pairing equation corresponding to P = 0 and hence j c = 0, where P denotes the 3-momentum of Cooper pairs in the lab frame, (ii) a μ-, Tand H-dependent pairing equation corresponding to P ≠ 0 and hence j c ≠ 0 and (iii) an equation relating Fermi energy E F with the number density of the chargecarriers n s . It was pointed out in [4]-Paper II hereafter, which was devoted to a study of the variation of j c (T, H) with T (for a fixed value of H) and H (for a fixed value of T) that the framework of Paper I was deficient in that 1) the limits of both the P = 0 and the P ≠ 0 equations were incorrect for a reason that will be given below, 2) the assumption that P = 0 and P ≠ 0 equations are characterized by the same interaction parameter is unjustifiable and hence should be done away with and 3) it employed an equation for n s which, strictly speaking, is valid World Journal of Condensed Matter Physics only when both T = 0 and H = 0, in lieu of which a more accurate μ-, Tand H-dependent number equation was employed in Paper II.…”

Section: Introductionmentioning

confidence: 94%

An Inquiry into Two Intriguing Values of the Critical Current Density of Bi-2212

Malik¹,

Varma²

2021

The empirically reported values of the critical current density (j c ) of Bi-2212 as 2.4 × 10 5 (j c1 ; Sample 1) and 1.0 × 10 6 A/cm 2 (j c2 ; Sample 2) are intriguing because both of them correspond to the same values of the temperature T = 4.2 K and the applied magnetic field H = 12 × 10 4 G. This difference is conventionally attributed to such factors-not all of which are quantifiable-as the geometry, dimensions and the nature of dopants and the manners of preparation of the samples which cause their granular structures, grain boundaries, alignment of the grains and so on to differ. Based on the premise the number density of the charge-carriers and their critical velocity, the number of occupied Landau levels and the magnetic interaction parameter.

“…A salient feature of our approach [21] is that, rather than employing any model to calculate J c , it is based directly on the definition of J c = N s e v c , where e is the electronic charge and v c the critical velocity of the electrons. As is well known, BCS theory sets the momentum (P) of the centre-of mass of the pairs as zero at the outset, which necessitates the employment of a model for the calculation of J c based indirectly on its dependence on the applied magnetic field.…”

Section: The Scope and The Plan Of The Present Papermentioning

confidence: 99%

“…This approach leads to the values of (q, y) corresponding to each pair of (h, j c ) at any T; we therefore call it the (q, y) approach which enables one to calculate several T-dependent properties of the SC such as N s , ξ, etc. The derivation of ( 13) with X and Y as in ( 16) has been given in [21].…”

Section: The Core Equationsmentioning

confidence: 99%

Compressed H3S: Fits to the Empirical Hc2(T) Data and a Discussion of the Meissner Effect

Malik,

Varma

2023

Based on μ-, Tand H-dependent pairing and number equations and the premise that μ(T) is predominantly the cause of the variation of the upper critical field H c2 (T), where μ, T and H denote the chemical potential, temperature and the applied field, respectively, we provide in this paper fits to the empirical H c2 (T) data of H 3 S reported by Mozaffari, et al. ( 2019) and deal with the issue of whether or not H 3 S exhibits the Meissner effect. Employing a variant of the template given by Dogan and Cohen (2021), we examine in detail the results of Hirsch and Marsiglio (2022) who have claimed that H 3 S does not exhibit the Meissner effect and Minkov, et al. (2023) who have claimed that it does. We are thus led to suggest that monitoring the chemical potential (equivalently, the number density of Cooper pairs N s at T = T c ) should shed new light on the issue being addressed.