Electronic density of states andTcinNb3Sn under pressure

Abstract

We have determined the effect of hydrostatic pressure on the electronic heat-capacity coefficient y of transforming Nb3Sn through measurements of the superconducting transition temperature T"the temperature derivative of the upper critical field near T"and the residual resistivity. We find that y and the bare density of electronic states are suppressed by pressure. Results are discussed in terms of a pressure-dependent d-band occupancy.

An experimental and computational study of srain sensitivity in superconducting Nb3Sn

“…This conclusion is consistent with the investigation of a number of authors, including Lim et al [147] who investigated the stress dependence of T c , µ 0 H c2 (0), and ρ n , Welch [197] who investigated the strain sensitivity of T c relative to µ 0 H c2 , and Cohen et al [198], who constructed a simple model to account for the temperature dependent normal state resistivity and the elastic constants, which according to McEvoy [199] can explain the pressure dependence of T c as well. It was argued by Godeke et al [200] that strain affects the elec-tron diffusion constant, which was one of the main reasons for performing experiments in which both the superconducting properties and the normal state resistivity is measured as a function of strain in this thesis.…”

Towards analysis of the electron density of states of Nb3Sn as a function of strain

“…R(λ tr ) is introduced into the formula to correct for deviations due to linearization of the Gorkov equation [19]. However, in general the deviation is small and is considered negligible in this particular case, so that R(λ tr ) ≈ 1 [7]. It has been shown [22] that the μ 0 H c2 (T) phase boundary is accurately described by the Maki-deGennes equation [23], with …”

“…While the critical temperature T c and critical magnetic field μ 0 H c2 of Nb 3 Sn have been expressed in terms of the phonon and electron DOS [2][3][4][5][6][7], it is not clear whether the effect of strain on the superconducting properties is related to changes in the phonon spectrum [5], the electron DOS [7] or both.…”

Estimate of density-of-states changes with strain in A15 Nb 3 Sn superconductors

“…Since the strain effects on the critical current density J c in the Nb-Sn system arise from the field-temperature phase boundary shifts and strain-dependent changes of the flux line to lattice interactions, the improved understanding of the strain sensitivity in superconducting Nb 3 Sn calls for an endeavor to determine the DOS at the Fermi surface N(E F ) as function of strain, which will help contribute to future studies on the microscopic-based strain description of the temperature-dependent upper critical field l 0 H c2 (T) [16]. The behavior of the bare DOS and its relationship of T c and strain is crucial to understand the microscopic mechanisms responsible for the strain sensitivity in A15 superconducting wires [13,14,19]. A study on the electronic DOS and the critical temperature T c in Nb 3 Sn under hydrostatic pressure conducted by Lim et al [13] determines that the coefficient of electron heat capacity as well as the bare electron DOS are suppressed by the pressure.…”

“…Several attempts at determining a generic parameterization for the critical properties (the critical temperature T c , the upper critical field l 0 H c2 , and the critical current density J c ) have been made in the past decades, which involves the empirical characterization and interpretation of uniaxial strain dependence [7][8][9], the microscopic modeling based on the strain-induced modifications in the electron-phonon spectrum [10][11][12], the electron density of states (DOS) [13,14] or both [15], and the models with a semi-empirical construction which balances the need for well-founded formalisms for the important features of the strain effects and practical engineering application to multifilamentary composite Nb 3 Sn wire measurements implementation [16][17][18]. Because of the failure to make explicit an underlying microscopic mechanisms, the description of the strain sensitivity in superconducting Nb 3 Sn offered by empirical/semi-empirical modeling and analytics exhibits its limitations in achieving the comprehensive characterizations [14,16].…”