Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBi

Abstract

We perform a detailed comparison of magnetotunneling in conventional low-T c Nb/Al-AlO x /Nb junctions with that in slightly overdoped Bi 2−y Pb y Sr 2 CaCu 2 O 8+δ [Bi(Pb)-2212] intrinsic Josephson junctions and with microscopic calculations. It is found that both types of junctions behave in a qualitatively similar way. Both magnetic field and temperature suppress superconductivity in the state-conserving manner. This leads to the characteristic sign change of tunneling magnetoresistance from the negative at the subgap to the positive at the sum-gap bias. We derived theoretically and verified experimentally scaling laws of magnetotunneling characteristics and employ them for accurate extraction of the upper critical field H c2 . For Nb an extended region of surface superconductivity at H c2 < H < H c3 is observed. The parameters of Bi(Pb)-2212 were obtained from self-consistent analysis of magnetotunneling data at different levels of bias, dissipation powers, and for different mesa sizes, which precludes the influence of self-heating. It is found that H c2 (0) for Bi(Pb)-2212 is 70 T and decreases significantly at T → T c . The amplitude of subgap magnetoresistance is suppressed exponentially at T > T c /2, but remains negative, although very small, above T c . This may indicate the existence of an extended fluctuation region, which, however, does not destroy the general second-order type of the phase transition at T c .

Low anisotropy of the upper critical field in a strongly anisotropic layered cuprateBi2.15Sr1.9CuO6+δ:Evidence for a paramagnetically limited superconductivity

“…Without flux-flow, H c2 would correspond to the onset of resistivity R ∼ 0, rather than R = R n . This has been demonstrated by simultaneous tunneling and transport measurements for conventional superconductors [16]. Without exact knowledge of the flux-flow contribution it is impossible to confidently extract H c2 from R(T, H) data at T < T c .…”

“…The negative c-axis MR persists both in the superconducting [16] and the normal states and is attributed to field suppression of either the superconducting gap ∆ [16] or the pseudogap ∆ P G [29]. For high-T c Bi-2212 [6,8] and Bi-2223 [53] cuprates the corresponding energies (∆ ∼ 30 − 50 meV, ∆ P G ∼ 30 − 70 meV) and fields (H c2 ∼ 100 − 200 T, H * ∼ 200 − 300 T) are similar [16,29] and separation of the two contributions is difficult. However, in the studied low-T c superconductor the separation becomes trivial because, as shown in Ref.…”

“…Below T c this leads to appearance of an intrinsic Josephson effect [54], observed in all Bi-based cuprates [6,8,16,53,55], including Bi-2201 [30,50,56]. Interlayer tunneling creates the basis for the intrinsic tunneling spectroscopy technique [6,8,16,30,53] and facilitates simultaneous magneto-transport and spectroscopic measurements, beneficial for analysis of H c2 [16]. Fig.…”

“…The high T c in combination with a strong coupling leads to a large superconducting energy gap ∆ ∼ 20 − 50 meV [6][7][8][9][10][11] and H c2 (0) ∼ 10 2 T [12][13][14][15][16][17][18][19]. Such strong fields may alter the ground state of the material.…”

High bias anomaly in YBa2Cu3O7−x/LaMnOGolod1, Rydh2, Krasnov3 et al. 2013Phys. Rev. BSelf Cite284290View full textAdd to dashboardCite

“…An out-of-plane magnetic field suppresses superconductivity due to the penetration of Abrikosov vortices [56,57]. However, an in-plane field of 10-17 T does not give rise to any visible suppression of superconductivity at T T c (see e.g.…”