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Giant paramagnetic Meissner effect in multiband superconductors.

da Silva RM, Milošević MV, Shanenko AA, Peeters FM, Aguiar JA - Sci Rep (2015)

Bottom Line: Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux.Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field.We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces.

View Article: PubMed Central - PubMed

Affiliation: Programa de Pós-Graduação em Ciência dos Materiais, Universidade Federal de Pernambuco, Av. Jorn. Aníbal Fernandes, s/n, 50670-901 Recife-PE, Brazil.

ABSTRACT
Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces.

No MeSH data available.


Related in: MedlinePlus

Maximal paramagnetic response in decreasing field at T = 0.94Tc (red) and its total cumulative value over the field span (black), as a function of v1/v2.Vertical lines indicate where Hc = Hc2, where the S-N surface energy changes sign (i.e. σSN = 0), and where long-range interaction of vortices changes sign (left to right, respectively), delimiting the crossover range between standard types of superconductivity.
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f3: Maximal paramagnetic response in decreasing field at T = 0.94Tc (red) and its total cumulative value over the field span (black), as a function of v1/v2.Vertical lines indicate where Hc = Hc2, where the S-N surface energy changes sign (i.e. σSN = 0), and where long-range interaction of vortices changes sign (left to right, respectively), delimiting the crossover range between standard types of superconductivity.

Mentions: In increasing field, all calculated magnetization loops exhibit a superheated Meissner state above the thermodynamic critical field Hc, where the superheating field Hsh agrees very well with the seminal calculations of Matricon and Saint-James for Hsh(κ) of single-band materials49. At H = Hsh, superconductivity is either destroyed (for v1/v2 < 0.34) or a jump to the mixed state occurs (for v1/v2 > 0.34). The delimiting value of v1/v2 = 0.34 exactly satisfies the condition Hc = Hc2. In decreasing magnetic field, the superconductivity nucleates at the surface superconductivity field Hc346. Indeed, the nucleated states were only superconducting at the surfaces of the slab, with a large normal domain in the interior of the slab. For further lowered field and v1/v2 < 0.34 the normal domain remains trapped until abruptly expelled from the sample at the expulsion field He. This analysis confirms that magnetic response of the system for v1/v2 < 0.34 is the one of Type-I superconductors, since typical superheating-supercooling picture holds there, Hc2 is smaller than Hc, and no vortices are found in the paramagnetic branch where flux was trapped upon nucleation of surface superconductivity. However, while decreasing field for v1/v2 > 0.34, where consequently Hc2 > Hc, the normal domain becomes unstable at field Hd but is not expelled; instead, it spreads into a vortex configuration, stable down to persistently lower expulsion field He as v1/v2 is increased. Simultaneously, flux trapping becomes notably more efficient, so that the vortex exit is hampered in decreasing field and paramagnetic response increases to its maximum at He. This tendency continues up to v1/v2 ≈ 0.53, for which paramagnetic response is almost an order of magnitude larger than the Meissner response at H = He, and approximately 30 times larger than the largest theoretical estimate of paramagnetic response to date (scaled to the diamagnetic response at a given field, see Ref. [16]). We therefore refer to this property as giant paramagnetic response (GPR). For v1/v2 > 0.53, the cumulative paramagnetic response is still very large but gradually decreases, and magnetization curves in decreasing field connect to zero without any abrupt flux expulsion. In other words, we approach the Type-II limit, in which magnetization is expected to hover around zero for descending field in the presence of surface barriers48. In Fig. 3, we summarize the observed maximal amplitude, Max(4πM/H) in the entire field range, and the total cumulative paramagnetic response, , as a function of v1/v2, extracted from Fig. 2.


Giant paramagnetic Meissner effect in multiband superconductors.

da Silva RM, Milošević MV, Shanenko AA, Peeters FM, Aguiar JA - Sci Rep (2015)

Maximal paramagnetic response in decreasing field at T = 0.94Tc (red) and its total cumulative value over the field span (black), as a function of v1/v2.Vertical lines indicate where Hc = Hc2, where the S-N surface energy changes sign (i.e. σSN = 0), and where long-range interaction of vortices changes sign (left to right, respectively), delimiting the crossover range between standard types of superconductivity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525483&req=5

f3: Maximal paramagnetic response in decreasing field at T = 0.94Tc (red) and its total cumulative value over the field span (black), as a function of v1/v2.Vertical lines indicate where Hc = Hc2, where the S-N surface energy changes sign (i.e. σSN = 0), and where long-range interaction of vortices changes sign (left to right, respectively), delimiting the crossover range between standard types of superconductivity.
Mentions: In increasing field, all calculated magnetization loops exhibit a superheated Meissner state above the thermodynamic critical field Hc, where the superheating field Hsh agrees very well with the seminal calculations of Matricon and Saint-James for Hsh(κ) of single-band materials49. At H = Hsh, superconductivity is either destroyed (for v1/v2 < 0.34) or a jump to the mixed state occurs (for v1/v2 > 0.34). The delimiting value of v1/v2 = 0.34 exactly satisfies the condition Hc = Hc2. In decreasing magnetic field, the superconductivity nucleates at the surface superconductivity field Hc346. Indeed, the nucleated states were only superconducting at the surfaces of the slab, with a large normal domain in the interior of the slab. For further lowered field and v1/v2 < 0.34 the normal domain remains trapped until abruptly expelled from the sample at the expulsion field He. This analysis confirms that magnetic response of the system for v1/v2 < 0.34 is the one of Type-I superconductors, since typical superheating-supercooling picture holds there, Hc2 is smaller than Hc, and no vortices are found in the paramagnetic branch where flux was trapped upon nucleation of surface superconductivity. However, while decreasing field for v1/v2 > 0.34, where consequently Hc2 > Hc, the normal domain becomes unstable at field Hd but is not expelled; instead, it spreads into a vortex configuration, stable down to persistently lower expulsion field He as v1/v2 is increased. Simultaneously, flux trapping becomes notably more efficient, so that the vortex exit is hampered in decreasing field and paramagnetic response increases to its maximum at He. This tendency continues up to v1/v2 ≈ 0.53, for which paramagnetic response is almost an order of magnitude larger than the Meissner response at H = He, and approximately 30 times larger than the largest theoretical estimate of paramagnetic response to date (scaled to the diamagnetic response at a given field, see Ref. [16]). We therefore refer to this property as giant paramagnetic response (GPR). For v1/v2 > 0.53, the cumulative paramagnetic response is still very large but gradually decreases, and magnetization curves in decreasing field connect to zero without any abrupt flux expulsion. In other words, we approach the Type-II limit, in which magnetization is expected to hover around zero for descending field in the presence of surface barriers48. In Fig. 3, we summarize the observed maximal amplitude, Max(4πM/H) in the entire field range, and the total cumulative paramagnetic response, , as a function of v1/v2, extracted from Fig. 2.

Bottom Line: Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux.Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field.We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces.

View Article: PubMed Central - PubMed

Affiliation: Programa de Pós-Graduação em Ciência dos Materiais, Universidade Federal de Pernambuco, Av. Jorn. Aníbal Fernandes, s/n, 50670-901 Recife-PE, Brazil.

ABSTRACT
Superconductors, ideally diamagnetic when in the Meissner state, can also exhibit paramagnetic behavior due to trapped magnetic flux. In the absence of pinning such paramagnetic response is weak, and ceases with increasing sample thickness. Here we show that in multiband superconductors paramagnetic response can be observed even in slab geometries, and can be far larger than any previous estimate - even multiply larger than the diamagnetic Meissner response for the same applied magnetic field. We link the appearance of this giant paramagnetic response to the broad crossover between conventional Type-I and Type-II superconductors, where Abrikosov vortices interact non-monotonically and multibody effects become important, causing unique flux configurations and their locking in the presence of surfaces.

No MeSH data available.


Related in: MedlinePlus