Magnetic field decoupling and 3D-2D crossover in Nb/Cu multilayers

Krasnov, Vladimir M.; Kovalev, A.E.; Oboznov, V. A.; Pedersen, Niels Falsig

doi:10.1103/physrevb.54.15448

Cited by 25 publications

(31 citation statements)

References 44 publications

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“…This field is much smaller than the in-plane H c2 and does not significantly affect superconductivity in the YBCO electrodes [56]. However it is sufficient for suppression of the weak, proximity induced phase coherence in the LMO layer, similar as observed for the conventional proximity effect in S/N multilayers [61].…”

Section: B Fowler-nordheim Tunneling Into the Conduction Band Of Thementioning

confidence: 67%

High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
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High bias anomaly in YBa 2 Cu 3 O 7 /LaMnO 3+δ /YBa 2 Cu 3 O 7 Superconductor/Ferromagnetic Insulator/Superconductor junctions: Evidence for a long-range superconducting proximity effect through the conduction band of a ferromagnetic insulator. We study the perpendicular transport characteristics of small superconductor/ ferromagnetic insulator/ superconductor (YBa2Cu3O7−x/ LaMnO 3+δ / YBa2Cu3O7−x) tunnel junctions. At a large bias voltage V ∼ 1 V we observe a step-like onset of excess current that occurs below the superconducting transition temperature T < Tc and is easily suppressed by a magnetic field. The phenomenon is attributed to a novel type of the superconducting proximity effect of non-equilibrium electrons injected into the conduction band of the ferromagnetic insulator via a Fowler-Nordheim tunneling process. The occurrence of a strongly non-equilibrium population is confirmed by the detection of photon emission at large bias voltage. Since the conduction band in our ferromagnetic insulator is strongly spin polarized, the long-range (20 nm) of the observed proximity effect provides evidence for an unconventional spin-triplet superconducting state. I. INTRODUCTIONThe manganite perovskite La 2−x (Ca,Sr) x MnO 3 exhibits a rich phase diagram of unusual electronic and magnetic properties. Most prominent is the so-called colossal magneto-resistance (CMR) effect which occurs at 0.15 < x < 0.5 in the context of a transition from a paramagnetic and insulating or poorly conducting state to a ferromagnetic and half metallic state [1,2]. At somewhat lower doping at 0.1 < x < 0.15, the corresponding transition leads into a ferromagnetic insulating (FI) state which is a consequence of charge localization below the spin-polaron mobility edge and orbital ordering at low T [3][4][5][6]. This FI state can also be achieved in off stoichiometric LaMnO 3+δ in which the hole doping is due to La or Mn vacancies. While half-metallic manganites are considered as promising spin-polarizers [7], the FI manganite can be an ideal spin-filter material for use in tunnel barriers with low leakage currents. Efficient spin-filters are on demand for spintronic applications [8]. Spin polarization depends on many parameters including the density of states (DOS) of electronic bands [7,[9][10][11][12], orbital hybridization and various material issues at interfaces and on the bias voltage [13]. Metallic ferromagnets provide only modest spin polarization because both majority (↑) and minority (↓) spin bands are crossing the Fermi level E F [14]. This problem is obviated in insulating and halfmetallic ferromagnets with separated majority and minority bands at E F , which, therefore, can facilitate an almost complete spin-polarization [8,[13][14][15].The antagonism between superconductivity (S) and ferromagnetism (F) leads to a variety of novel effects in hybrid S/F heterostructures [16,17], such as the stabilization of unconventional spin-triplet superconductivity [17,18], or the realization of π-Josephson junctions [19], that are interest...

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Section: B Fowler-nordheim Tunneling Into the Conduction Band Of Thementioning

confidence: 67%

High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
Self Cite
28
4
29
0
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“…A similar H ⊥ c2 (T ) was also reported for proximity coupled Nb/Cu multilayers. 72 Using thus extracted H c2 , we check the scaling of other experimental parameters such as the zero bias and the subgap conductances and the sum-gap resistance, shown by symbols in Figs. 5(a)-5(c).…”

Section: Extraction Of H C2 For Nbmentioning

confidence: 99%

Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBi
Krasnov
¹
,
Motzkau
²
,
Golod
³

et al. 2011
Phys. Rev. B
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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 .

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“…7 (a) demonstrates that H c2 (T ) ∝ √ T c − T . At the first glance, it resembles the behavior of H c2 (T ) in thin film multilayers [65,67],…”

Section: B Fluctuation Conductivitymentioning

confidence: 99%

“…It is seen that the behavior in both cases is very similar. Therefore, at H ab the flux-flow contribution to R ab is small either due to zero Lorentz force or a strong intrinsic pinning in the layered superconductor [65][66][67], which prevents motion of Josephson vortices across the planes. maximum at Θ = 0 • due to onset of the Josephson fluxflow phenomenon [61].…”

Section: Angular Magnetoresistance At T < Tcmentioning

confidence: 99%

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

et al. 2014

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We study angular-dependent magnetoresistance in a low Tc layered cuprate Bi2.15Sr1.9CuO 6+δ . The low Tc ∼ 4 K allows complete suppression of superconductivity by modest magnetic fields and facilitate accurate analysis of the upper critical field Hc2. We observe an universal exponential decay of fluctuation conductivity in a broad range of temperatures above Tc and propose a new method for extraction of Hc2(T ) from the scaling analysis of the fluctuation conductivity at T > Tc. Our main result is observation of a surprisingly low Hc2 anisotropy ∼ 2, which is much smaller than the effective mass anisotropy of the material ∼ 300. We show that the anisotropy is decreasing with increasing field and saturates at a small value when the field reaches the paramagnetic limit. We argue that the dramatic discrepancy of high field and low field anisotropies is a clear evidence for paramagnetically limited superconductivity.

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Magnetic field decoupling and 3D-2D crossover in Nb/Cu multilayers

Cited by 25 publications

References 44 publications

High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
Self Cite
28
4
29
0
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High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
Self Cite
28
4
29
0
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Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBi
Krasnov
¹
,
Motzkau
²
,
Golod
³

et al. 2011
Phys. Rev. B
Self Cite
23
6
50
0
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Low anisotropy of the upper critical field in a strongly anisotropic layered cuprateBi2.15Sr1.9CuO6+δ:Evidence for a paramagnetically limited superconductivity

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Magnetic field decoupling and 3D-2D crossover in Nb/Cu multilayers

Cited by 25 publications

References 44 publications

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

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

Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBiKrasnov1, Motzkau2, Golod3 et al. 2011Phys. Rev. BSelf Cite236500View full textAdd to dashboardCite

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

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High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
Self Cite
28
4
29
0
View full text Add to dashboard Cite

High bias anomaly in YBa2Cu3O7−x/LaMnO
Golod
¹
,
Rydh
²
,
Krasnov
³

et al. 2013
Phys. Rev. B
Self Cite
28
4
29
0
View full text Add to dashboard Cite

Comparative analysis of tunneling magnetoresistance in low-TcNb/Al-AlOx/Nb and high-TcBi
Krasnov
¹
,
Motzkau
²
,
Golod
³

et al. 2011
Phys. Rev. B
Self Cite
23
6
50
0
View full text Add to dashboard Cite