Time-resolved carrier dynamics and electron-phonon coupling strength in proximized weak ferromagnet-superconductor nanobilayers

Abstract

We present our femtosecond optical pump-probe studies of proximized ferromagnet-superconductor nanobilayers. The weak ferromagnetic nature of a thin NiCu film makes it possible to observe the dynamics of the nonequilibrium carriers through the near-surface optical reflectivity change measurements. The subpicosecond biexponential reflectivity decay has been identified as electron-phonon Debye and acoustic phonon relaxation times, and the decay of Debye phonons versus temperature dependence was used to evaluate the electronphonon coupling constants for both the pure Nb and proximized Nb/ NiCu heterostructures down to low temperatures. We have also demonstrated that the NiCu overlay on top of Nb dramatically reduced the slow, bolometric component of the photoresponse component, making such bilayers attractive for future radiation detector applications.

Structural dependent ultrafast electron-phonon coupling in multiferroic BiFeO3 films

“…A theoretical framework expressing s e-ph is related to the second moment of the Eliashberg function khx 2 i ¼ p 3 kBTe hseÀph , where hx 2 i is a mean-square phonon frequency. [19][20][21] This expression suggests that s e-ph is linearly dependent on temperature of electron T e . However, in our case, s e-ph is virtually pumpfluence independent although the amplitude of the initial peak of DR/R at zero time delay shows a linear pumpfluence dependence, as shown in Fig.…”

“…Detailed experimental data of eph relaxation process have not been systematically studied in multiferroic materials, though the relevant investigations have been collected for metals, 15,16 metal nanostructures, 17 graphite, 18 and high-temperature superconductors. [19][20][21][22] In this letter, the time-resolved pump-probe technique is employed to investigate the electronic energy relaxation in multiferroic BFO films. The sub-picosecond bi-exponential decay is identified as the recovery of photo-excited hot electrons via e-ph and spin-phonon (s-ph) relaxation processes.…”

Influence of the magnetic configuration on the vortex-lattice instability in Nb/permalloy bilayers

“…For example, it was experimentally proved that S/F hybrids are optimal systems to be used as ultrafast superconducting optical detectors and eventually even as single photon detectors, due to the small value of the penetration length of the superconducting correlations in the F layer, ξ F 6 nm, which determines better performance in terms of both photoresponse signal detection and sensitivity [3][4][5]. In fact, in these devices the light probes a distance α (the material optical penetration depth), which is typically smaller than 50 nm in the 400-900 nm visible light wavelength range [3,4]. If S/N hybrids were to be used (here N stands for normal metal), due to the value of the penetration length of the Cooper pairs in the N layer, ξ N , which at low temperatures can be of the order of hundreds of nanometers, a thin N layer would not be an effective perturbation to the S layer to detect effects induced by the proximity effect.…”

Interfacial effects revealed by ultrafast relaxation dynamics inBiFeO3/YBa2Cu3O7bilayers

“…It has proven to be a useful time-domain tool to probe dynamics of complex structures 5,[7][8][9][10] and coexisting 11 /competing 12,13 phases in superconductors. Thus ultrafast optical spectroscopy is well suited to study competing interactions in heterostructures containing HTSCs.…”