Ferromagnetism and superconductivity are antagonistic phenomena. Their coexistence implies either a modulated ferromagnetic order parameter on a lengthscale shorter than the superconducting coherence length or a weak exchange coupling between the itinerant superconducting electrons and the localized ordered spins. In some iron based pnictide superconductors the coexistence of ferromagnetism and superconductivity has been clearly demonstrated. The nature of the coexistence, however, remains elusive since no clear understanding of the spin structure in the superconducting state has been reached and the reports on the coupling strength are controversial. We show, by a direct optical pump-probe experiment, that the coupling is weak, since the transfer of the excess energy from the itinerant electrons to ordered localized spins is much slower than the electron-phonon relaxation, implying the coexistence without the short-lengthscale ferromagnetic order parameter modulation. Remarkably, the polarization analysis of the coherently excited spin wave response points towards a simple ferromagnetic ordering of spins with two distinct types of ferromagnetic domains.
COBISS.SI-ID: 28287783
Recently discovered ultrafast transition to the metastable hidden quantum state in 1T-TaS2 attracts a lot of interest due to its potential for practical application as an ultrafast memory. Controlling of the stability of the state is one of the crucial aspects. In the article we investigate relaxation dynamics of the hidden state and propose the ways for its stabilization at higher temperatures.
COBISS.SI-ID: 28753959
In this article we have studied nonequilibrium phase transition into the pseudogap state. The three-pulse experiments have revealed short correlation range of the dynamical state and individual character of the quasiparticle relaxation. Energy required for nonthermal destruction of the pseudogap scales linearly with the gap. This is explained with the model which accounts for subgap phonons generation.
COBISS.SI-ID: 28758311
The superconducting state in one-dimensional nanosystems is very delicate. While fluctuations of the phase of the superconducting wave function lead to the spontaneous decay of persistent supercurrents in thin superconducting wires and nanocircuits, discrete phase-slip fluctuations can also lead to more exotic phenomena, such as the appearance of metastable superconducting states in current-bearing wires. Here we show that switching between different metastable superconducting states in δ-MoN nanowires can be very effectively manipulated by introducing small amplitude electrical noise. Furthermore, we show that deterministic switching between metastable superconducting states with different numbers of phase-slip centres can be achieved in both directions with small electrical current pulse perturbations of appropriate polarity. The observed current-controlled bi-stability is in remarkable agreement with theoretically predicted trajectories of the system switching between different limit cycle solutions of a model one-dimensional superconductor.
COBISS.SI-ID: 29119015
Temperature and fluence dependence of the 1.55-eV optical transient reflectivity in BaFe2(As1−xPx)2 were measured and analysed in the low and high excitation density limit. The effective magnitude of the superconducting gap of ∼5 meV obtained from the low-fluence-data bottleneck model fit is consistent with the ARPES results for the γ-hole Fermi surface. The superconducting-state nonthermal optical destruction energy was determined from the fluence dependent data. The in-plane optical destruction energy scales well with T2c and is found to be similar in a number of different layered superconductors.
COBISS.SI-ID: 28936231