We apply the femtosecond optical pump-probe spectroscopy to study the relaxation dynamics in photoexcited Co-doped Ba(Fe1−xCox )2As2 single crystals in the underdoped spin-density wave (SDW) state region of the x − T phase diagram. Underdoped SDW samples with Co- 0 % and Co-2.5 % show a bottleneck in the relaxation as a consequence of the partial charge gap opening in the orthorhombic SDW phase, similar to previous results in other SDW iron-pnictides. Moreover, the charge gap magnitude decreases with increasing doping. The sample with Co- 5.1 % displays both a SDW ordering and superconductivity at low T .We were able to observe a 2-fold anisotropy in our samples, existing up to 200 K, without any applied uniaxial stress. We associate the 2-fold symmetry breaking in nominally tetragonal phase with nematic ordering of the Fe d orbitals.
COBISS.SI-ID: 26613287
We have used resonant inelastic X-ray scattering to measure the evolution of magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, from a strongly correlated insulator to a non-superconducting metal (0 ≤ x ≤ 0.40). For x = 0, well-defined magnon excitations were observed. These magnons broaden with doping, but they persist with a similar dispersion and comparable intensity all the way to the non-superconducting, heavily overdoped metallic phase. We have concluded that the destruction of HTS with overdoping is caused neither by the general disappearance nor by the overall softening of magnetic excitations.
COBISS.SI-ID: 27013927
We study theoretically how the dynamics of the resistive state in narrow superconducting channels shunted by an external resistor depends on channel length, applied current, and penetration depth of the electric field in nonequilibrium superconductors. We show that changing the latter dramatically affects both the behavior of the current-voltage characteristics of the superconducting channels and the dynamics of their order parameter.
COBISS.SI-ID: 26737703
We report nonequilibrium quasiparticle (QP) dynamics in underdoped Bi2212 crystals using ultrafast optical spectroscopy, which allows to analyze the dynamics associated with the superconducting (SC) and psuedogap (PG) QPs independently. In the saturation condition of the SC component, where the SC condensate is fully destroyed within the photoexcited volume, we found a delay of the SC state recovery associated with a transient normal state. The delay increases linearly with increasing the pump fluence. The QP dynamics also shows a contribution of the PG component, whose magnitude at the start of the SC state recovery was almost constant at various pump fluences, suggesting a critical level of PG order before the SC condensate can recover.
COBISS.SI-ID: 26979879
A table-top femtosecond, non-relativistic, electron diffraction setup is combined with a low-jitter, photo-triggered streak camera to follow the optically induced structural dynamics in complex solids. A temporal resolution of 550 fs is experimentally demonstrated, while the route to streaking with sub-250 fs temporal resolution is outlined. The streaking technique allows for parallel capturing of temporal information as opposed to the serial data acquisition in a conventional scanning femtosecond electron diffraction. Moreover, its temporal resolution is not corrupted by increasing the number of electrons per pulse. Thus, compared to the conventional scanning approach, a substantial increase in signal-to-noise ratio (SNR) can be achieved. These benefits are demonstrated by studying a photo-induced charge density wave phase transition in 4Hb-TaSe2 using both methods.
COBISS.SI-ID: 26875943