The peak effect (PE) in the critical current density of type II superconductors has been related to an order-disorder transition in the vortex lattice (VL), but its underlying physics remains a controversial issue. Intrinsic to the PE are strong metastabilities that frequently mask the stationary VL configurations. We follow shaking and thermal protocols in NbSe2 single crystals to access these configurations and examine them by linear ac susceptibility measurements that avoid VL reorganization. We identify three different regions. For TT2(H), configurations are fully disordered and no metastability is observed. In the T1

We study the different dynamical regimes of a vortex lattice driven by ac forces in the presence of random pinning via numerical simulations. The behavior of the different observables is characterized as a function of the applied force amplitude for different frequencies. We discuss the inconveniences of using the mean velocity to identify the depinning transition and we show that instead, the mean quadratic displacement of the lattice is the relevant magnitude to characterize different ac regimes. We discuss how the results depend on the initial configuration and we identify hysteretic effects which are absent in the dc driven systems.

We study the heat current through two capacitively coupled quantum dots coupled in series with two conducting leads in the spinless case (valid for a high applied magnetic field). Our results are also valid for the heat current through a single quantum dot with strongly ferromagnetic leads pointing in opposite directions (so that the electrons with given spin at the dot can jump only to one lead) or through a quantum dot with two degenerate levels with destructive quantum interference and high magnetic field. Although the charge current is always zero, the heat current is finite when the interdot Coulomb repulsion is taken into account due to many-body effects. We generalize previous results for high temperatures and particular parameters obtained by Yadalam and Harbola [Phys. Rev. B 99, 195449 (2019)]. In particular we consider temperatures for which an orbital Kondo regime takes place. In contrast to previous results, we find that the heat current is finite even for U → ∞. In the Kondo regime, for temperatures much less than the Kondo energy scale, we obtain that the dependence of the thermal current with the temperature difference ∆T is ∼ (∆T ) 4 when the cold lead is at TC ≪ ∆T , and linear in ∆T if TC ≫ ∆T . For large TC the current saturates. As a function of Coulomb strength U , for high ∆T and TC = 0, the charge current has a maximum for U ∼ 3∆T and decreases with increasing U reaching a finite value for U → ∞. We also consider the case of different energy levels of the dots for which the device has rectifying properties.

We study experimentally and theoretically, the reorganization of superconducting vortices driven by oscillatory forces near the plastic depinning transition. We show that the system can be taken to configurations that are tagged by the shaking parameters but keep no trace of the initial conditions. In experiments performed in NbSe 2 crystals, the periodic drive is induced by ac magnetic shaking fields and the overall order of the resulting configuration is determined by noninvasive ac susceptibility measurements. With a model of interacting particles driven over random landscapes, we perform molecular dynamics simulations that reveal the nature of the shaking dynamics as fluctuating states similar to those predicted for other interacting particle systems.