We present scanning tunneling spectroscopy measurements of the local quasiparticles excitation spectra of CeCoIn$_5$ between 440mK and 3K in samples with a bulk $T_{rm c}=2.25$K. The spectral shape of our low-temperature tunneling data, quite textboo
k nodal-gap conductance, allow us to confidently fit the spectra with a d-wave density of states considering also a shortening of quasiparticles lifetime term $Gamma$. The $Delta(0)$ value obtained from the fits yields a BCS ratio $2Delta/kT_{rm c} =7.73$ suggesting that CeCoIn$_5$ is an unconventional superconductor in the strong coupling limit. The fits also suggest that the height of coherence peaks in CeCoIn$_5$ is reduced with respect to a pure BCS spectra and therefore the coupling of quasiparticles with spin excitations should play a relevant role. In addition, the tunneling conductance shows a depletion at energies smaller than $Delta$ for temperatures larger than the bulk $T_{rm c}$, giving further support to the existence of a pseudogap phase that in our samples span up to $T^{*}sim 1.2 T_{rm c}$. The phenomenological scaling of the pseudogap temperature observed in various families of cuprates, $2Delta/kT^{*} sim 4.3 $, is not fulfilled in our measurements. This suggests that in CeCoIn$_5$ the strong magnetic fluctuations might conspire to close the local superconducting gap at a smaller pesudogap temperature-scale than in cuprates.
We detect the persistence of the solidification and order-disorder first-order transition lines in the phase diagram of nanocrystalline Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ vortex matter down to a system size of less than hundred vortices. The temperatu
re-location of the vortex solidification transition line is not altered by decreasing the sample size although there is a depletion of the entropy-jump at the transition with respect to macroscopic vortex matter. The solid order-disorder phase transition field moves upward on decreasing the system size due to the increase of the surface-to-volume ratio of vortices entailing a decrease on the average vortex binding energy.
In this work we revisit the vortex matter phase diagram in layered superconductors solving still open questions by means of AC and DC local magnetic measurements in the paradigmatic Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ compound. We show that measuring w
ith AC magnetic techniques is mandatory in order to probe the bulk response of vortex matter, particularly at high-temperatures where surface barriers for vortex entrance dominate. From the $T_{rm FOT}$-evolution of the enthalpy and latent-heat at the transition we find that, contrary to previous reports, the nature of the dominant interlayer coupling is electromagnetic in the whole temperature range. By studying the dynamic properties of the phase located at $T gtrsim T_{rm FOT}$, we reveal the spanning in a considerable fraction of the phase diagram of a non-linear vortex phase suggesting bulk pinning might play a role even in the liquid vortex phase.
The persistence of the first-order transition line in the phase diagram of mesoscopic Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ vortex matter is detected down to a system size of less than hundred vortices. Precise and highly-sensitive to bulk currents AC ma
gnetization techniques proved to be mandatory in order to obtain this information. The location of the vortex matter first-order transition lines are not altered by decreasing the sample size down to 20 $mu$m. Nevertheless, the onset of irreversible magnetization is affected by increasing the sample surface-to-volume ratio producing a noticeable enlargement of the irreversible vortex region above the second-peak transition.
We probe the local quasiparticles density-of-states in micron-sized SmFeAsO$_{1-x}$F$_{x}$ single-crystals by means of Scanning Tunnelling Spectroscopy. Spectral features resemble those of cuprates, particularly a dip-hump-like structure developed at
energies larger than the gap that can be ascribed to the coupling of quasiparticles to a collective mode, quite likely a resonant spin mode. The energy of the collective mode revealed in our study decreases when the pairing strength increases. Our findings support spin-fluctuation-mediated pairing in pnictides.
