Nonconstant electronic density of states tunneling inversion for A15 superconductors: Nb3Sn

We present a method to produce superconducting tips to be used in Scanning Tunneling Microscopy/Spectroscopy experiments. We use these tips to investigate the evolution of the electronic density of states of NbSe2 from 0.3K up to its critical temperature (7.2K). The use of a superconducting tip (Pb) as ounterelectrode provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves, along all the studied thermal range. The anal...

We theoretically investigate the effect of various symmetries of the superconducting order parameter Delta(omega) on the normalized tunneling conductance of SIN junctions by directly solving the real-axis Eliashberg equations (EEs) for a half-filled infinite band, with the simplifying assumption mu*=0. We analyze six different symmetries of the order parameter: s, d, s+id, s+d, extended s and anisotropic s, by assuming that the spectral function alpha^{2}F(Omega) contains an ...

We study the electronic density of states in a mesoscopic superconductor near a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy experiment, a substantial density of states is observed at sub-gap energies close to a ferromagnet. We compare our data with detailed calculations based on the Usadel equation, where the effect of the ferromagnet is treated as an effective boundary condition. We achieve an excellent agreement with theory when non-ideal qu...

Recent scanning tunnelling microscopy experiments in NbN thin disordered superconducting films found an emergent inhomogeneity at the scale of tens of nanometers. This inhomogeneity is mirrored by an apparent dimensional crossover in the paraconductivity measured in transport above the superconducting critical temperature $T_c$. This behavior was interpreted in terms of an anomalous diffusion of fluctuating Cooper pairs, that display a {\em quasi-confinement} (i.e., a slowing...

We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers as a function of Ni thickness, $d_F$. Our thinnest samples show the usual DOS peak at $\pm\Delta_0$, whereas intermediate-thickness samples have an anomalous ``double-peak'' structure. For thicker samples ($d_F \geq 3.5$ nm), we see an ``inverted'' DOS which has previously only been reported in superconductor/weak-ferromagnet structures. We analyze the data using the self-consistent non-li...

We develop an analytical tool to extract bulk electronic properties of unconventional superconductors through inelastic neutron scattering (INS) spectra. Since the spin excitation spectrum in the superconducting (SC) state originates from Bogoliubov quasiparticle scattering associated with Fermi surface nesting, its energy-momentum relation--the so called `hour-glass' feature--can be inverted to reveal the Fermi momentum dispersion of the single-particle spectrum as well as t...

Considering a possibility that the pseudogap state in the underdoped high-$T_{c}$ superconductors is not due to a superconducting correlation, we study the tunneling spectroscopy below $T_{c}$ based on the phenomenological models of the pseudogap state. Specifically we consider two cases: (1) the pseudogap is a simple suppression of the density of states with an unknown origin; (2) the pseudogap state is due to an antiferromagnetic correlation. For both cases we calculate $dI...

Low temperature scanning tunneling spectroscopy of HfNiSn shows a V^m(m < 1) zero bias anomaly around the Fermi level. This local density of states with a fractional power law shape is well known to be a consequence of electronic correlations. For comparison, we have also measured the tunneling conductances of other half-Heusler compounds with 18 valence electrons. ZrNiPb shows a metal-like local density of states, whereas ZrCoSb and NbFeSb show a linear and V^2 anomaly. One ...

HTS show many puzzling anomalies in their normal state properties. Among them are: - the presence of a peak in the c-axis resistance and its growth in external magnetic field - the anomalous negative magnetoresistance observed above Tc - the deviation from the Korringa law in the temperature dependence of the NMR relaxation rate - the opening of a large pseudo-gap in the c-axis optical conductivity well above Tc - the gap-like tunneling anomalies observed above Tc ...

We show that in ultra-small superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states. Instead, though exponentially suppressed at low energies, the tunneling density of states exhibits the ``soft gap'' behavior, vanishing linearly with excitation energy, as the energy approaches zero.