Related papers: Crossover from weak to strong pairing in unconvent…
It is shown that the temperature dependence of the value of energy gap in superconductors can be classified as the order-disorder transition with its characteristic features. The obtained relationship between the critical temperature and…
In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron based superconductors have the highest superconducting transition temperature next to copper oxides. In…
We analyze a simple model containing the physical ingredients of a Hund's metal, the local spin fluctuations with power-law correlators, $(\Omega_0/|\Omega|)^\gamma$, with $\gamma$ greater than one, interacting with electronic…
Unconventional superconductors such as the high-transition temperature cuprates, heavy-fermion systems and iron arsenide-based compounds exhibit antiferromagnetic fluctuations that are dominated by a resonance, a collective spin-one…
The BCS-BEC crossover from strongly overlapping Cooper pairs to non-overlapping composite bosons in the strong coupling limit has been a long-standing issue of interacting many-body fermion systems. Recently, FeSe semimetal with hole and…
By interpreting various experimental data for the new high temperature FeAs type superconductors in terms of lattice mediated multi gap superconductivity, it is shown that these systems strongly resemble MgB2, however, with the distinction…
The superconducting gap in a CeRu$_{2}$ single crystal is investigated by point contacts. BCS-like behavior of the gap $\Delta $ in the temperature range below T$_{c}^{*}<$T$_{c}$, where T$_{c}$ is the critical temperature, is established,…
The ionization energy theory is used to calculate the evolution of the resistivity and specific heat curves with respect to different doping elements in the recently discovered superconducting Pnictide materials. Subsequently, the…
The nature of the pairing state in iron-based superconductors is the subject of much debate. Here we argue that in one material, the stoichiometric iron pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state,…
The exotic superconductors, defined as those which follow the phenomenological trend of Uemura (Tc approximately proportional to penetration depth^-2), presently constitute the most broad and general class of superconductors which can…
Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic…
In cuprate superconductors, a pronounced maximum of superconducting Tc is observed in compounds that have an in-plane Cu-O distance close to ~1.92 Angstroms. On the other hand, direct measurements of the electron-phonon coupling lambda as a…
A notable aspect of high-temperature superconductivity in the copper oxides is the unconventional nature of the underlying paired-electron state. A direct manifestation of the unconventional state is a pairing energy - that is, the energy…
We experimentally study transport and intrinsic tunneling characteristics of a single-layer cuprate Bi(2+x)Sr(2-y)CuO(6+delta) with a low superconducting critical temperature Tc < 4 K. It is observed that the superconducting energy,…
Using a doping-determined multiband model spectrum of a "typical'' cuprate the effective mass of the paired carriers is calculated on the whole doping scale. Large $m_{ab}$ values quench rapidly with leaving the very underdoped region.…
In conventional metal superconductors such as aluminum, the large number of weakly bounded Cooper pairs become phase coherent as soon as they start to form. The cuprate high critical temperature ($T_c$) superconductors, in contrast, belong…
For a completely general anisotropic order parameter (including changes of sign), we show that weak coupling theory is incompatible with high values of the maximum \Delta_{M} of the zero temperature gap as compared to the critical…
Two-band electronic structures with a valence and a conduction band separated by a tunable energy gap and with pairing of electrons in different channels can be relevant to investigate the properties of two-dimensional multiband…
There is a clear discrepancy among the energy-gap values for different 90 K cuprates, inferred from tunneling measurements. By using the phase diagram for hole-doped cuprates we show that tunneling measurements performed on 90 K cuprates,…
The main purpose of this brief review is to present a sketch of the mechanism of high-Tc superconductivity based mainly on tunneling measurements in cuprates. In the review, we shall mostly discuss tunneling spectroscopy in Bi2212. Analysis…