Magnetic-field dependence of superconducting energy gaps inYNi2B2C: Evidence of multiband superconductivity

Abstract

We present results of in field directional point contact spectroscopy (DPCS) study in the quaternary borocarbide superconductor YNi 2 B 2 C, which is characterized by a highly anisotropic superconducting gap function. For I||a, the superconducting energy gap (∆), decreases linearly with magnetic field and vanishes around 3.25T which is well below the upper critical field (H c2~6 T) measured at the same temperature (2K). For I||c, on the other hand, ∆ decreases weakly with magnetic field but the broadening parameter (Γ) increases rapidly with magnetic field with the absence of any resolvable feature above 3.5T. From an analysis of the field variation of energy gaps and the zero bias density of states we show that the unconventional gap function observed in this material could originate from multiband superconductivity. 74.50.+r, 74.25.Ha, 74.70.Dd

Investigation of the superconducting energy gap in the compound LuNi2B2C by the method of point contact spectroscopy: two-gap approximation

“…The part of the Fermi surface responsible for nesting makes only (4.4 ± 0.5%) and shows up a slightly increased resistance for the current along 100 . 4 As was shown for point contacts with a ballistic transit of electrons in a many-band superconductor 7 , in any di- * Email address: yanson@ilt.kharkov.ua rection the contribution to conductivity from each band is proportional to the area of the Fermi surface projection from the corresponding band onto the interface. Since the fraction of the Fermi surface responsible for nesting is small, the nesting-related features are not obvious in the point-contact spectra.…”

Field-induced gapless electron pocket in the superconducting vortex phase ofYNi2B2Cas probed by magnetoacoustic quantum oscillations

“…Hence, in the mixed state the α pocket of YNi 2 B 2 C has indeed very likely a vanishingly small or zero gap while (most of) the other Fermi-surface sheets develop gaps in the superconducting state. These gaps have varying, anisotropic, and partially large values for the different bands as was evidenced by various studies [26][27][28]59]. Further, we suggest that a similar field-induced quenching mechanism might resolve the puzzle of the accidental point nodes (s+g wave) proposed by Maki et al [60] based on thermal conductivity [61] and NMR [62] studies performed in fields above 1 T.…”

“…The unusual properties in the superconducting state led to controversial debates on its nature. In particular, these materials were among the first for which multiband superconductivity was detected [26][27][28][29]. Furthermore, pronounced gap anisotropies have been suggested [30,31].…”

The Properties of the Superconducting State in YNi2B2C: The One-Band Eliashberg Approach

“…In the literature related to the topic there are some reports that the simplest version of the Eliashberg equations might not be able to cope with the description of all relevant physical quantities. In particular, the dependence of the upper critical field (H C2 ) on the temperature [11,12] or the results obtained with a use of the directional point-contact spectroscopy [13,14] suggest the necessity of the two-band model being used. On the other hand, some researchers basing on the thermal and spectroscopic experiments are moving toward the direction of the one-band models with a non-trivial wave symmetry (s + g or even d-wave symmetry) [15][16][17][18].…”