Point-contact-spectroscopy evidence of quasi-particle interactions in RNi2B2C (R=Ho, Y)

Abstract

The point-contact (PC) d2V/dI2-spectra of HoNi2B2C and YNl2B2C reveal structure at applied voltages corresponding to the phonon frequencies. At about 4 meV a maximum is observed in the phonondensity of states by analogy to the soft-phonon structure in neutron scattering experiments for LuNi2B2C [P. Dervenagas et al., Phys. Rev. B52, R9839 (1995)]and YNl2B2C [H. Kawano et al., Czech. J. Phys. 46, S2-825 (1996), Phys. Rev. Lett.77, 4628 (1996)]. In the Ho compound the low-energy phonon peak is suppressed by an applied magnetic field in an anisotropic way, pointing to an interaction between the phonons and the magnetic systems. Surprisingly, in the nonmagnetic Y compound the 4-meV peak is also suppressed by a magnetic field. In the Ho-compound contacts which show the 〈quasi-thermal〉 behavior, the detailed magnetic-field and temperature dependences of PC spectra suggest that the magnetic order is destroyed due to the coupled phonon-magnon subsystem which is driven out of equilibrium by electrons that pass through the contact, by analogy with the nonequilibrium phonon-induced destruction of the superconducting state in point contacts [I. K. Yanson et al., JETP Lett. 45, 543 (1987)]. The PC electron-phonon interaction(EPI) spectral functions are reconstructed and the estimates for the λ-parameter yield the values of the order of 0.1. Comparison with PC EPI spectra of nonsuperconducting and nonmagnetic LaNi2B2C. [I. K. Yanson et al., Phys. Rev. Lett. 78, 935 (1997)], as well as the comparative study of PC EPI and Andreev-reflection spectra for various contacts with superconducting Ho and Y compounds suggest that the low-energy part of the electron-quasi-particle interaction spectral function is responsible for the Cooper pairing in these materials. KeywordsPhonon electron interactions, Phonons, Superconducting compounds, Magnetic fields, Point contacts Disciplines Condensed Matter Physics CommentsThe following article appeared in Low Temperature Physics 23 (1997): 712 and may be found at http://dx.doi.org/10.1063/1.593378. RightsCopyright 1997 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The point-contact ͑PC͒ d 2 V/dI 2 -spectra of HoNi 2 B 2 C and YNl 2 B 2 C reveal structure at applied voltages corresponding to the phonon frequencies. At about 4 meV a maximum is observed in the phonon density of states by analogy to the soft-phonon structure in neutron scattering experiments for LuNi 2 B 2 C ͓P. Dervenagas et al., Phys. Rev. B52, R9839 ͑1995͔͒and YNl 2 B 2 C ͓H. Kawano et al., Czech. J. Phys. 46, S2-825 ͑1996͒, Phys. Rev. Lett. 77, 4628 ͑1996͔͒. In the Ho compound the low-energy phonon peak is suppressed by an applied magnetic field in an anisotropic way, pointing to an interaction between the phonons and the magnetic systems. Surprisingly, in the nonmagnetic Y compound the 4-meV peak is also suppressed by a magnetic field. In the Ho-compound contacts which show the ͗quasi-t...

Electron–quasiparticle interaction in DyNi2B2C measured by point-contact spectroscopy

“…The thermal feature in the PC spectra can be quite sharp if a phase transition occurs at a particular temperature T m , which leads to the jumplike increase in the temperature-dependent contribution to the resistivity. Such a situation holds in the HoNi 2 B 2 C contacts due to the magnetic transition [8], and, as we shall see below, in DyNi 2 B 2 C as well.…”

Point-contact spectroscopy of the antiferromagnetic superconductorHoNi2B2Cin the normal and superconducting state

“…Up to now, HoNi 2 B 2 C has been investigated by PC spectroscopy in [11,12,13,14]. The first three papers are devoted to investigations of the SC gap.…”

“…The PC EBI spectra for HoNi 2 B 2 C were studied and analyzed in Ref. [14]. There, the main attention was devoted to the study of the low energy part of the spectra and to the investigation and understanding of the so called 'soft' mode at about 4 meV in the electron-quasiparticle spectrum.…”

Andreev-Reflection and Point-Contact Spectroscopy of Superconducting Rare Earth Transition Metal Borocarbides

“…Quite definitely, the magnetic excitations should be involved. This follows from the strong temperature and magnetic field dependences of the intensity and energy position in HoNi 2 B 2 C [25,23]. It is difficult to interpret these dependences, since the magnetic phase diagram in HoNi 2 B 2 C is very complicated.…”

“…Summarizing the PCS study of EQI function, one can argue that the low frequency modes are characteristic of the superconducting compounds while the behaviour of high energy part of the spectra does not differ appreciably for superconducting and non-superconducting compounds [25,23,18]. …”