Hybridization gap in the heavy-fermion compound UPd2Al3 via quasiparticle scattering spectroscopy

Abstract

We present results from point-contact spectroscopy of the antiferromagnetic heavy-fermion superconductor UPd 2 Al 3 : conductance spectra are taken from single crystals with two major surface orientations as a function of temperature and magnetic field, and analyzed using a theory of co-tunneling into an Anderson lattice. Spectroscopic signatures are clearly identified including the distinct asymmetric double-peak structure arising from the opening of a hybridization gap when a coherent heavy Fermi liquid is formed. Both the hybridization gap, found to be 7.2 ± 0.3 meV at 4 K, and the conductance enhancement above a flat background decrease upon increasing temperature. While the hybridization gap is extrapolated to remain finite up to ~28 K, close to the temperature around which the magnetic susceptibility displays a broad peak, the conductance enhancement vanishes at ~18 K, slightly above the antiferromagnetic transition temperature (T N  14 K). This rapid decrease of the conductance enhancement is understood as a consequence of the junction drifting away from the ballistic regime due to increased scattering off magnons associated with the localized U 5f electrons. This shows that while the hybridization gap opening is not directly associated with the antiferromagnetic ordering, its visibility in the conductance is greatly affected by the temperature-dependent magnetic excitations. Our findings are not only consistent with the 5f dual-nature picture in the literature but also shed new light on the interplay between the itinerant and localized electrons in UPd 2 Al 3 .

Origin of gap-like behaviors in URu$_2$Si$_2$: Combined study via quasiparticle scattering spectroscopy and resistivity measurements

“…This indicates that AF-I is of different nature from AF-II, as speculated earlier. A similarly small gap-ratio (∼ 2) and the same kink-decay (instead of jump-decay) behavior are also observed in UPd 2 Al 3 [43], suggesting that AF-I is more likely due to local moments, consistent with a recent nuclear magnetic resonance study [54]. The strongly contrasting properties between AF-I and AF-II might be due to the different roles played by different chemical substitutions, as mentioned earlier.…”

“…33). This structure has been established as signifying an indirect gap in the hybridized bands through recent theoretical [36,[38][39][40] and experimental [8,9,20,[41][42][43] studies. The solid lines are best fit curves using the modified MDC model ( [36,40], also Sect.…”

Point-contact spectroscopy of heavy fermion superconductors Ce2PdIn8 and Ce3PdIn11 in comparison with CeCoIn5

“…We comment that the appearance of a conductance background in PCS measurements is not rare in other systems. For example, a V-shape background in iron-based and cuprate superconductors is present [50,51], while a sloping background was reported in UPd 2 Al 3 [52].…”

Electronic Structure of ThPd$_2$Al$_3$: an impact of the U $5f$ states in the electronic structure of UPd$_2$Al$_3$

“…In this scenario, the U 5 f states are formally divided into two subsystems: an itinerant f 1 component and a localized f 2 component. The result of the recent point contact spectroscopy study on UPd 2 Al 3 was also interpreted along with this scenario [12], but the microscopic information of the U 5 f states is still lacking. To understand the electronic structure of UPd 2 Al 3 , it is essential to identify the contribution of the U 5 f state to gain a greater insight regarding its nature in this compound.…”