Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 69: Focus Session: Superconductivity in the Vicinity of a Quantum Critical Point

TT 69.5: Invited Talk

Thursday, March 23, 2017, 17:15–17:45, HSZ 03

An Empirical Approach to the 2 mK Transition in YbRh₂Si₂ — •Christoph Geibel, Manuel Brando, and Alexander Steppke — Max Planck Institute for Chemical Physics of Solids, Dresden, Germany

The Kondo lattice system YbRh₂Si₂ is located extremely close to a quantum critical point (QCP) separating the magnetic ordered from the paramagnetic ground state. This results in a number of very unusual properties whose origins are controversially discussed. Recently an abrupt drop in the magnetic susceptibility at 2 mK provided evidence for a combined nuclear-electronic magnetic and superconducting transition [1]. However, the scenario proposed in [1], being based on a Landau model with a large number of free parameters, met some skepticism. Here we analyze the specific properties of YbRh₂Si₂ in view of possible mechanisms for this 2 mK transition. After introducing how hyperfine interaction works for Yb, we single out some very peculiar properties of YbRh₂Si₂ which result in a specific and unique situation for the interplay between 4f and nuclear moments. Below a few mK the AFM state formed at 70 mK, because of its tiny ordered 4f moment, becomes inherently unstable against the formation of a state with a larger ordered moment. Our analysis strongly supports the existence of a combined nuclear-electronic transition in the mK range in YbRh₂Si₂, but indicates that the ordered 4f moment should increase at this transition, in contrast to the decrease proposed in [1].

[1] E. Schuberth et al., Science 351, 485 (2016)