Wydarzenia

Seminarium w Instytucie Niskich Temperatur i Badań Strukturalnych PAN

Tracing the Kondo lattice in YbRh₂Si₂

Dr. Stefan Kirchner

Max Planck Institute for the Physics of Complex Systems, Drezno, Niemcy

The quantum superpositions underlying entanglement are at the heart of the intricate interplay of localized spin states and itinerant electronic states that gives rise to the Kondo effect. In a Kondo lattice, this interplay gives rise to the emergence of charge carriers with enhanced effective masses, but the precise nature of the coherent Kondo state responsible for the generation of these heavy fermions remains highly debated. YbRh₂Si₂ is one of the heavily investigated rare earth intermetallics. It is one of the heaviest of the heavy fermions and it displays unconventional quantum criticality, i.e. a continuous zero-temperature transition. After reviewing critical Kondo destruction as the most likely candidate of the quantum criticality realized in YbRh₂Si₂, I will report on the recent progress on the phase diagram of YbRh₂Si₂ and discuss novel Scanning Tunneling Microscope results on a generic Kondo lattice system, YbRh₂Si₂, which trace the onset of this entanglement [1]. We find that the hybridization of conduction and 4f states results in a gap-like feature in the tunneling conductance at the Fermi energy. In addition, we reveal unambiguously the Kondo renormalized crystal-field excitations of the Yb³⁺ ions. Finally, we investigate how the STM signatures will change when exploring the different phases of YbRh₂Si₂ and the quantum critical point separating them.

[1] S. Ernst, S. Kirchner, C. Krellner, C. Geibel, G. Zwicknagl, F. Steglich, S. Wirth, Nature 474, 363 (2011).