Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 89: Transport: Quantum Dots, Quantum Wires, Point Contacts 1 (jointly with HL)

TT 89.6: Vortrag

Donnerstag, 19. März 2015, 12:15–12:30, A 053

Electronic Transport through Cerium Nanocontacts — •Sebastian Kuntz¹, Oliver Berg¹, Christoph Sürgers¹, and Hilbert v. Löhneysen^1,2 — ¹Physikalisches Institut, Karlsruher Institut für Technologie, D-76128 Karlsruhe — ²Institut für Festkörperphysik, Karlsruher Institut für Technologie, D-76021 Karlsruhe

We report on conductance measurements of Ce nanocontacts in mechanically controlled break-junctions (MCBJ) made from polycrystalline wires. The wires were cut from two different Ce ingots. One ingot was taken as-prepared after cooling from the melt and one ingot was carefully annealed over ∼ one week. We investigate the effect of cooling rate and γ-β-α-phase transformation on the conductance G of the nanocontacts measured at low temperatures. From a number of measurements of G(Δ x) where Δ x is the distance between the two electrodes, we obtain conductance histograms. We focus on the conductance G^* of the “last plateau” before, with increasing Δ x, G drops to zero. For Ce, different G^* values between 0.6 and 1.7 G₀ (G₀ = 2e²/h) are observed, while for other rare-earth metals like Gd and Dy the last plateau occurs at G^*≃ 0.6 G₀ and G^*≃ 0.9 G₀, respectively. A possible explanation for the different G^* values of Ce is the additional contribution from the 4f state to the conductance whose distance from the Fermi level depends on the phase at low temperatures (α or β) and, hence, on the cooling rate of the sample.