DQMP Forum - High Field Superconductivity in Ternary MgB2 Polycrystals Prepared by a Rapid Synthesis Route - Anomalous Hall Effect in the Quantum Limit in the Layered Antiferromagnet Co1/3NbS2

26.03.2019 13:00 – 14:00

High Field Superconductivity in Ternary MgB2 Polycrystals Prepared by a Rapid Synthesis Route
Davide Matera (group of Prof. Senatore)

The upper critical field (Bc2) of MgB2 polycrystals is still far below the values up to 60T measured in highly-disordered C-doped films. With the goal of filling this performance gap in view of practical applications, we explored the potential of a rapid-synthesis route by means of
an induction furnace. Rapid heating (up to 1000 ÆC/min) followed by quenching (up to 2500 ÆC/min) at the end of reaction was applied in order to limit the grain growth and freeze the system in configurations with high structural disorder, as in films. We prepared a series of Cdoped
MgB2 polycrystals using a Design-of-Experiment approach to explore the synthesis parameter-space: dwell-temperature, dwell-time, ramp-rates and pressure. Based on extrapolations of resistive measurements in magnetic fields up to 19T, Bc2 values of ~25T at
10K were obtained reproducibly with distinct sets of synthesis parameters. A microstructural characterization complements the investigation of the physical properties to shed light on the
mechanisms behind the observed enhancement of BC2.


Anomalous Hall Effect in the Quantum Limit in the Layered Antiferromagnet Co1/3NbS2
Giulia Tenasini (group of Prof. Morpurgo)

The anomalous Hall effect (AHE), for long time considered as a characteristic trait of ferromagnets, can arise even in systems without a net magnetization provided that certain common symmetries are absent. The recent discovery of the AHE in antiferromagnets has in
fact underscored the deeper topological origin of the phenomenon, intrinsically connected to the Berry curvature of the electronic bands. In two dimensional magnetic systems, this allows for the existence of topologically non-trivial bands with integer Chern number Cn ≠ 0, and a
correspondingly quantized anomalous Hall conductivity σxy
A. All AFMs which have so far shown AHE are characterized by isotropic transport properties typical of three dimensional systems, where Cn is not a well-defined topological invariant. Here, we show magnetotransport measurements on exfoliated crystals of the layered antiferromagnet Co1/3NbS2, exhibiting a low-temperature anomalous Hall conductivity well in excess of e2/h per layer. This represents the first experimental observation of the AHE in the quantum limit in AFMs, and is
compatible with the presence of topologically non-trivial bands in Co1/3NbS2.

Forum Committee: C. Lichtensteiger, N. Ubrig, A. Tamai (19.3.2019)

Lieu

Bâtiment: Ecole de Physique

Auditoire Stückelberg

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