Special Condensed Matter Physics Seminar

Note special time:
4 p.m., Monday, February 19, 2007

Room 1201, Physics Building

 Probing the Berry Phase via Electrical Transport: Intrinsic Anomalous Hall Effect in MnSi

Minhyea Lee

(Princeton University)

Abstract:  The interplay between spin and charge of electrons in solids provides a rich setting for exploring collective behavior of many interacting quantum-mechanical particles. The Hall effect was discovered in 1879, and is one of the most fundamental probes of spin-charge coupling. In a simple metal, the Hall effect arises from the deflection of electrons in the applied magnetic field, and is related to the density of carriers. In ferromagnets, the spontaneous magnetization contributes to an additional Hall current and gives rise to the so- called anomalous Hall effect (AHE). Despite a long effort, it has not yet been clarified whether AHE originates from impurity scattering (extrinsic) or from the so-called Berry phase encoded in the electronic band structure (intrinsic). MnSi is one of the most compelling strongly correlated ferromagnets. It is known for a lack of inversion symmetry that drives the system into helical magnetic ordering, which can be tuned by hydrostatic pressure. MnSi is remarkably free of impurities with a low Curie temperature (Tc) and thus provides an excellent testing ground for theories of the AHE. I will present our recent results on the anomalous Hall conductivity in MnSi, which is found strictly proportional to the magnetization and temperature-independent below Tc. This result strongly demonstrates that the intrinstic contribution to AHE arising from the Berry phase is dominant in MnSi. I will compare this to results in other ferromagnetic systems (e.g. layered dichalgogenides). We have also recently discovered an anomaly in the Hall signal of MnSi under pressure. We believe this feature may indicate a strong sensitivity of the Hall effect to spin textures with non-trivial chirality.
Host:  Lobb
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