91̽»¨

Abstract:

We report on how the deposition of a nonmagnetic metal on the surface of a ferromagnetic insulator can provide a sensitive, albeit indirect, means of measuring the magnon Hall effect. This is inferred from the thermoelectric potential that develops across the metal layer as a consequence of the transverse thermal Hall gradient. Moreover, a manifestation of magnon surface states is observed via the drag which the surface spin currents of the ferromagnet impose on the conduction electrons of the adjacent metallic layer. This electron-magnon interaction operates across the interface, and the polarity of the resultant drag voltage is determined by the spin Nernst angle of the metal layer.

Abstract:

Chirality, a pervasive form of symmetry, is intimately connected to the physical properties of solids, as well as the chemical and biological activity of molecular systems. However, inducing chirality in a nonchiral material is challenging because this requires that all mirrors and all roto-inversions be simultaneously broken. Here, we show that chirality of either handedness can be induced in the nonchiral piezoelectric material boron phosphate (BPO₄) by irradiation with terahertz pulses. Resonant excitation of either one of two orthogonal, degenerate vibrational modes determines the sign of the induced chiral order parameter. The optical activity of the photo-induced phases is comparable to the static value of prototypical chiral α-quartz. Our findings offer new prospects for the control of out-of-equilibrium quantum phenomena in complex materials.