Sound velocity and attenuation measurements on the frustrated garnet material Gd3Ga5O12 (GGG) are presented as a function of field and temperature, using two different acoustic modes and with two different magnetic field orientations: [100] and [110]. We demonstrate that the phase diagram is highly anisotropic, with two distinct field-induced ordered phases for H|| [110] and only one for H|| [100]. Extensive lattice softening is found to occur at low fields, which can be associated with spin fluctuations. However, deep within the spin liquid phase a low-temperature stiffening of the lattice and reduced attenuation provides evidence for a spin gap which may be related to short-range antiferromagnetic correlations over minimal 10-spin loops.

We present a theory of an optically induced valley polarization in an interacting, time-reversal symmetric Weyl semimetal placed under strong magnetic fields. Because the application of a magnetic field reduces the symmetry of the crystal, the optical absorption intensity differs at Weyl nodes that were equivalent by symmetry at zero field. At strong magnetic field, the difference in the absorption intensity reaches 100% for a sizeable frequency interval of the incident light. This complete valley polarization originates from interband transitions involving the chiral Landau level, and can be controlled by changing the directions of the magnetic field and the light propagation. We identify the splitting of 0 → 1 or −1 → 0 inter Landau level transitions as an observable signature of the complete valley polarization, and discuss its manifestation in the TaAs family of materials. arXiv:1906.02607v1 [cond-mat.mes-hall]

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We report 51 V NMR, µSR and zero applied field 63,65 Cu NMR measurements on powder samples of Sr-vesignieite, SrCu3V2O8(OH) 2 , a S = 1/2 nearly-kagome Heisenberg antiferromagnet. Our results demonstrate that the ground state is a q = 0 magnetic structure with spins canting either in or out of the kagome plane, giving rise to weak ferromagnetism. We determine the size of ordered moments and the angle of canting for different possible q = 0 structures and orbital scenarios, thereby providing insight into the role of the Dzyaloshinskii-Moriya (DM) interaction in this material.