Discovery of a three-dimensional topological dirac semimetal, Na 3 Bi
Science 343:6173 (2014) 864-867
Abstract:
Three-dimensional (3D) topological Dirac semimetals (TDSs) represent an unusual state of quantum matter that can be viewed as "3D graphene." In contrast to 2D Dirac fermions in graphene or on the surface of 3D topological insulators, TDSs possess 3D Dirac fermions in the bulk. By investigating the electronic structure of Na3Bi with angle-resolved photoemission spectroscopy, we detected 3D Dirac fermions with linear dispersions along all momentum directions. Furthermore, we demonstrated the robustness of 3D Dirac fermions in Na3Bi against in situ surface doping. Our results establish Na3Bi as a model system for 3D TDSs, which can serve as an ideal platform for the systematic study of quantum phase transitions between rich topological quantum states.Far-from-equilibrium monopole dynamics in spin ice
Nature Physics 10:2 (2014) 135-139
Abstract:
Condensed matter in the low-temperature limit reveals exotic physics associated with unusual orders and excitations, with examples ranging from helium superfluidity to magnetic monopoles in spin ice. The far-from-equilibrium physics of such low-temperature states may be even more exotic, yet to access it in the laboratory remains a challenge. Here we demonstrate a simple and robust technique - the 'magnetothermal avalanche quench' - and its use in the controlled creation of non-equilibrium populations of magnetic monopoles in spin ice at millikelvin temperatures. These populations are found to exhibit spontaneous dynamical effects that typify far-from-equilibrium systems and yet are captured by simple models. Our method thus opens new directions in the study of far-from-equilibrium states in spin ice and other exotic magnets. © 2014 Macmillan Publishers Limited.Circularly polarized x-ray scattering investigation of spin-lattice coupling in TbMnO3 in crossed electric and magnetic fields
Physical Review B - Condensed Matter and Materials Physics 88:21 (2013)
Abstract:
We present a study of the magnetic and crystallographic structure of TbMnO3 in the presence of crossed electric and magnetic fields using circularly polarized x-ray nonresonant scattering. A comprehensive account is presented of the scattering theory and data analysis methods used in our earlier studies, and in addition we present interesting high magnetic field data and its analysis. We discuss in detail how polarization analysis was used to reveal structural information, including the arrangement of Tb moments which we proposed for H=0 T, and how the diffraction data for HTerahertz frequency electromagnon and magnon modes in multiferroic cupric oxide
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz (2013)
Abstract:
We examined the terahertz magnetoelectric response of cupric oxide, a high-temperature multiferroic with a cycloidal spin structure that induces an electrical polarisation. Terahertz time-domain spectroscopy at various temperatures and magnetic fields uncovered electromagnon and magnon modes, providing insights into the spin Hamiltonian. © 2013 IEEE.Hour-glass magnetic spectrum arising from a striped cluster spin-glass ground state in La1.75 Sr0.25 CoO4
Physical Review B - Condensed Matter and Materials Physics 88:16 (2013)