RESUMO
Precise angle-resolved magnetoresistance (ARMR) and magnetization measurements have revealed (i) strong charge transport and magnetic anisotropy and (ii) emergence of a huge number of magnetic phases in the ground state of isotopically11B-enriched single crystals of TmB12antiferromagnetic (AF) metal with fcc crystal structure and dynamic charge stripes. We analyze for the first time the angularH-φphase diagrams of AF state of Tm11B12reconstructed from experimental ARMR and magnetization data arguing that the symmetry lowering leads to the appearance of several radial phase boundaries between different phases in the AF state. It is proposed that the suppression of the indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange along ⟨110⟩ directions between nearest neighboring magnetic moments of Tm3+ions and subsequent redistribution of conduction electrons to quantum fluctuations of the electron density (dynamic stripes) are the main factors responsible for the anisotropy. Essential (more than 25% atT= 2 K) anisotropy of the Neel field in the (110) plane was found in Tm11B12unlike to isotropic AF-P boundary in theH-φphase diagrams of Ho11B12. Magnetoresistance components are discussed in terms of charge carrier scattering on the spin density wave, itinerant ferromagnetic nano-domains and on-site Tm3+spin fluctuations.
RESUMO
SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the [Formula: see text] state to appear Rashba split and explain the prominent [Formula: see text] state by a surface shift of the many-body resonance. We propose that the latter mechanism, which applies to several crystal terminations, can explain the unusual surface conductivity. While additional, as yet unobserved topological surface states cannot be excluded, our results show that a firm connection between the two material classes is still outstanding.
RESUMO
We investigate the phase diagram of TmB4, an Ising magnet on a frustrated Shastry-Sutherland lattice, by neutron diffraction and magnetization experiments. At low temperature we find Néel order at low field, ferrimagnetic order at high field, and an intermediate phase with magnetization plateaus at fractional values M/M_(sat)=1/7,1/8,1/9,... and spatial stripe structures. Using an effective S=1/2 model and its equivalent two-dimensional fermion gas we suggest that the magnetic properties of TmB4 are related to the fractional quantum Hall effect of a 2D electron gas.