Linda Ye

Massive Dirac fermions in a ferromagnetic kagome metal

The kagome lattice is a two-dimensional network of corner-sharing triangles that is known to host exotic quantum magnetic states. Theoretical work has predicted that kagome lattices may also host Dirac electronic states that could lead to topological and Chern insulating phases, but these states have so far not been detected in experiments. Here we study the d-electron kagome metal Fe3Sn2, which is designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature-independent intrinsic anomalous Hall conductivity that persists above room temperature, which is suggestive of prominent Berry curvature from the time-reversal-symmetry-breaking electronic bands of the kagome plane. Using angle-resolved photoemission spectroscopy, we observe a pair of quasi-two-dimensional Dirac cones near the Fermi level with a mass gap of 30 millielectronvolts, which correspond to massive Dirac fermions that generate Berry-curvature-induced Hall conductivity. We show that this behaviour is a consequence of the underlying symmetry properties of the bilayer kagome lattice in the ferromagnetic state and the atomic spin–orbit coupling. This work provides evidence for a ferromagnetic kagome metal and an example of emergent topological electronic properties in a correlated electron system. Our results provide insight into the recent discoveries of exotic electronic behaviour in kagome-lattice antiferromagnets and may enable lattice-model realizations of fractional topological quantum states.

Transport signatures of Fermi surface topology change in BiTeI

We report a quantum magnetotransport signature of a change in the Fermi surface topology in the Rashba semiconductor BiTeI with a systematic tuning of the Fermi level EF. Beyond the quantum limit, we observe a marked increase (decrease) in electrical resistivity when EF is above (below) the Dirac node that we show originates from the Fermi surface topology. This effect represents a measurement of the electron distribution on low-index (n = 0,−1) Landau levels and is uniquely enabled by the finite bulk kz dispersion along the c axis and strong Rashba spin-orbit coupling strength of the system. The Dirac node is independently identified by Shubnikov‐de Haas oscillations as a vanishing Fermi surface cross section at kz = 0. Additionally, we find that the violation of Kohler’s rule allows a distinct insight into the temperature evolution of the observed quantum magnetoresistance effects.

Extreme magnetoresistance in magnetic rare-earth monopnictides

The acute sensitivity of the electrical resistance of certain systems to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe

Electronic transport on the Shastry-Sutherland lattice in Ising-type rare-earth tetraborides

_{2}

Ultrafast manipulation of mirror domain walls in a charge density wave

and rare earth monopnictide La(Sb,Bi), these systems tend to be non-magnetic, nearly compensated semimetals and represent a platform for large magnetoresistance driven by intrinsic electronic structure. Here we explore electronic transport in magnetic members of the latter family of semimetals and find that XMR is strongly modulated by magnetic order. In particular, CeSb exhibits XMR in excess of

Thermoelectric probe for Fermi surface topology in the three-dimensional Rashba semiconductor BiTeI

1.6 \times 10^{6}

de Haas-van Alphen effect of correlated Dirac states in kagome metal Fe3Sn2.

% at fields of 9 T while the magnetoresistance itself is non-monotonic across the various magnetic phases and shows a transition from negative magnetoresistance to XMR with field above magnetic ordering temperature

Visualizing Magnetic Domains at Fractional Magnetization Plateaus in a Metallic Shastry-Sutherland Ising-type Rare Earth Tetraboride

T_{N}

Observation of Massive Dirac Fermions in Ferromagnetic Kagome metal Fe 3 Sn 2

. The magnitude of the XMR is larger than in other rare earth monopnictides including the non-magnetic members and follows an non-saturating power law to fields above 30 T. We show that the overall response can be understood as the modulation of conductivity by the Ce orbital state and for intermediate temperatures can be characterized by an effective medium model. Comparison to the orbitally quenched compound GdBi supports the correlation of XMR with the onset of magnetic ordering and compensation and highlights the unique combination of orbital inversion and type-I magnetic ordering in CeSb in determining its large response. These findings suggest a paradigm for magneto-orbital control of XMR and are relevant to the understanding of rare earth-based correlated topological materials.

Extreme Magnetoresistance in Magnetic Rare Earth Monopnictides

In the presence of a magnetic field frustrated spin systems may exhibit plateaus at fractional values of saturation magnetization. Such plateau states are stabilized by classical and quantum mechanisms including order-by-disorder, triplon crystallization, and various competing order effects. In the case of electrically conducting systems, free electrons represent an incisive probe for the plateau states. Here we study the electrical transport of Ising-type rare earth tetraborides