Anisotropic magnetic properties of a layered kagome-like system Cu 3 Bi(SeO 3) 2 O 2 Br have been studied by bulk magnetization and magnetic susceptibility measurements as well as powder and single-crystal neutron diffraction. At T N = 27.4 K the system develops an alternating antiferromagnetic order of (ab) layers, which individually exhibit canted ferrimagnetic moment arrangement, resulting from the competing ferro-and antiferro-magnetic intralayer exchange interactions. A magnetic field B C ∼ 0.8 T applied along the c axis (perpendicular to the layers) triggers a metamagnetic transition, when every second layer flips, i.e., resulting in a ferrimagnetic structure. Significantly higher fields are required to rotate the ferromagnetic component towards the b axis (∼7 T) or towards the a axis (∼15 T). The estimates of the exchange coupling constants and features indicative of an XY character of this quasi-2D system are presented.

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An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor La2−xSrxCuO4 with x = 0.145 and x = 0.17, as a function of binding energy and momentum, is presented. We observe that the scattering rate scales linearly with binding energy up to the high-energy scale E1 ∼ 0.4 eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-(π, π) direction. A possible connection to a quantum-critical point is discussed.

Neutron inelastic scattering has been used to probe the spin dynamics of the quantum (S=1/2) ferromagnet on the pyrochlore lattice Lu2V2O7. Well-defined spin waves are observed at all energies and wavevectors, allowing us to determine the parameters of the Hamiltonian of the system. The data are found to be in excellent overall agreement with a minimal model that includes a nearestneighbour Heisenberg exchange J = 8.22(2) meV and a Dzyaloshinskii-Moriya interaction (DMI) D = 1.5(1) meV. The large DMI term revealed by our study is broadly consistent with the model developed by Onose et al. to explain the magnon Hall effect they observed in Lu2V2O7 [1], although our ratio of D/J = 0.18(1) is roughly half of their value and three times larger than calculated by ab initio methods [2]. PACS numbers:The highly frustrated nature of the pyrochlore lattice leads to a rich diversity of fascinating properties when the lattice sites are decorated with "classical" (large S) spins [3]. Arguably the most celebrated example is ferromagnetically coupled Ising spins which give rise to spinice [4,5] and the emergence of magnetic monopoles [6,7]. While many examples of classical pyrochlores exist, there are few examples of pyrochlores where the spins of the magnetic ions are explicitly in the quantum (S=1/2) limit. Quantum effects can, however, play a decisive role even in classical pyrochlores if their low-energy physics maps onto an effective spin 1/2 model [3]. In either case, quantum effects may produce a range of novel phenomena including the realisation of a three-dimensional quantum spin-liquid ground state, emergent electromagnetism supporting photon-like excitations, etc. [8][9][10][11]. Interest in itinerant pyrochlore magnets is also motivated by the various anomalous transport properties they exhibit [12].Lu 2 V 2 O 7 is a ferromagnetic, small-gap Mott insulator that crystallises in the pyrochlore structure and displays a number of exceptional properties. Fig. 1(a) shows the V 4+ (S=1/2) sites in the pyrochlore lattice, which form a three-dimensionally coordinated network of corner sharing tetrahedra. Bulk measurements have established that the spins order ferromagnetically at T C =70 K [1,13]. Measurements of the thermal conductivity in Lu 2 V 2 O 7 by Onose et al. have been interpreted in terms of a magnon Hall effect [1], based on the observation that the thermal conductivity has a distinctive dependence on applied magnetic fields for temperatures below T C . This highly unusual and previously unreported phenomenon was shown to be consistent with a model in which the Dzyaloshinskii-Moriya interaction (DMI) between nearest neighbour spins deflects magnon wavepackets propagating from the hot to the cold side of the sample [1].Further evidence of the exceptional properties of Lu 2 V 2 O 7 was provided by Zhou et al. [13] who discovered that it displays a large (50%) magneto-resistance around 70 K in an applied magnetic field. Additionally, polarised neutron diffraction found evidence for an orbital ordered ground state ...

The Fermi and Rashba energies of surface states in the Bi x Pb 1−x /Ag(111) alloy can be tuned simultaneously by changing the composition parameter x. We report on unconventional Fermi surface spin textures observed by spin and angle-resolved photoemission spectroscopy that are correlated with a topological transition of the Fermi surface occurring at x = 0.5. We show that the surface states remain fully spin polarized upon alloying and that the spin polarization vectors are approximately tangential to the constant energy contours. We discuss the implications of the topological transition for the transport of spin. PACS numbers: 73.20.At, 71.70.Ej, Controlling the spin degree of freedom of the electron lies at the heart of spintronics [1]. One possibility to manipulate the electron spin without the need of any external magnetic field is found in the Rashba-Bychkov (RB) effect [2]. It appears in (quasi) two-dimensional electron or hole systems with a lack of inversion symmetry and plays a prominent role for a proposed spin field-effect transistor [3]. For most systems, the RB effect is small. Therefore, many of the related intriguing effects, such as a renormalization of the Fermi liquid parameters [4], changes in the electron-phonon coupling [5], enhanced superconductivity transition temperatures [6], and real space spin accumulation [7,8,9] remain for the most part experimentally unobservable.Recently, it has been shown that the RB effect is dramatically enhanced in the Bi/Ag (111)3)R30 • surface alloys due to an additional in-plane inversion asymmetry [10,11,12,13,14]. Furthermore, the band structure can be continuously tuned between these two systems by substituting Bi with Pb [15], as schematically illustrated in Fig. 1(a). The large RB effect combined with the tunability of the Fermi and the RB energies make Bi (111), an ideal model RB system to study the geometrical and the topological changes in the Fermi surface of its surface states [5,16]. It is clear that the large conductivity of the Ag substrate short-circuits possible spin currents at the surface of Bi x Pb 1−x /Ag(111), but RB semiconductors [17] or thin metallic films [18] might be found that are equally tunable and suited for technological applications.We present in this work spin and angle resolved photoemission spectroscopy (SARPES) data on surface states of Bi x Pb 1−x /Ag(111) to resolve the changes in their Fermi surface spin textures (FSST) as a function of composition x. We will argue that the spin transport is strongly affected by a topological transition of the Fermi surface taking place at the critical value x c = 0.5.The RB effect occurs at interfaces or surfaces whenever kx E ky Γ E0 k0 S EΓ E kx (b) (a) x=1 x=0 K1 K2 x=0.6 (c) EΓ DOS (arb. units) E (arb. units) (d) EΓ > EF E0 > EF > EΓ o i o i o i i o FIG. 1: (color online) (a) Qualitative plot of the surface state band structure of Bi/Ag(111) (x = 1) along the directionΓK in momentum space (adapted from Ref. [13]) showing the two Kramer's pairs K1 and K2. As x is decreased, the Ferm...