Brillouin zone

About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

Abstract: Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides exhibit a range of properties, including tunable insulator-superconductor-metal transitions, large magnetoresistance, coexisting ferromagnetism and superconductivity, and a spin splitting of a few meV (refs 10, 11). Strontium titanate (SrTiO3), the cornerstone of such oxide-based electronics, is a transparent, non-magnetic, wide-bandgap insulator in the bulk, and has recently been found to host a surface 2DEG (refs 12-15). The most strongly confined carriers within this 2DEG comprise two subbands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces. Using spin- and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these subbands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated. Moreover, in contrast to a simple Rashba system, the spin-polarized subbands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.

Nature and evolution of the band-edge states in MoS 2 : From monolayer to bulk

Abstract: Exploring two-dimensional layered materials, such as molybdenum disulfide $({\mathrm{MoS}}_{2})$, for (opto)electronic applications requires detailed knowledge of their electronic band structures. Using first-principles calculations we trace the evolution of the band structure as a function of the number of layers, starting from a monolayer, which has a direct gap, to the bulk material, which has an indirect gap. We find that, with respect to the vacuum level, the valence-band maximum (VBM) increases rapidly with the number of layers, while the conduction-band minimum (CBM) remains almost constant. For two or more layers the VBM always occurs at $\ensuremath{\Gamma}$ and the CBM occurs at K. These findings are analyzed in terms of the orbital composition of the valence- and conduction-band edges at the various high-symmetry points in the Brillouin zone.

Exciton band structure in layered MoSe2: from a monolayer to the bulk limit

Abstract: We present the micro-photoluminescence (μPL) and micro-reflectance contrast (μRC) spectroscopy studies on thin films of MoSe2 with layer thicknesses ranging from a monolayer (1L) up to 5L. The thickness dependent evolution of the ground and excited state excitonic transitions taking place at various points of the Brillouin zone is determined. Temperature activated energy shifts and linewidth broadenings of the excitonic resonances in 1L, 2L and 3L flakes are accounted for by using standard formalisms previously developed for semiconductors. A peculiar shape of the optical response of the ground state (A) exciton in monolayer MoSe2 is tentatively attributed to the appearance of a Fano-type resonance. Rather trivial and clearly decaying PL spectra of monolayer MoSe2 with temperature confirm that the ground state exciton in this material is optically bright in contrast to a dark exciton ground state in monolayer WSe2.

Nodal structure of unconventional superconductors probed by angle resolved thermal transport measurements

Abstract: Over the past two decades, unconventional superconductivity with gap symmetry other than s wave has been found in several classes of materials, including heavy fermion, high Tc, and organic superconductors. Unconventional superconductivity is characterized by anisotropic superconducting gap functions, which may have zeros (nodes) along certain directions in the Brillouin zone. The nodal structure is closely related to the pairing interaction, and it is widely believed that the presence of nodes is a signature of magnetic or some other exotic, rather than conventional phonon mediated, pairing mechanism. Therefore experimental determination of the gap function is of fundamental importance. However, the detailed gap structure, especially the direction of the nodes, is an unresolved issue for most unconventional superconductors. Recently it has been demonstrated that thermal conductivity and specific heat measurements under a magnetic field rotated relative to the crystal axes provide a powerful method for determining the shape of the gap and the nodal directions in the bulk. Here we review the theoretical underpinnings of the method and the results for the nodal structure of several unconventional superconductors, including borocarbide YNi2B2C, heavy fermions UPd2Al3, CeCoIn5 ,a nd PrOs 4Sb12, organic superconductor κ-(BEDT-TTF)2Cu(NCS)2, and ruthenate Sr2RuO4, determined through angular variation of the thermal conductivity and heat capacity.

Neutron Resonance: Modeling Photoemission and Tunneling Data in the Superconducting State of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

Abstract: Motivated by neutron scattering data, we develop a model of electrons interacting with a magnetic resonance and use it to analyze angle resolved photoemission and tunneling data in the superconducting state of Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+{delta}} . We not only can explain the peak-dip-hump structure observed near the ({pi},0) point, and its particle-hole asymmetry as seen in superconductor-insulator-normal tunneling spectra, but also its evolution throughout the Brillouin zone, including a velocity ''kink'' near the d -wave node.