We propose that the existence of local orbital angular momentum (OAM) on the surfaces of high-Z materials plays a crucial role in the formation of Rashba-type surface band splitting. Local OAM state in a Bloch wave function produces an asymmetric charge distribution (electric dipole). The surface-normal electric field then aligns the electric dipole and results in chiral OAM states and the relevant Rashba-type splitting. Therefore, the band splitting originates from electric dipole interaction, not from the relativistic Zeeman splitting as proposed in the original Rashba picture. The characteristic spin chiral structure of Rashba states is formed through the spin-orbit coupling and thus is a secondary effect to the chiral OAM. Results from first-principles calculations on a single Bi layer under an external electric field verify the key predictions of the new model.

We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.

We performed annealing and angle resolved photoemission spectroscopy studies on electron-doped cuprate Pr_{1-x}LaCe_{x}CuO_{4-δ} (PLCCO). It is found that the optimal annealing condition is dependent on the Ce content x. The electron number (n) is estimated from the experimentally obtained Fermi surface volume for x=0.10, 0.15 and 0.18 samples. It clearly shows a significant and annealing dependent deviation from the nominal x. In addition, we observe that the pseudo-gap at hot spots is also closely correlated with n; the pseudogap gradually closes as n increases. We established a new phase diagram of PLCCO as a function of n. Different from the x-based one, the new phase diagram shows similar antiferromagnetic and superconducting phases to those of hole doped ones. Our results raise a possibility for absence of disparity between the phase diagrams of electron- and hole-doped cuprates.

We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the surface sensitivity of angle resolved photoemission (ARPES). The symmetry in the electronic structure of transition metal dichalcogenides is used to uniquely determine the local orbital angular momentum (OAM) contribution to the circular dichroism (CD) in ARPES. The extracted CD signals for the K and K valleys are almost identical but their signs, which should be determined by the valley index, are opposite. In addition, the sign is found to be the same for the two spin-split bands, indicating that it is independent of spin state. These observed CD behaviors are what are expected from Berry curvature of a monolayer of WSe2. In order to see if CD-ARPES is indeed representative of hidden Berry curvature within a layer, we use tight binding analysis as well as density functional calculation to calculate the Berry curvature and local OAM of a monolayer WSe2. We find that measured CD-ARPES is approximately proportional to the calculated Berry curvature as well as local OAM, further supporting our interpretation. PACS numbers: 79.60.-i, 74.20.Pq, 73.20.-rThe broken inversion symmetry in a monolayer (ML) of transition metal dichalcogenides (TMDCs) 2H-MX 2 , together with strong spin-orbit coupling (SOC), results in inequivalent valleys with spin splitting at K and K in the Brillouin zone (BZ) [1][2][3][4]. These inequivalent valleys at K and K lead to the valley Hall effect which, unlike the ordinary Hall effect, produces not only charge but also spin imbalance at the edges [1,2,[5][6][7][8]. The valley Hall effect has been understood in terms of the Berry curvature [2,[9][10][11][12]16]; the symmetries in 1ML 2H-MX 2 causes sign change in the Berry curvature as one goes from one valley (K) to an inequivalent valley (K ) in the BZ [2,5,13,14,16,17]. This allows us to understand the valley Hall effect in terms of pseudo-spins, and provides possibilities to control the pseudo-spins by an external field [2,[18][19][20][21][22][23][24][25][26].On the other hand, the Berry curvature is expected to vanish in the bulk (so does the valley Hall effect) because the bulk TMDCs have an inversion symmetry [5,24]. However, one can imagine that the valley Hall in each layer could be non-vanishing -only the sum vanishes. This may naturally introduce the concept of "hidden Berry curvature", a non-vanishing Berry curvature localized in each layer. An analogous case can be found in the case of the hidden spin polarization proposed and mea-sured recently [3,5,[27][28][29][30]. Existence of hidden Berry curvature implies that the topology could be determined by local field; the local symmetry determines the physics [28,31,32]. While experimental verification of hidden Berry phase in the Bloch state is highly desired, standard measurements such as quantum oscillation [33][34][35] cannot reveal hidden Berry phase because these measurements represent an averaged quantity, with hidden quantity invisible.However, if we use a external field [25] or surface sensitive techni...

We have performed high resolution angle-resolved photoemission (ARPES) studies on electron-doped cuprate superconductors Sm2-xCexCuO4 (x=0.10, 0.15, 0.18), Nd2-xCexCuO4 (x=0.15), and Eu2-xCexCuO4 (x=0.15). Imaginary parts of the electron removal self energy show steplike features due to an electron-bosonic mode coupling. The steplike feature is seen along both nodal and antinodal directions but at energies of 50 and 70 meV, respectively, independent of the doping and rare earth element. Such energy scales can be understood as being due to preferential coupling to half- and full-breathing mode phonons, revealing the phononic origin of the kink structures. Estimated electron-phonon coupling constant lambda from the self energy is roughly independent of the doping and momentum. The isotropic nature of lambda is discussed in comparison with the hole-doped case where a strong anisotropy exists.