The Bristol HIDAC 2D-ACAR Spectrometer

Electronic correlations in vanadium revealed by electron-positron annihilation measurements

“…The reconstructed FS sheets of vanadium are shown in Fig. 5. bulged octahedron jungle-gym N-hole pocket The reconstruction reproduces all features of the vanadium Fermi surface discussed in earlier papers 16,20,22 . In the center of the Brillouin zone a hole-like volume is confined by the bulged octahedron FS sheet (violet in Fig.…”

“…12 Vanadium is a 3d transition metal element with the electronic configuration of [Ar] 3d 3 4s 2 . The electronic structure of vanadium has been intensively studied by electron-positron annihilation [13][14][15][16][17][18][19][20][21][22][23][24] and, less so, by the de Haas -van Alphen (dHvA) effect 25,26 and photoemission 27,28 . Indeed the characteristic Fermi Surface (FS) leads to a very pronounced signal in 2D-ACAR spectra projected along specific directions.…”

Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials

“…The results of our calculations show that this surface state can be exploited as a spectroscopic characterization tool for probing surfaces of topological materials. Since a significant fraction of positrons annihilate with electrons occupying Dirac cone states, 2D-ACAR experiments should be able to measure their momentum distribution with high precision 44 , and thus obtain information concerning the nature of the Dirac states which is complementary to that accessed through angle-resolved photoemission, scanning tunnelling and other surfacesensitive spectroscopies without complications of related matrix element effects 45 . PAES and Doppler broadening of the annihilation radiation 46 measurements can, in turn, be used to characterize the chemical composition of surfaces.…”

$L$-hole Pockets of the Palladium Fermi Surface Revealed by Positron Annihilation Spectroscopy

“…one sees the small circle shaped deeps in the center of this red squares corresponding to two out of six face centered X-hole pockets (square faces of fcc BZ); remaining four that over- lap could be identified at (X, W )-points as dark-blue squares; the "jungle-gym" (tubes together with X-hole fins) becomes also clearly visible in both EMD and 2D-ACAR back-folded spectra (plus shapes with center at either (Γ, X)-points or (X, W )-points); ellipsoid shaped L-hole pockets are well recognized in 2D-ACAR in both LDA and LDA+DMFT cases as well es in EMD for LDA+DMFT. Note that, redistribution of electronic momenta around the L-point due to the presence of electronic correlation or positrons does not alter the signal from the L-hole pockets and it should be visible in a high resolution 2D-ACAR experiment e.g., using a spectrometer based on high-density avalanche chambers 46 . In Fig.…”