81 research outputs found
Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4
Using density-functional theory calculations and experimental investigations
on structural, magnetic and dielectric properties, we have elucidated a unique
tetragonal ground state for MnTi2O4, a Ti^{3+} (3d^1)-ion containing
spinel-oxide. With lowering of temperature around 164 K, cubic MnTi2O4
undergoes a structural transition into a polar P4_1 tetragonal structure and at
further lower temperatures, around 45 K, the system undergoes a paramagnetic to
ferrimagnetic transition. Magnetic superexchange interactions involving Mn and
Ti spins and minimization of strain energy associated with co-operative
Jahn-Teller distortions plays a critical role in stabilization of the unique
tetramer-orbital ordered ground state which further gives rise to lattice
chirality through subtle Ti-Ti bond-length modulations
Two Distinct Phases of Bilayer Graphene Films on Ru(0001)
By combining angle-resolved photoemission spectroscopy and scanning tunneling
microscopy we reveal the structural and electronic properties of multilayer
graphene on Ru(0001). We prove that large ethylene exposure allows to
synthesize two distinct phases of bilayer graphene with different properties.
The first phase has Bernal AB stacking with respect to the first graphene
layer, displays weak vertical interaction and electron doping. The long-range
ordered moir\'e pattern modulates the crystal potential and induces replicas of
the Dirac cone and minigaps. The second phase has AA stacking sequence with
respect to the first layer, displays weak structural and electronic modulation
and p-doping. The linearly dispersing Dirac state reveals the
nearly-freestanding character of this novel second layer phase
A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6
Besides a drastic reduction in saturation magnetization of disordered
Sr2FeMoO6 compared to highly ordered samples, magnetizations as a function of
the temperature for different disordered samples may also show qualitatively
different behaviors. We investigate the origin of such diversity by performing
spatially resolved photoemission spectroscopy on various disordered samples.
Our results establish that extensive electronic inhomogeneity, arising most
probably from an underlying chemical inhomogeneity in disordered samples is
responsible for the observed magnetic inhomogeneity. It is further pointed out
that these inhomogeneities are connected with composition fluctuations of the
type Sr2Fe1+xMo1-xO6 with Fe-rich (x>0) and Mo-rich (x<0) regions.Comment: 14 pages, 4 figure
Band Structure of Topological Insulator BiSbTe1.25Se1.75
We present our angle resolved photoelectron spectroscopy (ARPES) and density
functional theory results on quaternary topological insulator (TI)
BiSbTe1.25Se1.75 (BSTS) confirming the non-trivial topology of the surface
state bands (SSBs) in this compound. We find that the SSBs, which are are
sensitive to the atomic composition of the terminating surface have a partial
3D character. Our detailed study of the band bending (BB) effects shows that in
BSTS the Dirac point (DP) shifts by more than two times compared to that in
Bi2Se3 to reach the saturation. The stronger BB in BSTS could be due to the
difference in screening of the surface charges. From momentum density curves
(MDCs) of the ARPES data we obtained an energy dispersion relation showing the
warping strength of the Fermi surface in BSTS to be intermediate between those
found in Bi2Se3 and Bi2Te3 and also to be tunable by controlling the ratio of
chalcogen/pnictogen atoms. Our experiments also reveal that the nature of the
BB effects are highly sensitive to the exposure of the fresh surface to various
gas species. These findings have important implications in the tuning of DP in
TIs for technological applications
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