1,667 research outputs found
Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy
Pb1-xSnxSe hosts 3D massive Dirac fermions across the entire composition
range for which the crystal structure is cubic. In this work, we present a
comprehensive experimental mapping of the 3D band structure parameters of
Pb1-xSnxSe as a function of composition and temperature. We cover a parameter
space spanning the band inversion that yields its topological crystalline
insulator phase. A non-closure of the energy gap is evidenced in the vicinity
of this phase transition. Using magnetooptical Landau level spectroscopy, we
determine the energy gap, Dirac velocity, anisotropy factor and topological
character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2
(111). Our results are evidence that Pb1-xSnxSe is a model system to study
topological phases and the nature of the phase transition.Comment: Submitte
A note on Gauge Theories Coupled to Gravity
We analyze the bound on gauge couplings , suggested by
Arkani-Hamed et.al. We show this bound can be derived from simple
semi-classical considerations and holds in spacetime dimensions greater than or
equal to four. Non abelian gauge symmetries seem to satisfy the bound in a
trivial manner. We comment on the case of discrete symmetries and close by
performing some checks for the bound in higher dimensions in the context of
string theory.Comment: 15 pages, 1 figure, Late
Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms
We study the angular correlation function of speckle patterns that result
from multiple scattering of photons by cold atomic clouds. We show that this
correlation function becomes larger than the value given by Rayleigh law for
classical scatterers. These large intensity fluctuations constitute a new
mesoscopic interference effect specific to atom-photon interactions, that could
not be observed in other systems such as weakly disordered metals. We provide a
complete description of this behavior and expressions that allow for a
quantitative comparison with experiments.Comment: 4 pages, 2 figure
Massive and massless Dirac fermions in Pb1-xSnxTe topological crystalline insulator probed by magneto-optical absorption
Dirac fermions in condensed matter physics hold great promise for novel
fundamental physics, quantum devices and data storage applications. IV-VI
semiconductors, in the inverted regime, have been recently shown to exhibit
massless topological surface Dirac fermions protected by crystalline symmetry,
as well as massive bulk Dirac fermions. Under a strong magnetic field (B), both
surface and bulk states are quantized into Landau levels that disperse as
B^1/2, and are thus difficult to distinguish. In this work, magneto-optical
absorption is used to probe the Landau levels of high mobility Bi-doped
Pb0.54Sn0.46Te topological crystalline insulator (111)-oriented films. The high
mobility achieved in these thin film structures allows us to probe and
distinguish the Landau levels of both surface and bulk Dirac fermions and
extract valuable quantitative information about their physical properties. This
work paves the way for future magnetooptical and electronic transport
experiments aimed at manipulating the band topology of such materials.Comment: supplementary material included, to appear in Scientific Report
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
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