1,358 research outputs found
Polyakov-Mellin Bootstrap for AdS loops
We consider holographic CFTs and study their large expansion. We use
Polyakov-Mellin bootstrap to extract the CFT data of all operators, including
scalars, till . We add a contact term in Mellin space, which
corresponds to an effective theory in AdS and leads to anomalous
dimensions for scalars at . Using this we fix anomalous
dimensions for double trace operators finding perfect agreement with
\cite{loopal} (for ). Our approach generalizes this to any
dimensions and any value of conformal dimensions of external scalar field. In
the second part of the paper, we compute the loop amplitude in AdS which
corresponds to non-planar correlators of in CFT. More precisely, using CFT data
at we fix the AdS bubble diagram and the triangle diagram for the
general case.Comment: 22 pages, 4 figures, version published in JHE
Fundamental exciton linewidth broadening in monolayer transition metal dichalcogenides
Monolayer Transition Metal Dichalcogenides (TMDS) are highly luminescent
materials despite being sub-nanometer thick due to the ultra-short ( ps)
radiative lifetime of the strongly bound bright excitons hosted by these
materials. The intrinsically short radiative lifetime results in a large
broadening in the exciton band with a magnitude that is about two orders
greater than the spread of the light cone itself. The situation calls for a
need to revisit the conventional light cone picture. We present a modified
light cone concept which places the light line as the generalized
lower bound for allowed radiative recombination. A self-consistent methodology,
which becomes crucial upon inclusion of large radiative broadening in the
exciton band, is proposed to segregate the radiative and the non-radiative
components of the homogeneous exciton linewidth. We estimate a fundamental
radiative linewidth of meV, owing purely to finite radiative
lifetime in the absence of non-radiative dephasing processes. As a direct
consequence of the large radiative limit, we find a surprisingly large ( meV) linewidth broadening due to zero-point energy of acoustic phonons.
This obscures the precise experimental determination of the intrinsic radiative
linewidth and sets a fundamental limit on the non-radiative linewidth
broadening at K
Bandstructure Effects in Ultra-Thin-Body DGFET: A Fullband Analysis
This paper discusses a few unique effects of ultra-thin-body double-gate
NMOSFET that are arising from the bandstructure of the thin film Si channel.
The bandstructure has been calculated using 10-orbital
tight-binding method. A number of intrinsic properties including band gap,
density of states, intrinsic carrier concentration and parabolic effective mass
have been derived from the calculated bandstructure. The spatial distributions
of intrinsic carrier concentration and effective mass, arising from the
wavefunction of different contributing subbands are analyzed. A self-consistent
solution of Poisson-Schrodinger coupled equation is obtained taking the full
bandstructure into account, which is then applied to an insightful analysis of
volume inversion. The spatial distribution of carriers over the channel of a
DGFET has been calculated and its effects on effective mass and channel
capacitance are discussed.Comment: 13 pages, 21 figure
Self-Powered, Highly Sensitive, High Speed Photodetection Using ITO/WSe2/SnSe2 Vertical Heterojunction
Two dimensional transition metal di-chalcogenides (TMDCs) are promising
candidates for ultra-low intensity photodetection. However, the performance of
these photodetectors is usually limited by ambience induced rapid performance
degradation and long lived charge trapping induced slow response with a large
persistent photocurrent when the light source is switched off. Here we
demonstrate an indium tin oxide (ITO)/WSe/SnSe based vertical double
heterojunction photoconductive device where the photo-excited hole is confined
in the double barrier quantum well, whereas the photo-excited electron can be
transferred to either the ITO or the SnSe layer in a controlled manner. The
intrinsically short transit time of the photoelectrons in the vertical double
heterojunction helps us to achieve high responsivity in excess of A/W
and fast transient response time on the order of s. A large built-in
field in the WSe sandwich layer results in photodetection at zero external
bias allowing a self-powered operation mode. The encapsulation from top and
bottom protects the photo-active WSe layer from ambience induced
detrimental effects and substrate induced trapping effects helping us to
achieve repeatable characteristics over many cycles
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