21 research outputs found
Atomic-scale observation of localized phonons at FeSe/SrTiO3 interface
In single unit-cell FeSe grown on SrTiO3, the superconductivity transition
temperature features a significant enhancement. Local phonon modes at the
interface associated with electron-phonon coupling may play an important role
in the interface-induced enhancement. However, such phonon modes have eluded
direct experimental observations. Indeed, the complicated atomic structure of
the interface brings challenges to obtain the accurate structure-phonon
relation knowledge from either experiment or theory, thus hindering our
understanding of the enhancement mechanism. Here, we achieve direct
characterizations of atomic structure and phonon modes at the FeSe/SrTiO3
interface with atomically resolved imaging and electron energy loss
spectroscopy in a scanning transmission electron microscope. We find several
phonon modes highly localized (~1.3 nm) at the unique double layer Ti-O
termination at the interface, one of which (~ 83 meV) engages in strong
interactions with the electrons in FeSe based on ab initio calculations. The
electron-phonon coupling strength for such a localized interface phonon with
short-range interactions is comparable to that of Fuchs-Kliewer (FK) phonon
mode with long-rang interactions. Thus, our atomic-scale study provides new
insights into understanding the origin of superconductivity enhancement at the
FeSe/SrTiO3 interface
Thermodynamic behavior of correlated electron-hole fluids in van der Waals heterostructures
Coupled two-dimensional electron-hole bilayers provide a unique platform to
study strongly correlated Bose-Fermi mixtures in condensed matter. Electrons
and holes in spatially separated layers can bind to form interlayer excitons,
composite Bosons expected to support high-temperature exciton superfluids. The
interlayer excitons can also interact strongly with excess charge carriers when
electron and hole densities are unequal. Here, we use optical spectroscopy to
quantitatively probe the local thermodynamic properties of strongly correlated
electron-hole fluids in MoSe2/hBN/WSe2 heterostructures. We observe a
discontinuity in the electron and hole chemical potentials at matched electron
and hole densities, a definitive signature of an excitonic insulator ground
state. The excitonic insulator is stable up to a Mott density of ~ and has a thermal ionization temperature of ~70 K.
The density dependence of the electron, hole, and exciton chemical potentials
reveals strong correlation effects across the phase diagram. Compared with a
non-interacting uniform charge distribution, the correlation effects lead to
significant attractive exciton-exciton and exciton-charge interactions in the
electron-hole fluid. Our work highlights the unique quantum behavior that can
emerge in strongly correlated electron-hole systems
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Charge Transfer Dynamics in MoSe2/hBN/WSe2 Heterostructures.
Ultrafast charge transfer processes provide a facile way to create interlayer excitons in directly contacted transition metal dichalcogenide (TMD) layers. More sophisticated heterostructures composed of TMD/hBN/TMD enable new ways to control interlayer exciton properties and achieve novel exciton phenomena, such as exciton insulators and condensates, where longer lifetimes are desired. In this work, we experimentally study the charge transfer dynamics in a heterostructure composed of a 1 nm thick hBN spacer between MoSe2 and WSe2 monolayers. We observe the hole transfer from MoSe2 to WSe2 through the hBN barrier with a time constant of 500 ps, which is over 3 orders of magnitude slower than that between TMD layers without a spacer. Furthermore, we observe strong competition between the interlayer charge transfer and intralayer exciton-exciton annihilation processes at high excitation densities. Our work opens possibilities to understand charge transfer pathways in TMD/hBN/TMD heterostructures for the efficient generation and control of interlayer excitons
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Charge transfer dynamics in MoSe/hBN/WSe heterostructures
Ultrafast charge transfer processes provide a facile way to create interlayer
excitons in directly contacted transition metal dichalcogenide (TMD) layers.
More sophisticated heterostructures composed of TMD/hBN/TMD enable new ways to
control interlayer exciton properties and achieve novel exciton phenomena, such
as exciton insulators and condensates, where longer lifetimes are desired. In
this work, we experimentally study the charge transfer dynamics in a
heterostructure composed of a 1 nm thick hBN spacer between MoSe and
WSe monolayers. We observe the hole transfer from MoSe to WSe
through the hBN barrier with a time constant of 500 ps, which is over 3 orders
of magnitude slower than that between TMD layers without a spacer. Furthermore,
we observe strong competition between the interlayer charge transfer and
intralayer exciton-exciton annihilation processes at high excitation densities.
Our work opens possibilities to understand charge transfer pathways in
TMD/hBN/TMD heterostructures for the efficient generation and control of
interlayer excitons
Phosphorus Availability Affects the Photosynthesis and Antioxidant System of Contrasting Low-P-Tolerant Cotton Genotypes
Phosphorus (P) is an essential macronutrient, and an important component of plant metabolism. However, little is known about the effects of low P availability on P absorption, the photosynthetic electron transport chain, and the antioxidant system in cotton. This study used cotton genotypes (sensitive FJA and DLNTDH and tolerant BX014 and LuYuan343) with contrasting low-P tolerance in a hydroponic experiment under 15 µM, 50 µM, and 500 μM P concentrations. The results showed that low P availability reduced plant development and leaf area, shoot length, and dry weight in FJA and DLNADH, compared to BX014 and LuYuan343. The low P availability decreased the gas-exchange parameters such as the net photosynthetic rate, transpiration rate, and stomatal conductance, and increased the intercellular CO2 concentration. Chlorophyll a fluorescence demonstrated that the leaves’ absorption and trapped-energy flux were largely steady. In contrast, considerable gains in absorption and trapped-energy flux per reaction center resulted from decreases in the electron transport per reaction center under low-P conditions. In addition, low P availability reduced the activities of antioxidant enzymes and increased the content of malondialdehyde in the cotton genotypes, especially in FJA and DLNTDH. Moreover, low P availability reduced the activity of PEPC and generated a decline in the content of ATP and NADPH. Our research can provide a theoretical physiological basis for the growth and tolerance of cotton under low-P conditions