60 research outputs found
Stacking-dependent electronic structure of trilayer graphene resolved by nanospot angle-resolved photoemission spectroscopy
The crystallographic stacking order in multilayer graphene plays an important
role in determining its electronic structure. In trilayer graphene,
rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band
with an electric-field tunable band gap. Such electronic structure is distinct
from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA), and is
promising for nanoscale electronics, optoelectronics applications. So far clean
experimental electronic spectra on the first two stackings are missing because
the samples are usually too small in size (um or nm scale) to be resolved by
conventional angle-resolved photoemission spectroscopy (ARPES). Here by using
ARPES with nanospot beam size (NanoARPES), we provide direct experimental
evidence for the coexistence of three different stackings of trilayer graphene
and reveal their distinctive electronic structures directly. By fitting the
experimental data, we provide important experimental band parameters for
describing the electronic structure of trilayer graphene with different
stackings
Evidence for quasi-one-dimensional charge density wave in CuTe by angle-resolved photoemission spectroscopy
We report the electronic structure of CuTe with a high charge density wave
(CDW) transition temperature Tc = 335 K by angle-resolved photoemission
spectroscopy (ARPES). An anisotropic charge density wave gap with a maximum
value of 190 meV is observed in the quasi-one-dimensional band formed by Te px
orbitals. The CDW gap can be filled by increasing temperature or electron
doping through in situ potassium deposition. Combining the experimental results
with calculated electron scattering susceptibility and phonon dispersion, we
suggest that both Fermi surface nesting and electron-phonon coupling play
important roles in the emergence of the CDW
Disorder induced multifractal superconductivity in monolayer niobium dichalcogenides
The interplay between disorder and superconductivity is a subtle and
fascinating phenomenon in quantum many body physics. The conventional
superconductors are insensitive to dilute nonmagnetic impurities, known as the
Anderson's theorem. Destruction of superconductivity and even
superconductor-insulator transitions occur in the regime of strong disorder.
Hence disorder-enhanced superconductivity is rare and has only been observed in
some alloys or granular states. Because of the entanglement of various effects,
the mechanism of enhancement is still under debate. Here we report
well-controlled disorder effect in the recently discovered monolayer NbSe
superconductor. The superconducting transition temperatures of NbSe
monolayers are substantially increased by disorder. Realistic theoretical
modeling shows that the unusual enhancement possibly arises from the
multifractality of electron wave functions. This work provides the first
experimental evidence of the multifractal superconducting state
Widely tunable band gap in a multivalley semiconductor SnSe by potassium doping
SnSe, a group IV-VI monochalcogenide with layered crystal structure similar
to black phosphorus, has recently attracted extensive interests due to its
excellent thermoelectric properties and potential device applications.
Experimental electronic structure of both the valence and conduction bands is
critical for understanding the effects of hole versus electron doping on the
thermoelectric properties, and to further reveal possible change of the band
gap upon doping. Here, we report the multivalley valence bands with a large
effective mass on semiconducting SnSe crystals and reveal single-valley
conduction bands through electron doping to provide a complete picture of the
thermoelectric physics. Moreover, by electron doping through potassium
deposition, the band gap of SnSe can be widely tuned from 1.2 eV to 0.4 eV,
providing new opportunities for tunable electronic and optoelectronic devices
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