173 research outputs found
Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS single crystals
The promising thermoelectric material TiS can be easily chemically doped
and intercalated. We present here studies of single crystals that are
intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the
intrinsic impact of these dopants on the thermal transport in the absence of
grain boundary scattering. We show that Ta doping has the greatest impact on
the thermal scattering rate per ion added, leading to a five-fold reduction in
the lattice thermal conductivity as compared to stoichiometric single crystals.Comment: 5 pages, 2 figure
Strong photo-absorption by a single quantum wire in waveguide-transmission spectroscopy
We measured the absorption spectrum of a single T-shaped, 14x6 nm
lateral-sized quantum wire embedded in an optical waveguide using
waveguide-transmission spectroscopy at 5 K. In spite of its small volume, the
one-dimensional-exciton ground state shows a large absorption coefficient of 80
/cm, or a 98 % absorption probability for a single pass of the 500-um-long
waveguide.Comment: 4 pages, 3 figure
Room-temperature excitonic absorption in quantum wires
We measured absorption spectra of T-shaped quantum wires at room temperature
using waveguide-transmission spectroscopy. Strong and narrow room-temperature
one-dimensional-exciton absorption peak was observed, which shows peak modal
absorption coefficient of 160 cm per 20 wires with -factor of
, width of 7.2 meV, and strong polarization anisotropy.Comment: 3pages, 3figure, 1tabl
Entropy production in a longitudinally expanding YangâMills field with use of the Husimi function: semiclassical approximation
We investigate the possible thermalization process of the highly occupied and weakly coupled YangâMills fields expanding along the beam axis through an evaluation of the entropy, particle number, and pressure anisotropy. The time evolution of the system is calculated by solving the equation of motion for the Wigner function in the semiclassical approximation with initial conditions mimicking the glasma. For the evaluation of the entropy, we adopt HusimiâWehrl (HW) entropy, which is obtained by using the Husimi function, a positive semidefinite quantum distribution function given by smearing the Wigner function. By numerical calculations at g = 0.1 and 0.2, the entropy production is found to occur together with the particle creation in two distinct stages: In the first stage, the particle number and entropy at low longitudinal momenta grow rapidly. In the second stage, the particle number and entropy of higher longitudinal momentum modes show a slower increase. The pressure anisotropy remains in our simulation and implies that the system is still out of equilibrium
Imaging of emission patterns in a T-shaped quantum wire laser
Spatially and spectrally resolved microscopic images of spontaneous and
stimulated emissions are imaged at the mirror facets of a GaAs T-shaped quantum
wire laser with high uniformity. Laser emission from the one-dimensional ground
state reveals a circular image located at the core of a T-shaped optical
waveguide but significantly smaller in area than the low power spontaneous
emission from the same waveguide. These images unambiguously allow assignment
of all spontaneous and laser emissions to the wire ground state and respective
intersecting wells in the structure.Comment: 4 pages, 3 figure
Giant enhancement of cryogenic thermopower by polar structural instability in the pressurized semimetal MoTe2
We found that a high mobility semimetal 1T'-MoTe2 shows a significant
pressure-dependent change in the cryogenic thermopower in the vicinity of the
critical pressure, where the polar structural transition disappears. With the
application of a high pressure of 0.75 GPa, while the resistivity becomes as
low as 10 {\mu}{\Omega}cm, thermopower reached the maximum value of 60
{\mu}VK-1 at 25 K, leading to a giant thermoelectric power factor of 300
{\mu}WK-2cm-1. Based on semiquantitative analyses, the origin of this behavior
is discussed in terms of inelastic electron-phonon scattering enhanced by the
softening of zone center phonon modes associated with the polar structural
instability.Comment: 13 pages, 4 figures Physical review B (accepted
Superconductivity in a ferroelectric-like topological semimetal SrAuBi
Given the rarity of metallic systems that exhibit ferroelectric-like
transitions, it is apparently challenging to find a system that simultaneously
possesses superconductivity and ferroelectric-like structural instability.
Here, we report the observation of superconductivity at 2.4 K in a layered
semimetal SrAuBi characterized by strong spin-orbit coupling (SOC) and
ferroelectric-like lattice distortion. Single crystals of SrAuBi have been
successfully synthesized and found to show a polar-nonpolar structure
transition at 214 K, which is associated with the buckling of Au-Bi honeycomb
lattice. On the basis of the band calculations considering SOC, we found
significant Rashba-type spin splitting and symmetry-protected multiple Dirac
points near the Fermi level. We believe that this discovery opens up new
possibilities of pursuing exotic superconducting states associated with the
semimetallic band structure without space inversion symmetry and the
topological surface state with the strong SOC.Comment: 17 pages, 6 figures (npj Quantum Materials in press
Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe
Tantalum ditelluride TaTe belongs to the family of layered transition
metal dichalcogenides but exhibits a unique structural phase transition at
around 170 K that accompanies the rearrangement of the Ta atomic network from a
"ribbon chain" to a "butterfly-like" pattern. While multiple mechanisms
including Fermi surface nesting and chemical bonding instabilities have been
intensively discussed, the origin of this transition remains elusive. Here we
investigate the electronic structure of single-crystalline TaTe with a
particular focus on its modifications through the phase transition, by
employing core-level and angle-resolved photoemission spectroscopy combined
with first-principles calculations. Temperature-dependent core-level
spectroscopy demonstrates a splitting of the Ta core-level spectra through
the phase transition indicative of the Ta-dominated electronic state
reconstruction. Low-energy electronic state measurements further reveal an
unusual kink-like band reconstruction occurring at the Brillouin zone boundary,
which cannot be explained by Fermi surface nesting or band folding effects. On
the basis of the orbital-projected band calculations, this band reconstruction
is mainly attributed to the modifications of specific Ta states, namely
the orbitals (the ones elongating along the ribbon chains) at the
center Ta sites of the ribbon chains. The present results highlight the strong
orbital-dependent electronic state reconstruction through the phase transition
in this system and provide fundamental insights towards understanding complex
electron-lattice-bond coupled phenomena.Comment: 21 pages, 5 figure
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