15 research outputs found
Anomalous Cooper pair interference on Bi2Te3 surface
It is believed that the edges of a chiral p-wave superconductor host Majorana
modes, relating to a mysterious type of fermions predicted seven decades ago.
Much attention has been paid to search for p-wave superconductivity in
solid-state systems, including recently those with strong spin-orbit coupling
(SOC). However, smoking-gun experiments are still awaited. In this work, we
have performed phase-sensitive measurements on particularly designed
superconducting quantum interference devices constructing on the surface of
topological insulators Bi2Te3, in such a way that a substantial portion of the
interference loop is built on the proximity-effect-induced superconducting
surface. Two types of Cooper interference patterns have been recognized at low
temperatures. One is s-wave like and is contributed by a zero-phase loop
inhabited in the bulk of Bi2Te3. The other, being identified to relate to the
surface states, is anomalous for that there is a phase shift between the
positive and negative bias current directions. The results support that the
Cooper pairs on the surface of Bi2Te3 have a 2\pi Berry phase which makes the
superconductivity p_x+ip_y-wave-like. Mesoscopic hybrid rings as constructed in
this experiment are presumably arbitrary-phase loops good for studying
topological quantum phenomena.Comment: supplementary material adde
Phase evolution and superconductivity enhancement in Se-substituted MoTe thin films
The strong spinorbit coupling (SOC) and numerous crystal phases in
fewlayer transition metal dichalcogenides (TMDCs) MX (MW, Mo, and
XTe, Se, S) has led to a variety of novel physics, such as Ising
superconductivity and quantum spin Hall effect realized in monolayer 2H and
TdMX, respectively. Consecutive tailoring of the MX structure from
2H to Td phase may realize the longsought topological superconductivity in
one material system by incorporating superconductivity and quantum spin Hall
effect together. In this work, by combing Raman spectrum, X-ray photoelectron
spectrum (XPS), scanning transmission electron microscopy imaging (STEM) as
well as electrical transport measurements, we demonstrate that a consecutively
structural phase transitions from Td to 1T to 2H polytype can be realized as
the Se-substitution concentration increases. More importantly, the
Sesubstitution has been found to notably enhance the superconductivity of
the MoTe thin film, which is interpreted as the introduction of the
twoband superconductivity. The chemical constituent induced phase transition
offers a new strategy to study the s superconductivity and the possible
topological superconductivity as well as to develop phasesensitive devices
based on MX materials.Comment: 27 pages, 5 figure
Transport evidence of asymmetric spin-orbit coupling in fewlayer superconducting 1TdMoTe
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) MX2 (M=W, Mo,
Nb, and X=Te, Se, S) with strong spin-orbit coupling (SOC) possess plenty of
novel physics including superconductivity. Due to the Ising SOC, monolayer
NbSe and gated MoS of 2H structure can realize the Ising
superconductivity phase, which manifests itself with in-plane upper critical
field far exceeding Pauli paramagnetic limit. Surprisingly, we find that a
few-layer 1Td structure MoTe also exhibits an in-plane upper critical field
() which goes beyond the Pauli paramagnetic limit. Importantly, the
in-plane upper critical field shows an emergent two-fold symmetry which is
different from the isotropic in 2H structure TMDCs. We show that
this is a result of an asymmetric SOC in 1Td structure TMDCs. The asymmetric
SOC is very strong and estimated to be on the order of tens of meV. Our work
provides the first transport evidence of a new type of asymmetric SOC in TMDCs
which may give rise to novel superconducting and spin transport properties.
Moreover, our findings mostly depend on the symmetry of the crystal and apply
to a whole class of 1Td TMDCs such as 1Td-WTe which is under intense study
due to its topological properties.Comment: 34 pages, 12 figure
On the origin of the giant Hall effect in magnetic granular metals
A large, by a factor of similar to 10(3)-10(4), enhancement of Hall effect in cosputtered magnetic granular metals such as (NiFe)(x)-(SiO2)(1-x) near the metal-insulator transition has been termed giant Hall effect (GHE). It is associated with a high resistivity which increases slowly with decreasing temperature. We suggest that particle-size distribution which is singular at zero and quantum size effects may be responsible for these phenomena. From our scaling analysis of the relations between resistivity, and the ordinary and extraordinary Hall effects, it follows that the extraordinary Hall resistivity rho(xys) scales with mobility as-rho(xys)proportional to mu(-gamma) with the exponent gamma approximate to 0.5, which is characteristically different from the predictions of both the skew scattering (gamma approximate to 1) and the side jump (gamma approximate to 2) theories in homogeneous ferromagnets
Observation of weak anti-localization and electron-electron interaction on few-layer 1T′-MoTe2 thin films
Electronic transports of few-layer 1T'-MoTe2 films are measured at temperatures down to 0.26 K. The lowtemperature conductivity exhibits logarithmic temperature dependence and negative magneto response. The negative magnetoconductivity can be well fitted by the two-dimensional weak anti-localization theory taking a single channel of electrons into account, with the parameters α ≈ -0.5 and lφ ∝ T-0.5. The logarithmic temperature dependence has a positive slope κ ≈ 0.75, indicating the dominance of electron-electron interaction over the weak anti-localization effect, with an apparently negative Coulomb screening factor F that demands future work for clarification.NRF (Natl Research Foundation, S’pore