16 research outputs found
Optoelectronic characterisation of twisted germanium sulfide nanowires with experimental observation of intrinsic ferroelectricity
We report the optoelectrical characterisation of Eshelby twisted Germanium
sulfide (GeS) nanowires with first experimental observation of ferroelectric
order at room temperature in GeS which is an otherwise centrosymmetric
molecule. The chemical composition and structure of these nanowires were
confirmed by various spectroscopic, microscopic and diffractive techniques. In
addition, the nanowires were found to be stable over time. From the
optoelectronic measurements we found that these p-type semiconducting GeS
nanowires have up to two orders higher charge carrier mobility than GeS
nanosheets and have sustainable, robust photo-switching property. The existence
of room temperature ferroelectricity is confirmed by piezoresponse force
microscopy which showed hysteresis and butterfly loop, characteristics of a
ferroelectric material. Our observations reveal that the properties of twisted
GeS nanowires can be harnessed in making efficient electric sensors,
photodetectors, data memories and flexible electronics
Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor SbSe
Majority of the AB type chalcogenide systems with strong spin-orbit
coupling, like BiSe, BiTe and SbTe etc., are
topological insulators. One important exception is SbSe, where a
topological non-trivial phase was argued to be possible under ambient
conditions, but such a phase could be detected to exist only under pressure. In
this Letter, we show that like BiSe, SbSe, displays generation
of highly spin-polarized current under mesoscopic superconducting point
contacts as measured by point contact Andreev reflection spectroscopy. In
addition, we observe a large negative and anisotropic magnetoresistance in
SbSe, when the field is rotated in the basal plane. However, unlike in
BiSe, in case of SbSe a prominent quasiparticle interference
(QPI) pattern around the defects could be obtained in STM conductance imaging.
Thus, our experiments indicate that SbSe is a regular band insulator
under ambient conditions, but due to it's high spin-orbit coupling, non-trivial
spin-texture exists on the surface and the system could be on the verge of a
topological insulator phase.Comment: 5 pages, 4 figures, supplemental material not include
Generation of strain-induced pseudo-magnetic field in a doped type-II Weyl semimetal
In Weyl semimetals, there is an intriguing possibility of realizing a
pseudo-magnetic field in presence of small strain due to certain special cases
of static deformations. This pseudo-magnetic field can be large enough to form
quantized Landau levels and thus become observable in Weyl semimetals. In this
paper, we experimentally show the emergence of a pseudo-magnetic field (~ 3
Tesla) by Scanning Tunneling Spectroscopy (STS) on the doped Weyl semimetal
Re-MoTe2, where distinct Landau level oscillations in the tunneling conductance
are clearly resolved. The crystal lattice is intrinsically strained where large
area STM imaging of the surface reveals differently strained domains where
atomic scale deformations exist forming topographic ripples with varying
periodicity in the real space. The effect of pseudo-magnetic field is clearly
resolved in areas under maximum strain.Comment: 6 pages, 4 figure
Local ferroelectric polarization switching driven by nanoscale distortions in thermoelectric
A remarkable decrease in the lattice thermal conductivity and enhancement of thermoelectric figure of merit were recently observed in rock-salt cubic SnTe, when doped with germanium (Ge). Primarily, based on theoretical analysis, the decrease in lattice thermal conductivity was attributed to local ferroelectric fluctuations induced softening of the optical phonons which may strongly scatter the heat carrying acoustic phonons. Although the previous structural analysis indicated that the local ferroelectric transition temperature would be near room temperature in , a direct evidence of local ferroelectricity remained elusive. Here we report a direct evidence of local nanoscale ferroelectric domains and their switching in using piezoeresponse force microscopy(PFM) and switching spectroscopy over a range of temperatures near the room temperature. From temperature dependent (250–300 K) synchrotron X-ray pair distribution function (PDF) analysis, we show the presence of local off-centering distortion of Ge along the rhombohedral direction in global cubic . The length scale of the Ge off-centering is 0.25–0.10 Å near the room temperatures (250–300 K). This local emphatic behaviour of cation is the cause for the observed local ferroelectric instability, thereby low lattice thermal conductivity in