18 research outputs found
Non-topological Origin of the Planar Hall Effect in Type-II Dirac Semimetal NiTe2
Dirac and Weyl semimetals are new discovered topological nontrivial materials
with the linear band dispersions around the Dirac/Weyl points. When applying
non-orthogonal electric current and magnetic field, an exotic phenomenon called
chiral anomaly arises and negative longitudinal resistance can be detected.
Recently, a new phenomenon named planer Hall effect (PHE) is considered to be
another indication of chiral anomaly which has been observed in many
topological semimetals. However, it still remains a question that is the PHE
only attributed to chiral anomaly? Here we demonstrate the PHE in a
new-discovered type-II Dirac semimetal NiTe2 by low temperature transport.
However, after detailed analysis, we conclude that the PHE results from the
trivial orbital magnetoresistance. This work reveals that PHE is not a
sufficient condition of chiral anomaly and one need to take special care of
other non-topological contribution in such studies
Oscillating planar Hall response from the surface electrons in bulk crystal Sn doped Bi1.1Sb0.9Te2S
We report the low-temperature magneto-transport in the bulk-insulating single
crystal of topological insulator Sn doped Bi1.1Sb0.9Te2S. The Shubnikov-de Haas
oscillations appear with their reciprocal frequency proportional to cos/theta ,
demonstrating the dominant transport of topological surface states. While the
magnetic field is rotating in the sample surface, the planar Hall effect arises
with sizeable oscillations following a relation of cos/theta sin/theta . Its
amplitude reaches the maximum at the lowest temperature and drops to nearly
zero at the temperature higher than 100 K. All these evidences consolidate such
planar Hall oscillations as a new golden criterion on the topological surface
transport
Lateral Heterojunction Sb2Te3/Bi2Te3 and its topological transport
A lateral heterojunction of topological insulator Sb2Te3/Bi2Te3 was
successfully synthesized using a two-step solvothermal method. The two
crystalline components were separated well by a sharp lattice-matched interface
when the optimized procedure was used. Inspecting the heterojunction using
high-resolution transmission electron microscopy showed that epitaxial growth
occurred along the horizontal plane. A rectification curve was observed at low
temperatures. Quantum correction from the weak antilocalization reveals the
transport of the topological surface state. There was, therefore, a
staggered-gap lateral heterojunction with a small junction voltage, which is
appealing for a platform for spin filters and one-dimensional topological
interface states
Approaching the Type-II Dirac Point and Concomitant Superconductivity in Pt-doping Stabilized Metastable 1T-phase IrTe2
Topological semimetal is a topic of general interest in material science.
Recently, a new kind of topological semimetal called type-II Dirac semimetal
with tilted Dirac cones is discovered in PtSe2 family. However, the further
investigation is hindered due to the huge energy difference from Dirac points
to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we
characterize the optimized type-II Dirac dispersions in a metastable 1T phase
of IrTe2. Our strategy of Pt doping protects the metastable 1T phase in low
temperature and tunes the Fermi level to the Dirac point. As demonstrated by
angle-resolved photoemission spectra and first principle calculations, the
Fermi surface of Ir1-xPtxTe2 is formed by only a single band with type-II Dirac
cone which is tilted strongly along kz momentum direction. Interesting
superconductivity is observed in samples for Dirac point close to Fermi level
and even survives when Fermi level aligns with the Dirac point as finite
density of states created by the tilted cone dispersion. This advantage offers
opportunities for possible topological superconductivity and versatile Majorana
devices in type-II Dirac semimetals
Experimental evidence on the dissipationless transport of chiral edge state of the high-field Chern insulator in MnBi2Te4 nanodevices
We demonstrate the dissipationless transport of the chiral edge state (CES)
in the nanodevices of quantum anomalous Hall insulator candidate MnBi2Te4. The
device presents a near-zero longitudinal resistance together with a quantized
Hall plateau in excess of 0.97 h/e2 over a range of temperatures from very low
up to the Neel temperature of 22 K. Each of four-probe nonlocal measurements
gives near-zero resistance and two-probe measurements exhibit a plateau of +1
h/e2, while the results of three-probe nonlocal measurements depend on the
magnetic field. This indicates non-dissipation as well as the chirality of the
edge state. The CES shows three regimes of temperature dependence, i.e.,
well-preserved dissipationless transport below 6 K, variable range hopping
while increasing the temperature and thermal activation at higher than 22 K.
Even at the lowest temperature, a current of over 1.4 {\mu}A breaks the
dissipationless transport. These form a complete set of evidences of the Chern
insulator state in the MnBi2Te4 systems.Comment: 4 figure
Mimicing the Kane-Mele type spin orbit interaction by spin-flexual phonon coupling in graphene devices
On the efforts of enhancing the spin orbit interaction (SOI) of graphene for
seeking the dissipationless quantum spin Hall devices, unique Kane-Mele type
SOI and high mobility samples are desired. However, common external decoration
often introduces extrinsic Rashba-type SOI and simultaneous impurity
scattering. Here we show, by the EDTA-Dy molecule dressing, the Kane-Mele type
SOI is mimicked with even improved carrier mobility. It is evidenced by the
suppressed weak localization at equal carrier densities and simultaneous
Elliot-Yafet spin relaxation. The extracted spin scattering time is
monotonically dependent on the carrier elastic scattering time, where the
Elliot-Yafet plot gives the interaction strength of 3.3 meV. Improved quantum
Hall plateaus can be even seen after the external operation. This is attributed
to the spin-flexural phonon coupling induced by the enhanced graphene ripples,
as revealed by the in-plane magnetotransport measurement
Phase transition and anomalous scaling in the quantum Hall transport of topological insulator Sn-Bi1.1Sb0.9Te2S devices
The scaling physics of quantum Hall transport in optimized topological
insulators with a plateau precision of ~1/1000 e2/h is considered. Two
exponential scaling regimes are observed in temperature-dependent transport
dissipation, one of which accords with thermal activation behavior with a gap
of 2.8 meV (> 20 K), the other being attributed to variable range hopping (1-20
K). Magnetic field-driven plateau-to-plateau transition gives scaling relations
of (dR/dB) \propto T and \DeltaB \propto
T with a consistent exponent of \kappa ~ 0.2, which is half the
universal value for a conventional two-dimensional electron gas. This is
evidence of percolation assisted by quantum tunneling, and reveals the
dominance of electron-electron interaction of the topological surface states
Experimental observation of the gate-controlled reversal of the anomalous Hall effect in the intrinsic magnetic topological insulator MnBi2Te4 device
Here we report the reserved anomalous Hall effect (AHE) in the
5-septuple-layer van der Waals device of the intrinsic magnetic topological
insulator MnBi2Te4. By employing the top/bottom gate, a negative AHE loop
gradually decreases to zero and changes to a reversed sign. The reversed AHE
exhibits distinct coercive fields and temperature dependence from the previous
AHE. It reaches the maximum inside the gap of the Dirac cone. The newly-seen
reversed AHE is attributed to the competition of the intrinsic Berry curvature
and the Dirac-gap enhanced extrinsic skew scattering. Its gate-controlled
switching contributes a scheme for the topological spin field-effect
transistors
Stepwise quantized surface states and delayed Landau level hybridization in Co cluster-decorated BiSbTeSe2 topological insulator devices
In three-dimensional topological insulators (TIs), the nontrivial topology in
their electronic bands casts a gapless state on their solid surfaces, using
which dissipationless TI edge devices based on the quantum anomalous Hall (QAH)
effect and quantum Hall (QH) effect have been demonstrated. Practical TI
devices present a pair of parallel-transport topological surface states (TSSs)
on their top and bottom surfaces. However, due to the no-go theorem, the two
TSSs always appear as a pair and are expected to quantize synchronously.
Quantized transport of a separate Dirac channel is still desirable, but has
never been observed in graphene even after intense investigation over a period
of 13 years, with the potential aim of half-QHE. By depositing Co atomic
clusters, we achieved stepwise quantization of the top and bottom surfaces in
BiSbTeSe2 (BSTS) TI devices. Renormalization group flow diagrams13, 22 (RGFDs)
reveal two sets of converging points (CVPs) in the (Gxy, Gxx) space, where the
top surface travels along an anomalous quantization trajectory while the bottom
surface retains 1/2 e2/h. This results from delayed Landau-level (LL)
hybridization (DLLH) due to coupling between Co clusters and TSS Fermions
Magneto-transport and Shubnikov-de Haas oscillations in the layered ternary telluride Ta3SiTe6 topological semimetal
Topological semimetals characterize a novel class of quantum materials
hosting Dirac/Weyl fermions. The important features of topological fermions can
be exhibited by quantum oscillations. Here we report the magnetoresistance and
Shubnikov-de Haas (SdH) quantum oscillation of longitudinal resistance in the
single crystal of topological semimetal Ta3SiTe6 with the magnetic field up to
38 T. Periodic amplitude of the oscillations reveals related information about
the Fermi surface. The fast Fourier transformation spectra represent a single
oscillatory frequency. The analysis of the oscillations shows the Fermi pocket
with a cross-section area of 0.13 angstrom power minus 2. Combining
magneto-transport measurements and the first-principles calculation, we find
that these oscillations come from the hole pocket. Hall resistivity and the SdH
oscillations recommend that Ta3SiTe6 is a hole dominated system.Comment: 18 pages, 4 figure