26 research outputs found
Significant change in the electronic behavior associated with structural distortions in the single crystalline SrAg4As2
We report a combined study of transport and thermodynamic measurements on the
layered pnictide material SrAg4As2. Upon cooling, a drop in electrical and Hall
resistivity, a jump in heat capacity and an increase in susceptibility and
magnetoresistance (MR) are observed around 110 K. These observations suggest
that non-magnetic phase transitions emerge at around 110 K, that are likely
associated with structural distortions. In sharp contrast with the
first-principles calculations based on the crystal structure at room
temperature, quantum oscillations reveal small Fermi pockets with light
effective masses, suggesting a significant change in the Fermi surface topology
caused by the low temperature structural distortion. No superconductivity
emerges in SrAgAs down to 2 K and under pressures up to 2.13 GPa;
instead, the low temperature structural distortion increases linearly with
temperature at a rate of ~13 K/GPa above 0.89 GPa
Topological surface electronic states in candidate nodal-line semimetal CaAgAs
We investigate systematically the bulk and surface electronic structure of
the candidate nodal-line semimetal CaAgAs by angle resolved photoemission
spectroscopy and density functional calculations. We observed a metallic,
linear, non--dispersive surface band that coincides with the
high-binding-energy part of the theoretical topological surface state, proving
the topological nontriviality of the system. An overall downshift of the
experimental Fermi level points to a rigid-band-like -doping of the samples,
due possibly to Ag vacancies in the as-grown crystals.Comment: 6 pages, 5 figure
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A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling.
Magnetic topological insulators (TI) provide an important material platform to explore quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. Their successful material realization is thus essential for our fundamental understanding and potential technical revolutions. By realizing a bulk van der Waals material MnBi4Te7 with alternating septuple [MnBi2Te4] and quintuple [Bi2Te3] layers, we show that it is ferromagnetic in plane but antiferromagnetic along the c axis with an out-of-plane saturation field of ~0.22 T at 2 K. Our angle-resolved photoemission spectroscopy measurements and first-principles calculations further demonstrate that MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively. Additionally, its superlattice nature may make various heterostructures of [MnBi2Te4] and [Bi2Te3] layers possible by exfoliation. Therefore, the low saturation field and the superlattice nature of MnBi4Te7 make it an ideal system to investigate rich emergent phenomena
Unconventional pressure-driven metamagnetic transitions in topological van der Waals magnets
Activating metamagnetic transitions between ordered states in van der Waals
magnets and devices bring great opportunities in spintronics. We show that
external pressure, which enhances the interlayer hopping without introducing
chemical disorders, triggers multiple metamagnetic transitions upon cooling in
the topological van der Waals magnets Mn(BiSb)Te, where the
antiferromagnetic interlayer superexchange coupling competes with the
ferromagnetic interlayer coupling mediated by the antisite Mn spins. The
temperature-pressure phase diagrams reveal that while the ordering temperature
from the paramagnetic to ordered states is almost pressure-independent, the
metamagnetic transitions show non-trivial pressure and temperature dependence,
even re-entrance. For these highly anisotropic magnets, we attribute the former
to the ordering temperature being only weakly dependent on the intralayer
parameters, the latter to the parametrically different pressure and temperature
dependence of the two interlayer couplings. Our independent probing of these
disparate magnetic interactions paves an avenue for efficient magnetic
manipulations in van der Waals magnets.Comment: 10 pages, 4 figure