22 research outputs found
Interplay between moment-dependent and field-driven unidirectional magnetoresistance in CoFeB/InSb/CdTe heterostructures
Magnetoresistance effects are crucial for understanding the charge/spin
transport as well as propelling the advancement of spintronic applications.
Here we report the coexistence of magnetic moment-dependent (MD) and magnetic
field-driven (FD) unidirectional magnetoresistance (UMR) effects in
CoFeB/InSb/CdTe heterostructures. The strong spin-orbital coupling of InSb and
the matched impedance at the CoFeB/InSb interface warrant a distinct MD-UMR
effect at room temperature, while the interaction between the in-plane magnetic
field and the Rashba effect at the InSb/CdTe interface induces the marked
FD-UMR signal that dominates the high-field region. Moreover, owning to the
different spin transport mechanisms, these two types of nonreciprocal charge
transport show opposite polarities with respect to the magnetic field
direction, which further enable an effective phase modulation of the
angular-dependent magnetoresistance. Besides, the demonstrations of both the
tunable UMR response and two-terminal spin-orbit torque-driven magnetization
switching validate our CoFeB/InSb/CdTe system as a suitable integrated building
block for multifunctional spintronic device design
Dichotomy of Electronic Structure and Superconductivity between Single-Layer and Double-Layer FeSe/SrTiO3 Films
The latest discovery of possible high temperature superconductivity in the
single-layer FeSe film grown on a SrTiO3 substrate, together with the
observation of its unique electronic structure and nodeless superconducting
gap, has generated much attention. Initial work also found that, while the
single-layer FeSe/SrTiO3 film exhibits a clear signature of superconductivity,
the double-layer FeSe/SrTiO3 film shows an insulating behavior. Such a dramatic
difference between the single-layer and double-layer FeSe/SrTiO3 films is
surprising and the underlying origin remains unclear. Here we report our
comparative study between the single-layer and double-layer FeSe/SrTiO3 films
by performing a systematic angle-resolved photoemission study on the samples
annealed in vacuum. We find that, like the single-layer FeSe/SrTiO3 film, the
as-prepared double-layer FeSe/SrTiO3 film is insulating and possibly magnetic,
thus establishing a universal existence of the magnetic phase in the
FeSe/SrTiO3 films. In particular, the double-layer FeSe/SrTiO3 film shows a
quite different doping behavior from the single-layer film in that it is hard
to get doped and remains in the insulating state under an extensive annealing
condition. The difference originates from the much reduced doping efficiency in
the bottom FeSe layer of the double-layer FeSe/SrTiO3 film from the FeSe-SrTiO3
interface. These observations provide key insights in understanding the origin
of superconductivity and the doping mechanism in the FeSe/SrTiO3 films. The
property disparity between the single-layer and double-layer FeSe/SrTiO3 films
may facilitate to fabricate electronic devices by making superconducting and
insulating components on the same substrate under the same condition.Comment: 19 pages, 4 figure
Direct observation of high temperature superconductivity in one-unit-cell FeSe films
Heterostructure based interface engineering has been proved an effective
method for finding new superconducting systems and raising superconductivity
transition temperature (TC). In previous work on one unit-cell (UC) thick FeSe
films on SrTiO3 (STO) substrate, a superconducting-like energy gap as large as
20 meV, was revealed by in situ scanning tunneling microscopy/spectroscopy
(STM/STS). Angle resolved photoemission spectroscopy (ARPES) further revealed a
nearly isotropic gap of above 15 meV, which closes at a temperature of ~ 65 K.
If this transition is indeed the superconducting transition, then the 1-UC FeSe
represents the thinnest high TC superconductor discovered so far. However, up
to date direct transport measurement of the 1-UC FeSe films has not been
reported, mainly because growth of large scale 1-UC FeSe films is challenging
and the 1-UC FeSe films are too thin to survive in atmosphere. In this work, we
successfully prepared 1-UC FeSe films on insulating STO substrates with
non-superconducting FeTe protection layers. By direct transport and magnetic
measurements, we provide definitive evidence for high temperature
superconductivity in the 1-UC FeSe films with an onset TC above 40 K and a
extremely large critical current density JC ~ 1.7*106 A/cm2 at 2 K. Our work
may pave the way to enhancing and tailoring superconductivity by interface
engineering