37 research outputs found
Systematics of molecular self-assembled networks at topological insulators surfaces
The success of topological insulators (TI) in creating devices with unique
functionalities is directly connected to the ability of coupling their helical
spin states to well defined perturbations. However, up to now, TI-based
heterostructures always resulted in very disordered interfaces, characterized
by strong mesoscopic fluctuations of the chemical potential which make the
spin-momentum locking ill-defined over length scales of few nanometers or even
completely destroy topological states. These limitations call for the ability
to control topological interfaces with atomic precision. Here, we demonstrate
that molecular self-assembly processes driven by inherent interactions among
the constituents offer the opportunity to create well-defined networks at TIs
surfaces. Even more remarkably, we show that the symmetry of the overlayer can
be finely controlled by appropriate chemical modifications. By analyzing the
influence of the molecules on the TI electronic properties, we rationalize our
results in terms of the charge redistribution taking place at the interface.
Overall, our approach offers a precise and fast way to produce tailor-made
nanoscale surface landscapes. In particular, our findings make organic
materials ideal TIs counterparts, since they offer the possibility to
chemically tune both electronic and magnetic properties within the same family
of molecules, thereby bringing us a significant step closer towards an
application of this fascinating class of materials.Comment: Nano Letters (2015
Impurity screening and stability of Fermi arcs against Coulomband magnetic scattering in a Weyl monopnictide
We present a quasiparticle interference study of clean and Mn surface-doped
TaAs, a prototypical Weyl semimetal, to test the screening properties as well
as the stability of Fermi arcs against Coulomb and magnetic scattering.
Contrary to topological insulators, the impurities are effectively screened in
Weyl semimetals. The adatoms significantly enhance the strength of the signal
such that theoretical predictions on the potential impact of Fermi arcs can be
unambiguously scrutinized. Our analysis reveals the existence of three
extremely short, previously unknown scattering vectors. Comparison with theory
traces them back to scattering events between large parallel segments of
spin-split trivial states, strongly limiting their coherence. In sharp contrast
to previous work [R. Batabyal et al., Sci. Adv. 2, e1600709 (2016)], where
similar but weaker subtle modulations were interpreted as evidence of
quasiparticle interference originating from Femi arcs, we can safely exclude
this being the case. Overall, our results indicate that intra- as well as
inter-Fermi arc scattering are strongly suppressed and may explain why-in spite
of their complex multiband structure-transport measurements show signatures of
topological states in Weyl monopnictides
Non-Majorana modes in diluted spin chains proximitized to a superconductor
Spin chains proximitized with superconducting condensates have emerged as one
of the most promising platforms for the realization of Majorana modes. Here, we
craft diluted spin chains atom-by-atom following seminal theoretical proposal
suggesting indirect coupling mechanisms as a viable route to trigger
topological superconductivity. Starting from single adatoms hosting deep Shiba
states, we use the highly anisotropic Fermi surface of the substrate to create
spin chains characterized by different magnetic configurations along distinct
crystallographic directions. By scrutinizing a large set of parameters we
reveal the ubiquitous emergence of boundary modes. Although mimicking
signatures of Majorana modes, the end modes are identified as topologically
trivial Shiba states. Our work demonstrates that zero-energy modes in spin
chains proximitized to superconductors are not necessarily a link to Majorana
modes while simultaneously identifying new experimental platforms, driving
mechanisms, and test protocols for the determination of topologically
non-trivial superconducting phases
Microscopic manipulation of ferroelectric domains in SnSe monolayers at room temperature
Two-dimensional (2D) van der Waals ferroelectrics provide an unprecedented
architectural freedom for the creation of artificial multiferroics and
non-volatile electronic devices based on vertical and co-planar heterojunctions
of 2D ferroic materials. Nevertheless, controlled microscopic manipulation of
ferroelectric domains is still rare in monolayer-thick 2D ferroelectrics with
in-plane polarization. Here we report the discovery of robust ferroelectricity
with a critical temperature close to 400 K in SnSe monolayer plates grown on
graphene, and the demonstration of controlled room temperature ferroelectric
domain manipulation by applying appropriate bias voltage pulses to the tip of a
scanning tunneling microscope (STM). This study shows that STM is a powerful
tool for detecting and manipulating the microscopic domain structures in 2D
ferroelectric monolayers, which is difficult for conventional approaches such
as piezoresponse force microscopy, thus facilitating the hunt for other 2D
ferroelectric monolayers with in-plane polarization with important
technological applications
Direct observation of many-body charge density oscillations in a two-dimensional electron gas
Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an ‘anomalous’ energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale