73 research outputs found
Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy
Pb1-xSnxSe hosts 3D massive Dirac fermions across the entire composition
range for which the crystal structure is cubic. In this work, we present a
comprehensive experimental mapping of the 3D band structure parameters of
Pb1-xSnxSe as a function of composition and temperature. We cover a parameter
space spanning the band inversion that yields its topological crystalline
insulator phase. A non-closure of the energy gap is evidenced in the vicinity
of this phase transition. Using magnetooptical Landau level spectroscopy, we
determine the energy gap, Dirac velocity, anisotropy factor and topological
character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2
(111). Our results are evidence that Pb1-xSnxSe is a model system to study
topological phases and the nature of the phase transition.Comment: Submitte
Miniband engineering and topological phase transitions in topological - normal insulator superlattices
Periodic stacking of topologically trivial and non-trivial layers with
opposite symmetry of the valence and conduction bands induces topological
interface states that, in the strong coupling limit, hybridize both across the
topological and normal insulator layers. Using band structure engineering, such
superlattices can be effectively realized using the IV-VI lead tin
chalcogenides. This leads to emergent minibands with a tunable topology as
demonstrated both by theory and experiments. The topological minibands are
proven by magneto-optical spectroscopy, revealing Landau level transitions both
at the center and edges of the artificial superlattice mini Brillouin zone.
Their topological character is identified by the topological phase transitions
within the minibands observed as a function of temperature. The critical
temperature of this transition as well as the miniband gap and miniband width
can be precisely controlled by the layer thicknesses and compositions. This
witnesses the generation of a new fully tunable quasi-3D topological state that
provides a template for realization of magnetic Weyl semimetals and other
strongly interacting topological phases.Comment: 21 pages, 8 figure
Tunable Dirac interface states in topological superlattices
Relativistic Dirac fermions are ubiquitous in condensed matter physics. Their
mass is proportional to the material energy gap and the ability to control and
tune the mass has become an essential tool to engineer quantum phenomena that
mimic high energy particles and provide novel device functionalities. In
topological insulator thin films, new states of matter can be generated by
hybridizing the massless Dirac states that occur at material surfaces. In this
work, we experimentally and theoretically introduce a platform where this
hybridization can be continuously tuned: the Pb1-xSnxSe topological
superlattice. In this system, topological Dirac states occur at the interfaces
between a topological crystalline insulator Pb1-xSnxSe and a trivial insulator,
realized in the form of topological quantum wells (TQW) epitaxially stacked on
top of each other. Using magnetooptical transmission spectroscopy on high
quality MBE grown Pb1-xSnxSe superlattices, we show that the penetration depth
of the TQW interface states and therefore their Dirac mass is continuously
tunable with temperature. This presents a new pathway to engineer the Dirac
mass of topological systems and paves the way towards the realization of
emergent quantum states of matter using Pb1-xSnxSe topological superlattices.Comment: See journal for supplementary material acces
Observation of Weyl and Dirac fermions at smooth topological Volkov-Pankratov heterojunctions
Weyl and Dirac relativistic fermions are ubiquitous in topological matter.
Their relativistic character enables high energy physics phenomena like the
chiral anomaly to occur in solid state, which allows to experimentally probe
and explore fundamental relativistic theories. Here we show that on smooth
interfaces between a trivial and a topological material, massless Weyl and
massive Dirac fermions intrinsically coexist. The emergence of the latter,
known as Volkov-Pankratov states, is directly revealed by magneto-optical
spectroscopy, evidencing that their energy spectrum is perfectly controlled by
the smoothness of topological interface. Simultaneously, we reveal the optical
absorption of the zero-energy chiral Weyl state, whose wavefunction is
drastically transformed when the topological interface is smooth. Artificial
engineering of the topology profile thus provides a novel textbook system to
explore the rich relativistic energy spectra in condensed matter
heterostructures.Comment: 21 pages 10 figure
Avoided level crossing at the magnetic field induced topological phase transition due to spin-orbital mixing
In 3D topological insulators, an effective closure of the bulk energy gap
with increasing magnetic field expected at a critical point can yield a band
crossing at a gapless Dirac node. Using high-field magnetooptical Landau level
spectroscopy on the topological crystalline insulator Pb1-xSnxSe, we
demonstrate that such a gap closure does not occur, and an avoided crossing is
observed as the magnetic field is swept through the critical field. We
attribute this anticrossing to orbital parity and spin mixing of the N=0
levels. Concurrently, we observe no gap closure at the topological phase
transition versus temperature suggesting that the anticrossing is a generic
property of topological phase transitions.Comment: submitte
Liquid Tissue: Proteomic Profiling of Formalin-Fixed Tissues
Identification and quantitation of candidate biomarker proteins in large numbers of individual tissues is required to validate specific proteins, or panels of proteins, for clinical use as diagnostic, prognostic, toxicological, or therapeutic markers. Mass spectrometry (MS) provides an exciting analytical methodology for this purpose. Liquid Tissue MS protein preparation allows researchers to utilize the vast, already existing, collections offormalin-fixed paraffin-embedded (FFPE) tissues for the procurement of peptides and the analysis across a variety of MS platforms
PAGE-1, an X chromosome-linked GAGE-like gene that is expressed in normal and neoplastic prostate, testis, and uterus
Spatio-temporal assessment of illicit drug use at large scale: evidence from 7 years of international wastewater monitoring
Spatio-temporal assessment of illicit drug use at large scale: evidence from 7 years of international wastewater monitoring
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