Intrinsic emergence of Majorana modes in Luttinger j=3/2 systems

We analyze theoretically two different setups for s-wave superconductivity (SC) proximitized $j=3/2$ particles in Luttinger materials that are able to host Majorana bound states (MBSs). First, we consider a one-dimensional SC wire with intrinsic bulk inversion asymmetry (BIA). In contrast to wires, modeled by a quadratic dispersion with Rashba spin-orbit coupling, there are two topological phase transitions in our systems at finite magnetic fields. Second, we analyze a two-dimensional Josephson junction on the Luttinger model finding a topological region even in the absence of BIA and Rashba spin-orbit couplings. This originates from the hybridization of the light and heavy hole bands of the $j=3/2$ states in combination with the SC pairing. As a consequence, both systems can be driven into a topological phase hosting MBSs. Hence, we predict that MBSs form in any SC proximitized Josephson junction on 2D Luttinger materials by the application of magnetic field alone. This opens a new avenue for the search of topological SC.Comment: 7 pages, 4 figure

Interplay of Dirac nodes and Volkov-Pankratov surface states in compressively strained HgTe

Preceded by the discovery of topological insulators, Dirac and Weyl semimetals have become a pivotal direction of research in contemporary condensed matter physics. While easily accessible from a theoretical viewpoint, these topological semimetals pose a serious challenge in terms of experimental synthesis and analysis to allow for their unambiguous identification. In this work, we report on detailed transport experiments on compressively strained HgTe. Due to the superior sample quality in comparison to other topological semimetallic materials, this enables us to resolve the interplay of topological surface states and semimetallic bulk states to an unprecedented degree of precision and complexity. As our gate design allows us to precisely tune the Fermi level at the Weyl and Dirac points, we identify a magnetotransport regime dominated by Weyl/Dirac bulk state conduction for small carrier densities and by topological surface state conduction for larger carrier densities. As such, similar to topological insulators, HgTe provides the archetypical reference for the experimental investigation of topological semimetals.Comment: 8 pages, 7 figures, accepted in PRX, added kp calculation and supplementar

Counterpropagating topological and quantum Hall edge channels

The survival of the quantum spin Hall edge channels in presence of an external magnetic field has been a subject of experimental and theoretical research. The inversion of Landau levels that accommodates the quantum spin Hall effect is destroyed at a critical magnetic field, and a trivial insulating gap appears in the spectrum for stronger fields. In this work, we report the absence of this transport gap in disordered two dimensional topological insulators in perpendicular magnetic fields of up to 16 T. Instead, we observe that a topological edge channel (from band inversion) coexists with a counterpropagating quantum Hall edge channel for magnetic fields at which the transition to the insulating regime is expected. For larger fields, we observe only the quantum Hall edge channel with transverse resistance close to $h/e^2$. By tuning the disorder using different fabrication processes, we find evidence that this unexpected $\nu=1$ plateau originates from extended quantum Hall edge channels along a continuous network of charge puddles at the edges of the device.Comment: 8+3 pages, 5+2 figure

Monocyte subtype expression patterns in septic patients with diabetes are distinct from patterns observed in obese patients

BackgroundSepsis causes a high rate of mortality and long-term morbidity, associated with an imbalance of innate immunity against infections and inflammation. Obesity and diabetes increase the risk for disease severity. Monocyte dysfunction plays a major role and justify further investigations.ObjectiveTo investigate the distribution and inflammatory phenotypes in circulating monocyte subsets in patients manifesting with sepsis including septic shock with and without obesity and diabetes.MethodsA total of 235 blood samples were tested from critically ill adult patients registered at the intensive care unit (ICU). The cohorts were divided into non-diabetic groups with or without obesity and diabetic groups with or without obesity, suffering from sepsis or septic shock. We determined frequencies of total monocytes and of monocyte subsets in the circulation and density expression levels of functional markers, including CD14, CD16, HLA-DR, CD33, CD163, CD206, and arginase-1 by flow cytometric analysis.ResultsWhen progressing to septic shock in non-diabetic and diabetic patients, the percentages of total monocytes among the leukocyte population and of CD33+ and CD14+ monocytes among the monocyte population were consistently down-regulated compared to non-sepsis in non-diabetic and diabetic patients, respectively. Non-diabetic sepsis patients further presented with decreased CD33 and up-regulated CD163 expression density, which was absent in diabetic patients. We subsequently addressed obesity-related changes of monocytes in non-diabetic and diabetic septic patients. Obese septic patients with diabetes were unique in displaying increased monocytic CD16 and CD163 expression. However, obese septic patients without diabetes solely presented with lower amounts of non-classical monocytes. Body mass index (BMI) dependent changes were restricted to diabetic septic patients, with a significantly higher diminution of the classical monocyte subset and concomitantly increased CD16 expression densities.ConclusionDistribution and phenotypes of monocyte subsets were differentially modulated in critically ill patients with and without metabolic disease when progressing to sepsis or septic shock. Only diabetic septic patients displayed decline of classical monocytes and increase of CD16 expression densities. Therefore, diabetes but not obesity appears to promote the inflammatory phenotype of circulating monocytes in critically ill patients

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Topologische Phasen in Luttinger Materialien

The hunt for topological materials is one of the main topics of recent research in condensed matter physics. We analyze the 4-band Luttinger model, which considers the total angular momentum $j = 3/2$ hole states of many semiconductors. Our analysis shows that this model hosts a wide array of topological phases and allows analytical calculations of the related topological surface states. The existence of these surface states is highly desired due to their strong protection against perturbations. In the first part of the thesis, we predict the existence of either one or two two-dimensional (2D) surface states of topological origin in the three-dimensional (3D) quadratic-node semimetal phase of the Luttinger model, called the Luttinger semimetal phase. We associate the origin of these states with the inverted order of s and p-orbital states in the band structure and approximate chiral symmetry around the node. Hence, our findings are essential for many materials, including HgTe, α-Sn, and iridate compounds. Such materials are often modified with strain engineering by growing the crystal on a substrate with a different lattice constant, which adds a deformation potential to the electrons. While tensile strain is often used to drive such materials into a gapped topological insulator regime, we apply compressive strain to induce a topological semimetal regime. Here, we differentiate between Dirac and Weyl semimetals based on inversion and time-reversal symmetry being simultaneously present or not. One major part of this thesis is the theoretical study of the evolution of the Luttinger semimetal surface states in these topological semimetal phases. The relative strength of the compressive strain and typical bulk inversion asymmetry (BIA) terms allow the definition of a symmetry hierarchy in the system. The cubic symmetric $O_h$ Luttinger model is the highest symmetry low-energy parent model. Since the BIA terms in the Weyl semimetal phase are small in most materials, we find a narrow energy and momentum range around the Weyl points where the surface states form Fermi arcs between two Weyl nodes with opposite chirality. Consequently, we see 2D momentum planes between the Weyl points, which can be considered as effective 2D Chern insulators with chiral edge states connecting the valence and conduction band in the bulk gap. Exceeding the range of the BIA terms, the compressive strain becomes dominating, and the system behaves like a Dirac semimetal with two doubly degenerate linear Dirac nodes in the band structure. For energies larger than the compressive strain strength, the quadratic terms in the Luttinger model dominate and surface band structure is indistinguishable from an unperturbed Luttinger semimetal. To conclude this symmetry hierarchy, we analyze the limit of the Luttinger model when the remote $j = 1/2$ electron states show a considerable hybridization with the $j = 3/2$ hole states around the Fermi level. Here, the Luttinger model is not valid anymore and one needs to consider more complicated models, like the 6-band Kane Hamiltonian. In the second part of this thesis, we analyze theoretically two different setups for s-wave superconductivity proximitized $j = 3/2$ particles in Luttinger materials under a magnetic field. First, we explore a one-dimensional wire setup, where the intrinsic BIA of inversion asymmetric crystals opens a topological gap in the bulk states. In contrast to wires, modeled by a quadratic dispersion with Rashba or Dresselhaus spin-orbit coupling, we find two topological phase transitions due to the different effects of magnetic fields to $|j_z| = 3/2$ heavy-hole (HH) and $|j_z| = 1/2$ light-hole (LH) states. Second, we discuss a two-dimensional Josephson junction setup, where we find Andreev-bound states inside the superconducting gap. Here, the intrinsic spin-orbit coupling of the Luttinger model is sufficient to open a topological gap even in the presence of inversion symmetry. This originates from the hybridization of the light and heavy-hole bands in combination with the superconducting pairing. Consequently, both setups can form Majorana-bound states at the boundaries of the system. The existence of these states are highly relevant in the scientific community due to their nonabelian braiding statistics and stability against decoherence, making them a prime candidate for the realization of topological quantum computation. Majorana-bound states form at zero energy and are protected by the topological gap. We predict that our findings of the topological superconductor phase of the Luttinger model are valid for both semimetal and metal phases. Hence, our study is additionally relevant for metallic systems, like p-doped GaAs. This opens a new avenue for the search for topological superconductivity.Die Suche nach topologischen Materialien ist ein beherrschendes Thema der aktuellen Forschung im Bereich der kondensierten Materie. In dieser Arbeit wird das 4-Band Luttinger-Modell untersucht, welches die $j = 3/2$ Zustände vieler Halbleiter beschreibt. Dieses Modell beschreibt eine Vielzahl von topologischen Zuständen und ermöglicht die analytische Betrachtung der zugehörigen topologischen Oberflächenzustände. Die Existenz dieser Oberflächenzustände ist überaus erstrebenswert, da sie auf Grund ihrer topologischen Natur besonders gegen kleine Störungen geschützt sind. Im ersten Teil dieser Arbeit wird die Existenz von einem oder zwei Oberflächenzuständen in Abhängigkeit des Verhältnisses der effektive Massen in der quadratischen Luttinger-Halbmetallphase vorhergesagt. Diese Zustände mit topologischen Ursprung können mit den invertierten s- und p-Orbitalen aus der Bandstruktur und der angenäherten chiralen Symmetrie des Kreuzungspunktes in Verbindung gebracht werden. Daher sind die Resultate dieser Arbeit relevant für eine Vielzahl an Materialien, wie HgTe, α-Sn und Iridium-Verbindungen. Diese Materialien werden häufig mit Hilfe von Deformation bearbeitet, indem der Kristall auf einem Substrat mit unterschiedlicher Gitterkonstanten gewachsen wird. Dies führt zu Deformationspotentialen, welche auf die Elektronen wirken. Während Dehnungen häufig verwendet werden, um einen topologisch isolierenden Zustand mit einer Bandlücke zu erzeugen, wird in dieser Arbeit Kompression betrachtet, um eine topologische Halbmetallphase herbeizuführen. Hierbei unterscheidet man zwischen Dirac- und Weyl-Halbmetallen, in Abhängigkeit von der gleichzeitigen Präsenz von Inversions- und Zeitumkehrsymmetrie. Ein Hauptteil dieser Arbeit ist die theoretische Untersuchung der Oberflächenzustände in Luttinger-Halbmetallen beim Übergang in diese topologischen Halbmetallphasen. Die relative Stärke des Kompressionspotentials im Vergleich zu Termen, welche mithilfe gängiger Inversionssymmetrie berechnet wurden, erlaubt die Definition einer Symmetriehierarche für das System. Hierbei bildet das Luttinger-Modell mit kubischer Symmetrie das Ursprungsmodell für kleine Energien mit der höchsten Symmetrie. Da die Inversionssymmetrie brechenden Terme in der Weyl-Halbmetallphase schwach in vielen Materialien sind, lässt sich ein kleiner Energie und Impulsbereich finden, in dem die Oberflächenzustände Fermi-Bögen zwischen zwei Weyl- Punkten mit unterschiedlicher Chiralität ausbilden. Als Konsequenz existieren zweidimensionale (2D) Impulsebenen zwischen den Weyl-Punkten, die als effektive 2D Chern-Isolatoren mit chiralen Randzuständen in der Bandlücke angesehen werden können. Außerhalb des Bereichs der Inversion brechenden Terme dominieren die Kompressionspotentiale und das System ist ein effektives Dirac-Halbmetall mit zwei doppelt entarteten Dirac-Punkten in der Bandstruktur. Im Energiebereich außerhalb der Kompressionsstärke dominieren die quadratischen Terme des Luttinger-Modells und das Energiespektrum lässt sich nicht von einem ungestörten Luttinger- Halbmetall unterscheiden. Um die Symmetriehierarchie abzuschließen, werden die Grenzen des Luttinger-Modells untersucht, bei dem die entfernten $j = 1/2$ Zustände einen signifikanten Effekt auf die $j = 3/2$ Zustände aufweisen. Hier verliert das Luttinger-Modell seine Gültigkeit und kompliziertere Modelle, wie das 6-Band Kane-Modell, müssen in Betracht gezogen werden. Im zweiten Teil dieser Arbeit werden theoretisch zwei verschiedene Systeme für s-wellenartige, supraleitende $j = 3/2$ Teilchen in Luttinger-Materialien unter dem Einfluss eines Magnetfeldes analysiert. Zuerst wird der Fokus auf eine eindimensionale Kette gelegt, bei der die intrinsische Spin-Orbit-Kopplung von inversionsassymetrischen Kristallen eine topologische Bandlücke öffnet. Im Gegensatz zu Atomketten, die mit einer herkömmlichen quadratischen Dispersion mit Rashba- oder Dresselhaus-Spin-Orbit Kopplung modelliert werden, bilden sich zwei topologische Phasenübergänge wegen des unterschiedlichen Effekts des Magnetfeldes auf die $|j_z| = 3/2$ und $|j_z| = 1/2$ Zustände. Darüber hinaus wird ein 2D Josephson-Kontakt mit lokalisierten Andreev-Zuständen innerhalb der supraleitenden Bandlücke diskutiert. Hierbei ist die intrinsische Spin-Orbit-Kopplung des Luttinger-Modells ausreichend, um eine topologische Bandlücke zu öffnen, selbst mit intakter Inversionssymmetrie. Dies resultiert aus der Hybridisierung der $|j_z| = 1/2$ und $|j_z| = 3/2$ Zustände in Kombination mit der supraleitenden Kopplung. Konsequenterweise können beide Systeme Majorana-Randzustände bilden. Diese sind höchst relevant für die wissenschaftliche Forschung wegen ihrer nichtabelschen Austauschstatistik und ihrer Stabilität gegen Dekoherenz, was sie prädestiniert für die Realisierung topologischer Quantencomputer macht. Diese Majorana-Randzustände haben eine flache Energiedispersion und werden von der topologischen Bandlücke geschützt. Interessanterweise lassen sich die Resultate dieser Arbeit für die topologisch supraleitende Phase im Luttinger-Modell sowohl auf das Halbmetall- als auch auf das Metallregime anwenden. Dies induziert eine Relevanz für metallische Systeme, wie zum Beispiel p-dotiertem GaAs. Hierduch werden neue Möglichkeiten für die Realisierung topologischer Supraleitung eröffnet

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts.The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that -80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAFPeer reviewe

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number