On calculating the Berry curvature of Bloch electrons using the KKR method

We propose and implement a particularly effective method for calculating the Berry curvature arising from adiabatic evolution of Bloch states in wave vector k space. The method exploits a unique feature of the Korringa-Kohn-Rostoker (KKR) approach to solve the Schr\"odinger or Dirac equations. Namely, it is based on the observation that in the KKR method k enters the calculation via the structure constants which depend only on the geometry of the lattice but not the crystal potential. For both the Abelian and non-Abelian Berry curvature we derive an analytic formula whose evaluation does not require any numerical differentiation with respect to k. We present explicit calculations for Al, Cu, Au, and Pt bulk crystals.Comment: 13 pages, 5 figure

Gauge freedom for degenerate Bloch states

In nonmagnetic crystals with inversion symmetry the electronic bands are twofold degenerate. As a consequence, any orthonormalized linear combination of the two corresponding eigenfunctions can represent the electron wave function. A priori it is not obvious which superposition, gauge, should be chosen to calculate a quantity which is not gauge invariant within a certain approximation. Here we consider gauge options appropriate under particular physical conditions

First-principles calculations of the Berry curvature of Bloch states for charge and spin transport of electrons

Recent progress in wave packet dynamics based on the insight of Berry pertaining to adiabatic evolution of quantum systems has led to the need for a new property of a Bloch state, the Berry curvature, to be calculated from first principles. We report here on the response to this challenge by the ab initio community during the past decade. First we give a tutorial introduction of the conceptual developments we mentioned above. Then we describe four methodologies which have been developed for first-principle calculations of the Berry curvature. Finally, to illustrate the significance of the new developments, we report some results of calculations of interesting physical properties such as the anomalous and spin Hall conductivity as well as the anomalous Nernst conductivity and discuss the influence of the Berry curvature on the de Haas–van Alphen oscillation

Lorenz function of Bi2_{2}Te3_{3}/Sb2_{2}Te3_{3} superlattices

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices and their bulk constituents. It was found that already for the bulk materials Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods

Altered tumor formation and evolutionary selection of genetic variants in the human MDM4 oncogene

A large body of evidence strongly suggests that the p53 tumor suppressor pathway is central in reducing cancer frequency in vertebrates. The protein product of the haploinsufficient mouse double minute 2 (MDM2) oncogene binds to and inhibits the p53 protein. Recent studies of human genetic variants in p53 and MDM2 have shown that single nucleotide polymorphisms (SNPs) can affect p53 signaling, confer cancer risk, and suggest that the pathway is under evolutionary selective pressure (1–4). In this report, we analyze the haplotype structure of MDM4, a structural homolog of MDM2, in several different human populations. Unusual patterns of linkage disequilibrium (LD) in the haplotype distribution of MDM4 indicate the presence of candidate SNPs that may also modify the efficacy of the p53 pathway. Association studies in 5 different patient populations reveal that these SNPs in MDM4 confer an increased risk for, or early onset of, human breast and ovarian cancers in Ashkenazi Jewish and European cohorts, respectively. This report not only implicates MDM4 as a key regulator of tumorigenesis in the human breast and ovary, but also exploits for the first time evolutionary driven linkage disequilibrium as a means to select SNPs of p53 pathway genes that might be clinically relevant

Altered tumor formation and evolutionary selection of genetic variants in the human MDM4 oncogene

A large body of evidence strongly suggests that the p53 tumor suppressor pathway is central in reducing cancer frequency in vertebrates. The protein product of the haploinsufficient mouse double minute 2 (MDM2) oncogene binds to and inhibits the p53 protein. Recent studies of human genetic variants in p53 and MDM2 have shown that single nucleotide polymorphisms (SNPs) can affect p53 signaling, confer cancer risk, and suggest that the pathway is under evolutionary selective pressure (1–4). In this report, we analyze the haplotype structure of MDM4, a structural homolog of MDM2, in several different human populations. Unusual patterns of linkage disequilibrium (LD) in the haplotype distribution of MDM4 indicate the presence of candidate SNPs that may also modify the efficacy of the p53 pathway. Association studies in 5 different patient populations reveal that these SNPs in MDM4 confer an increased risk for, or early onset of, human breast and ovarian cancers in Ashkenazi Jewish and European cohorts, respectively. This report not only implicates MDM4 as a key regulator of tumorigenesis in the human breast and ovary, but also exploits for the first time evolutionary driven linkage disequilibrium as a means to select SNPs of p53 pathway genes that might be clinically relevant

Giant spin Hall effect in graphene grown by chemical vapour deposition

Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels. Here, we show that graphene grown by chemical vapour deposition on copper is equally promising for spintronics applications. In contrast to natural graphene, our experiments demonstrate that chemically synthesized graphene has a strong spin-orbit coupling as high as 20 meV giving rise to a giant spin Hall effect. The exceptionally large spin Hall angle ∼0.2 provides an important step towards graphene-based spintronics devices within existing complementary metal-oxide-semiconductor technology. Our microscopic model shows that unavoidable residual copper adatom clusters act as local spin-orbit scatterers and, in the resonant scattering limit, induce transverse spin currents with enhanced skew-scattering contribution. Our findings are confirmed independently by introducing metallic adatoms-copper, silver and gold on exfoliated graphene samples

Distinguishing dxz+idyzd_{xz}+id_{yz} and dx2−y2d_{x2−y2} pairing in Sr2RuO4Sr_2RuO_4 by high magnetic field H-T phase diagrams

Employing a realistic tight-binding model describing the Fermi surface in the normal state of $Sr_2RuO_4$ we map out magnetic field versus temperature phase diagrams for $d_{x2−y2}(B_{1g})$ and $d_{xz}+id_{yz}(E_g)$ pairing types. Both produce (i) a similar Knight shift suppression of ∼80% and (ii) a bicritical point at $T=0.88K$ separating low field second order phase transitions from high field Pauli limiting first order transitions. We find, however, strikingly different phase behaviour within the high field Pauli limiting region. For $d_{x2−y2}$ pairing symmetry an additional lower critical line of first order transitions is found (terminating in a critical point at $T=0.09−0.22K$ depending on the choice of Hubbard U parameters) while for $d_{xz}+id_{yz}$ no such additional high field phase transitions are found for any choice of Hubbard U. In conjunction with our earlier finding [{\it Physical Review B} {\bf 102} (23), 235203] for $p$-wave helical pairing of a still different high field phase structure (a lower critical field line meeting the upper critical field line exactly at the bicritical point), we suggest high field Pauli limiting phase structure as a possible route to distinguish pairing symmetries in this material

Superconducting double transition and substantial Knight shift in Sr2RuO₄

Recent nuclear magnetic resonance experiments measuring the Knight shift in Sr2RuO4 have challenged the widely accepted picture of chiral pairing in this superconductor. Here we study the implications of helical pairing on the superconducting state while comparing our results with the available experimental data on the upper critical field and Knight shift. We solve the Bogoliubov–de Gennes equation employing a realistic three-dimensional tight-binding model that captures the experimental Fermi surface very well. In agreement with experiments we find a Pauli limiting to the upper critical field and, at low temperatures and high fields, a second superconducting transition. These transitions, which form a superconducting subphase in the H-T phase diagram are first-order in nature and merge into a single second-order transition at a bicritical point (T∗,H∗),for which we find (0.8 K, 2.4 T) with experiment reporting (0.8 K,∼1.2 T) [Phys. Rev. B93, 184513 (2016)]. Furthermore, we find a substantial drop in the Knight shift in agreement with recent experiments