Topology and Interactions in a Frustrated Slab: Tuning from Weyl Semimetals to C > 1 Fractional Chern Insulators

We show that, quite generically, a [111] slab of spin-orbit coupled pyrochlore lattice exhibits surface states whose constant energy curves take the shape of Fermi arcs, localized to different surfaces depending on their quasimomentum. Remarkably, these persist independently of the existence of Weyl points in the bulk. Considering interacting electrons in slabs of finite thickness, we find a plethora of known fractional Chern insulating phases, to which we add the discovery of a new higher Chern number state which is likely a generalization of the Moore-Read fermionic fractional quantum Hall state. By contrast, in the three-dimensional limit, we argue for the absence of gapped states of the flat surface band due to a topologically protected coupling of the surface to gapless states in the bulk. We comment on generalizations as well as experimental perspectives in thin slabs of pyrochlore iridates.Comment: Published. 6+4 page

Effects of Fermi surface and superconducting gap structure in the field-rotational experiments: A possible explanation of the cusp-like singularity in YNi2_2B2_2C

We have studied the field-orientational dependence of zero-energy density of states (FODOS) for a series of systems with different Fermi surface and superconducting gap structures. Instead of phenomenological Doppler-shift method, we use an approximate analytical solution of Eilenberger equation together with self-consistent determination of order parameter and a variational treatment of vortex lattice. First, we compare zero-energy density of states (ZEDOS) when a magnetic field is applied in the nodal direction ($\nu_{node}(0)$) and in the antinodal direction ($\nu_{anti}(0)$), by taking account of the field-angle dependence of order parameter. As a result, we found that there exists a crossover magnetic field $H^*$ so that $\nu_{anti}(0) > \nu_{node}(0)$ for $H \nu_{anti}(0)$ for $H > H^*$, consistent with our previous analyses. Next, we showed that $H^*$ and the shape of FODOS are determined by contribution from the small part of Fermi surface where Fermi velocity is parallel to field-rotational plane. In particular, we found that $H^*$ is lowered and FODOS has broader minima, when a superconducting gap has point nodes, in contrast to the result of the Doppler-shift method. We also studied the effects of in-plane anisotropy of Fermi surface. We found that in-plane anisotropy of quasi-two dimensional Fermi surface sometimes becomes larger than the effects of Doppler-shift and can destroy the Doppler-shift predominant region. In particular, this tendency is strong in a multi-band system where superconducting coherence lengths are isotropic. Finally, we addressed the problem of cusp-like singularity in YNi$_2$B$_2$C and present a possible explanation of this phenomenon.Comment: 13pages, 23figure

Charge density wave instabilities of type-II Weyl semimetals in a strong magnetic field

Shortly after the discovery of Weyl semimetals, properties related to the topology of their bulk band structure have been observed, e.g., signatures of the chiral anomaly and Fermi arc surface states. These essentially single particle phenomena are well understood, but whether interesting many-body effects due to interactions arise in Weyl systems remains much less explored. Here, we investigate the effect of interactions in a microscopic model of a type-II Weyl semimetal in a strong magnetic field. We identify a charge density wave (CDW) instability even for weak interactions stemming from the emergent nesting properties of the type-II Weyl Landau level dispersion. We map out the dependence of this CDW on magnetic field strength. Remarkably, as a function of decreasing temperature, a cascade of CDW transitions emerges and we predict characteristic signatures for experiments.This work was supported by Emmy Noether program (BE 5233/1-1) of the Deutsche Forschungs- gemeinschaft, the Swedish Research Council (VR), and the Wallenberg Academy Fellows program of the Knut and Alice Wallenberg Foundation. J.K. is supported by the Marie Curie Programme under EC Grant Agreement No. 703697

Tuning from Weyl Semimetals to C>1 Fractional Chern Insulators

We show that, quite generically, a [111] slab of spin-orbit coupled pyrochlore lattice exhibits surface states whose constant energy curves take the shape of Fermi arcs, localized to different surfaces depending on their quasimomentum. Remarkably, these persist independently of the existence of Weyl points in the bulk. Considering interacting electrons in slabs of finite thickness, we find a plethora of known fractional Chern insulating phases, to which we add the discovery of a new higher Chern number state which is likely a generalization of the Moore-Read fermionic fractional quantum Hall state. By contrast, in the three-dimensional limit, we argue for the absence of gapped states of the flat surface band due to a topologically protected coupling of the surface to gapless states in the bulk. We comment on generalizations as well as experimental perspectives in thin slabs of pyrochlore iridates

‘A Slow Build-Up of a History of Kindness’: Exploring the Potential of Community-Led Housing in Alleviating Loneliness

This article explores the potential of community-led housing (CLH) in combatting loneliness, and represents a mixed-methods research project carried out from just before the beginning of the pandemic, through 2020. Methods comprised a nationwide quantitative online survey of members of CLH groups (N = 221 respondents from England and Wales), followed by five case studies of communities representing a range of different CLH models. This qualitative element comprised participant observation, and semi-structured interviews at each group. The article also considers data from a smaller research project carried out by the same team in July 2020, that aimed to capture the experience of the pandemic for CLH groups, and comprising an online questionnaire followed by 18 semi-structured interviews. We conclude that members of CLH projects are measurably less lonely than those with comparable levels of social connection in wider society, and that such benefits are achieved through combinations of multiple different elements that include physical design, social design and through social processes. Notably, not all aspects of communities that contribute positively are a result of explicit intentionality, albeit the concept is considered key to at least one of the models

The effects inhibiting the proliferation of cancer cells by far-infrared radiation (FIR) are controlled by the basal expression level of heat shock protein (HSP) 70A

We developed a tissue culture incubator that can continuously irradiate cells with far-infrared radiation (FIR) of wavelengths between 4 and 20 μm with a peak of 7–12 μm, and found that FIR caused different inhibiting effects to five human cancer cell lines, namely A431 (vulva), HSC3 (tongue), Sa3 (gingiva), A549 (lung), and MCF7 (breast). Then, in order to make clear the control system for the effect of FIR, the gene expression concerned to the inhibition effect by FIR were analyzed. In consequence, basal expression level of HSP70A mRNA was higher in A431 and MCF7 cells than in the FIR-sensitive HSC3, Sa3, and A549 cells. Also, the over expression of HSP70 inhibited FIR-induced growth arrest in HSC3 cells, and an HSP70 siRNA inhibited the proliferation of A431 cells by irradiation with FIR. These results indicate that the effect of a body temperature range of FIR suppressing the proliferation of some cancer cells is controlled by the basal expression level of heat shock protein (HSP) 70A. This finding suggested that FIR should be very effective medical treatment for some cancer cells which have a low level of HSP70. Still more, if the level of HSP70 in any cancer of a patient was measured, the effect of medical treatment by FIR can be foreseen for the cancer

Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the 6^{6}He + 209^{209}Bi System at Near-Coulomb-Barrier Energies

Based on an approach recently proposed by us, simultaneous $\chi^{2}$-analyses are performed for elastic scattering, direct reaction (DR) and fusion cross sections data for the $^{6}$He+$^{209}$Bi system at near-Coulomb-barrier energies to determine the parameters of the polarization potential consisting of DR and fusion parts. We show that the data are well reproduced by the resultant potential, which also satisfies the proper dispersion relation. A discussion is given of the nature of the threshold anomaly seen in the potential

Phenomenological local potentials for \pi^- + ^{12}C scattering from 120 to 766 MeV

Pion-nucleus scattering cross sections are calculated by solving a Schr\"{o}dinger equation reduced from the Klein-Gordon equation. Local potentials are assumed, and phenomenological potential parameters are searched energy-dependently for $\pi^{-} + ^{12}$C system so as to reproduce not only elastic differential cross sections but also total elastic, reaction and total cross sections at 13 pion incident energies from 120 to 766 MeV. The real and imaginary parts of the local potentials thus obtained are shown to satisfy the dispersion relation. The imaginary part of the potentials as a function of the pion energy is found to peak near the $\Delta$(1232)-resonance energy. The strong absorption radius of the pion projectile with incident energies near the $\Delta$-resonance region is found to be about $1.6 A^{1/3}$ fm, which is consistent with previous studies of the region where the decay of the $\Delta$'s takes place in nuclei. The phenomenological local potentials are then compared with the local potentials exactly phase-shift equivalent to Kisslinger potentials for pion energies near the $\Delta$-resonance