The Critical Hopping Parameter in O(a) improved Lattice QCD

We calculate the critical value of the hopping parameter, $\kappa_c$, in O(a) improved Lattice QCD, to two loops in perturbation theory. We employ the Sheikholeslami-Wohlert (clover) improved action for Wilson fermions. The quantity which we study is a typical case of a vacuum expectation value resulting in an additive renormalization; as such, it is characterized by a power (linear) divergence in the lattice spacing, and its calculation lies at the limits of applicability of perturbation theory. The dependence of our results on the number of colors $N$, the number of fermionic flavors $N_f$, and the clover parameter $c_{SW}$, is shown explicitly. We compare our results to non perturbative evaluations of $\kappa_c$ coming from Monte Carlo simulations.Comment: 11 pages, 2 EPS figures. The only change with respect to the original version is inclusion of the standard formulae for the gauge fixing and ghost parts of the action. Accepted for publication in Physical Review

Multiple Broken Symmetries in Striped La2−x_{2-x}Bax_{x}CuO4_{4} detected by the Field Symmetric Nernst Effect

We report on a thermoelectric investigation of the stripe and superconducting phases of the cuprate La$_{2-x}$Ba$_{x}$CuO$_{4}$ near the $x=1/8$ doping known to host stable stripes. We use the doping and magnetic field dependence of field-symmetric Nernst effect features to delineate the phenomenology of these phases. Our measurements are consistent with prior reports of time-reversal symmetry breaking signatures above the superconducting $T_{{\rm c}}$, and crucially detect a sharp, robust, field-invariant peak at the stripe charge order temperature, $T_{{\rm {\scriptscriptstyle CO}}}$. Our observations suggest the onset of a nontrivial charge ordered phase at $T_{{\rm {\scriptscriptstyle CO}}}$, and the subsequent presence of spontaneously generated vortices over a broad temperature range before the emergence of bulk superconductivity in LBCO

Effects of doping on thermally excited quasiparticles in the high-TcT_c superconducting state

The physical properties of low energy superconducting quasiparticles in high- $T_c$ superconductors are examined using magnetic penetration depth and specific heat experimental data. We find that the low energy density of states of quasiparticles of La$_{2-x}$Sr$_x$CuO$_4$ scales with $(x-x_c)/T_c$ to the leading order approximation, where $x_c$ is the critical doping concentration below which $T_c=0$. The linear temperature term of the superfluid density is renormalized by quasiparticle interactions and the renormalization factor times the Fermi velocity is found to be doping independent.Comment: 3 pages, 3 figures, minor change to the content, fig1 is reploted, to appear in Phys Rev

Systematic behaviour of the in-plane penetration depth in d-wave cuprates

We report the temperature T and oxygen concentration dependences of the penetration depth of grain-aligned YBa_2Cu_3O_{7-\delta} with \delta= 0.0, 0.3 and 0.43. The values of the in-plane \lambda_{ab}(0) and out-of-plane \lambda_{c}(0) penetration depths, the low temperature linear term in \lambda_{ab}(T), and the ratio \lambda_{c}(0) /\lambda_{ab}(T) were found to increase with increasing $\delta$. The systematic changes of the linear term in \lambda_{ab}(T) with T_c found here and in recent work on HgBa_2Ca_{n-1} Cu_nO_{2n+2+\delta} (n = 1 and 3) are discussed.Comment: 4 pages, 4 figure

An Ultra-High-Vacuum Rotating Sample Manipulator with Cryogenic Cooling

We report a homebuilt ultra-high-vacuum (UHV) rotating sample manipulator with cryogenic cooling. The sample holder is thermally anchored to a built-in cryogenic cold head through flexible copper beryllium strips, permitting continuous sample rotation. A similar contact mechanism is implemented for the electrical wiring to the sample holder for thermometry. The apparatus thus enables continuous sample rotation at regulated cryogenic temperatures in a UHV environment. We discuss the potential applications of this apparatus for cryogenic sputtering.Comment: Cryogenics, ultra-high vacuum, sample manipulato

Penetration depth study of LaOs4_4Sb12_{12}: Multiband s-wave superconductivity

We measured the magnetic penetration depth $\lambda(T)$ in single crystals of LaOs$_{4}$Sb$_{12}$ ($T_c$=0.74 K) down to 85 mK using a tunnel diode oscillator technique. The observed low-temperature exponential dependence indicates a s-wave gap. Fitting the low temperature data to BCS s-wave expression gives the zero temperature gap value $\Delta (0)= (1.34 \pm 0.07) k_B T_c$ which is significantly smaller than the BCS value of 1.76$k_B T_c$. In addition, the normalized superfluid density $\rho(T)$ shows an unusually long suppression near $T_c$, and are best fit by a two-band s-wave model.Comment: 5 pages, 2 figure

Intrinsic Structural Disorder and the Magnetic Ground State in Bulk EuTiO3

The magnetic properties of single-crystal EuTiO3 are suggestive of nanoscale disorder below its cubic-tetragonal phase transition. We demonstrate that electric field cooling acts to restore monocrystallinity, thus confirming that emergent structural disorder is an intrinsic low-temperature property of this material. Using torque magnetometry, we deduce that tetragonal EuTiO3 enters an easy-axis antiferromagnetic phase at 5.6 K, with a first-order transition to an easy-plane ground state below 3 K. Our data is reproduced by a 3D anisotropic Heisenberg spin model.Comment: 5 pages, 4 figure

Long-range electronic reconstruction to a dxz,yzd_{xz,yz}-dominated Fermi surface below the LaAlO3_3/SrTiO3_3 interface

Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear. Examining LaAlO$_3$/SrTiO$_3$ heterostructures at previously unexplored carrier densities $n_{2D}\geq6.9\times10^{14}$ cm$^{-2}$, we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential $d_{xz,yz}$ orbital occupancy extending over at least 100~nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO$_3$ emerge simultaneously at higher $n_{2D}$. We distinguish three areas in doped perovskite heterostructures: narrow ($<20$ nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far ($>120$ nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.Comment: Supplementary material available at Scientific Reports websit

When the Genome Plays Dice: Circumvention of the Spindle Assembly Checkpoint and Near-Random Chromosome Segregation in Multipolar Cancer Cell Mitoses

Background: Normal cell division is coordinated by a bipolar mitotic spindle, ensuring symmetrical segregation of chromosomes. Cancer cells, however, occasionally divide into three or more directions. Such multipolar mitoses have been proposed to generate genetic diversity and thereby contribute to clonal evolution. However, this notion has been little validated experimentally.Principal Findings: Chromosome segregation and DNA content in daughter cells from multipolar mitoses were assessed by multiphoton cross sectioning and fluorescence in situ hybridization in cancer cells and non-neoplastic transformed cells. The DNA distribution resulting from multipolar cell division was found to be highly variable, with frequent nullisomies in the daughter cells. Time-lapse imaging of H2B/GFP-labelled multipolar mitoses revealed that the time from the initiation of metaphase to the beginning of anaphase was prolonged and that the metaphase plates often switched polarity several times before metaphase-anaphase transition. The multipolar metaphase-anaphase transition was accompanied by a normal reduction of cellular cyclin B levels, but typically occurred before completion of the normal separase activity cycle. Centromeric AURKB and MAD2 foci were observed frequently to remain on the centromeres of multipolar ana-telophase chromosomes, indicating that multipolar mitoses were able to circumvent the spindle assembly checkpoint with some sister chromatids remaining unseparated after anaphase. Accordingly, scoring the distribution of individual chromosomes in multipolar daughter nuclei revealed a high frequency of nondisjunction events, resulting in a near-binomial allotment of sister chromatids to the daughter cells.Conclusion: The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells. Spindle multipolarity could thus be a highly efficient generator of genetically diverse minority clones in transformed cell populations