Phase transition in the 3 Kelvin phase in the eutectic Sr2RuO4-Ru

The inhomogeneous 3-Kelvin (3K) phase of the eutectic Sr2RuO4 with Ru inclusions nucleates superconductivity at the interface between Ru and Sr2RuO4. The structure of the interface state and its physical properties are examined here. Two superconducting phases are identified between the transitions to the bulk phase at 1.5K and to the 3K phase. The nucleation of the 3K phase results in a state conserving time reversal symmetry, which generates an intrinsically frustrated superconducting network in samples with many Ru inclusions. At a lower temperature (>1.5K), a discontinuous (first order) transition to an interface state breaking time reversal symmetry is found leading to an unfrustrated network phase. It is shown that this phase transition located at a temperature between 1.5 and 3K would yield the anomalous property that the critical current in such a network depends on the sign of the current, reproducing recent experimental observations.Comment: This paper has been withdrawn by the authors. 5 pages, 6 figure

Symmetry of boundary conditions of the Dirac equation for electrons in carbon nanotubes.

We consider the effective mass model of spinless electrons in single wall carbon nanotubes that is equivalent to the Dirac equation for massless fermions. Within this framework we derive all possible energy independent hard wall boundary conditions that are applicable to metallic tubes. The boundary conditions are classified in terms of their symmetry properties and we demonstrate that the use of different boundary conditions will result in varying degrees of valley degeneracy breaking of the single particle energy spectrum

Anomalous Transport through the p-Wave Superconducting Channel in the 3-K Phase of Sr2RuO4

Using micro fabrication techniques, we extracted individual channels of 3-Kelvin (3-K) phase superconductivity in Sr2RuO4-Ru eutectic systems and confirmed odd-parity superconductivity in the 3-K phase, similar to pure Sr2RuO4. Unusual hysteresis in the differential resistance-current and voltage-current characteristics observed below 2 K indicates the internal degrees of freedom of the superconducting state. A possible origin of the hysteresis is current-induced chiral-domain-wall motion due to the chiral p-wave state.Comment: 4 pages, 5 figures, accepted for publication in Phys. Rev. Let

Chirality induced anomalous-Hall effect in helical spin crystals

Under pressure, the itinerant helimagnet MnSi displays unusual magnetic properties. We have previously discussed a BCC helical spin crystal as a promising starting point for describing the high pressure phenomenology. This state has topologically nontrivial configurations of the magnetization field. Here we note the consequences for magneto-transport that arise generally from such spin textures. In particular a skyrmion density induced `topological' Hall effect, with unusual field dependence, is described.Comment: 4 pages, 3 figures, to appear in the proceedings of SCES 07 (the international conference on strongly correlated electron systems 2007 in Houston, USA

The impact of HTLV-1 on the cellular genome.

Human T-lymphotropic virus type-1 (HTLV-1) is the causative agent of adult T-cell leukaemia/lymphoma (ATL), an aggressive CD4+ T-cell malignancy. The mechanisms of leukaemogenesis in ATL are incompletely understood. Insertional mutagenesis has not previously been thought to contribute to the pathogenesis of ATL. However, the recent discovery that HTLV-1 binds the key chromatin architectural protein CTCF raises the hypothesis that HTLV-1 deregulates host gene expression by causing abnormal chromatin looping, bringing the strong HTLV-1 promoter-enhancer near to host genes that lie up to 2Mb from the integrated provirus. Here we review current opinion on the mechanisms of oncogenesis in ATL, with particular emphasis on the local and distant impact of HTLV-1 on the structure and expression of the host genome

Tunneling properties at the interface between superconducting Sr2RuO4 and a Ru micro-inclusion

We have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr2RuO4-Ru. Electric contacts to individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jpn. vol. 74 no.

Multiple superconducting transitions in the Sr3Ru2O7 region of Sr3Ru2O7-Sr2RuO4 eutectic crystals

We report superconducting properties of Sr3Ru2O7-Sr2RuO4 eutectic crystals, consisting of the spin-triplet superconductor Sr2RuO4 with a monolayer stacking of RuO2 planes and the metamagnetic normal metal Sr3Ru2O7 with a bilayer stacking. Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far, our AC susceptibility measurements revealed multiple superconducting transitions occurring in the Sr3Ru2O7 region of the eutectic crystals. The diamagnetic shielding essentially reached the full fraction at low AC fields parallel to the c axis. However, both the shielding fraction and the onset temperature are easily suppressed by AC fields of larger than 0.1 mT-rms and no anomaly was observed in the specific heat. Moreover, the critical field curves of these transitions have a positive curvature near zero fields, which is different from the upper critical field curve of the bulk Sr2RuO4. These facts suggest that the superconductivity observed in the Sr3Ru2O7 region is not a bulk property. To explain these experimental results, we propose the scenario that stacking RuO2 planes, the building block of superconducting Sr2RuO4, are contained in the Sr3Ru2O7 region as stacking faults.Comment: 8 pages, 10 figures, accepted for publication in Phys. Rev.

Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals

Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic system as grown by the flux-feeding floating zone technique. A supercurrent flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances that are far beyond those expected in a conventional proximity scenario. The current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered ruthenate. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr2RuO4 inclusions within the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the Sr2RuO4 inclusions.Comment: Pages 4, figures 3, submitted to Phys. Rev. Let

The human leukemia virus HTLV-1 alters the structure and transcription of host chromatin in cis

Chromatin looping controls gene expression by regulating promoter-enhancer contacts, the spread of epigenetic modifications, and the segregation of the genome into transcriptionally active and inactive compartments. We studied the impact on the structure and expression of host chromatin by the human retrovirus HTLV-1. We show that HTLV-1 disrupts host chromatin structure by forming loops between the provirus and the host genome; certain loops depend on the critical chromatin architectural protein CTCF, which we recently discovered binds to the HTLV-1 provirus. We show that the provirus causes two distinct patterns of abnormal transcription of the host genome in cis: bidirectional transcription in the host genome immediately flanking the provirus, and clone-specific transcription in cis at non-contiguous loci up to >300 kb from the integration site. We conclude that HTLV-1 causes insertional mutagenesis up to the megabase range in the host genome in >104 persistently-maintained HTLV-1+ T-cell clones in vivo