Satoshi Tanda

Optical-vortex laser ablation

Laser ablation of Ta plates using nanosecond optical vortex pulses was carried out, for the first time. It was suggested that owing to orbital angular momentum of optical vortex, clearer and smoother processed surfaces were obtained with less ablation threshold fluence, in comparison with the ablation by a nonvortex annular beam modified from a spatially Gaussian beam.

Crystal topology: A Möbius strip of single crystals

A Möbius strip is produced by twisting a ribbon of material through 180° and joining its two ends, resulting in a distinct, one-sided topology. Here we describe a Möbius structure formed by crystals of a compound of niobium and selenium, NbSe3. It is surprising that a crystalline ribbon should adopt this exotic topology in view of its inherent rigidity, which would be expected to prevent it from either bending or twisting.

X-Ray Study of Charge Density Wave Structure in 1T-TaS2

Positions of satellite reflections in charge density wave (CDW) phases of 1T-TaS 2 were measured by X-ray diffraction. In the commensurate (C-) phase, stacking of CDW layers is considerably disordered. On heating from the C-phase there appears a new incommensurate triclinic structure up to 280 K, where anomalies have been observed in various properties.

Chiral Charge-Density Waves

We discovered the chirality of charge-density waves (CDW) in 1T-TiSe₂ by using STM and time-domain optical polarimetry. We found that the CDW intensity becomes Ia₁∶Ia₂∶Ia₃ = 1∶0.7 ± 0.1∶0.5 ± 0.1, where Ia(i) (i=1,2,3) is the amplitude of the tunneling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise. The chirality in CDW results in the threefold symmetry breaking. Macroscopically, twofold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H(CDW) ≡ q₁·(q₂×q₃), where q(i) are the CDW q vectors, which is independent of the symmetry of components. The nonzero H(CDW)-the triple-q vectors do not exist in an identical plane in the reciprocal space-should induce a real-space chirality in CDW system.

Rotating Black Hole in Extended Chern-Simons Modified Gravity

We investigate a slowly rotating black hole in four-dimensional extended Chern-Simons modified gravity. We obtain an approximate solution that reduces to the Kerr solution when a coupling constant vanishes. The Chern-Simons correction effectively reduces the frame-dragging effect around a black hole in comparison with that of the Kerr solution. Subject Index: 420, 453

Global evaluation of closed-loop electron dynamics in quasi-one-dimensional conductors using polarization vortices

We evaluate the quasi-one-dimensional (1D) electron dynamics in a NbSe3 ring crystal using polarization vortex pulses with various azimuthal distributions. The single particle relaxation component reveals a large anisotropy on the crystal, indicating that the electrons in the ring maintain their 1D character. The results also suggest that the polarization vortex evaluates the global polarization property of the closed-loop electron that plays an important role in the quantum correlation phenomena such as the Aharonov-Bohm effect.

Aharonov-Bohm effect in charge-density wave loops with inherent temporal current switching

The Aharonov-Bohm (AB) effect has been accepted and has promoted interdisciplinary scientific activities in modern physics. To observe the AB effect in condensed matter physics, the whole system needs to maintain phase coherence, in a tiny ring of the diameter 1 µm and at low temperatures below 1 K. We report that AB oscillations have been measured at high temperature 79 K by use of charge-density wave (CDW) loops in TaS3 ring crystals. CDW condensate maintained macroscopic quantum coherence, which extended over the ring circumference 85 µm. The periodicity of the oscillations is h/2e in accuracy within a 10 % range. The observation of the CDW AB effect implies Frohlich superconductivity in terms of macroscopic coherence and will provide a novel quantum interference device running at room temperature.

Field-Induced Discommensuration in Charge Density Waves in o-TaS3

We report a synchrotron X-ray study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist in the temperature range of 130 - 50 K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors qc ¼ 0:252cand 0:250c � , respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric current dependence of the intensity of the two CDWs. The result implies for the first time that discommensurations are induced in the commensurate CDW by applying an electric field.

Flat rotation curves in Chern-Simons modified gravity

Introduction.—There are three fundamental unsolved issues in the theory of gravity: quantization of gravity, dark energy, and dark matter. The string theory [1] is a promising candidate for a consistent quantum theory of gravity. Many attempts in quantizing gravity, however, have not been successful. In astronomy/astrophysics, a number of observations suggest the existence of dark energy [2, 3] and dark matter [3, 4]. Although many surveys of astrophysical objects have been conducted [5], it has not yet been revealed what is dark matter. For instance, the flat rotation curves of galaxies [6] have been considered to be a robust evidence of dark matter. The velocity v of a star orbiting around the center of a galaxy becomes a constant at a certain distance r far from the center. While the Newtonian gravity yields a relation v ∝ 1/ √ r. At present, we usually attribute the discrepancy to dark matter. However it may be still possible to explain the phenomenon based on a theory without dark matter. In this paper, we propose a model to solve this discrepancy in the framework of the Chern-Simons (CS) gravity.

A Möbius strip of single crystals

A Möbius strip is produced by twisting a ribbon of material through 180° and joining its two ends, resulting in a distinct, one-sided topology. Here we describe a Möbius structure formed by crystals of a compound of niobium and selenium, NbSe3. It is surprising that a crystalline ribbon should adopt this exotic topology in view of its inherent rigidity, which would be expected to prevent it from either bending or twisting.