Three-orbital study on the orbital distillation effect in the high Tc cuprates

Our recent study has revealed that the mixture of the dz2 orbital component into the Fermi surface suppresses Tc in the cuprates such as La2CuO4. We have also shown that applying hydrostatic pressure enhances Tc due to smaller mixing of the Cu4s component. We call these the "orbital distillation" effect. In our previous study, the 4s orbital was taken into account through the hoppings in the dx2-y2 sector, but here we consider a model in which of the dx2-y2, dz2 and 4s orbitals are all considered explicitly. The present study reinforces our conclusion that smaller 4s hybridization further enhances Tc.Comment: 4 pages, 2 figures, submitted as a proceeding of ISS2012(Tokyo

Self-Reduction Rate of a Microtubule

We formulate and study a quantum field theory of a microtubule, a basic element of living cells. Following the quantum theory of consciousness by Hameroff and Penrose, we let the system to reduce to one of the classical states without measurement if certain conditions are satisfied(self-reductions), and calculate the self-reduction time $\tau_N$ (the mean interval between two successive self-reductions) of a cluster consisting of more than $N$ neighboring tubulins (basic units composing a microtubule). $\tau_N$ is interpreted there as an instance of the stream of consciousness. We analyze the dependence of $\tau_N$ upon $N$ and the initial conditions, etc. For relatively large electron hopping amplitude, $\tau_N$ obeys a power law $\tau_N \sim N^b$, which can be explained by the percolation theory. For sufficiently small values of the electron hopping amplitude, $\tau_N$ obeys an exponential law, $\tau_N \sim \exp(c' N)$. By using this law, we estimate the condition for $\tau_N$ to take realistic values $\tau_N$ \raisebox{-0.5ex}{$\stackrel{>}{\sim}$} $10^{-1}$ sec as $N$ \raisebox{-0.5ex} {$\stackrel{>}{\sim}$} 1000.Comment: 7 pages, 9 figures, Extended versio

Field-angle Dependence of the Zero-Energy Density of States in the Unconventional Heavy-Fermion Superconductor CeCoIn5

Field-angle dependent specific heat measurement has been done on the heavy-fermion superconductor CeCoIn5 down to ~ 0.29 K, in a magnetic field rotating in the tetragonal c-plane. A clear fourfold angular oscillation is observed in the specific heat with the minima (maxima) occurring along the [100] ([110]) directions. Oscillation persists down to low fields H << Hc2, thus directly proving the existence of gap nodes. The results indicate that the superconducting gap symmetry is most probably of dxy type.Comment: 8 pages, 3 figures, to be published in J. Phys. Condens. Matte

Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7

We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7 as a function of magnetic field and temperature using 17O-NMR. This system sits close to a metamagnetic quantum critical point (MMQCP) for the field perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior at low temperatures except for a narrow field region close to the MMQCP. The nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced on approaching the metamagnetic critical field of 7.9 T and at the critical field 1/T1T continues to increase and does not show Fermi- liquid behavior down to 0.3 K. The temperature dependence of T1T in this region suggests the critical temperature Theta to be 0 K, which is a strong evidence that the spin dynamics possesses a quantum critical character. Comparison between uniform susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of two-dimensional ferromagnetic fluctuations dominate the spin fluctuation spectrum at the critical field, which is unexpected for itinerant metamagnetism.Comment: 5 pages, 4 figures, Accepted by Phys. Rev. Let

Quasiquartet CEF ground state with possible quadrupolar ordering in the tetragonal compound YbRu2_{2}Ge2_{2}

e have investigated the magnetic properties of YbRu$_{2}$Ge$_{2}$ by means of magnetic susceptibility $\chi$(T), specific heat C(T) and electrical resistivity $\rho$(T) measurements performed on flux grown single crystals. The Curie-Weiss behavior of $\chi$(T) along the easy plane, the large magnetic entropy at low temperatures and the weak Kondo like increase in $\rho$(T) proves a stable trivalent Yb state. Anomalies in C(T), $\rho$(T) and $\chi$(T) at T$_{0}$ = 10.2 K, T$_{1}$ = 6.5 K and T$_{2}$ = 5.7 K evidence complex ordering phenomena, T$_{0}$ being larger than the highest Yb magnetic ordering temperature found up to now. The magnetic entropy just above T$_{0}$ amounts to almost Rln4, indicating that the crystal electric field (CEF) ground state is a quasiquartet instead of the expected doublet. The behavior at T$_{0}$ is rather unusual and suggest that this transition is related to quadrupolar ordering, being a consequence of the CEF quasiquartet ground state. The combination of a quasiquartet CEF ground state, a high ordering temperature, and the relevance of quadrupolar interactions makes YbRu$_{2}$Ge$_{2}$ a rather unique system among Yb based compounds.Comment: 11 pages, 5 figure, submitted to PRB rapi

Sign reversal of field-angle resolved heat capacity oscillations in a heavy fermion superconductor CeCoIn5_5 and dx2−y2d_{x^2-y^2} pairing symmetry

To identify the superconducting gap symmetry in CeCoIn5 (Tc=2.3 K), we performed angle-resolved specific heat (C_\phi) measurements in a field rotated around the c-axis down to very low temperatures 0.05Tc and detailed theoretical calculations. In a field of 1 T, a sign reversal of the fourfold angular oscillation in C_\phi has been observed at T ~ 0.1Tc on entering a quasiclassical regime where the maximum of C_\phi corresponds to the antinodal direction, coinciding with the angle-resolved density of states (ADOS) calculation. The C_\phi behavior, which exhibits minima along [110] directions, unambiguously allows us to conclude d_{x^2-y^2} symmetry of this system. The ADOS-quasiclassical region is confined to a narrow T and H domain within T/Tc ~ 0.1 and 1.5 T (0.13Hc2).Comment: 4 pages, 4 figure

Measurement of temperature field of a Rayleigh-Bénard convection using two-color laser-induced fluorescence

The two-color laser-induced fluorescence technique developed by Sakakibara and Adrian (1999) for the measurement of planar turbulent temperature fields in water has been refined to reduce the RMS error of the instantaneous measurement by an order of magnitude. The technique achieves higher sensitivity by employing two high-resolution 14-bit monochrome CCD cameras. Further refinement is achieved by post-processing the data using a convolution method that matches the degree of the image blurring of the two images. The method is demonstrated by application to turbulent Rayleigh-Bénard convection wherein the random error is shown to be less than 0.17 K