Yuki Fuseya

Realization of Odd-Frequency p-Wave Spin–Singlet Superconductivity Coexisting with Antiferromagnetic Order near Quantum Critical Point

A possibility of the realization of the p -wave spin–singlet superconductivity ( p SS), whose gap function is odd both in momentum and in frequency, is investigated by solving the gap equation with the phenomenological interaction mediated by the antiferromagnetic spin fluctuation. The p SS is realized prevailing over the d -wave singlet superconductivity ( d SS) in the vicinity of antiferromagnetic quantum critical point (QCP) both on the paramagnetic and on the antiferromagnetic sides. Off the QCP in the paramagnetic phase, however, the d SS with line-nodes is realized as conventional anisotropic superconductivity. For the present p SS state, there is no gap in the quasiparticle spectrum everywhere on the Fermi surface due to its odd frequency. These features can give a qualitative understanding of the anomalous behaviors of NQR relaxation rate on CeCu 2 Si 2 or CeRhIn 5 where the antiferromagnetism and superconductivity coexist on a microscopic level.A possibility of the realization of the p -wave spin–singlet superconductivity ( p SS), whose gap function is odd both in momentum and in frequency, is investigated by solving the gap equation with the phenomenological interaction mediated by the antiferromagnetic spin fluctuation. The p SS is realized prevailing over the d -wave singlet superconductivity ( d SS) in the vicinity of antiferromagnetic quantum critical point (QCP) both on the paramagnetic and on the antiferromagnetic sides. Off the QCP in the paramagnetic phase, however, the d SS with line-nodes is realized as conventional anisotropic superconductivity. For the present p SS state, there is no gap in the quasiparticle spectrum everywhere on the Fermi surface due to its odd frequency. These features can give a qualitative understanding of the anomalous behaviors of NQR relaxation rate on CeCu 2 Si 2 or CeRhIn 5 where the antiferromagnetism and superconductivity coexist on a microscopic level.

Angle-resolved Landau spectrum of electrons and holes in bismuth

In elemental bismuth, emptying the low-index Landau levels is accompanied by giant Nernst quantum oscillations. The Nernst response sharply peaks each time a Landau level intersects the chemical potential. By studying the evolution of these peaks when the field rotates in three perpendicular planes defined by three high-symmetry axes, we have mapped the angle-resolved Landau spectrum of the system up to 12 T. A theoretical model treating electrons at L point with an extended Dirac Hamiltonian is confronted with the experimentally-resolved spectrum. We obtain a set of theoretical parameters yielding a good but imperfect agreement between theory and experiment for all orientations of the magnetic field in space. The results confirm the relevance of the Dirac spectrum to the electron pockets and settle the longstanding uncertainty about the magnitude of the g-factor for holes. According to our analysis, a magnetic field exceeding 2.5 T applied along the bisectrix axis puts all carriers of the three electron pockets in their lowest(

Interband contributions from the magnetic field on Hall effects for dirac electrons in bismuth.

j=0

On the Puzzle of Odd-Frequency Superconductivity

) spin-polarized Landau level. On top of this complex angle-dependent spectrum, experiment detects additional and unexpected Nernst peaks of unidentified origin.

Angle Dependence of the Orbital Magnetoresistance in Bismuth

The Hall conductivity sigma_{xy} of Dirac electrons with a spin-orbit interaction is examined. It is shown that there is an unconventional contribution to sigma_{xy} generated by the interband effects of a magnetic field, which is remarkable near the band edges and does not depend on impurity scatterings so much, suggesting the same origin as the known large diamagnetism. Correspondingly, the Hall coefficient exhibits unexpected peaks at around the band edges. Implications of the present results to bismuth alloys are discussed.

Landau spectrum and twin boundaries of bismuth in the extreme quantum limit

Since the first theoretical proposal by Berezinskii, an odd-frequency superconductivity has encountered the fundamental problems on its thermodynamic stability and rigidity of a homogenous state accompanied by unphysical Meissner effect. Recently, Solenov et al. [Phys. Rev. B 79 (2009) 132502] have asserted that the path-integral formulation gets rid of the difficulties leading to a stable homogenous phase with an ordinary Meissner effect. Here, we show that it is crucial to choose the appropriate saddle-point solution that minimizes the effective free energy, which was assumed implicitly in the work by Solenov and co-workers. We exhibit the path-integral framework for the odd-frequency superconductivity with general type of pairings, including an argument on the retarded functions via the analytic continuation to the real axis.

Spin-Hall Effect and Diamagnetism of Dirac Electrons

We present an extensive study of angle-dependent transverse magnetoresistance in bismuth, with a magnetic field perpendicular to the applied electric current and rotating in three distinct crystallographic planes. The observed angular oscillations are confronted with the expectations of semi-classic transport theory for a multi-valley system with anisotropic mobility and the agreement allows us to quantify the components of the mobility tensor for both electrons and holes. A quadratic temperature dependence is resolved. As Hartman argued long ago, this indicates that inelastic resistivity in bismuth is dominated by carrier-carrier scattering. At low temperature and high magnetic field, the threefold symmetry of the lattice is suddenly lost. Specifically, a

Anomalous Fermi Liquid Effects in Two-Dimensional Hubbard Model near Half-Filling

2\pi/3

Transport and spin conversion of multicarriers in semimetal bismuth

rotation of magnetic field around the trigonal axis modifies the amplitude of the magneto-resistance below a field-dependent temperature. By following the evolution of this anomaly as a function of temperature and magnetic field, we mapped the boundary in the (field, temperature) plane separating two electronic states. In the less-symmetric state, confined to low temperature and high magnetic field, the three Dirac valleys cease to be rotationally invariant. We discuss the possible origins of this spontaneous valley polarization, including a valley-nematic scenario.

Unconventional superconductivity with a radial-node gap in quasi-one-dimensional metals

The Landau spectrum of bismuth is complex and includes many angle-dependent lines in the extreme quantum limit. The adequacy of single-particle theory to describe this spectrum in detail has been an open issue. Here, we present a study of angle-resolved Nernst effect in bismuth, which maps the angle-resolved Landau spectrum for the entire solid angle up to 28 T. The experimental map is in good agreement with the results of a theoretical model with parabolic dispersion for holes and an extended Dirac Hamiltonian for electrons. The angular dependence of additional lines in the Landau spectrum allows us to uncover the mystery of their origin. They correspond to the lines expected for the hole Landau levels in a secondary crystal tilted by 108°, the angle between twinned crystals in bismuth. According to our results, the electron reservoirs of the two identical tilted crystals have different chemical potentials, and carriers across the twin boundary have different concentrations. An exceptional feature of this junction is that it separates two electron-hole compensated reservoirs. The link between this edge singularity and the states wrapping a three-dimensional electron gas in the quantum limit emerges as an outstanding open question.