Masashige Matsumoto

On Boundary Effect in d-Wave Superconductors

The boundary effect in d -wave superconductors is studied for specular and rough surfaces. In particular, the local density of states near the boundary is examined to see how the d -wave symmetry shows up in the direction dependence of the surface relative to the order parameter.

Quantum magnets under pressure: controlling elementary excitations in TlCuCl3.

We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point.

Magnon dispersion in the field-induced magnetically ordered phase of TlCuCl3.

The magnetic properties of the interacting dimer system TlCuCl3 are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

Quasiparticle States near the Surface and the Domain Wall in a px ± ipy-Wave Superconductor

The electronic states near a surface or a domain wall in the p -wave superconductor are studied for the order parameter of the form p x ± i p y -wave, which is a unitary odd-parity state with broke...

Coexistence of different symmetry order parameters near a surface in d-wave superconductors II

In a previous paper a possibility of coexistence of two superconducting order parameters was discussed for the (1, 1, 0) surface of d x 2 - y 2 -wave superconductors. In the present report physical properties are examined particularly for the time-reversal-breaking state ( s ± i d ) near the (1, 1, 0) surface. The nature of coexisting order parameters shows up in the local density of states. It is also shown that the superconducting current flows along the surface due to the time reversal breaking and induces the magnetic field. The induced magnetic field can be used to detect the time-reversal-breaking states experimentally.

Crystal-Field Excitations, Magnetic-Field-Induced Phase Transition and Neutron-Scattering Spectra in PrOs4Sb12

One possible origin of the field-induced ordered phase (FIOP) in PrOs 4 Sb 12 is an interaction of quadrupolar moments of Pr 4 f electrons in the singlet–triplet crystal-field (CF) levels. We study...

Exciton Mediated Superconductivity in PrOs4Sb12

The most important character of the exotic superconductor PrOs 4 Sb 12 is the existence of low-lying excitations (excitons) with a finite energy gap and it appears as the magnetic field-induced order above 4.5 T. We focus on the a u conduction band, which hybridizes with a Pr 4 f 2 state strongly, coupled to the excitons. It results in an attractive interaction between the conduction electrons. The symmetry of the superconducting order parameter is determined by dispersion relation of the exciton. For the bcc system PrOs 4 Sb 12 , a d -wave state ( k x k y + ω k y k z + ω 2 k z k x , ω=e ±i 2π/3 ) is stabilized with broken time reversal symmetry.

Magnetic Excitation and Electric Polarization in Strongly Coupled Spin Monomer and Dimer System Cu3Mo2O9

Magnetic excitation in strongly coupled spin monomer and dimer system is studied theoretically focusing on Cu 3 Mo 2 O 9 as an typical example, where Cu 3 Mo 2 O 9 shows an antiferromagnetic long-range order at zero field. Introducing formfactors of dimers, we present the formulation for magnetic excitations. Under an external magnetic field, an additional field-induced quantum phase transition takes place due to the stabilization of a triplet state of the dimer. The recent experimental study revealed that Cu 3 Mo 2 O 9 shows an multiferroic behavior with an electric polarization in the magnetically ordered state. According to the field-induced transition, we find that the electric polarization should change drastically.

Roles of Multipoles and Excitons in Superconductor PrOs4Sb12 with Th Symmetry

A possibility of exciton-mediated mechanism is studied to describe the superconductivity in a Pr skutterudite PrOs 4 Sb 12 . In this compound the low-lying crystal-field states of Pr form a pseudo-quartet consisting of Γ 1 singlet ground and Γ 4 (2) triplet excited states. The dispersive crystal-field excitations (excitons) have been detected experimentally. The conduction electrons couple both magnetically and nonmagnetically with the pseudo-quartet. Believing that this coupling should be crucial for various properties of PrOs 4 Sb 12 , we determine the effective interaction between conduction electrons and the Pr pseudo-quartet states. It turns out that the nature of exchange processes is related closely to a u and t u components of the conduction electrons that correspond to the molecular orbitals of an Sb 12 cage surrounding a Pr ion. By the second-order perturbation in the exchange coupling, Cooper pairing interactions are derived both for singlet and triplet superconductivities. First, they are clas...

Vortex charging effect in a chiral p x ± ip y -wave superconductor

Quasiparticle states around a single vortex in a p x ′ip y -wave superconductor are studied on the basis of the Bogoliubov-de Gennes (BdG) theory, where both charge and current screenings are taken into account. Due to theviolation of time-reversal symmetry, there are two types of vortices which are distinguished by their winding orientations relative to the angular momentum of the chiral Cooper pair. The BdG solution shows that the charges of the two types of vortices are quite different, reflecting the rotating Cooper pair of the p x ′ip y -wave paring state.