セミナー情報

The high transition-temperature superconductivity in cuprates has been a long-standing mystery. Recently, accumulating experimental and theoretical results point to the presence of spin vortices, vortices in spin configuration formed by spins of electrons at lattice sites. In this talk, I first show that the hourglass-shaped magnetic excitation spectraobserved in neutron scattering experiments is strong evidence for the existence of such objects. It is also shown that the Drude-like peak in the optical conductivity is due to excitations to novel spin-wave excited states that emerge when spin vortices are present; thus, it is indicated that the coherent motion of doped holes may not be realized in underdoped cuprates.

Next, an alternative current generation mechanism is presented that does not require coherent motion of doped holes; in this mechanism, a fictitious magnetic field from spin vortices generates loop currents around spin vortices. The enhanced Nernst signals observed in the pseudo gap phase is considered as evidence for such currents; actually, the Nernst signal is shown to arise from a fictitious electric field from spin vortices. Lastly, I will discuss how superconducting transition occurs in underdoped cuprates.

References

[1] S. Miyaki, K. Makoshi, and H. Koizumi, J. Phys. Soc. Jpn. 77, 034702 (2008).

[2] H. Koizumi, J. Phys. Soc. Jpn. 77, 034712 (2008).

[3] H. Koizumi, J. Phys. Soc. Jpn. 77, 104704 (2008).

[4] H. Koizumi, to appear in J. Phys. Soc. Jpn.