Search

We present a possible explanation for a recently observed magnetic field induced charge order in cuprate superconductors (Edkins et al.~arXiv:1802.04673 [cond-mat.supr-con]). We argue that it arises from the reorganization of spin-vortex-induced loop current (SVILC) pattern due to supercurrent-flow caused by the magnetic field. The reorganization is from the most stable tiling of $4a times 6a$ spin-vortex quartets ($a$ is the lattice constant in the CuO$_2$ plane, and a spin-vortex quartet is stable of unit of spin-vortices that contains four holes, four spin-vortices, and four SVILCs) to that of $4a times 8a$ spin-vortex quartets. The consequence of this reorganization will lead to the enhancement of $8a$ charge order, and reduction of $6a$ charge order. The former is observed in the experiment, but the latter is not confirmed, so far. However, it may be confirmed if the experimental result is carefully reexamined.

Tanabe and Sugano's personal accounts are given for the birth of the Tanabe-Sugano diagrams and the advent of laser.

When Schrodinger solved the Schrodinger equation for the hydrogen atom, he assumed the single-valuedness of the electronic wave function. Thereafter, this assumption has been one of the fundamental postulates of quantum mechanics. When wave functions are multi-component, however, the imposing of the single-valued condition may become nontrivial. The spin-degree-of-freedom of electron makes electronic wave functions two-component. When spin-vortices are created by the conduction electrons and they move in the self-consistent field with the spin-vortices, the twisting of the spin basis occurs; then, the imposing of the single-valued condition becomes nontrivial, and a vector potential is induced. As a consequence, the effective vector potential becomes the sum of the vector potential from the induced one and that originates from the electric current. This effective vector potential is gauge invariant and the persistent current is generated by it. In the present work, we argue that if interactions that are omitted in the BCS reduced Hamiltonian are included, spin-vortices may be generated upon the application of a magnetic field. Then, the vector potential is induced and provides with the phase variable, θ, of the electron pair amplitude. The appearance of the spin-vortex provides with a new origin of θ; it originates from the induced gauge potential. This origin is compatible with the superselection rule for charge in contrast to the currently-accepted origin.

(The PDF contains the full conference program, the list of sponsors and the conference poster.) The 21st International Symposium on the Jahn-Teller effect was held at the University of Tsukuba, Japan, from 26–31 August 2012. People from 23 different countries participated and the number of registered participants was 118. In this symposium, the phrase 'Jahn-Teller effect' was taken to have a rather broad meaning. We discussed the Jahn-Teller and pseudo Jahn-Teller distortions. We also discussed general vibronic problems, and the problems associated with the conical intersections of the potential energy surfaces. As is indicated in the subtitle of the present symposium, 'Physics and Chemistry of Symmetry Breaking', a number of different topics concerning symmetry breaking were also extensively discussed. In particular, we had many discussions on magnetism, ferroelectricity, and superconductivity. A subtle but important problem that was dealt with was the appearance of multi-valuedness in the use of multi-component wave functions. In the Jahn-Teller problems, we almost always use the multi-component wave functions, thus, the knowledge of the proper handling of multi-valuedness is very important. Digital computers are not good at dealing with multi-valuedness, but we need to somehow handle it in our calculations. A very well known example of successful handling is found in the problem of the molecular system with the conical intersection: we cannot obtain the solution that satisfies the single-valuedness of wave functions (SVWF) just using the potential energy surface generated by a package program, and solving the Schrodinger equation with the quantum Hamiltonian constructed from the classical counterpart by replacing the classical variables with the corresponding operators; however, if a gauge potential is included and the double-valuedness of the electronic wave functions around the conical intersections is taken into account, the solution that satisfies the SVWF is obtained. A related problem also arises when dealing with the so-called adiabatic–diabatic transformation (ADT) that removes coupling terms between different Born–Oppenheimer electronic states. It is known that an exact ADT does not exist in general, however, digital computers do this impossible task erroneously if we just plug in numbers. The results obtained may be good in practice; however, we need to be aware that such calculations may miss some important details. I asked Professor Mead to write a note on this matter since there is still confusion in the treatment of the ADT. The proper handling on the ADT may be a topic in the next Jahn-Teller symposium. Although more than a quarter of a century has passed since its discovery, the mechanism of cuprate superconductivity is still actively discussed. In the cuprate, the multi-valuedness problem arises when the conduction electrons create spin-vortices and the twisting of the spin basis occurs. Since a number of experiments and theories indicate the presence of spin-vortices in the cuprate, a proper handling of the multi-valuedness arising from the spin-degree-of-freedom will be important. It has been argued that such multi-valuedness induces a vector potential that generates the persistent current. As the papers in this proceedings indicate, the Jahn-Teller effects are ubiquitous in physics and chemistry. The ideas and methodologies developed in this community have very wide applicability. I believe that this community will continue to contribute to the advancement of science in a fundamental way. Hiroyasu Koizumi Tsukuba, February 2013

We consider a persistent current generation by the fictitious magnetic field generated by spin-vortices in a solid with two-dimensional conduction layers. Each center of the spin-vortices is a singularity that imposes the sign-change boundary condition on the wavefunction for the conduction electron. We handle the sign-change boundary condition by introducing a fictitious magnetic field and show that loop currents are generated by it even in the ground state. Actually, a distribution of NV singularities causes the ground state to be -fold degenerate with different current patterns. When an external magnetic field is applied, this degeneracy is partly lifted and the one that expels the magnetic field is chosen. This response strongly resembles the Meissner effect seen in superconductors. The flux quantization also occurs with the unit h/2e as in superconductors.

We first present our molecular orbital cluster calculation results that indicate the presence of strong interaction between doped holes and the underlying lattice in the cuprate. It is also indicated that the naive Zhang-Rice singlet picture for the local electronic state needs to be revised: the doped hole is mainly concentrated in a single bridging oxygen, and the bridging oxygen p orbital and two nearby copper dx2-y2 orbitals form a valence bond type bonding; this state is stabilized by local lattice distortions and the doped hole becomes a small polaron. Next, we consider the current generation mechanism compatible with the above small polaron formation; actually, we present a new current generation mechanism that is effective even if all the doped holes become self-trapped small polarons. The current generation here reverses a long-standing belief that at half-filing the effective Hamiltonian for the U >> t Hubbard model is the Heisenberg model, thus, possible low energy excitations are those include spin degrees of freedom only. The new current generation mechanism yields the Fermi arc seen in the ARPES simulation; it also suggests that the phase of the superconductivity order parameter in underdoped cuprates arises without Cooper pair formation; i.e., the London current formula with effective charge 2e is realized without the Cooper pair formation. The electric current here is generated by a fictitious magnetic field induced by spin vortices: because the presence of spin vortices causes a sign ambiguity of wave functions for electron hoping motion, a phase factor that ensures the single-valuedness of the wave function appears; and this phase factor gives rise to a vector potential for the fictitious magnetic field. The strong hole-lattice interaction stabilizes spin vortices by pinning each center at a polaron occupied site; thus, it will also stabilize the spin vortex induced current. Based on the new current generation mechanism, possibility of an artificial superconducting nano wire is presented. It is made in the Cu-O plane, and consists of pining centers of nonmagnetic atoms arranged in two parallel lines; here the nonmagnetic atoms play the role of lattice small polarons; and the region between the two arrays of vortex centers is a superconducting wire where a thermodynamically stable current flows.