arXiv subjects

K. -S. Park

Publications and source records attributed to K. -S. Park.

3 recordsLinked to original sources

arXiv2017

Metal-insulator (fermion-boson)-crossover origin of pseudogap phase of cuprates I: anomalous heat conductivity, insulator resistivity boundary, nonlinear entropy

Among all experimental observations of cuprate physics, the metal-insulator-crossover (MIC), seen in the pseudogap (PG) region of the temperature-doping phase diagram of copper-oxides under a strong magnetic field, when the superconductivity is suppressed, is most likely the most intriguing one. Since it was expected that the PG-normal state for these materials, as for conventional superconductors, is conducting. This MIC, revealed in such phenomena as heat conductivity downturn, anomalous Lorentz ratio, insulator resistivity boundary, nonlinear entropy, resistivity temperature upturn, insulating ground state, nematicity- and stripe-phases and Fermi pockets, unambiguously indicates on the insulating normal state, from which the high-temperature superconductivity (HTS) appears. In the present work (article I), we discuss the MIC phenomena mentioned in the title of article. The second work (article II) will be devoted to discussion of other listed above MIC phenomena and also to interpretation of the recent observations in the hidden magnetic order and scanning tunneling microscopy (STM) experiments spin and charge fluctuations as the intra PG and HTS pair ones. We find that all these MIC (called in the literature as non-Fermi liquid) phenomena can be obtained within the Coulomb single boson and single fermion two liquid model, which we recently developed, and the MIC is a crossover of single fermions into those of single bosons. We show that this MIC originates from bosons of Coulomb two liquid model and fermions, whose origin is these bosons. At an increase of doping up to critical value or temperature up to PG boundary temperature, the boson system undegoes bosonic insulator - bosonic metal - fermionic metal transitions.

cond-mat.supr-con↗

arXiv2011

Index theorem, spin Chern Simons theory and fractional magnetoelectric effect in strongly correlated topological insulators

Making use of index theorem and spin Chern Simons theory, we construct an effective topological field theory of strongly correlated topological insulators coupling to a nonabelian gauge field $ SU(N) $ with an interaction constant $ g $ in the absence of the time-reversal symmetry breaking. If $ N $ and $ g $ allow us to define a t'Hooft parameter $ λ$ of effective coupling as $ λ= N g^{2} $, then our construction leads to the fractional quantum Hall effect on the surface with Hall conductance $ σ_{H}^{s} = \frac{1}{4λ} \frac{e^{2}}{h} $. For the magnetoelectric response described by a bulk axion angle $ θ$, we propose that the fractional magnetoelectric effect can be realized in gapped time reversal invariant topological insulators of strongly correlated bosons or fermions with an effective axion angle $ θ_{eff} = \fracπ{2 λ} $ if they can have fractional excitations and degenerate ground states on topologically nontrivial and oriented spaces. Provided that an effective charge is given by $ e_{eff} = \frac{e}{\sqrt{2 λ}} $, it is shown that $ σ_{H}^{s} = \frac{e_{eff}^{2}}{2h} $, resulting in a surface Hall conductance of gapless fermions with $ e_{eff} $ and a pure axion angle $ θ= π$.

cond-mat.str-el↗

arXiv2010

Dirac Quantization and Fractional Magnetoelectric Effect on Interacting Topological Insulators

We use Dirac quantization of flux to study fractional charges and axion angles θin interacting topological insulators with gapless surface modes protected by time-reversal symmetry. In interacting topological insulators, there are two types of fractional axion angle due to conventional odd and nontrivial even flux quantization at the boundary. On even flux quantization in a gapped time reversal invariant system, we show that there is a halved quarter fractional quantum Hall effect on the surface with Hall conductance of p/4q e2/2h with p and q odd integers. The gapless surface modes can be characterized by a nontrivial Z2 anomaly emerged from the even flux quantization. It is suggested that the electron can be regarded as a bound state of fractionally charged quarks confined by a nonabelian color gauge field on the Dirac quantization of complex spinor fields.

cond-mat.str-el↗