arXiv subjects

C. -H. Park

Publications and source records attributed to C. -H. Park.

8 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↗

arXiv2017

Normal state pair nematicity and hidden magnetic order and metal-insulator (fermion-boson)- crossover origin of pseudogap phase of cuprates II

In the present paper II, we will gain an understanding of the nematicity, insulating ground state (IGS), nematicity to stripe phase transition, Fermi pockets evolution, and resistivity temperature upturn, as to be metal - insulator (fermion-boson)- crossover (MIC) phenomena for the pseudogap (PG) region of cuprates. While in the paper I [1], we obtained an understanding of the observed heat conductivity downturn, anomalous Lorentz ratio, insulator resistivity boundary, nonlinear entropy as manifestations of the same MIC. The recently observed nematicity and hidden magnetic order are related to the PG pair intra charge and spin fluctuations. We will try to obtain an answer on the question: why ground state of YBCO is Fermi liquid oscillating and of Bi-2212 is insulating? We will also clarify the physics of the recently observed MIC results of Laliberté et al. [2] and explain the long-discussed transition of the electric charge density from doping to doping+1 dependence at the critical doping. We predict that at the upturns this density should have the temperature dependence $n\sim T^3n_2$ for $T\rightarrow 0$, where $n_2$ is density for dopings close to the critical value. We understood that the upturns before and after the first critical doping have the same nature. We will find understanding of all above mentioned phenomena within the PG pair physics.

cond-mat.supr-con↗

arXiv2016

Intra pseudogap- and superconductivity-pair spin and charge fluctuations and underdome metal-insulator (fermion-boson)-crossover phenomena as keystones of cuprate physics

The most intriguing observation of cuprate experiments is most likely the metal-insulator-crossover (MIC), seen in the underdome region of the temperature-doping phase diagram of copper-oxides under a strong magnetic field, when the superconductivity is suppressed. This MIC, which results in such phenomena as heat conductivity downturn, anomalous Lorentz ratio, nonlinear entropy, insulating ground state, nematicity- and stripe-phases and Fermi pockets, reveals the nonconventional dielectric property of the pseudogap-normal phase. Since conventional superconductivity appears from a conducting normal phase, the understanding of how superconductivity arises from an insulating state becomes a fundamental problem and thus the keystone for all of cuprate physics. Recently, in interpreting the physics of visualization in scanning tunneling microscopy (STM) real space nanoregions (NRs), which exhibit an energy gap, we have succeeded in understanding that the minimum size for these NRs provides pseudogap and superconductivity pairs, which are single bosons. In this work, we discuss the intra-particle magnetic spin and charge fluctuations of these bosons, observed recently in hidden magnetic order and STM experiments. We find that all the mentioned MIC phenomena can be obtained in the Coulomb single boson and single fermion two liquid model, which we recently developed, and the MIC is a crossover of sample percolating NRs of single fermions into those of single bosons.

cond-mat.supr-con↗

arXiv2012

Nanoscale Phenomenology from Visualizing Pair Formation Experiment

Recently, Gomes et al. [1] have visualized the gap formation in nanoscale regions (NRs) above the critical temperature T_c in the high-T_c superconductor Bi_2Sr_2CaCu_2O_{8+δ}. It has been found that, as the temperature lowers, the NRs expand in the bulk superconducting state consisted of inhomogeneities. The fact that the size of the inhomogeneity [2] is close to the minimal size of the NR [1] leads to a conclusion that the superconducting phase is a result of these overlapped NRs. In the present paper we perform the charge and percolation regime analysis of NRs and show that at the first critical doping x_{c1}, when the superconductivity starts on, each NR carries the positive electric charge one in units of electron charge, thus we attribute the NR to a single hole boson, and the percolation lines connecting these bosons emerge. At the second critical doping x_{c2}, when the superconductivity disappears, our analysis demonstrates that the charge of each NR equals two. The origin of x_{c2} can be understood by introducing additional normal phase hole fermions in NRs, whose concentration appearing above x_{c1} increases smoothly with the doping and breaks the percolation lines of bosons at x_{c2}. The last one results in disappearing the bulk bosonic property of the pseudogap (PG) region, which explains the upper bound for existence of vortices in Nernst effect [3]. Since [1] has demonstrated the absence of NRs at the PG boundary one can conclude that along this boundary, as well as in x_{c2}, all bosons disappear.

cond-mat.supr-con↗

arXiv2007

Analytic approach to the ground state energy of charged anyon gases in the high magnetic field

We present analytic formulas for the ground state energy of the two-dimensional (2D) anyon gas in the quantum limit of a perpendicular magnetic field (Landau level filling factor ν_L\le 1). These formulas, for the cases without and with Coulomb interaction, are obtained by applying the harmonic potential regularization for vanishing confinement to the harmonically confined Coulomb anyon gas as in our previous paper for the case without magnetic field. For the case without Coulomb interaction our analytic expression is exact. It contains a contribution deriving from the anyon gauge field (characterizing the fractional statistics by the anyon parameter ν) and depends on νand ν_L. For the case with Coulomb interaction we introduce a function, depending on ν, ν_L and the density parameter r_s, which is determined by fitting to the interpolation formula of Fano and Ortolani in the fractional quantum Hall regime for spin-polarized fermions in conjunction with results of Yoshioka for the ground state energy of the 2D Coulomb boson gas in high magnetic fields. With their dependence on ν, our formulas apply not only to fermions (ν=1) but quite generally to anyons (0\le ν\le 1).

cond-mat.str-el↗

arXiv2007

Anyon related correlations in two-dimensional Coulomb gases

In our recent paper (Phys. Rev. B 76, 075403 (2007)), we have applied the anyon concept to derive an approximate analytic formula for the ground state energy, which applies to two-dimensional (2D) Coulomb systems from the bosonic to the fermionic limit. We make use of these results here to draw attention to correlation effects for two special cases: the spin-polarized 2D fermion system and the charged anyon system close to the bosonic limit. By comparison with quantum Monte-Carlo data (for the former) and exact results obtained in the hypernetted-chain and Bogolyubov approximations (for the latter) we can conclude on correlation effects, which have their origin in the bosonic systems and come into play by using the anyon concept. To our knowledge, these correlations are not yet considered in the literature.

cond-mat.str-el↗

arXiv2007

Bosonization of 2D Fermions due to Spin and Statistical Magnetic Field Coupling and Possible Nature of Superconductivity and Pseudogap Phases Below E_g

A ground state energy variational calculation of anyon gas with Hamiltonian included the interaction of spins of particles with anyon vector potential induced, i.e. statistical, magnetic field exhibits exact cancelation of terms connected with fractional statistics. This leads to bosonization of anyons due to coupling of their spins with statistical magnetic field. We presume that at the dense gas fluctuations of effective spins destroy the coupling and bosons become anyons. At the assumption that pseudogap (PG) boundary is temperature independent and when anyons are fermions we use this model to interpret experimental phase diagrams of Tallon and Loram hole and electron doped High-T_c superconductors below PG energy E_g and find the qualitative and quantitative agreement. We do the hypothesis that phase transition (PT) of bosons into Bose-Einstein condensate is not of second order, but of first order, close to second one, PG regime is meta stable phase of bosons, and E_g=0 is the critical point of this PT. Bosons undergo PT into fermions on PG boundary. Described in the literature non-Fermi quasi-particles might be related to bosons with effective spins.

cond-mat.supr-con↗

arXiv2006

Examination of Current-Induced Magnetic Field in the Slab Geometry: Possible Origin of Spin Hall Effect

We estimate the strength of current-induced magnetic field (CIMF) in the two-dimensional slab geometry for Spin Hall Effect (SHE) observed recently by Kato et al. and Wunderlich et al. and show that if the factor gm^*/m, where g is the Lande factor and m^* and m are effective and pure masses, respectively, is equal to the numerical value at the surface of the semiconductor, then the CIMF can describe the SHE.

cond-mat.mes-hall↗