arXiv subjects

J. Jung

Publications and source records attributed to J. Jung.

24 records · Page 2Linked to original sources

arXiv2001

Zigzag Filamentary Theory of Broken Symmetry of Neutron and Infrared Vibronic Spectra of YBa2Cu3O(6+x)

Filamentary high-temperature superconductivity (HTSC) theory differs fundamentally from continuous HTSC theories because it emphasizes self-organized, discrete dopant networks and does not make the effective medium approximation (EMA). Analysis of neutron and infrared (especially with c-axis polarization) vibrational spectra, primarily for YBa2Cu3O(6+x), within the filamentary framework, shows that the observed vibronic anomalies near 400 cm-1 (50 meV) are associated with curvilinear filamentary paths. these paths pass through cuprate chains and planes, as well as resonant tunneling centers in the BaO layers. The analysis and the data confirm earlier filamentary structural models containing ferroelastic domains of 3-4 nm in the CuO2 planes; it is these nanodomains that are responsible for the discrete glassy nature of both electronic and vibronic properties. Chemical trends in vibronic energies and oscillator strengths, both for neutron and photon scattering, that were anomalous in continuum models, are readily explained by the filamentary model.

cond-mat.supr-con↗

arXiv2001

Nanodomain Structure and Function in HTSC

The causes of high-temperature superconductivity (HTSC) are still mysterious, although more than 50,000 experiments have studied this subject. The most severe test of any microscopic theory is generally considered to be its ability to predict the results of future experiments. Here we examine recent (99-01)studies of BSCCO films by STM, which have revealed nanodomain structure on a scale of 3 nm which is closely correlated with both superconductive gaps and pseudogaps. This structure and these correlations were predicted as part of a discrete filamentary model of HTSC in 90. The nanodomain diameter of 3 nm was identified in experiments on YBCO in 96. While none of the experiments can directly establish causes, in the predictive theoretical model it was proposed that the underlying forces generating the nanostructure are ferroelastic. It was also predicted that the strong correlations of the superconductive gap and pseudogap electronic structure with nanostructure are the result of dopant self-organization. Here we describe a new method of preparing boride alloys, and we predict that it may produce materials with Tc ~ 150K or more.

cond-mat.supr-con↗

arXiv2000

Various regimes of flux motion in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals

Four regimes of vortex motion were identified in the magnetoresistance of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals: (1) thermally activated flux flow (TAFF) in samples with surface defects caused by thermal annealing; (2) TAFF-like plastic motion of highly entangled vortex liquid at low temperatures, with $U_{pl} \sim (1-T/T_c)/H^{1/2}$; (3) pure free flux flow above the region of (2) in clean and optimally doped samples; or, in its place, (4) a combination of (2) and (3). This analysis gives an overall picture of flux motion in Bi cuprates.

cond-mat.supr-con↗

arXiv2000

Experimental fitting to the bipolaronic model of the normal-state resistance of Bi_2Sr_2CaCu_2O_8 single crystals

Normal-state resistance data from Bi_2Sr_2CaCu_2O_8 single crystals were fitted to the (bi)polaronic conduction model, $R=R_0 (T+σ_b T^2)/(1+bT)$, with satisfactory agreement over a wide temperature range. The fluctuating conduction region is found to be much narrower than that in the usual sense, as is the case for a charged Bose-gas. We estimate the effective (bi)polaron mass to be ~ 4m_e.

cond-mat.supr-con↗

arXiv1999

Observation of a Universial Low Temperature Limit of the Free Flux Flow Resistivity in Superclean Bi_2Sr_2CaCu_2O_8 Whiskers

We report peculiar vortex motion in clean Bi$_2$Sr$_2$CaCu$_2$O$_8$ single crystals, which reveals nearly linear-$T$ resistivity tails extending to low temperatures. The resistivity was found to satisfy the classical Bardeen-Stephen model for free flux flow, which is otherwise hard to observe under normal experimental conditions in high-$T_c$ cuprates. Moreover, in the superclean regime, a universal temperature-independent value for the flux flow resistivity was observed, $ρ_f = 1.4(B-B^*)$. We interpret this carrier-relaxation {\it independent} behavior as being related to the dissipation caused by the minigap states within the vortex core. The results are in agreement with theoretical calculations (N. B. Kopnin and G. E. Volovik, Phys. Rev. Lett. {\bf 79}, 1377 (1997)).

cond-mat.supr-con↗

arXiv1999

Evidence of Structural Instability Near T*~250 K in the Resistivity of Bi_2Sr_2CaCu_2O_8 Whiskers

We report anomalous features in the normal-state resistivity of single crystalline Bi_2Sr_2CaCu_2O_8 whiskers near some characteristic temperature T* \~ 250 K. From these varied oxygen-doping samples, the resistance (R) was found to deviate {\it upward} from the linear-T relation for T< T*, while R keeps decreasing with T. The deviation, $ΔR \equiv R - (a + bT)$, reaches a maximum in a temperature range of ~ 25 K just before R-T follows the well-known descent associated with the pseudogap opening in the underdoped samples. A second kink was also found in some samples immediately following the first one, resulting in an S-shaped feature in the R-T curve. The resistance then resumes nearly linear-T decrease below the anomalies in contrast to the first case. We interpret these features as being related to crystal structure transformation (or lattice distortion), as was evidenced in thermal and elastic property measurements. These structural instabilities seem to be connected to the subsequent dynamics as T is further lowered.

cond-mat.supr-con↗