arXiv subjects

H. Oesterreicher

Publications and source records attributed to H. Oesterreicher.

3 recordsLinked to original sources

arXiv2016

Compositions in YBa2Cu3Oy for 3-D bond order superconductors

Self-doping in YBa2Cu3Oy starts to switch from a charge balancing of chain metal reduction and plane oxidation to one of chain ligand oxidation (O-) and plane reduction on quenching from >600K. Amongst the responses are plane expansions and types of unusually strong superconductivity such as elevated temperature superconductivity (ETS), observed through laser pulsing (Tc=552K*) and upon shot quenching (Tc=200K*). We ascribe ETS to limited 3-D superconductivity due to a correlated system of bond ordering within chain-plane sandwiches and propose how to stabilize it. Accordingly, plane expanding n-doping arises from self-doping charge equilibration with local chain Cu of two-fold O coordination (2). The dumbbell type bonds of both apical O- are a result of high-energy environment and comparable in their metric with electron pairs on the plane. Following empirical Tc=%(2)x11 we suggest increasing %(2) to cause the observed retrograde rise in Tc (photo-induced reflectivity edge) to a theoretical limit of Tc=1100K* at 100%(2). We propose compositions and heat treatments based on charge-lattice commensurability. Paired charge concentrations on planes, determined by bond ordering based on magic number counts, suggest several promising candidates such as c=0.22=2/3a0x3b0, c=0.17=2/3x4 or c=0.080=2/5x5. The latter could be achieved with 32%(2) and display Tc=352K* not only in laser pulsed but in shot quenched materials.

cond-mat.mtrl-sci↗

arXiv2015

Elevated Tc levels in YBa2Cu3O6.5 modeled on a 3-dimensional doped bond structure of chain and plane pairs

The complex phenomenology of shot quenched YBa2Cu3O6.5 with Tc=100K and 200K levels is compared with laser pulsed analogs with an eye on explaining the presumed Tc=552K of the latter. Shot quenching can produce metastable states with pronounced increases in plane metric and cell volume, accompanied by a rough doubling of Tc to a 100K level of an orthorhombic with 3-fold O coordinated chain Cu (O3 type). These states decay over a non-superconducting transition range to the conventional Tc=50K level of O24. We consider the plane expanded laser pulsed materials to contain aspects of O42 plane n-doped counterparts of the O3 n-doped version of shot quench preparations. In addition, we assume that highly charged p-doped chains of 4-fold O coordination form hole pairs at trijugate position, allowing close approach of the apical O to the electron-doped planes. They are now capable of participating in the bonding with the plane pairs at corresponding 3a0/2 location. The overall pair number is therefore multiplied, and the coupling strengthened, by limited 3-D effects within the Plane-Chain-Plane sandwich. The latter can be seen as an extended chemical bonding system that has the potential to equilibrate contractive and expansive pairs and so obviate the need for distinction of doping type as it may exchange it dynamically. It is argued that indications for a Tc=200K level on shot quenching has a related origin and represents one in series of predicted Tc levels based on bond order principles. Predictions are made where similar effects can be expected in other compound classes.

cond-mat.supr-con↗

arXiv2008

A predictive bond order model connects covalent superconductivity, including cuprates, oxypnictides or HfN based materials

A phenomenological bond order model predicting doping curves [Tc vs doped charge, c] of cuprates is found to have wider applicability. In this model Tc is dependent on the density of electronic pair crystals [EC] in a covalently bonding layer structure and on a layer Isolation factor, f [ECI model]. Characteristic doping curve events such as optima are correlated with a select number of EC with pair repeats corresponding to multiples of lattice parameters such as c=2/3x4=0.167, where 3x4 represent pair periodicity of 3a0 and 4b0. At these EC all doped charge is converted into pairs according to c=2np. For Tc prediction one writes Tc=2npfTe, where Te=600K and 300K as empirical constants for hole and electron doping. Doping curves for YBa2Cu3Oy with their sharp optima or kinks, separated by near linear ranges, or Tc plateaus on different preparations, can express the stability of special EC. Examples are c=0.22=2/32 for the sharp optimum or the Tc=90K plateau, and c= 0.17 for the 60K plateau, the latter depicting also the optimum for other systems such as La2-wSrwCuO4. For oxypnictides R[O1-xFx]FeAs one writes Tc=300x and expects EC with optimal dopings at x=0.11 and 0.17, as corroborated experimentally. Other examples include HfN derivatives such as Li0.17HfNCl.

cond-mat.supr-con↗