The fifth interaction: universal long range force between spins

In this paper we present a review of our investigations on universal long range force between spins mediated by a massless axial vector gauge field which we name as “axial photon”. The invariance of the Lagrangian field theory of particles, possessing spin degrees of freedom, under local Lorentz transformations, necessitates the introduction of such an axial vector gauge field which interacts with spin current of the particles. Classical as well as quantum dynamics of electrons interacting with photon and axial photon are worked out. The new interaction is found to be asymptotically free. It is shown thatqed can be made finite if the coupling strengths of electron to photon and axial photon can be made equal. Experimental consequences of the existence of axial photon are discussed and the strength of the interaction is estimated by comparing predictions of the theory with experiments.     

High temperature superconductivity in Bi-Sr-Ca-Cu-O oxide system

Stable, reproducible high temperature superconductivity with onset temperatures of 90 K and above is confirmed in the oxide system with nominal metal ion composition BiSrCaCu₂O _x . The onset is nearly the same, but zero-resistance temperatures depend on the heat treatment. Sample quenched from 850 C in air (close to melting) to liquid nitrogen temperature is non-superconducting. BiSr_0.5Ca_1.5Cu₂O _x is also found to be superconducting in which a two-step drop in resistance is observed, one starting around 118 K and the other around 80 K.     

Magnetic field dependence of critical current density in YBa2Cu3O7

We have measured the transport critical current densityJ _cof sintered YBa₂Cu₃O₇, in various applied fields up to 185 Oe at 77 K. We find a sharp decay ofJ _cwith magnetic field. We show that this sharp decay is consistent with the low field hysteresis results of Groveret al. We argue that the observed field dependence is not caused by intragranular weak links.     

Effect of Si addition on the valence state of Ce in CePd3

It is observed that Si can be added to CePd₃, which has the AuCu₃ type cubic structure, to form alloys of the type CePd₃Si_x where 0 ≤ x ≤ 0.3. Addition of Si preserves the structure but results in an expansion of the cell volume. The expansion is much larger in CePd₃ than in LaPd₃ for the same silicon concentration. In CePd₃, cerium is in a mixed-valent state and its susceptibility tends to a temperature independent value at low temperature. However, as Si is added to CePd₃, the susceptibility progressively increases and shows a Curie-Weiss behavior with effective moment close to that of Ce³⁺ ions. Thus from lattice parameters and susceptibility measurements, it is inferred that Si addition causes a change in the valence of Ce in CePd₃ from mixed valent to nearly trivalent.     

Influence of hydrogen on structure and magnetic properties of Ho6Fe23 and Er6Fe23

The pressure composition isotherm of the Er₆Fe₂₃-H₂ system studied at 0°C reveals the presence of three different hydride phases. Maximum absorption is typically 14 hydrogen atoms/formula unit in Er₆Fe₂₃ and Ho₆Fe₂₃ compared to about 22 in the isostructural Mn compounds. During hydrogenation Ho₆Fe₂₃ remains cubic with lattice parameter which increases from 12.034 Å to 12.399 Å. Upon hydrogenation Er₆Fe₂₃ exhibits the very surprising behavior of transforming from a cubic ($\text{a}\text{= 12.004}\text{A}\text{?}$) to a tetragonal structure ($\text{a}\text{= 12.131}\text{A}\text{?}$, $\text{c}\text{= 12.601}\text{A}\text{?}$). In spite of their contrasting crystallographic features both hydrides exhibit similar magnetic behavior, relative to the parent compounds, namely, lowering of both the saturation moment at 4.2 and the compensation temperature and an increase in the saturation moment at room temperature. The results of magnetic measurements may be understood by assuming an increase in the iron moment in these compounds on hydrogen absorption.