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Phases of matter are usually identified through spontaneous symmetry breaking, especially regarding unconventional superconductivity and the interactions from which it originates. In that context, the superconducting state of the quasi-two-dimensional and strongly correlated perovskite Sr.sub.2RuO.sub.4 is considered to be the only solid-state analogue to the superfluid .sup.3He-A phase.sup.1,2, with an odd-parity order parameter that is unidirectional in spin space for all electron momenta and breaks time-reversal symmetry. This characterization was recently called into question by a search for an expected 'split' transition in a Sr.sub.2RuO.sub.4 crystal under in-plane uniaxial pressure, which failed to find any such evidence; instead, a dramatic rise and a peak in a single-transition temperature were observed.sup.3,4. Here we use nuclear magnetic resonance (NMR) spectroscopy of oxygen-17, which is directly sensitive to the order parameter via hyperfine coupling to the electronic spin degrees of freedom, to probe the nature of superconductivity in Sr.sub.2RuO.sub.4 and its evolution under strain. A reduction of the Knight shift is observed for all strain values and at temperatures below the critical temperature, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results contradict a body of previous NMR work reporting no change in the Knight shift.sup.5 and the most prevalent theoretical interpretation of the order parameter as a chiral p-wave state. Sr.sub.2RuO.sub.4 is an extremely clean layered perovskite and its superconductivity emerges from a strongly correlated Fermi liquid, and our work imposes tight constraints on the order parameter symmetry of this archetypal system. .sup.17O nuclear magnetic resonance measurements on Sr.sub.2RuO.sub.4 reveal a drop of the Knight shift in the superconducting state, contradicting previous work and imposing tight constraints on the order parameter symmetry of the system., Author(s): A. Pustogow [sup.1] , Yongkang Luo [sup.1] [sup.2] , A. Chronister [sup.1] , Y.-S. Su [sup.1] , D. A. Sokolov [sup.3] , F. Jerzembeck [sup.3] , A. P. Mackenzie [...]

The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state [...]

Low-temperature phase transitions and the associated quantum critical points are a major field of research, but one in which experimental information about thermodynamics is sparse. Thermodynamic information is vital for the understanding of quantum many-body problems. We show that combining measurements of the magnetocaioric effect and specific heat allows a comprehensive study of the entropy of a system. We present a quantitative measurement of the entropic landscape of [Sr.sub.3][Ru.sub.2][O.sub.7], a quantum critical system in which magnetic field is used as a tuning parameter. This allows us to track the development of the entropy as the quantum critical point is approached and to study the thermodynamic consequences of the formation of a novel electronic liquid crystalline phase in its vicinity.

The nature of the metallic phase in the high-transition-temperature (high-[T.sub.c]) copper oxide superconductors, and its evolution with carrier concentration, has been a long-standing mystery (1). A central question is how [...]

Condensed systems of strongly interacting electrons are ideal for the study of quantum complexity. It has become possible to promote the formation of new quantum phases by explicitly tuning systems toward special low-temperature quantum critical points. So far, the clearest examples have been appearances of superconductivity near pressure-tuned antiferromagnetic quantum critical points. We present experimental evidence for the formation of a non-superconducting phase in the vicinity of a magnetic field-tuned quantum critical point in ultrapure crystals of the ruthenate metal [Sr.sub.3][Ru.sub.2][O.sub.7], and we discuss the possibility that the observed phase is due to a spin-dependent symmetry-breaking Fermi surface distortion., The field of quantum criticality continues to attract widespread theoretical and experimental attention because of its importance to the global effort to understand the behavior of correlated electron systems (1-4). [...]

Superconductivity is of considerable scientific and practice interest and to gain further information about the properties of the superconductor, the intensity of the flux-line lattice (Fll) signal must be understood, or the magnitude of the Fourier components. A small-angle neutron-scattering measurement of magnetic flux lines in the Sr(sub2)RuO(sub4) perovskite superconductor was taken. Magnetic flux lines were found to form a square lattice over broad field and temperature fields.

These are exciting times for superconductivity research and for studying the physics of materials with strongly interacting electrons. We are witnessing a revolution in our understanding of new and exotic [...]

Abstract: We present a brief review of the physical properties of Sr3Ru2O7, in which the approach to a magnetic-field-tuned quantum critical point is cut off by the formation of a novel phase with transport characteristics consistent with those of a nematic electronic liquid crystal. Our goal is to summarise the physics that led to that conclusion being drawn, describing the key experiments and discussing the theoretical approaches that have been adopted. Throughout the review we also attempt to highlight observations that are not yet understood, and to discuss the future challenges that will need to be addressed by both experiment and theory. [Copyright &y& Elsevier]

Objective: Currently, physicians manage preterm premature rupture of membranes (PPROM) by expectant management or termination of the gestation. A therapy aimed at sealing membranes would be optimal to maintain the pregnancy and achieve a normal neonate. Our objective was to compare an endoscopic technique for intrauterine closure of fetal membrane defects after both iatrogenic and spontaneous rupture of membranes. Methods: Our technique was performed on four patients experiencing PPROM spontaneously and four patients after genetic amniocentesis. Intrauterine endoscopy allowed direct visualization of membrane defects. Rapid sequential injections of platelets, fibrin glue and powdered collagen slurry were administered at the site of the defect and of trocar placement. Sonography for amniotic fluid index, nitrazine and fern testing and pad count were performed after each procedure at three intervals: immediately post-procedure, and after 24 and 48 h. Results: Eight patients underwent endoscopic intrauterine sealing of ruptured membranes between 16 and 24 weeks of gestation: four were spontaneous ruptures and four were ruptures post-amniocentesis. In the post-amniocentesis group, three patients delivered viable infants at 26, 32 and 34 weeks. In one patient, the membranes ruptured again 12 h after the sealing procedure and she decided to undergo termination of pregnancy. Of the four spontaneous rupture patients, two experienced preterm labor and delivery within 2 days of the procedure. One patient was diagnosed with fetal demise 12 h post-procedure, and one patient delivered a neonate at 31 weeks of gestation with severe respiratory distress syndrome. Conclusions: This technique for sealing ruptured membranes is effective after amniocentesis, but may not be of benefit with spontaneous rupture. [ABSTRACT FROM AUTHOR]