J. E. Gordon

Limit on the Electron Electric Dipole Moment in Gadolinium-Iron Garnet

A new method for the detection of the electron edm using a solid is described. The method involves the measurement of a voltage induced across the solid by the alignment of the samples magnetic dipoles in an applied magnetic field, H. A first application of the method to GdIG has resulted in a limit on the electron edm of 5E-24 e-cm, which is a factor of 40 below the limit obtained from the only previous solid-state edm experiment. The result is limited by the imperfect discrimination of an unexpectedly large voltage that is even upon the reversal of the sample magnetization.

Using the Earth as a Polarized Electron Source to Search for Long-Range Spin-Spin Interactions

In Search of Unparticles The standard model of particle physics, which describes the basic building blocks of the universe and the interactions among them, is incomplete. Numerous theoretical extensions have been proposed, some of which predict long-range, spin-spin interactions. To test whether such interactions exist, a laboratory spin source is normally used. Hunter et al. (p. 928) used Earth as a polarized spin source and looked for these interactions by changing the geographical position and the orientation of the measurement apparatus. The polarized spins mainly come from the electrons in iron-containing minerals of Earths mantle, which align in Earths magnetic field. The large numbers of such polarized electrons allowed the extraction of upper bounds on some of the exotic spin-spin interactions far lower than those obtained in the laboratory. Improved bounds on exotic spin-spin interactions were obtained from a study of polarized spins in Earths mantle. Many particle-physics models that extend the standard model predict the existence of long-range spin-spin interactions. We propose an approach that uses the Earth as a polarized spin source to investigate these interactions. Using recent deep-Earth geophysics and geochemistry results, we create a comprehensive map of electron polarization within the Earth induced by the geomagnetic field. We examine possible long-range interactions between these spin-polarized geoelectrons and the spin-polarized electrons and nucleons in three laboratory experiments. By combining our model and the results from these experiments, we establish bounds on torsion gravity and possible long-range spin-spin forces associated with the virtual exchange of either spin-one axial bosons or unparticles.

Chapter 5: The Specific Heat of High-TC Superconductors

Publisher Summary This chapter discusses the information that has been obtained from specific heat measurements on conventional superconductors. An example of the zero-field specific heat of YBa2Cu3O7–δ (YBCO) sample is given. The principal features are compared with those of conventional superconductors, and the experimental problems and complications in the analysis of the data are summarized. The contributions to the specific heat of high- Tc superconductors (HTSC) and their temperature and magnetic field dependences are discussed. Most analyses of the specific heat into its component contributions have been made at low temperatures or in the vicinity of Tc, and the general methods employed in those analyses are outlined. The general features of the lattice heat capacity and the nature of analyses of the data at intermediate and high temperatures are described in the chapter. The feature of the specific heat of HTSC that has received the most attention is the “linear” term—a term proportional to temperature— that occurs in the zero-field specific heat.

Specific heat of YBa2Cu3O7

Specific heat measurements, including measurements in magnetic fields and at both low temperatures and nearTc, on a number of YBa2Cu3O7 samples have revealed several correlations among strongly sample-dependent parameters. These correlations suggest that the sample dependence of the parameters reflects a sample dependence of the volume fraction of superconductivity, which is in turn correlated with a low concentration of Cu2+ moments. The correlations give a criterion for recognizing the values of the parameters characteristic of the fully superconducting material. Preliminary results on the effects of sample heat treatment are reported. New data on the “linear term” is presented and discussed.

Specific heat of Nd(1−x)SrxMnO3

Abstract The specific heat ( C ) of the colossal magnetoresistance material Nd 0.67 Sr 0.33 MnO 3 was measured for 0.35 T H ⩽ 9 T. Estimates were made of contributions to C from the hyperfine interactions, the lattice, Nd 3+ magnetic ordering, ferromagnetic ordering of the Mn ions near T c ≈ 205 K, and a low- T γT term. The entropy associated with the last three terms is essentially equal to that expected for the ordering of the Nd and Mn moments.

Is there an intrinsic linear term in the specific heat of YBa2Cu3O7

Abstract A reanalysis of specific-heat data suggests the existence of an intrinsic contribution to the linear term of the order of 2 mJ/mole. K 2 in YBCO. On the basis of comparison with other high-T c oxide superconductors it appears that the intrinsic contribution may be unique to YBCO, and therefore probably associated with the CuO chains.

A magnetization sensitive potential at garnet–metal interfaces

Abstract We investigate a magnetization-dependent voltage that appears at the interface between garnets and various metals. The voltage is even in the applied magnetic field and is dependent on the surface roughness and the pressure holding the surfaces together. Large variations in the size, sign and magnetic dependence are observed between different metal surfaces. Some patterns have been identified in the measured voltages and a simple model is described that can accommodate the gross features. The bulk magnetoelectric response of one of our polycrystalline YIG samples is measured and is found to be consistent with a term in the free energy that is quadratic in both the electric and magnetic fields. However, the presence of such a term does not fully explain the complex magnetization dependence of the measured voltages.

A Study of the Paramagnetic to Ferromagnetic Transition in the Optimally Doped CMR Compound La0.65Ca0.35MnO3 and Its Dependence on Oxygen Mass

We present a study of the paramagnetic to ferromagnetic transition in the CMR compound La0.65Ca0.35MnO3 and its dependence on magnetic field and oxygen mass. The transition is characterized by two temperatures, the thermodynamic transition temperature at Tc, obtained from specific heat and thermal expansion data, and the resistive transition obtained from the resistivity maximum. The resistive transition occurs well within the paramagnetic range. The magnetic susceptibility in the paramagnetic range is isotope dependent up to 400 K. The magnitude of the Curie-Weiss constant indicates the presence of small clusters of about 4–5 unit cells. The resistive transition occurs when the percolation limit for these clusters is reached.

Specific heat of YBa2Cu3O7−σ: paramagnetic centers; evidence for line nodes in the energy gap

Specific-heat data on YBa 2 Cu 3 O 7-δ , 0 < δ <0.2, have been analyzed to show the presence of spin-2, as well as spin-1/2, paramagnetic centers. Evidence of line nodes in the energy gap, including conformity to a predicted scaling relation, is reported.

High-Tc Superconductors: Thermodynamic Properties

Thermodynamic properties, primarily the specific heat, of the high-Tc cuprate superconductors are reviewed. This topic was covered in a number of reviews that appeared in the early years of research on these materials. Here the emphasis is on more recent experimental results, including many measurements in magnetic fields, and on features related to phenomena that have been recognized more recently. Calorimetric evidence bearing on the symmetry of the order parameter, the nature of the transition at Tc, the effects of chemical substitutions, fluctuation effects, the melting of the vortex lattice, the existence of a pseudogap, and effects that appear to be related to stripe formation are discussed. Brief summaries of the different experimental techniques, with evaluations of their strengths and weaknesses, and of the problems and uncertainties that arise in analyses of the data are included.