Metastable-atom deexcitation spectroscopy using singlet ${(}^1$S ${\mathrm{He}}^{\mathrm{*}}$) as well as triplet ${(}^3$S ${\mathrm{He}}^{\mathrm{*}}$${,}^3$P ${\mathrm{Ne}}^{\mathrm{*}}$${,}^3$P ${\mathrm{Ar}}^{\mathrm{*}}$) species reveals that NO chemisorbed on Pd(111) or Pt(111) surfaces remains paramagnetic (on a time scale ${>10\mathrm{}}^{\mathrm{-}13}$ sec) with its 2π̃ level close to the Fermi level. The 1π̃-5σ̃ and 4σ̃ metastable-atom deexcitation spectroscopy peaks show characteristic multiplet splittings which are, however, considerably smaller than with free NO. No paramagnetic properties are found for NO adsorbed on Cu(110) which is attributed to a stronger coupling between the 2π level and the metal.

Optical second-harmonic studies show that the electronic structure in the top 75–130 Å of a crystalline Si surface loses cubic order only 150 fsec after the Si is excited by an intense 100-fsec optical pulse. This suggests that atomic disorder can be induced directly by electronic excitation, before the material becomes vibrationally excited. In contrast, the electronic properties of the equilibrium molten phase are not obtained for several hundreds of femtoseconds.

In the vicinity of a nonmagnetic impurity locally, a charge-density wave is formed (Friedel oscillation). The pinning of a linearly polarized spin-density wave by an impurity is due to the mismatches of the charge and spin oscillations. For comparison it is shown that for an intermediate-strength impurity the ratio of the pinning energies of a spin-density wave and of a charge-density wave with the same gap is larger than ${10}^{\mathrm{-}1}$ which is well beyond any previous estimation. The experimental consequences are also discussed.

We used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to substitute preferentially on the Cu(2) and Cu(1) sites in the ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ superconductor. Small doping of Ga induces an orthorhombic-to-tetragonal structural transition, but the values of ${\mathrm{T}}_{\mathrm{c}}$ are as high as 81 K in the tetragonal phase. Our results indicate that the oxygen-vacancy order, or the linear-chain structure, is not essential. We also find that the Cu(2) sites are much more crucial than the Cu(1) sites in sustaining the high ${\mathrm{T}}_{\mathrm{c}}$.

The critical behavior of disordered single-particle systems without time-reversal symmetry is described by a nonlinear σ model defined over a graded pseudounitary coset space. With use of the Migdal-Kadanoff approximate renormalization group relations, the fixed point of this model is studied for d=2+ε and d=3 dimensions. It is found that the properties of the fixed point for d=3 are dominated by the noncompact degrees of freedom of the model. The critical exponent ν for d=3 satisfies the inequality recently derived by Chayes et al.

We report a direct experimental observation of Pancharatnam’s phase, which is closely related to Berry’s topological phase. The experiment involves measurement of the phase change in one beam of a laser interferometer as the polarization state of light is taken along a closed circuit on the Poincaré sphere. The phase change is found to be equal to half the solid angle subtended by the circuit at the center of the Poincaré sphere. Apart from providing a striking demonstration of the topological phase, the experiment demonstrates that unitary time evolution of a system is not essential for the appearance of the topological phase.

We report the direct observation of a topological phase, i.e., an Aharonov-Bohm-type phase, as a fringe shift in an optical interferometer, which consisted of a modified Mach-Zehnder interferometer, in which the light traveled along nonplanar paths in its two arms. These arms were arranged symmetrically so as to have nearly equal path lengths, but opposite senses of handedness. The relationship between the phase acquired by a circularly polarized light beam and the solid angle subtended by the circuit of the spin vector of a photon in this beam was found to be a linear one with a slope of unity. The sign of the fringe shift also agreed with theory.

Aharonov and Anandan have recently reformulated and generalized Berry’s phase by showing that a quantum system which evolves through a circuit C in projective Hilbert space acquires a geometrical phase β(C) related to the topology of the space and the geometry of the circuit. We present NMR interferometry experiments in a three-level system which demonstrate the Aharonov-Anandan phase and its topological invariance for different circuits.

An infinite number of ways are developed for representing a function in terms of the eigenfunctions of a three-dimensional scattering problem and simple known auxiliary functions. The utility of the new expansions, which generalize both the Fourier and Radon transforms, is shown by derivation of a new representation of the scatterer for the near- (far-) field inverse problem. Further, the scattering amplitude and potential are shown to be a generalized Fourier-transform pair.

Seemingly contradictory results from Eötvös-type experiments have been reported by Thieberger and by Adelberger and collaborators. Attempts to reconcile the discrepancy have mainly focused on a single moderate-ranged (of order hundreds of meters) force, coupled to various charges. However, because the local geologies are significantly different in these two experiments, they may be compatible with an alternative scenario: new spin-1 graviphoton and spin-0 graviscalar partners of the graviton, both with longer ranges (tens to hundreds of kilometers). We discuss this and other new data in terms of these two concepts.

By means of a recent analysis of the high-energy limit of string scattering, linear relations between string scattering amplitudes are derived. These are shown to hold order by order in perturbation theory. If one assumes that they hold for the full theory, they suggest the existence of an enormous string-broken symmetry which is restored at high energies. Some speculations as to the nature of this symmetry are presented.

QCD corrections may substantially enhance a techniquark condensate relative to a technilepton condensate when the technicolor β function is small. This enhancement factor appears in quark-lepton mass ratios. There is much less enhancement of the techniquark-technilepton mass ratio.

Consideration of the decay Υ into gluon plus axigluon, in a chiral color theory, places a lower bound on the axigluon mass of at least 9 GeV. The corresponding toponium decay will give a better mass bound on (or confirmation of) a light axigluon.

We present a study of $D^0$ mixing using events of the type $D^{\mathrm{*}+}$→${\pi }^{+}$$D^0$, with $D^0$→$K^{+}$${\pi }^{\mathrm{-}}$ and $D^0$→$K^{+}$${\pi }^{\mathrm{-}}$${\pi }^{+}$${\pi }^{\mathrm{-}}$. The decay time is used to separate mixing from doubly Cabibbo-suppressed decays. We observe no evidence for mixing in either mode. Combining the results from the two decay modes, we find $r_M$=0.0005 ±0.0020 or $r_M$<0.0037 at the 90% confidence level, where $r_M$ is the ratio of wrong-sign decays from mixing to right-sign decays. We also present limits on doubly Cabibbo-suppressed decays and consider the effect of possible interference.

Let u’=Mu+Nf be a general linear iterative process for solving the system Lu=f, with L=${\mathrm{L}}^{\mathrm{T}}$ and with 1=M+NL. Provided that Γ≡1/2(${\mathit{L}}^{\mathrm{-}1}$-${\mathit{ML}}^{\mathrm{-}1}$${\mathit{M}}^{\mathrm{T}}$${)}^{\mathrm{-}1}$ is a positive-definite matrix, it is shown that one can explicitly construct a corresponding stochastic algorithm which satisfies the homogeneous-state condition with respect to the probability distribution exp(-βS), where S=(1/2${\mathrm{u}}^{\mathrm{T}\mathrm{Lu}\mathrm{-}{\mathrm{f}}^{\mathrm{T}\mathrm{u}}}$. When ${\mathrm{M}}^{\mathrm{T}\mathrm{L}=\mathrm{LM}}$, the algorithm also satisfies the detailed-balance condition.

The lattice-regularized U(1) Higgs model in an external electromagnetic field is studied by Monte Carlo techniques. In the Coulomb phase magnetic flux can flow through uniformly. The Higgs phase splits into a region where magnetic flux can penetrate only in the form of vortices and a region where the magnetic flux is completely expelled, the relativistic analog of the Meissner effect in superconductivity. We present evidence for symmetry restoration in strong external fields.

SU(3) gauge theory with a light isodoublet and a heavier strange quark is simulated on a 4×$8^3$ lattice. A first-order chiral-symmetry–restoring phase transition is found and metastable states are exhibited. The gluon, isodoublet, and strange-quark contributions to the energy density are in the ratio 8:4:1 and each internal energy jumps discontinuously at ${\mathrm{T}}_{\mathrm{c}}$.

Evidence for optical guiding of 1.7-mm-wavelength radiation along an electron beam in a Raman free-electron laser is obtained experimentally and compared with numerical simulations. Optical guiding is manifest as the interference effect of several waveguide modes; this is observed beyond the point of electron-beam termination. The experiment operates in the regime of exponential signal gain and appreciable electron-beam space charge.

Streak-camera detection of moving interference fringes with single-photon resolution constitutes a novel Young’s experiment in which the exact frequency of each detected photon cannot be specified without destroying the visibility of the interference pattern. The experiment demonstrates first-order cross spectral coherence between resolvable frequencies, in which case the optical frequency of the detected light must be calculated in terms of a time-dependent spectrum.

Transient, time-delayed, four-wave mixing (TDFWM) experiments have been performed on the Na D doublet with use of a novel angled-beam geometry. The effects of petahertz superposition-state modulations have been observed in the integrated TDFWM signal as a function of the time delay. As the time delay is varied, the lowest-order mixing signal modulates with a period of 980 as—corresponding to the sum frequency of the two Na D lines. Higher-diffraction-order mixing signals contain modulation components at integral multiples of the doublet sum frequency.