Quantum critical behavior in disordered itinerant ferromagnets: Logarithmic corrections to scaling

The quantum critical behavior of disordered itinerant ferromagnets is determined exactly by solving a recently developed effective field theory. It is shown that there are logarithmic corrections to a previous calculation of the critical behavior, and that the exact critical behavior coincides with that found earlier for a phase transition of undetermined nature in disordered interacting electron systems. This confirms a previous suggestion that the unspecified transition should be identified with the ferromagnetic transition. The behavior of the conductivity, the tunneling density of states, and the phase and quasiparticle relaxation rates across the ferromagnetic transition is also calculated.Comment: 15pp., REVTeX, 8 eps figs, final version as publishe

Anderson-Mott Transition in a Magnetic Field: Corrections to Scaling

It is shown that the Anderson-Mott metal-insulator transition of paramagnetic, interacting disordered electrons in an external magnetic field is in the same universality class as the transition from a ferromagnetic metal to a ferromagnetic insulator discussed recently. As a consequence, large corrections to scaling exist in the magnetic-field universality class, which have been neglected in previous theoretical descriptions. The nature and consequences of these corrections to scaling are discussed.Comment: 5pp., REVTeX, no figs, final version as publishe

Nonanalytic Magnetization Dependence of the Magnon Effective Mass in Itinerant Quantum Ferromagnets

The spin wave dispersion relation in both clean and disordered itinerant quantum ferromagnets is calculated. It is found that effects akin to weak-localization physics cause the frequency of the spin-waves to be a nonanalytic function of the magnetization m. For low frequencies \Omega, small wavevectors k, and small m, the dispersion relation is found to be of the form \Omega ~ m^{1-\alpha} k^2, with \alpha = (4-d)/2 (2<d<4) for disordered systems, and \alpha = (3-d) (1<d<3) for clean ones. In d=4 (disordered) and d=3 (clean), \Omega ~ m ln(1/m) k^2. Experiments to test these predictions are proposed.Comment: 4 pp., REVTeX, no fig

A Quantum Adiabatic Evolution Algorithm Applied to Random Instances of an NP-Complete Problem

A quantum system will stay near its instantaneous ground state if the Hamiltonian that governs its evolution varies slowly enough. This quantum adiabatic behavior is the basis of a new class of algorithms for quantum computing. We test one such algorithm by applying it to randomly generated, hard, instances of an NP-complete problem. For the small examples that we can simulate, the quantum adiabatic algorithm works well, and provides evidence that quantum computers (if large ones can be built) may be able to outperform ordinary computers on hard sets of instances of NP-complete problems.Comment: 15 pages, 6 figures, email correspondence to [email protected] ; a shorter version of this article appeared in the April 20, 2001 issue of Science; see http://www.sciencemag.org/cgi/content/full/292/5516/47

Rovibrational, excitation of molecules by atoms

The results of close coupling (CC) and infinite order sudden (IOS) approximation calculations of cross sections for rovibrational excitation of both para and ortho H(_2) by He are presented. Large discrepancies are found between the present CC results and those of Lin and Secrest (1979) and Lin (1979). The v = O → 1 vibrationally inelastic cross sections are found to differ from those of Lin by factors attaining four orders of magnitude close to the v = 1 excitation threshold. Also, structure in the variation of both vibrationally elastic and inelastic cross sections with energy, reported by Lin and Secrest, and Lin, is absent in the present results. The present CC results are found to be in good quantitative agreement with the coupled states calculations of Alexander and McGuire (1976). Agreement with the IOS calculations is only qualitative but improves with increasing collision energy, consistent with the progressive failure of the energy sudden component of the IOS approximation as the collision energy falls. The values of the vibrational relaxation rate coefficient calculated from the CC results fall below the experimental data of Audibert et al. (1976) at low temperature. This is most probably due to the relatively poor description of the H(_2) system employed, in particular the interaction potential of Gordon and Secrest (1970). The CC results are employed to investigate the accuracy of two energy sudden factorisation schemes. The factorisation which includes off-energy-shell effects is shown to be more accurate than that which does not. However, neither scheme produces cross sections which obey detailed balance. The present IOS results are in good agreement with the adiabatic distorted wave IOS calculations of Bieniek (1980) at low energy. However, as the collision energy increases significant discrepancies appear. For H(_2) + He it appears that at energies sufficiently high for the IOS approximation to be valid the use of adiabatic distorted wave techniques is not valid. Exploratory IOS calculations of rovibrational excitation of H(_2) by h(^+) are reported and discussed. There appears to be evidence that the comparison between theoretical and experimental values of rovibrational cross sections presented by Schinke et al. (1980) and Schinke (1980) is distorted by their restricted numerical methods and faults in their basis wavefunctions

Metal-superconductor transition at zero temperature: A case of unusual scaling

An effective field theory is derived for the normal metal-to-superconductor quantum phase transition at T=0. The critical behavior is determined exactly for all dimensions d>2. Although the critical exponents \beta and \nu do not exist, the usual scaling relations, properly reinterpreted, still hold. A complete scaling description of the transition is given, and the physics underlying the unusual critical behavior is discussed. Quenched disorder leads to anomalously strong T_c-fluctuations which are shown to explain the experimentally observed broadening of the transition in low-T_c thin films.Comment: 4 pp., no figs, final version as publishe

Earthquake slip surfaces identified by biomarker thermal maturity within the 2011 Tohoku-Oki earthquake fault zone.

Extreme slip at shallow depths on subduction zone faults is a primary contributor to tsunami generation by earthquakes. Improving earthquake and tsunami risk assessment requires understanding the material and structural conditions that favor earthquake propagation to the trench. We use new biomarker thermal maturity indicators to identify seismic faults in drill core recovered from the Japan Trench subduction zone, which hosted 50 m of shallow slip during the Mw9.1 2011 Tohoku-Oki earthquake. Our results show that multiple faults have hosted earthquakes with displacement ≥ 10 m, and each could have hosted many great earthquakes, illustrating an extensive history of great earthquake seismicity that caused large shallow slip. We find that lithologic contrasts in frictional properties do not necessarily determine the likelihood of large shallow slip or seismic hazard