Charge Friedel oscillations in a Mott insulator

When a metal undergoes a transition to an insulator it will lose its electronic Fermi surface. Interestingly in some situations a `ghost' Fermi surface of electrically neutral spin carrying fermions may survive into the insulator. Such a novel ghost Fermi surface has been proposed to underlie the properties of a few different materials but its direct detection has proven elusive. In this paper we show that the ghost Fermi surface leads to slowly decaying spatial oscillations of the electron density near impurities or other defects. These and related oscillations stem from the sharpness of the ghost Fermi surface and are direct analogs of the familiar Friedel oscillations in metals. The oscillation period contains geometric information about the shape of the ghost Fermi surface which can be potentially exploited to detect its existence.Comment: 6 pages, 3 figure

Stripe melting and quantum criticality in correlated metals

We study theoretically quantum melting transitions of stripe order in a metallic environment, and the associated reconstruction of the electronic Fermi surface. We show that such quantum phase transitions can be continuous in situations where the stripe melting occurs by proliferating pairs of dislocations in the stripe order parameter without proliferating single dislocations. We develop an intuitive picture of such phases as "Stripe Loop Metals" where the fluctuating stripes form closed loops of arbitrary size at long distances. We obtain a controlled critical theory of a few different continuous quantum melting transitions of stripes in metals . At such a (deconfined) critical point the fluctuations of the stripe order parameter are strongly coupled, yet tractable. They also decouple dynamically from the Fermi-surface. We calculate many universal properties of these quantum critical points. In particular we find that the full Fermi-surface and the associated Landau quasiparticles remain sharply defined at the critical point. We discuss the phenomenon of Fermi surface reconstruction across this transition and the effect of quantum critical stripe fluctuations on the superconducting instability. We study possible relevance of our results to several phenomena in the cuprates.Comment: 22 pages, 22 figure

The two-impurity Kondo model with spin-orbit interactions

We study the two-impurity Kondo model (TIKM) in two dimensions with spin-orbit coupled conduction electrons. In the first part of the paper we analyze how spin-orbit interactions of Rashba as well as Dresselhaus type influence the Kondo and RKKY interactions in the TIKM, generalizing results obtained by H. Imamura {\em et al.} (2004) and J. Malecki (2007). Using our findings we then explore the effect from spin-orbit interactions on the non-Fermi liquid quantum critical transition between the RKKY-singlet and Kondo-screened RKKY-triplet states. We argue that spin-orbit interactions under certain conditions produce a line of critical points exhibiting the same leading scaling behavior as that of the ordinary TIKM. In the second part of the paper we shift focus and turn to the question of how spin-orbit interactions affect the entanglement between two localized RKKY-coupled spins in the parameter regime where the competition from the direct Kondo interaction can be neglected. Using data for a device with two spinful quantum dots patterned in a gated InAs heterostructure we show that a gate-controlled spin-orbit interaction may drive a maximally entangled state to one with vanishing entanglement, or vice versa (as measured by the concurrence). This has important implications for proposals using RKKY interactions for nonlocal control of qubit entanglement in semiconductor heterostructures.Comment: Revised version; new title and introduction in response to referee suggestion, expanded discussion of results, added references. 14 pages, 5 figure

Spin and pair density wave glasses

Spontaneous breaking of translational symmetry---known as `density wave' order---is common in nature. However such states are strongly sensitive to impurities or other forms of frozen disorder leading to fascinating glassy phenomena. We analyze impurity effects on a particularly ubiquitous form of broken translation symmetry in solids: a Spin Density Wave (SDW) with spatially modulated magnetic order. Related phenomena occur in Pair Density Wave (PDW) superconductors where the superconducting order is spatially modulated. For weak disorder, we find that the SDW / PDW order can generically give way to a SDW / PDW glass---new phases of matter with a number of striking properties, which we introduce and characterize here. In particular, they exhibit an interesting combination of conventional (symmetry-breaking) and spin glass (Edwards-Anderson) order. This is reflected in the dynamic response of such a system, which---as expected for a glass---is extremely slow in certain variables, but---surprisingly---is fast in others. Our results apply to all uniaxial metallic SDW systems where the ordering vector is incommensurate with the crystalline lattice. In addition, the possibility of a PDW glass has important consequences for some recent theoretical and experimental work on $La_{2-x}Ba_xCu_2O_4$.Comment: 10 pages, 5 figure

Bosonic Analogue of Dirac Composite Fermi Liquid

We introduce a particle-hole-symmetric metallic state of bosons in a magnetic field at odd-integer filling. This state hosts composite fermions whose energy dispersion features a quadratic band touching and corresponding $2\pi$ Berry flux protected by particle-hole and discrete rotation symmetries. We also construct an alternative particle-hole symmetric state---distinct in the presence of inversion symmetry---without Berry flux. As in the Dirac composite Fermi liquid introduced by Son, breaking particle-hole symmetry recovers the familiar Chern-Simons theory. We discuss realizations of this phase both in 2D and on bosonic topological insulator surfaces, as well as signatures in experiments and simulations.Comment: 8 pages, 5 figure

Symmetry and duality in bosonization of two-dimensional Dirac fermions

Recent work on a family of boson-fermion mappings has emphasized the interplay of symmetry and duality: Phases related by a particle-vortex duality of bosons (fermions) are related by time-reversal symmetry in their fermionic (bosonic) formulation. We present exact mappings for a number of concrete models that make this property explicit on the operator level. We illustrate the approach with one- and two-dimensional quantum Ising models, and then similarly explore the duality web of complex bosons and Dirac fermions in (2+1) dimensions.Comment: 31 pages, 9 figure

Anomalous Quasiparticle Symmetries and Non-Abelian Defects on Symmetrically Gapped Surfaces of Weak Topological Insulators

We show that boundaries of 3D weak topological insulators can become gapped by strong interactions while preserving all symmetries, leading to Abelian surface topological order. The anomalous nature of the weak topological insulators manifests itself in a non-trivial action of symmetries on the quasiparticles; most strikingly, translations change the anyon types in a manner impossible in strictly 2D systems with the same symmetry. As a further consequence, screw dislocations form non-Abelian defects that trap $\mathbb{Z}_4$ parafermion zero modes.Comment: 6 pages, 4 figure

Formulation and Implementation of Environmental Strategies in Printing Firms: A Comparison between the U.S. and Germany

This thesis will guide the reader through the investigation process of a research area previously ignored in the research literature: the formulation and implementation of environmental strategies in printing companies. It will address strategies in printing firms, primarily from a cultural and structural point of view, which are formulated and implemented to help protect the environment and to save resources. The investigation will include a review of previous literature regarding strategy, environmental management and technology, and health and safety management. It will introduce the research questions, the methodology, and the analysis of research findings. Through the exploratory case study method, the researcher will show how some printing companies integrate environmental protection within their strategic decision process. The researcher investigated two small and two large printing firms in the U.S. and Germany to learn how company size and cultural background influence environmental strategy formulation and implementation processes. In addition, the researcher wanted to know about the individual competitive context, adapted by Porter and Kramer (2002) that influences each firm in its strategic decision-process. The analysis of the four case studies shows that the environmental strategies of printing companies differ, depending on each individual company and the competitive forces it faces. Though the history of each firm\u27s environmental strategy development is distinctive, all four companies succeeded in creating a competitive edge, gaining a range of common and in some cases individual benefits. Some key factors driving the firms\u27 strategic decision-making processes kept reappearing in the studies: organizational structure, ownership, location, company size, and the history and cultural background of the company. The factor conditions turned out to be the most important element of the competitive context for all four cases. This involves particularly leadership and personal commitment of the members of the firm (employees, the chairman of the board, the CEO, or the mother organization). The demand conditions seemed to be more important to the small firms than to the large firms investigated. All four companies concentrated on process improvements and the resulting increased efficiency and saved resources, thereby reducing environmental impact and saving costs. From the strategy focus and competitive context of each firm it was possible to ascertain its strategy type: emergent or deliberate. Both small firms deliberately use their environmental stance, and thus have formal strategies. The large firms have an informal feel to their environmental initiatives. The overall goal of this thesis research was to provide the printing industry with valuable information regarding the adoption of environmental strategies. The investigator hoped to help close the gap in the printing literature and to encourage more printing companies to start integrating environmental issues in their strategic decisions in order to become more competitive and socially responsible businesses

Study of lubricant jet flow phenomena in spur gears

Lubricant jet flow impingement and penetration depth into a gear tooth space were measured at 4920 and 2560 rpm using a 8.89 cm (3.5 inch) pitch diameter 8 pitch spur gear at oil pressures from 70,000 to 410,000 n/sqm (10 psi to 60 psi). A high speed motion picture camera was used with xenon and high speed stroboscopic lights to slow down and stop the motion of the oil jet. An analytical model was developed for the vectorial impingement dept and for the impingement depth with tooth space windage effects included. The windage effects for oil drop size greater than .0076 cm (.003 inches). The analytical impingement dept compared favorably with experimental results above an oil jet pressure of 70,000 n/sqm (10psi). There was further penetration into the tooth space after impingement, but much of this oil was thrown out of the tooth space without further contacting the gear teeth