2,936 research outputs found
Currents and pseudomagnetic fields in strained graphene rings
We study the effects of strain on the electronic properties and persistent
current characteristics of a graphene ring using the Dirac representation. For
a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic
(gauge) fields that may effectively reduce or enhance locally the applied
magnetic flux through the ring. Flux-induced persistent currents in a flat ring
have full rotational symmetry throughout the structure; in contrast, we show
that currents in the presence of a circularly symmetric deformation are
strongly inhomogeneous, due to the underlying symmetries of graphene. This
result illustrates the inherent competition between the `real' magnetic field
and the `pseudo' field arising from strains, and suggest an alternative way to
probe the strength and symmetries of pseudomagnetic fields on graphene systems
Graphene zigzag ribbons, square lattice models and quantum spin chains
We present an extended study of finite-width zigzag graphene ribbons (ZGRs)
based on a tight-binding model with hard-wall boundary conditions. We provide
an exact analytic solution that clarifies the origin of the predicted width
dependence on the conductance through junctions of ribbons with different
widths. An analysis of the obtained solutions suggests a new description of
ZGRs in terms of coupled chains. We pursue these ideas further by introducing a
mapping between the ZGR model and the Hamiltonian for N-coupled quantum chains
as described in terms of 2N Majorana fermions. The proposed mapping preserves
the dependence of ribbon properties on its width thus rendering metallic
ribbons for N odd and zero-gap semiconductor ribbons for N even. Furthermore,
it reveals a close connection between the low-energy properties of the ZGR
model and a continuous family of square lattice model Hamiltonians with similar
width-dependent properties that includes the flux and the trivial square
lattice models. As a further extension, we show that this new description makes
it possible to identify various aspects of the physics of graphene ribbons with
those predicted by models of quantum spin chains (QSCs)
Relations of Parenting Quality, Interparental Conflict, and Overnights with Mental Health Problems of Children in Divorcing Families with High Legal Conflict
The current study examined the associations between child mental health problems and the quality of maternal and paternal parenting, and how these associations were moderated by three contextual factors, quality of parenting by the other parent, interparental conflict, and the number of overnights parents had with the child. Data for the current study come from a sample of divorcing families who are in high legal conflict over developing or maintaining a parenting plan following divorce. Analyses revealed that the associations between child mental health problems and positive maternal and paternal parenting were moderated by the quality of parenting provided by the other parent and by the number of overnights children spent with parents, but not by the level of interparental conflict. When both parenting by the other parent and number of overnights were considered in the same model, only number of overnights moderated the relations between parenting and child behavior problems. The results support the proposition that the well-being of children in high conflict divorcing families is better when they spend adequate time with at least one parent who provides high quality parenting
Quantum phase transitions into Kondo states in bilayer graphene
We study a magnetic impurity intercalated in bilayer graphene. A
representative configuration generates a hybridization function with strong
dependence on the conduction-electron energy, including a full gap with one
hard and one soft edge. Shifts of the chemical potential via gating or doping
drive the system between non-Kondo (free-moment) and Kondo-screened phases,
with strong variation of the Kondo scale. Quantum phase transitions near the
soft edge are of Kosterlitz-Thouless type, while others are first order. Near
the hard edge, a bound-state singlet appears inside the gap; although of
single-particle character, its signatures in scanning tunneling spectroscopy
are very similar to those arising from a many-body Kondo resonance
Kondo regime in triangular arrangements of quantum dots: Molecular orbitals, interference and contact effects
Transport properties of an interacting triple quantum dot system coupled to
three leads in a triangular geometry has been studied in the Kondo regime.
Applying mean-field finite-U slave boson and embedded cluster approximations to
the calculation of transport properties unveils a set of rich features
associated to the high symmetry of this system. Results using both calculation
techniques yield excellent overall agreement and provide additional insights
into the physical behavior of this interesting geometry. In the case when just
two current leads are connected to the three-dot system, interference effects
between degenerate molecular orbitals are found to strongly affect the overall
conductance. An S=1 Kondo effect is also shown to appear for the perfect
equilateral triangle symmetry. The introduction of a third current lead results
in an `amplitude leakage' phenomenon, akin to that appearing in beam splitters,
which alters the interference effects and the overall conductance through the
system.Comment: 14 pages, 9 figures, submitted to PR
Developmental cascade models of a parenting-focused program for divorced families on mental health problems and substance use in emerging adulthood
A developmental cascade model from functioning in adolescence to emerging adulthood was tested using data from a 15-year longitudinal follow-up of 240 emerging adults whose families participated in a randomized, experimental trial of a preventive program for divorced families. Families participated in the program or literature control condition when the offspring were ages 9–12. Short-term follow-ups were conducted 3 months and 6 months following completion of the program when the offspring were in late childhood/early adolescence. Long-term follow-ups were conducted 6 years and 15 years after program completion when the offspring were in middle to late adolescence and emerging adulthood, respectively. It was hypothesized that the impact of the program on mental health and substance use outcomes in emerging adulthood would be explained by developmental cascade effects of program effects in adolescence. The results provided support for a cascade effects model. Specifically, academic competence in adolescence had cross-domain effects on internalizing problems and externalizing problems in emerging adulthood. In addition, adaptive coping in adolescence was significantly, negatively related to binge drinking. It was unexpected that internalizing symptoms in adolescence were significantly negatively related to marijuana use and alcohol use. Gender differences occurred in the links between mental health problems and substance use in adolescence and mental health problems and substance use in emerging adulthood
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