4,949 research outputs found
Competition between Superconductivity and Charge Density Wave Ordering in the LuIr(SiGe) Alloy System
We have performed bulk measurements such as dc magnetic susceptibility,
electrical resistivity and heat capacity on the pseudo-ternary alloys
LuIr(SiGe) to study the interplay and competition
between superconductivity and the charge density wave (CDW) ordering
transition. We track the evolution of the superconducting transition
temperature T and the CDW ordering temperature T as a function
of x (concentration of Ge) (). We find that increasing x
(increasing disorder) suppresses the T rapidly with the concomitant
increase in T. We present a temperature-concentration (or volume) phase
diagram for this system and compare our results with earlier work on
substitution at the Lu or Ir site to show how dilution at the Si site presents
a different situation from these other works. The heat capacity data in the
vicinity of the CDW transition has been analyzed using a model of critical
fluctuations in addition to a mean-field contribution and a smooth lattice
background. We find that the critical exponents change appreciably with
increasing disorder. This analysis suggests that the strong-coupling and non
mean-field like CDW transition in the parent compound LuIrSi
changes to a mean-field like transition with increasing Ge concentration.Comment: 14 pages and 8 figures. Accepted for publication in Phys. Rev.
Zero Temperature Insulator-Metal Transition in Doped Manganites
We study the transition at T=0 from a ferromagnetic insulating to a
ferromagnetic metallic phase in manganites as a function of hole doping using
an effective low-energy model Hamiltonian proposed by us recently. The model
incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly
coupled to orbitally degenerate electrons as well as strong Coulomb correlation
effects and leads naturally to the coexistence of localized (JT polaronic) and
band-like electronic states. We study the insulator-metal transition as a
function of doping as well as of the correlation strength U and JT gain in
energy E_{JT}, and find, for realistic values of parameters, a ground state
phase diagram in agreement with experiments. We also discuss how several other
features of manganites as well as differences in behaviour among manganites can
be understood in terms of our model.Comment: To be published in Europhysics Letter
Perceptions of employability among London's low-paid: 'self-determination' or ethnicity?
We investigate how ethnicity, gender and other characteristics affect low-paid workers’ perceptions of their employability in London’s labour market, examining ‘self-determination’, ethnic and dual labour market theories. We find that perceptions vary considerably, both between genders and ethnicities and in the extent to which they are ‘justified’ by human capital attributes. Optimism varies between genders and ethnic groups but individuals’ perceptions vary to an even greater extent within genders and ethnic groups. Hence, individual-level ‘self-determination’ explanations of these perceptions appear to have greatest explanatory power though ethnic theories also have utility
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