8 research outputs found

    Non-zero temperature transport near quantum critical points

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    We describe the nature of charge transport at non-zero temperatures (TT) above the two-dimensional (dd) superfluid-insulator quantum critical point. We argue that the transport is characterized by inelastic collisions among thermally excited carriers at a rate of order kBT/k_B T/\hbar. This implies that the transport at frequencies ωkBT/\omega \ll k_B T/\hbar is in the hydrodynamic, collision-dominated (or `incoherent') regime, while ωkBT/\omega \gg k_B T/\hbar is the collisionless (or `phase-coherent') regime. The conductivity is argued to be e2/he^2 / h times a non-trivial universal scaling function of ω/kBT\hbar \omega / k_B T, and not independent of ω/kBT\hbar \omega/k_B T, as has been previously claimed, or implicitly assumed. The experimentally measured d.c. conductivity is the hydrodynamic ω/kBT0\hbar \omega/k_B T \to 0 limit of this function, and is a universal number times e2/he^2 / h, even though the transport is incoherent. Previous work determined the conductivity by incorrectly assuming it was also equal to the collisionless ω/kBT\hbar \omega/k_B T \to \infty limit of the scaling function, which actually describes phase-coherent transport with a conductivity given by a different universal number times e2/he^2 / h. We provide the first computation of the universal d.c. conductivity in a disorder-free boson model, along with explicit crossover functions, using a quantum Boltzmann equation and an expansion in ϵ=3d\epsilon=3-d. The case of spin transport near quantum critical points in antiferromagnets is also discussed. Similar ideas should apply to the transitions in quantum Hall systems and to metal-insulator transitions. We suggest experimental tests of our picture and speculate on a new route to self-duality at two-dimensional quantum critical points.Comment: Feedback incorporated into numerous clarifying remarks; additional appendix discusses relationship to transport in dissipative quantum mechanics and quantum Hall edge state tunnelling problems, stimulated by discussions with E. Fradki

    Generalized thermoelastic diffusion in a thick circular plate including heat source

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    The present paper is aimed at studying thermoelastic diffusion interactions in a thick circular plate of infinite extent and finite thickness subjected to an axisymmetric heat supply and a heat source in the context of Lord–Shulman theory of generalized thermoelastic diffusion. The upper and the lower surfaces of the thick plate are traction free and the chemical potential is assumed to be a known function of time. Integral transform techniques are used to find the analytic solution in the transform domain. Mathematical model is prepared for Copper material plate and the numerical results are discussed and illustrated graphically

    Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors

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    In this Perspective, we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented as part of an AlGaAs Workshop held at American University, Washington, DC, from 15 August to 17 August 2022, bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes as well as optical metrology on large-area (similar to 10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these semiconductor-based coatings.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:// creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.014066

    Imaging Features of Primary Tumors of the Hand

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