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- Grinenko, V., et al.
(författare)
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State with spontaneously broken time-reversal symmetry above the superconducting phase transition
- 2021
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Ingår i: Nature Physics. - : Springer Nature. - 1745-2473 .- 1745-2481. ; 17:11, s. 1254-1259
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Tidskriftsartikel (refereegranskat)abstract
- The most well-known example of an ordered quantum state—superconductivity—is caused by the formation and condensation of pairs of electrons. Fundamentally, what distinguishes a superconducting state from a normal state is a spontaneously broken symmetry corresponding to the long-range coherence of pairs of electrons, leading to zero resistivity and diamagnetism. Here we report a set of experimental observations in hole-doped Ba1−xKxFe2As2. Our specific-heat measurements indicate the formation of fermionic bound states when the temperature is lowered from the normal state. However, when the doping level is x ≈ 0.8, instead of the characteristic onset of diamagnetic screening and zero resistance expected below the superconducting phase transition, we observe the opposite effect: the generation of self-induced magnetic fields in the resistive state, measured by spontaneous Nernst effect and muon spin rotation experiments. This combined evidence indicates the existence of a bosonic metal state in which Cooper pairs of electrons lack coherence, but the system spontaneously breaks time-reversal symmetry. The observations are consistent with the theory of a state with fermionic quadrupling, in which long-range order exists not between Cooper pairs but only between pairs of pairs.
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| 2. |
- Khansili, Akash, et al.
(författare)
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Calorimetric measurement of nuclear spin-lattice relaxation rate in metals
- 2023
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 107:19
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Tidskriftsartikel (refereegranskat)abstract
- The quasiparticle density of states in correlated and quantum-critical metals directly probes the effect of electronic correlations on the Fermi surface. Measurements of the nuclear spin-lattice relaxation rate provide one such experimental probe of quasiparticle mass through the electronic density of states. By far the most common way of accessing the spin-lattice relaxation rate is via nuclear magnetic resonance and nuclear quadrupole resonance experiments, which require resonant excitation of nuclear spin transitions. Here we report nonresonant access to spin-lattice relaxation dynamics in AC-calorimetric measurements. The nuclear spin-lattice relaxation rate is inferred in our measurements from its effect on the frequency dispersion of the thermal response of the calorimeter-sample assembly. We use fast, lithographically defined nanocalorimeters to access the nuclear spin-lattice relaxation times in metallic indium from 0.3 to 7 K and in magnetic fields up to 35 T.
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| 3. |
- Palmer-Fortune, J. E., et al.
(författare)
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Thin Film NiCr-, TiCr- and CuNi-Based Cermets for Low-Temperature Ultra-Low Magnetoresistance Thermometers
- 2024
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Ingår i: JOM. - 1047-4838 .- 1543-1851.
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Tidskriftsartikel (refereegranskat)abstract
- Many thermal measurements in high magnetic fields-including heat capacity, thermal conductivity, thermopower, magnetocaloric and thermal Hall effect measurements-require thermometers that are sensitive over a wide temperature range, are low mass, have a rapid thermal response and have a minimal, easily correctable magnetoresistance. We recently reported the development of a new granular-metal oxide ceramic composite (cermet) for this purpose formed by co-sputtering of the metallic alloy nichrome (Ni0.8\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.8}$$\end{document}Cr0.2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.2}$$\end{document}) and the insulator silicon dioxide (SiO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}). In this earlier work, we found that co-sputtering of NiCr alloy and SiO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} in a reactive oxygen and inert argon gas mixture can produce resistive thin-film thermometers sensitive enough to be used in calorimetry and related measurements from room temperature down to below 100 mK in magnetic fields up to at least 35 T. In this work, we present results for thin cermet films grown with Cu0.55\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.55}$$\end{document}Ni0.45\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.45}$$\end{document} and Ti0.05\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.05}$$\end{document}Cr0.95\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{0.95}$$\end{document}. Growth of CuNi-based thin-film cermets generally requires more oxygen in the working gas compared to NiCr and TiCr and yields thermometers that are much less sensitive than comparable NiCr-based thermometers. TiCr-based cermet thin-film thermometers have somewhat higher resistivity for similar sensitivities compared to NiCr-based cermet thin-film thermometers.
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