| 1. |
- LaBarre, P. G., et al.
(författare)
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Magnetoquantum oscillations in the specific heat of a topological Kondo insulator
- 2022
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 34:36
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Tidskriftsartikel (refereegranskat)abstract
- Surprisingly, magnetoquantum oscillations (MQOs) characteristic of a metal with a Fermi surface have been observed in measurements of the topological Kondo insulator SmB6. As these MQO have only been observed in measurements of magnetic torque (dHvA) and not in measurements of magnetoresistance (SdH), a debate has arisen as to whether the MQO are an extrinsic effect arising from rare-earth impurities, defects, and/or aluminum inclusions or an intrinsic effect revealing the existence of charge-neutral excitations. We report here the first observation of MQO in the low-temperature specific heat of SmB6. The observed frequencies and their angular dependence for these flux-grown samples are consistent with previous results based on magnetic torque for SmB6 but the inferred effective masses are significantly larger than previously reported. Such oscillations can only be observed if the MQO are of bulk thermodynamic origin; the measured magnetic-field dependent oscillation amplitude and effective mass allow us to rule out suggestions of an extrinsic, aluminum inclusion-based origin for the MQO.
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| 2. |
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| 3. |
- Boris, Andrey A., et al.
(författare)
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Evidence for Nonlocal Electrodynamics in Planar Josephson Junctions
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:11
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Tidskriftsartikel (refereegranskat)abstract
- We study the temperature dependence of the critical current modulation I-c(H) for two types of planar Josephson junctions: a low-T-c Nb/CuNi/Nb and a high-T-c YBa2Cu3O7-delta bicrystal grain-boundary junction. At low T both junctions exhibit a conventional behavior, described by the local sine-Gordon equation. However, at elevated T the behavior becomes qualitatively different: the I-c(H) modulation field Delta H becomes almost T independent and neither Delta H nor the critical field for the penetration of Josephson vortices vanish at T-c. Such an unusual behavior is in good agreement with theoretical predictions for junctions with nonlocal electrodynamics. We extract absolute values of the London penetration depth lambda from our data and show that a crossover from local to nonlocal electrodynamics occurs with increasing T when lambda(T) becomes larger than the electrode thickness.
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| 4. |
- 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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| 5. |
- Kacmarcik, J., et al.
(författare)
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Unusual Interplay between Superconductivity and Field-Induced Charge Order in YBa2Cu3Oy
- 2018
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 121:16
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study of the temperature (T) and magnetic field (H) dependence of the electronic density of states (DOS) at the Fermi level, as deduced from specific heat and Knight shift measurements in underdoped YBa2Cu3Oy. We find that the DOS becomes field independent above a characteristic field H-DOS, and that the H-DOS (T) line displays an unusual inflection near the onset of the long-range 3D charge-density wave order. The unusual S shape of H-DOS (T) is suggestive of two mutually exclusive orders that eventually establish a form of cooperation in order to coexist at low T. On theoretical grounds, such a collaboration could result from the stabilization of a pair-density wave state, which calls for further investigation in this region of the phase diagram.
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| 6. |
- 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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| 7. |
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| 8. |
- 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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| 9. |
- Truccato, M., et al.
(författare)
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Photoconductivity effects in mixed-phase BSCCO whiskers
- 2012
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Ingår i: Superconductors Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- We report on combined photoconductivity and annealing experiments in whisker-like crystals of the Bi-Sr-Ca-Cu-O (BSCCO) high-T-c superconductor. Both single-phase Bi2Sr2CaCu2O8+delta (Bi-2212) samples and crystals of the mixed phases Bi2Sr2Ca2Cu3O10+x (Bi-2223)/Bi-2212 have been subjected to annealing treatments at 90 degrees C in air in a few hours steps, up to a maximum total annealing time of 47 h. At every step, samples have been characterized by means of electrical resistance versus temperature (R versus T) and resistance versus time at fixed temperature (R versus t) measurements, both in the dark and under illumination with a UV-Vis halogen arc lamp. A careful comparison of the results from the two techniques has shown that, while for single-phase samples no effect is recorded, for mixed-phase samples an enhancement in the conductivity that increases with increasing annealing time is induced by the light at the nominal temperature T = 100 K, i.e. at an intermediate temperature between the critical temperatures of the two phases. A simple pseudo-1D model based on the Kudinov's scheme (Kudinov et al, 1993 Phys. Rev. B 47 9017-28) has been developed to account for the observed effects, which is based on the existence of Bi-2223 filaments embedded in the Bi-2212 matrix and on the presence of electronically active defects at their interfaces. This model reproduces fairly well the photoconductive experimental results and shows that the length of the Bi-2223 filaments decreases and the number of defects increases with increasing annealing time.
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| 10. |
- Adami, Johanna, et al.
(författare)
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Cancer risk following organ transplantation : a nationwide cohort study in Sweden
- 2003
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Ingår i: British Journal of Cancer. - : Springer Science and Business Media LLC. - 0007-0920 .- 1532-1827. ; 89:7, s. 1221-1227
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Tidskriftsartikel (refereegranskat)abstract
- A substantial excess risk of lymphomas and nonmelanoma skin cancer has been demonstrated following organ transplantation. Large sample size and long follow-up time may, however, allow more accurate risk estimates and detailed understanding of long-term cancer risk. The objective of the study was to assess the risk of cancer following organ transplantation. A nationwide cohort study comprising 5931 patients who underwent transplantation of kidney, liver or other organs during 1970-1997 in Sweden was conducted. Complete follow-up was accomplished through linkage to nationwide databases. We used comparisons with the entire Swedish population to calculate standardised incidence ratios (SIRs), and Poisson regression for multivariate internal analyses of relative risks (RRs) with 95% confidence intervals (CI). Overall, we observed 692 incident first cancers vs 171 expected (SIR 4.0; 95% CI 3.7-4.4). We confirmed marked excesses of nonmelanoma skin cancer (SIR 56.2; 95% CI 49.8-63.2), lip cancer (SIR 53.3; 95% CI 38.0-72.5) and of non-Hodgkin's lymphoma (NHL) (SIR 6.0; 95% CI 4.4-8.0). Compared with patients who underwent kidney transplantation, those who received other organs were at substantially higher risk of NHL (RR 8.4; 95% CI 4.3-16). Besides, we found, significantly, about 20-fold excess risk of cancer of the vulva and vagina, 10-fold of anal cancer, and five-fold of oral cavity and kidney cancer, as well as two- to four-fold excesses of cancer in the oesophagus, stomach, large bowel, urinary bladder, lung and thyroid gland. In conclusion, organ transplantation entails a persistent, about four-fold increased overall cancer risk. The complex pattern of excess risk at many sites challenges current understanding of oncogenic infections that might become activated by immunologic alterations.
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