The dependence of the electrical resistivity of P b on hydrostatic pressure is determined over major portions of the temperature and pressure ranges 1-300 K and &lo G P a (100 kbar), respectively. and for Sn at 300 K. The results are compared to a simple Bloch-Gruneisen law including volume changes due to thermal contraction. It is demonstrated that both Pb and Sn are ideally suited for use as accurate resistive manometers, enabling a reliable continuous determination of pressure over a wide temperature range. The agreement between the pressure at low temperatures indicated by both resistive and superconducting (T,) Pb manometers is excellent. T,(P) calibration curves are given to 22 G P a for Pb and to 5 G P a for Sn and In. A general method is presented which shows how pressure can be used to test for the presence of electron-electron scattering; in the temperature range studied. T 2 7.2 K, electron-phonon scattering constitutes the dominant scattering mechanism in Pb. as expected.
The dependence of the superconducting transition temperature T(c) on nearly hydrostatic pressure has been determined to 67 GPa in an ac susceptibility measurement for a Li sample embedded in helium pressure medium. With increasing pressure, superconductivity appears at 5.47 K for 20.3 GPa, T(c) rising rapidly to approximately 14 K at 30 GPa. The T(c)(P) dependence to 67 GPa differs significantly from that observed in previous studies where no pressure medium was used. Evidence is given that superconductivity in Li competes with symmetry breaking structural phase transitions which occur near 20, 30, and 62 GPa. In the pressure range 20-30 GPa, T(c) is found to decrease rapidly in a dc magnetic field, the first evidence that Li is a type I superconductor.
Divalent Eu (4f;{7}, J=7/2) possesses a strong local magnetic moment which suppresses superconductivity. Under sufficient pressure it is anticipated that Eu will become trivalent (4f;{6}, J=0) and a weak Van Vleck paramagnet, thus opening the door for a possible superconducting state, in analogy with Am metal (5f;{6}, J=0) which superconducts at 0.79 K. We present ac susceptibility and electrical resistivity measurements on Eu metal for temperatures 1.5-297 K to pressures as high as 142 GPa. At approximately 80 GPa Eu becomes superconducting at T_{c} approximately 1.8 K; T_{c} increases linearly with pressure to 2.75 K at 142 GPa. Eu metal thus becomes the 53rd known elemental superconductor in the periodic table.
In those cases where charge-stripe order has been observed in cuprates, the crystal structure is such that the average rotational symmetry of the CuO2 planes is reduced from fourfold to twofold. As a result, one could argue that the reduced lattice symmetry is essential to the existence of stripe order. We use pressure to restore the average fourfold symmetry in a single crystal of La1.875Ba0.125CuO4, and show by x-ray diffraction that charge-stripe order still occurs. Thus, electronically driven stripe order can spontaneously break the lattice symmetry.
The dependence of T c on hydrostatic (He-gas) pressure for superconducting MgB 2 has been determined to 0.7 GPa. We find that T c decreases linearly and reversibly under pressure at the rate dT c /dP ≃ −1.11 ± 0.02 K/GPa. These studies were carried out on the same sample used in earlier structural studies under He-gas pressure which yielded the bulk modulus B = 147.2 ± 0.7 GPa. The value of the logarithmic volume derivative of T c is thus accurately determined, d ln T c /d ln V = +4.16 ± 0.08, allowing quantitative comparison with theory. The present results support the emerging picture that MgB 2 is a BCS superconductor with electron-phonon pairing interaction. 1The recent discovery [1] of superconductivity in MgB 2 at T c ≃ 39 K has sparked worldwide a torrent of experimental and theoretical activity, reminiscent of the frenzy following the observation [2] of superconductivity in La-Ba-Cu-O at a comparable temperature almost 15 years ago. Replacing 10 B with 11 B results in a sizeable isotope shift [3] to lower temperatures which points to BCS superconductivity. Other experiments, such as heat capacity [4,5], photoemission spectroscopy [6], and inelastic neutron scattering [7,8] also support the picture that MgB 2 is a phonon-mediated superconductor in the weak-to-moderate coupling regime.High pressure studies traditionally play an important role in superconductivity. A large magnitude of the pressure derivative dT c /dP is a good indication that higher values of T c may be obtained through chemical means. It is not widely appreciated, however, that the pressure dependence T c (P ), like the isotope effect, contains valuable information on the superconducting mechanism itself. For example, in simple-metal BCS superconductors, like Al, In, Sn, and Pb, T c invariably decreases under pressure due to the reduced electron-phonon coupling from lattice stiffening [9]. More generally, an accurate determination of the dependence of both T c and the lattice parameters on pressure yields the functional dependence T c = T c [a(P ), b(P ), c(P )] which provides a critical test of theoretical models. Hirsch [10] and Hirsch and Marsiglio [11] have applied a theory of hole superconductivity to MgB 2 and predicted that for an optimally doped sample T c should increase with pressure, in contrast to the expected decrease in T c from lattice stiffening.Precise structural data on MgB 2 at room temperature (RT) have recently been obtained by Jorgensen et al.[12] for hydrostatic pressures to 0.6 GPa in a He-gas neutron diffraction facility which yield the anisotropic compressibilities d ln a/dP = −1.87 × 10 −3 GPa −1 , d ln b/dP = −3.07 × 10 −3 GPa −1 , and the bulk modulus B = 147.2 ± 0.7 GPa; the compressibility along the c axis is thus significantly (64%) larger than that along the a axis. The binding within the boron layers is evidently much stronger than between the layers. These results are in reasonable agreement with electronic structure calculations by Loa and Syassen [13].Recent synchrotron x-ray diffraction studi...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.