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.
Lysine acetylation is thought to provide a mechanism for regulating metabolism in diverse bacteria. Indeed, many studies have shown that the majority of enzymes involved in central metabolism are ...acetylated and that acetylation can alter enzyme activity. However, the details regarding this regulatory mechanism are still unclear, specifically with regard to the signals that induce lysine acetylation. To better understand this global regulatory mechanism, we profiled changes in lysine acetylation during growth of
on the hexose glucose or the pentose xylose at both high and low sugar concentrations using label-free mass spectrometry. The goal was to see whether lysine acetylation differed during growth on these two different sugars. No significant differences, however, were observed. Rather, the initial sugar concentration was the principal factor governing changes in lysine acetylation, with higher sugar concentrations causing more acetylation. These results suggest that acetylation does not target specific metabolic pathways but rather simply targets accessible lysines, which may or may not alter enzyme activity. They further suggest that lysine acetylation principally results from conditions that favor accumulation of acetyl phosphate, the principal acetate donor in
Bacteria alter their metabolism in response to nutrient availability, growth conditions, and environmental stresses using a number of different mechanisms. One is lysine acetylation, a posttranslational modification known to target many metabolic enzymes. However, little is known about this regulatory mode. We investigated the factors inducing changes in lysine acetylation by comparing growth on glucose and xylose. We found that the specific sugar used for growth did not alter the pattern of acetylation; rather, the amount of sugar did, with more sugar causing more acetylation. These results imply that lysine acetylation is a global regulatory mechanism that is responsive not to the specific carbon source
but rather to the accumulation of downstream metabolites.
Tuning the electronic properties of transition‐metal and rare‐earth compounds by virtue of changes of the crystallographic lattice constants offers controlled access to new forms of order. The ...development of tungsten carbide (WC) and moissanite Bridgman cells conceived for studies of the electrical resistivity up to 10 GPa, as well as bespoke diamond anvil cells (DACs) developed for neutron depolarization studies up to 20 GPa is reviewed. For the DACs, the applied pressure changes as a function of temperature in quantitative agreement with the thermal expansion of the pressure cell. A setup is described that is based on focusing neutron guides for measurements of the depolarization of a neutron beam by samples in a DAC. The technical progress is illustrated in terms of three examples. Measurements of the resistivity and neutron depolarization provide evidence of ferromagnetic order in SrRuO3 up to 14 GPa close to a putative quantum phase transition. Combining hydrostatic, uniaxial, and quasi‐hydrostatic pressure, the emergence of incipient superconductivity in CrB2 is observed. The temperature dependence of the electrical resistivity in CeCuAl3 is consistent with emergent Kondo correlations and an enhanced coupling of magneto‐elastic excitations with the conduction electrons at low and intermediate temperatures, respectively.
The development of high‐pressure equipment, including a setup for neutron depolarization measurements in diamond anvil cells (DACs) is reviewed. The progress is showcased in terms of high‐pressure studies of the ferromagnetic order in SrRuO3, the emergence of incipient superconductivity in CrB2 under quasi‐hydrostatic conditions, and resistivity measurements addressing the magneto‐elastic coupling in CeCuAu3.
The only alkali metal known to be superconducting at ambient pressure is Li at 0.4 mK. Under 30 GPa pressure Tc for Li rises to 14 K. In addition, nearly 50 years ago the heavy alkali metal Cs was ...reported to become superconducting near 1.3 K at 12 GPa. In the present experiment the superconductivity of Cs under pressure is confirmed. In addition, strong evidence is presented in electrical resistivity measurements that neighboring Rb also becomes superconducting near 2 K at 55 GPa as it enters the oC16 phase, as for Cs, where Tc decreases under the application of pressure. It would seem likely that under the right temperature/pressure conditions all alkali metals, including metallic hydrogen, will join the ranks of the superconducting elements. With the addition of Rb, 55 of the 92 naturally occurring elements are superconducting at ambient or high pressure.
•At an atomically sharp interface between the two non-superconducting materials Fe1+yTe and Bi2Te3 2D superconductivity occurs in a thin layer.•Neither the mechanism of the interfacial ...superconductivity nor the exact nature of the proximity-induced superconductivity in BiTe3 is known.•We present electrical transport experiments on this heterostructure under the influence of hydrostatic helium gas pressure.•We observe a sharpening of the superconducting transition and a suppression of magnetic scattering due to a pressure-induced ordering of interstitial iron in Fe1+yTe.•We observe that the superconducting critical temperature is increased under pressure, indicating that the interface has the potential for higher critical temperatures.
We investigate the hydrostatic pressure dependence of interfacial superconductivity occurring at the atomically sharp interface between two non-superconducting materials: the topological insulator (TI) Bi2Te3 and the parent compound Fe1+yTe of the chalcogenide iron-based superconductors. Under pressure, a significant increase in the superconducting transition temperature Tc is observed. We interpret our data in the context of a pressure-induced enhanced coupling of the Fe1+yTe interfacial layer with the Bi2Te3 surface state, which modifies the electronic properties of the interface layer in a way that superconductivity emerges and becomes further enhanced under pressure. This demonstrates the important role of the TI in the interfacial superconducting mechanism.
The antiferromagnetic semi-Heusler compound CuMnSb has been investigated under high pressure by electrical resistivity and angle dispersive synchrotron x-ray diffraction measurements to 53 and 36 ...GPa, respectively. The Néel temperature at ∼50 K is found to initially increase rapidly with pressure, reaching 83 K at 7 GPa. However, near 8 GPa at ambient temperature a sluggish first-order structural transition begins from a semimetallic cubic phase to a likely semimetallic tetragonal phase; thermal cycling to 355∘C at 9.6 GPa serves to complete the transition. In the tetragonal phase no sign of magnetic ordering is visible in the resistivity R(T) over the measured temperature range 4–295 K. This suggests that magnetic ordering may have shifted to temperatures well above ambient. Indeed, density functional calculations find the magnetic ground state in the tetragonal phase to be antiferromagnetic. Following decompression to 1 bar at ambient temperature, the high-pressure tetragonal phase is retained.
High pressure studies have played an important role in the field of superconductivity since the first experiments by Sizoo and Onnes in Leiden in 1925. A rapid dependence of the transition ...temperature on pressure signals that the material is capable of higher values of Tc at ambient pressure. Significant extensions of the pressure range, most recently to pressures above 1Mbar using the diamond-anvil cell, have resulted in the discovery of many new superconductors. The transition temperature of Y metal has very recently been pushed by 1.15Mbar pressure to 20K, a value for an elemental superconductor second only to that of Ca at Mbar pressures. Such enormous pressures are even sufficient to destroy the free-electron character of the conduction electrons in the alkali metals. Selected experiments are discussed which illustrate these features.
It is anticipated that all insulating materials will become metallic under sufficiently high pressure. Insulating compounds containing a high concentration of hydrogen may metalize at lower pressures ...than pure hydrogen, perhaps exhibiting superconductivity at relatively high temperatures. Recent electronic structure calculations indicate that benzene C
6
H
6
may enter a metallic, molecular state under pressure in the region 180-200 GPa. Optical transmission studies, however, fail to reveal metallic behavior in benzene to 209 GPa at ambient temperature. A partial Raman spectrum of benzene was measured to 43.9 GPa.
Transport and magnetic studies of PbTaSe2 under pressure suggest the existence of two superconducting phases with the low temperature phase boundary at ∼0.25 GPa that is defined by a very sharp, ...first order, phase transition. The first order phase transition line can be followed via pressure dependent resistivity measurements, and is found to be near 0.12 GPa near room temperature. Transmission electron microscopy and x-ray diffraction at elevated temperatures confirm that this first order phase transition is structural and occurs at ambient pressure near ~425 K. The new, high temperature/high pressure phase has a similar crystal structure and slightly lower unit cell volume relative to the ambient pressure, room temperature structure. Based on first-principles calculations this structure is suggested to be obtained by shifting the Pb atoms from the 1a to 1e Wyckoff position without changing the positions of Ta and Se atoms. PbTaSe2 has an exceptionally pressure sensitive, structural phase transition with ΔTs/ΔP≈−1400 K/GPa near room temperature, and ≈−1700 K/GPa near 4 K. This first order transition causes a ~1 K (~25%) steplike decrease in Tc as pressure is increased through 0.25 GPa.
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