Effect of pressure on the superconductingTcof lanthanum

Abstract

The effect of pressure on the superconducting transition temperature T c of La was studied up to 50 GPa. T c (P) shows a rather complicated variation with a discontinuous increase in T c at about 2.2 GPa due to the first-order phase transition from dhcp to fcc structure. At about 5.4 GPa a sharp peak is observed due to the soft-mode phase transition from fcc to the distorted fcc structure and two broad maxima are found within the stability region of the distorted fcc structure around 12 and 39 GPa. Some differences between these and previous low-pressure data for metastable fcc La are noticed. The results are discussed in connection with pressure-induced structural phase transitions found in earlier x-ray-diffraction experiments and band-structure calculations giving evidences for van Hove singularities in the density of states.

Potential high- T c superconducting lanthanum and yttrium hydrides at high pressure

“…We calculated a T c of 6-7 K for fcc La under ambient pressure using μ* = 0.1-0.13, which is close to previous theoretical (46) and experimental work (T c = 6 K) (48), and consistent with high-pressure behavior (T c = 13 K at 20 GPa) (45,48). Likewise, our method gives the T c of elemental Y under pressure to be 15-16 K using μ* = 0.1-0.13, which is also consistent with previous theoretical (15) and experimental studies (T c = 17 K at 89 GPa) (49).…”

Pressure-induced superconductivity in Sc to74GPa

“…[18], dot-dashed line from Ref. [19]. Vertical arrows mark values of r a /r c for the respective metal at ambient pressure [26].…”

“…Indeed, Wittig et al were the first to show this to be true for Lu [15,16], Y [5], and Sc [17]. Whereas in La T c (P ) passes through a maximum near 13 K [18,19], that for Y continues to increase to the highest pressure applied (≃ 20 K at 1.2 Mbar). T c for Lu [16] and Sc [17] also increases under pressure, but only reaches values of 2.5 K and 0.35 K at 22 GPa and 21.5 GPa, respectively.…”

Comparison of the pressure dependences ofTcin the trivalentd-electron superconductors Sc, Y, La, and Lu up to megabar pressures

“…In superconductors containing transition metals, where d -electrons dominate the conduction band properties, T c can initially rise or fall under pressure and exhibit a highly nonlinear T c (P ) dependence at higher pressures (see, for example, Refs. [14,15,16,17]). With such complexity in T c (P ), it would seem useful to search for a simple, underlying mechanism to account for the observed changes in T c as a function of decreasing interatomic spacing as pressure is applied.…”

“…As the relative increase in N d with pressure is particularly large for the "early" transition metals where N d is small, we focus our attention first on the four trivalent d-electron metals Sc, Y, La, and Lu, of which only La superconducts at ambient pressure. Previous high-pressure studies on Sc [23], Y [10], La [15], and Lu [24] were restricted to pressures of 74, 115, 50, and 28 GPa, respectively. Here we present new data which determine T c (P ) for Sc and Lu to the significantly higher pressures of 123 and 174 GPa, respectively.…”