Niobium substitution suppresses the superconducting critical temperature of pressurized MoB2
Niobium substitution suppresses the superconducting critical temperature of pressurized
MoB2
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铌替代抑制了加压 MoB2 的超导临界温度
DOI：
10.1103/physrevb.108.094501
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发表时间：
2023
影响因子：
3.7
通讯作者：
J. Hamlin
中科院分区：
文献类型：
--
作者：
J. Lim;S. Sinha;A. Hire;J. Kim;P. Dee;R. S. Kumar;D. Popov;R. Hemley;R. Hennig;P. Hirschfeld;G. Stewart;J. Hamlin
最近的一项研究表明，MoB$_2$转变为与MgB$_2$相同的结构（$P6/mmm$），在30 K以上接近100 GPa [C的温度下具有超导性。Pei $et$ al$。国家的。科学。[j] ., [j] ., [j] ., nwad034(2023)]，和nb -取代在MoB$_2$中稳定$P6/mmm$结构到环境压力[A]。C.雇用$et$ al$。理论物理。[j].生物工程学报，2016,32(5):444 - 444。本文研究了铌取代的MoB$_2$ （Nb$_{0.25}$Mo$_{0.75}$B$_2$）的高压超导行为。高压x射线衍射测量表明，样品在环境压力下保持在$P6/mmm$结构，至少达到160 GPa。电阻率测量表明，从环境压力$T_c$为8 K（由比热证实为体效应）开始，临界温度在50 GPa时被抑制到4 K，然后在170 GPa时逐渐上升到5.5 K。高压下的临界温度明显低于高压（30k）下的临界温度，表明nb取代对超导临界温度有较强的抑制作用。我们的计算确实发现Nb$_{0.25}$Mo$_{0.75}$B$_2$中的电子-声子耦合减少了，但并不能完全解释观察到的抑制，这也可能是由非均匀性和增强的自旋涨落引起的。
A recent work has demonstrated that MoB$_2$, transforming to the same structure as MgB$_2$ ($P6/mmm$), superconducts at temperatures above 30 K near 100 GPa [C. Pei $et$ $al$. Natl. Sci. Rev., nwad034 (2023)], and Nb-substitution in MoB$_2$ stabilizes the $P6/mmm$ structure down to ambient pressure [A. C. Hire $et$ $al$. Phys. Rev. B 106, 174515 (2022)]. The current work explores the high pressure superconducting behavior of Nb-substituted MoB$_2$ (Nb$_{0.25}$Mo$_{0.75}$B$_2$). High pressure x-ray diffraction measurements show that the sample remains in the ambient pressure $P6/mmm$ structure to at least 160 GPa. Electrical resistivity measurements demonstrate that from an ambient pressure $T_c$ of 8 K (confirmed by specific heat to be a bulk effect), the critical temperature is suppressed to 4 K at 50 GPa, before gradually rising to 5.5 K at 170 GPa. The critical temperature at high pressure is thus significantly lower than that found in MoB$_2$ under pressure (30 K), revealing that Nb-substitution results in a strong suppression of the superconducting critical temperature. Our calculations indeed find a reduced electron-phonon coupling in Nb$_{0.25}$Mo$_{0.75}$B$_2$, but do not account fully for the observed suppression, which may also arise from inhomogeneity and enhanced spin fluctuations.