LaHx-LaDy超导体的德拜温度
Debye temperature in LaHx-LaDy superconductors
摘要：
德拜温度T ${_θ}$ =（h/2 $π$）/k ${_B}$ $ω$ $_θ$，其中德拜频率$ω$ $_θ$是全声子谱的积分特征频率$α$ $^2$（$ω$）F（$ω$）。在BCS理论中，T ${_θ}$与电子-声子耦合强度参数$λ$ $_{e-ph}$一起确定超导转变温度Tc。尽管更精确的电子-声子介导的超导理论需要全声子谱的知识，$α$ $^2$（$ω$）F（$ω$），这可以通过第一原理计算技术非常精确地计算，但没有实验技术可以测量高度压缩的近室温（NRT）超导体中的$α$ $^2$（$ω$）F（$ω$）。因此，$ω$ $_θ$仍然是全声子谱的唯一可测量的参数，$α$ $^2$（$ω$）F（$ω$），它可以通过实验的温度相关电阻数据R（T）与Bloch-Grüneisen方程的拟合来推导。考虑到在电子-声子介导的超导理论中，两个同位素对应物（或者，在NRT超导体的情况下，在不同压力下的相同超导相），由下标1和2表示，应该服从T ${_θ}_1$ /T ${_θ}_2$ =T ${_c}_1$ /T ${_c}_2$的关系，有一种方法来重申/反驳NRT超导的电子-声子机制。本文对不同压力下H_3S的R_3 m相以及LaH_x-LaDy系统中的几种超导体进行了分析，发现T ${_θ}_1$ /T ${_θ}_2$ =T ${_c}_1$ /T ${_c}_2$与实验数据有很大的偏差。考虑到最近在H_3S-D_3S体系中报道的类似分歧，可以得出结论，NRT超导性的起源仍有待发现。
英文摘要：
The Debye temperature, T${_θ}$=(h/2$π$)/k${_B}$$ω$$_θ$, where the Debye frequency $ω$$_θ$ is integrated characteristic frequency of full phonon spectrum, $α$$^2$($ω$)F($ω$). In the BCS theory, T${_θ}$ in conjunction with electron-phonon coupling strength parameter, $λ$$_{e-ph}$, determines the superconducting transition temperature, Tc. Despite a fact that more accurate theory of electron-phonon mediated superconductivity requires the knowledge of full phonon spectrum, $α$$^2$($ω$)F($ω$), which can be very accurately computed by first principles calculation technique, there is no experimental technique which can measure $α$$^2$($ω$)F($ω$) in highly-compressed near-room-temperature (NRT) superconductors. Thus, $ω$$_θ$ remains to be the only measurable parameter of full phonon spectrum, $α$$^2$($ω$)F($ω$), which can be deduced by the fit of experimental temperature-dependent resistance data, R(T), to Bloch-Grüneisen equation. Taking in account that within electron-phonon mediated theory of superconductivity two isotopic counterparts (or, in case of NRT superconductors, the same superconducting phase at different pressures), designated by subscripts of 1 and 2, should be obey the relation of T${_θ}_1$/T${_θ}_2$=T${_c}_1$/T${_c}_2$, there is a way to reaffirm/disprove the electron-phonon mechanism of NRT superconductivity. In this paper, we perform the analysis for R3m-phase of H3S at different pressure, as well as for several superconductors in LaHx-LaDy system and show that there is a large disagreement between experimental data and T${_θ}_1$/T${_θ}_2$=T${_c}_1$/T${_c}_2$. Taking in account that similar disagreement has recently reported in H3S-D3S system, it can be concluded that primary origin for NRT superconductivity remains to be discovered.
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