Sc_2B_3的轨道杂化超导电性
Superconductivity in Scandium Borocarbide with orbital hybridization
摘要：
在轻元素化合物中的超导电性的探索引起了相当大的关注，因为这些材料可以容易地实现高的$T_{c}$超导电性，例如${\mathrm{LnNi}}_{2}{\mathrm{B}_{2}}{\mathrm{C}}$（$T_{c}$ =17 K）、${\mathrm{Mg}}{\mathrm{B}}_{2}$（$T_{c}$ =39 K）以及最近在压力下的超导电性（$T_{c}$ =250 K）。在这里，我们报告的发现，在7.8 K的体超导性的钪硼碳化物${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$的结构变化的基础上的化合物的${\mathrm{Sc}}_{3}{\mathrm{C}}_{4}$与非常少的B掺杂的四方晶格。磁化强度和比热测量显示体超导性。确定了上临界场为Hc 2（0）~ 8 T。低温比热表明该系统是BCS全能隙s波超导体。电子结构计算表明，与${\mathrm{Sc}}_{3}{\mathrm{C}}_{4}$相比，${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$中Sc的3d电子与C-C（B）-C碎片中的2 p电子有更多的轨道重叠和杂化，形成了Sc-C（B）-Sc新的导电路径，这些变化影响了费米能级的能带结构，可能是${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$超导电性的原因.
英文摘要：
Exploration of superconductivity in light element compounds has drawn considerable attention because those materials can easily realize the high $T_{c}$ superconductivity, such as ${\mathrm{LnNi}}_{2}{\mathrm{B}_{2}}{\mathrm{C}}$ ($T_{c}$ =17 K), ${\mathrm{Mg}}{\mathrm{B}}_{2}$ ($T_{c}$ =39 K), and very recently super-hydrides under pressure ($T_{c}$ =250 K). Here we report the discovery of bulk superconductivity at 7.8 K in scandium borocarbide ${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$ with a tetragonal lattice which structure changes based on the compound of ${\mathrm{Sc}}_{3}{\mathrm{C}}_{4}$ with very little B doping. Magnetization and specific heat measurements show bulk superconductivity. An upper critical field of Hc2(0) ~ 8 T is determined. Low temperature specific-heat shows that this system is a BCS fully gapped s-wave superconductor. Electronic structure calculations demonstrate that compared with ${\mathrm{Sc}}_{3}{\mathrm{C}}_{4}$ there are more orbital overlap and hybridization between Sc 3d electrons and 2p electrons of C-C(B)-C fragment in ${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$, which form a new electric conduction path of Sc-C(B)-Sc. Those changes influence the band structure at the Fermi level and may be the reason of superconductivity in ${\mathrm{Sc}}_{20}{\mathrm{B}}{\mathrm{C}}_{27}$.
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