Superconductivity is observed in borides with Tc up to 32K

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The superconducting phase diagram of MoB2 as a function of pressure is summarized in Fig. Using a diamond anvil cell (DAC) (left), it can be seen that the superconducting state emerges around 20 GPa, then Tc increases further with applied pressure and growth beyond the structure-transition pressure (Pc ∼ 70 GPa) slows down the DC speed. The Tc of MoB2 rises up to ~32 K at a pressure of 109.7 GPa and still does not exhibit a trend of saturation. Further theoretical calculations show that the out-of-plane phonon mode of Mo atoms strongly couples to the Mo d electrons near the EF (right). These results reveal the study of the superconducting mechanism in high-pressure α-MoB2, shedding light on exploring new phonon-mediated high-Tc superconductors in transition metal borides. Credit: Science China Press

Superconductors with high transition temperatures (high-tc SCs) are long-sought targets in the condensed matter physics and materials communities due to their significant scientific and applied values. Since the discovery of superconductivity in mercury a hundred years ago, only a few systems d.c Above 30 K

Scientists at Shanghai Tech University and their collaborators at Renmin University in China have discovered superconductivity up to 32 K in MoB.2 Under pressure, it has a very high dc In transition-metal borides until now. Their findings, published in the journal National Science ReviewIllumination for the study of high-Tc Superconductors in transition metal borides.

Molybdenum diboride (MoB2) is unique among MB2 α-MoB is the only material family with two structural forms2 Phase (AlB2-type) and β-MoB2 phase (CaSi2-type).

Synchrotron X-ray diffraction (XRD) measurements indicated that β-MoB2 Converts to α-MoB2 At about 65 GPa, it has the same crystal structure as MgB2.

„A question naturally arises: Can superconductivity be achieved in MoB?2 at high pressure?” said Dr. Yanpeng Qi, an assistant professor at Shanghai Tech University’s School of Physical Science and Technology and one of the corresponding authors.

„Therefore, we performed in situ high-pressure electrical transport measurements. Superconductivity is observed at 21.7 GPa and T.c increases with pressure. Beyond the critical pressure (pc = 70 GPa) structural phase transition, development of Tc decreases and maximum dc 32.4 K is achieved at P = 109.7 GPa, the highest pressure we apply to the sample.”

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Although further theoretical calculations are shortened MoB2 Similar structure and comparable dc with MgB2The superconducting mechanism of the former is quite different from the latter: the d-electrons and phonon modes of transition metal Mo atoms play an entirely dominant role in the emergence of superconductivity, in contrast to the dominance of p-electrons and phonon modes. B atoms in the superconductivity of MgB2.

The results shown in this work highlight the roles of transition metals in superconductivity in borides, which was previously underestimated in borides. Their discovery of the superconductivity of MoB2 With high dc may shed light on the study of high-Tc Superconductivity in systems containing light elements considering the combined effects of high-frequency phonon modes and light elements with strongly correlated electrons in transition metals.

More information:
Qing Bei et al., Pressure-induced superconductivity in MoB2 at 32 K, National Science Review (2023) DOI: 10.1093/nsr/nwad034

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