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Register a new userRobust Weyl Semimetal and Pressure-induced Superconductivity in Quasi-One-Dimensional (NbSe4)2I
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A search for the single material system that simultaneously exhibits topological phase and intrinsic superconductivity has been largely limited, although such a system is far more favorable especially for the quantum device applications. Except artificially engineered topological superconductivity in heterostructure systems, another alternative is to have superconductivity arising from the topological materials by pressure or other clean technology. Here, based on first-principles calculations, we first show that quasi-one-dimensional compound (NbSe4)2I represents a rare example of a chiral Weyl semimetal in which the set of symmetry-related Weyl points (WPs) exhibit the same chiral charge at a certain energy. The net chiral charge (NCC) of the below Fermi level EF (or a certain energy) can be tuned by pressure. In addition, a partial disorder induced by pressure accompanied with superconductivity emerges. Although amorphization of the iodine sub-lattice under high pressure, the one-dimensional NbSe4 chains in (NbSe4)2I remain intact and provide a superconducting channel in one dimension. Our combined theoretical and experimental research provide critical insight into a new phase of the one-dimensional system, in which distinctive phase transitions and correlated topological states emerge upon compression.
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The recently discovered Dirac and Weyl semimetals are new members of topological materials. Starting from them, topological superconductivity may be achieved, e.g. by carrier doping or applying pressure. Here we report high-pressure resistance and X-ray diffraction study of the three-dimensional topological Dirac semimetal Cd3As2. Superconductivity with Tc ~ 2.0 K is observed at 8.5 GPa. The Tc keeps increasing to about 4.0 K at 21.3 GPa, then shows a nearly constant pressure dependence up to the highest pressure 50.9 GPa. The X-ray diffraction measurements reveal a structure phase transition around 3.5 GPa. Our observation of superconductivity in pressurized topological Dirac semimetal Cd3As2 provides a new candidate for topological superconductor, as argued in a recent point contact study and a theoretical work.
Recently monolayer jacutingaite (Pt2HgSe3), a naturally occurring exfoliable mineral, discovered in Brazil in 2008, has been theoretically predicted as a candidate quantum spin Hall system with a 0.5 eV band gap, while the bulk form is one of only a few known dual-topological insulators which may host different surface states protected by symmetries. In this work, we systematically investigate both structure and electronic evolution of bulk Pt2HgSe3 under high pressure up to 96 GPa. The nontrivial topology persists up to the structural phase transition observed in the high-pressure regime. Interestingly, we found that this phase transition is accompanied by the appearance of superconductivity at around 55 GPa and the critical transition temperature Tc increases with applied pressure. Our results demonstrate that Pt2HgSe3 with nontrivial topology of electronic states displays new ground states upon compression and raises potentials in application to the next-generation spintronic devices.
We report systematical studies of a new quasi-one-dimensional (1D) compound Ba3TiTe5 and the high-pressure induced superconductivity therein. Ba3TiTe5 was synthesized at high pressure and high temperature. It crystallizes into a hexagonal structure (P63/mcm), which consists of infinite face-sharing octahedral TiTe6 chains and Te chains along the c axis, exhibiting a strong 1D characteristic structure. The first-principles calculations demonstrate that Ba3TiTe5 is a well-defined 1D conductor and thus, it can be considered a starting point to explore the exotic physics induced by pressure via enhancing the interchain hopping to move the 1D conductor to a high dimensional metal. For Ba3TiTe5, high-pressure techniques were employed to study the emerging physics dependent on interchain hopping, such as the Umklapp scattering effect, spin/charge density wave (SDW/CDW), superconductivity and non-Fermi Liquid behavior. Finally, a complete phase diagram was plotted. The superconductivity emerges from 8.8 GPa, near which the Umklapp gap is mostly suppressed. Tc is enhanced and reaches the maximum ~6 K at about 36.7 GPa, where the spin/charge density wave (SDW/CDW) is completely suppressed, and a non-Fermi Liquid behavior appears. Our results suggest that the appearance of superconductivity is associated with the fluctuation due to the suppression of Umklapp gap and the enhancement of Tc is related with the fluctuation of the SDW/CDW.
Topological nodal-line semimetals (TNLSMs) are materials whose conduction and valence bands cross each other, meeting a topologically-protected closed loop rather than discrete points in the Brillouin zone (BZ). The anticipated properties for TNLSMs include drumhead-like nearly flat surface states, unique Landau energy levels, special collective modes, long-range Coulomb interactions, or the possibility of realizing high-temperature superconductivity. Recently, SrAs3 has been theoretically proposed and then experimentally confirmed to be a TNLSM. Here, we report high-pressure experiments on SrAs3, identifying a Lifshitz transition below 1 GPa and a superconducting transition accompanied by a structural phase transition above 20 GPa. A topological crystalline insulator (TCI) state is revealed by means of density functional theory (DFT) calculations on the emergent high-pressure phase. As the counterpart of topological insulators, TCIs possess metallic boundary states protected by crystal symmetry, rather than time reversal. In consideration of topological surface states (TSSs) and helical spin texture observed in the high-pressure state of SrAs3, the superconducting state may be induced in the surface states, and is most likely topologically nontrivial, making pressurized SrAs3 a strong candidate for topological superconductor.
By replacing the alkali element in the newly discovered K2Mo3As3 superconductor, we successfully synthesized ternary molybdenum pnictides Rb2Mo3As3 and Cs2Mo3As3 through solid state reaction method. Powder X-ray diffraction analysis reveals the same quasi-one-dimensional (Q1D) hexagonal crystal structure and space group of P-6m2 (No. 187) as K2Mo3As3. The refined lattice parameters are a = 10.432 (1) {AA}, c = 4.4615 (6) {AA} for Rb2Mo3As3 and a = 10.7405 (6) {AA}, c = 4.4654 (5) {AA} for Cs2Mo3As3. Electrical resistivity and magnetic susceptibility characterizations exhibit the occurrence of superconductivity in both compounds with the onset Tc at 10.6 K and 11.5 K for Rb2Mo3As3 and Cs2Mo3As3 respectively, which exhibit weak negative chemical pressure effect in these A2Mo3As3 (A = K, Rb, Cs) superconductors contrary to the isostructural A2Cr3As3 superconductors. More interestingly, the Cs2Mo3As3 superconductor exhibits much higher upper critical field around 60 T at zero temperature. The discovery of these MoAs/CrAs-based superconductors provide a unique platform for the study of exotic superconductivity correlated with both 3d and 4d electrons in these Q1D compounds.
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