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Register a new userChiral singlet superconductivity in the weakly correlated metal LaPt3P
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Topological superconductors (SCs) are novel phases of matter with nontrivial bulk topology. They host at their boundaries and vortex cores zero-energy Majorana bound states, potentially useful in fault-tolerant quantum computation. Chiral SCs are particular examples of topological SCs with finite angular momentum Cooper pairs circulating around a unique chiral axis, thus spontaneously breaking time-reversal symmetry (TRS). They are rather scarce and usually feature triplet pairing: best studied examples in bulk materials are UPt3 and Sr2RuO4 proposed to be f-wave and p-wave SCs respectively, although many open questions still remain. Chiral triplet SCs are, however, topologically fragile with the gapless Majorana modes weakly protected against symmetry preserving perturbations in contrast to chiral singlet SCs. Using muon spin relaxation (muSR) measurements, here we report that the weakly correlated pnictide compound LaPt3P has the two key features of a chiral SC: spontaneous magnetic fields inside the superconducting state indicating broken TRS and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt3P is chiral d-wave singlet.
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The metal-metal bond in metal-rich chalcogenide is known to exhibit various structures and dominate interesting physical properties. Ta2Se can be obtained by both arc-melting and solid-state pellet methods. Ta2Se crystallizes a layered tetragonal structure with space group P4/nmm (S.G.129, Pearson symbol tP6). Each unit cell consists of four layers of body-centered closed packing Ta atoms sandwiched between two square nets of Se atoms, forming the Se-Ta-Ta-Ta-Ta-Se networks. A combined result of magnetic susceptibility, resistivity, and heat capacity measurements on Ta2Se indicate the bulk superconductivity with Tc = 3.8 (1) K. According to the first-principal calculations, the d orbitals in Ta atoms dominate the Fermi level in Ta2Se. The flat bands at gamma-point in the Brillouin zone (BZ) yield to the van Hove singularities in density of states (DOS) around the Fermi level, which is intensified by introducing spin-orbit coupling (SOC) effect, thus, could be critical for the superconductivity in Ta2Se. The physical properties especially superconductivity is completely different from Ta-rich alloys or transition metal dichalcogenide TaSe2.
Electrical resistivity, specific heat and NMR measurements classify non-centrosymmetric $rm Mo_3Al_2C$ ($beta$-Mn type, space group $P4_132$) as a strong-coupled superconductor with $T_c = 9$~K deviating notably from BCS-like behaviour. The absence of a Hebbel-Slichter peak, a power law behaviour of the spin-lattice relaxation rate (from $^{27}$Al NMR), a $T^3$ temperature dependence of the specific heat and a pressure enhanced $T_c$ suggest unconventional superconductivity with a nodal structure of the superconducting gap. Relativistic DFT calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favouring a mix of spin-singlet and spin triplet components in the superconducting condensate, in absence of strong correlations among electrons.
Monovalent metals contain half filled band (HFB) of s-electrons. Emphasizing importance of Coulomb repulsions in HFB in 2D and 1D monovalent systems we sketched a theory (2018) for ambient temperature granular superconductivity reported by Thapa and Pandey (2018) in Au-Ag nanostructures (updated by Thapa et al., 2019). Sharpening our theory, we suggest that textit{Coulomb repulsions in certain structurally perturbed regions (atomic clusters, stacking faults, grain boundaries etc.) create nanoscale reservoirs of singlet electron pairs}. These low dimensional patches are hybridized to a background 3D jellium metal and produce observed ambient Tc granular superconductivity via proximity Josephson effect. Using repulsive Hubbard model we show presence of singlet reservoirs and physics of doped Mott insulators. Needed charge transfer arises from differing electronegativities. Our theory predicts that textit{all elemental monovalent (alkali, Cu, Ag and Au) metals, under suitable structural perturbations, are likely to exhibit ambient temperature superconductivity}.
We solve by Dynamical Mean Field Theory a toy-model which has a phase diagram strikingly similar to that of high $T_c$ superconductors: a bell-shaped superconducting region adjacent the Mott insulator and a normal phase that evolves from a conventional Fermi liquid to a pseudogapped semi-metal as the Mott transition is approached. Guided by the physics of the impurity model that is self-consistently solved within Dynamical Mean Field Theory, we introduce an analytical ansatz to model the dynamical behavior across the various phases which fits very accurately the numerical data. The ansatz is based on the assumption that the wave-function renormalization, that is very severe especially in the pseudogap phase close to the Mott transition, is perfectly canceled by the vertex corrections in the Cooper pairing channel.A remarkable outcome is that a superconducting state can develop even from a pseudogapped normal state, in which there are no low-energy quasiparticles. The overall physical scenario that emerges, although unraveled in a specific model and in an infinite-coordination Bethe lattice, can be interpreted in terms of so general arguments to suggest that it can be realized in other correlated systems.
Recently superconductivity was discovered in the Kagome metal AV3Sb5 (A = K, Rb, and Cs), which has an ideal Kagome lattice of vanadium. These V-based superconductors also host charge density wave (CDW) and topological nontrivial band structure. Here we report the ultralow-temperature thermal conductivity and high pressure resistance measurements on CsV3Sb5 with Tc = 2.5 K, the highest among AV3Sb5. A finite residual linear term of thermal conductivity at zero magnetic field and its rapid increase in fields suggest nodal superconductivity. By applying pressure, the Tc of CsV3Sb5 increases first, then decreases to lower than 0.3 K at 11.4 GPa, showing a clear first superconducting dome peaked around 0.8 GPa. Above 11.4 GPa, superconductivity re-emerges, suggesting a second superconducting dome. Both nodal superconductivity and superconducting domes point to unconventional superconductivity in this V-based superconductor. While our finding of nodal superconductivity puts a strong constrain on the pairing state of the first dome, which should be related to the CDW instability, the superconductivity of the second dome may present another exotic pairing state in this ideal Kagome lattice of vanadium.
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