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Register a new userOrbital Selective Superconductivity in Two-Orbital Asymmetric t-J Models
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We present the zero-temperature superconducting (SC) ground states of the two-orbital asymmetric $t-J$ model on a square lattice by means of the auxiliary-boson approach. Besides the two-gap SC phase, we find an orbital selective SC (OSSC) phase, which is simultaneously SC in one orbit and normal in another orbit. The novel OSSC phase is stable only for sufficient asymmetric degree in orbital space and doping concentration. The pairing symmetry of the SC phase is s-wave-like in most doping regime, against the d-wave symmetry of the single-orbital $t-J$ model in a square lattice. The implication of the present scenario on multi-orbital heavy fermion and iron-based superconductors is also discussed.
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Motivated by the recent contradiction of the superconducting pairing symmetry in the angle-resolved photoemission spectra (ARPES) and the nuclear magnetic resonance (NMR) data in the FeAs superconductors, we present the theoretical results on the phase diagram, the temperature dependent Fermi surfaces in normal state, the ARPES character of quasiparticles and the spin-lattice relaxation 1/T$_{1}$ of the two-orbital t-t$^{}$-J-J$^{}$ models. Our results show that most of the properties observed in iron-based superconductors could be comprehensively understood in the present scenario qualitatively, indicating that the pairing symmetry of the ironpnictides is anisotropic nodeless s-wave, mainly originating from the band structures and the Fermi surface topology.
We study a three-orbital Hubbard model with negative Hund coupling in infinite dimensions, combining dynamical mean-field theory with continuous time quantum Monte Carlo simulations. This model, which is relevant for the description of alkali-doped fullerides, has previously been shown to exhibit a spontaneous orbital selective Mott phase in the vicinity of the superconducting phase. Calculating the pair potential and double occupancy in each orbital, we study the competition between different homogeneous ordered states and determine the corresponding finite temperature phase diagram of the model. We identify two distinct types of spontaneous orbital-selective Mott states and show that an orbital-selective $s$-wave superconducting state with one superconducting and two metallic orbitals is spontaneously realized between the conventional $s$-wave superconducting phase and these two kinds of spontaneously orbital-selective Mott states.
An important challenge in condensed matter physics is understanding iron-based superconductors. Among these systems, the iron selenides hold the record for highest superconducting transition temperature and pose especially striking puzzles regarding the nature of superconductivity. The pairing state of the alkaline iron selenides appears to be of $d$-wave type based on the observation of a resonance mode in neutron scattering, while it seems to be of $s$-wave type from the nodeless gaps observed everywhere on the Fermi surface (FS). Here we propose an orbital-selective pairing state, dubbed $s tau_{3}$, as a natural explanation of these disparate properties. The pairing function, containing a matrix $tau_{3}$ in the basis of $3d$-electron orbitals, does not commute with the kinetic part of the Hamiltonian. This dictates the existence of both intraband and interband pairing terms in the band basis. A spin resonance arises from a $d$-wave-type sign change in the intraband pairing component whereas the quasiparticle excitation is fully gapped on the FS due to an $s$-wave-like form factor associated with the addition in quadrature of the intraband and interband pairing terms. We demonstrate that this pairing state is energetically favored when the electron correlation effects are orbitally selective. More generally, our results illustrate how the multiband nature of correlated electrons affords unusual types of superconducting states, thereby shedding new light not only on the iron-based materials but also on a broad range of other unconventional superconductors such as heavy fermion and organic systems.
In the present study, we explore superconductivity in NdNiO$_2$ and LaNiO$_2$ employing a first-principles derived low-energy model Hamiltonian, consisting of two orbitals: Ni $x^{2}$-$y^{2}$, and an {it axial} orbital. The {it axial} orbital is constructed out of Nd/La $d$, Ni 3$z^{2}$-$r^{2}$ and Ni $s$ characters. Calculation of the superconducting pairing symmetry and pairing eigenvalue of the spin-fluctuation mediated pairing interaction underlines the crucial role of inter-orbital Hubbard interaction in superconductivity, which turns out to be orbital-selective. The axial orbital brings in materials dependence in the problem, making NdNiO$_2$ different from LaNiO$_2$, thereby controlling the inter-orbital Hubbard interaction assisted superconductivity.
Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.
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