A minimal tight-binding model for the quasi-one-dimensional superconductor K₂Cr₃As₃

Abstract

We present a systematic derivation of a minimal five-band tight-binding model for the description of the electronic structure of the recently discovered quasi-one-dimensional superconductor K 2 Cr 3 As 3 . Taking as a reference the density-functional theory (DFT) calculation, we use the outcome of a Löwdin procedure to refine a Wannier projection and fully exploit the predominant weight at the Fermi level of the states having the same symmetry of the crystal structure. Such states are described in terms of five quasi-atomic d orbitals: four planar orbitals, two d xy and two d x y 2 2 -, and a single out-of-plane one, d z 2 . We show that this minimal model reproduces with great accuracy the DFT band structure in a broad energy window around the Fermi energy. Moreover, we derive an explicit simplified analytical expression of such model, which includes three nearest-neighbor (NN) hopping terms along the z direction and one NN term within the xy plane. This model captures very efficiently the energy spectrum of the system and, consequently, can be used to study transport properties, superconductivity and dynamical effects in this novel class of superconductors.

Magnetoelectrically tunable Andreev bound state spectra and spin polarization in p -wave Josephson junctions

“…On the side of materials, we point out that there exists a long list of quasi 1D systems that have already shown experimental fingerprints of spin-triplet superconducting pairing and appear as prominent building blocks for fabricating the proposed hybrid devices. For instance, this is the case for the organic Bechgaard salts [88,89], the purple molybdenum bronze Li 0.9 Mo 6 O 17 [90], and more recently the Cr-based pnictide superconductors [91,92]. Moreover, we remark that the design of spinful triplet superconductivity can also rely on harnessing the orbital degrees of freedom, as it has been demonstrated for 2D electron gases [103] and multi-orbital optical-lattice systems exhibiting superfluidity [104].…”

“…Interestingly, in some of these experiments [68, 71-73, 79, 83], spin-polarized scanning tunneling microscopy (STM) emerged as a powerful tool to detect MBSs by means of the elecronic spin polarization they induce [84][85][86][87]. Nonetheless, such a detection strategy has not yet been pursued to confirm intrinsic p-wave superconductivity in prominent candidate materials, e.g., the Bechgaard salts [88,89], lithium molybdenum purple bronze [90], and more recently in the Cr-based pnictide K 2 Cr 3 As 3 [91,92].…”

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP

“…Although many interesting studies have been so far reported on these and other similar compounds, both theoretical [12][13][14][15][16][17][18][19][20][21][22][23][24][25] and experimental [26][27][28][29][30][31][32][33][34][35][36], only a limited amount of information on WP single crystal system is until now available [8]. The aim of this paper is to give a contribution to the investigation of the properties of WP compound, providing electronic structure calculations and a consistent description of resistivity measurements from experiments carried out on WP single crystal samples.…”

Nodal Andreev spectra in multi-Majorana three-terminal Josephson junctions

“…Although spin-triplet pairing is less common than the conventional spin-singlet one, experimental observations in the last decades have gathered many evidences for spintriplet superconductivity in a large variety of materials, such as heavy-fermion compounds [31][32][33], noncentrosymmetric materials [34,35], organic conductors [36][37][38], layered oxides [39], doped topological insulators [40], and more recently in the Cr-based pnictide K 2 Cr 3 As 3 [41,42]. In addition to intrinsic materials, artificial spin-triplet SCs can be engineered in a large variety of quantum-material and -device platforms based on conventional spin-singlet pairing.…”