Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userVisualizing the $d$-vector in a nematic triplet superconductor
82
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Recent experiments show strong evidences of nematic triplet superconductivity in doped Bi$_2$Se$_3$ and in Bi$_2$Te$_3$ thin film on a superconducting substrate, but with varying identifications of the direction of the $d$-vector of the triplet that is essential to the topology of the underlying superconductivity. Here we show that the $d$-vector can be directly visualized by scanning tunneling measurements: At subgap energies the $d$-vector is along the leading peak wave-vector in the quasi-particle-interference pattern for potential impurities, and counter-intuitively along the elongation of the local density-of-state profile of the vortex. The results provide a useful guide to experiments, the result of which would in turn pose a stringent constraint on the pairing symmetry.
rate research
Read More
We investigate the states of triplet pairing in a candidate nematic superconductor versus typical material parameters, using the mean field theory for two- and three-dimensional tight-binding models with local triplet pairing in the $E_u$ representation. In the two-dimensional model, the system favors the fully gapped chiral state for weaker warping or lower filling level, while a nodal and nematic $Delta_{4x}$ state is favorable for stronger warping or higher filling, with the $d$-vector aligned along the principle axis. In the presence of lattice distortion, relative elongation along one of the principle axes, ${bf a}$, tends to rotate the nematic $d$-vector orthogonal to ${bf a}$, resulting in the nematic $Delta_{4y}$ state at sufficient elongation. Three-dimensionality is seen to suppress the chiral state in favor of the nematic ones. Our results may explain the variety in the probed direction of the $d$-vector in existing experiments.
In this work, we study even-parity spin-singlet orbital-triplet pairing states for a two-band superconductor. An orbital $mathbf{d}_o(mathbf{k})$-vector is introduced to characterize orbital-dependent pairings, in analogy to the spin $mathbf{d}_s(mathbf{k})$-vector that describes spin-triplet pairings in $^3$He superfluid. Naively, one might think the double degeneracy of orbitals would be lifted by inter-orbital hybridizations due to crystal fields or electron-electron repulsive interactions, then spin-singlet orbital-dependent pairings may be severely suppressed. However, we demonstrate that orbital-triplet pairing, represented by the orbital $mathbf{d}_o(mathbf{k})$-vector, could exist under some circumstances. Remarkably, it could even coexist with nematic orders or charge-density-wave orders induced by interactions. The generalization to a single-band superconductor with two valleys (e.g.~honeycomb lattice with two sublattices) is also discussed. Moreover, the complex orbital $mathbf{d}_o$-vector spontaneously breaks time-reversal symmetry (TRS), which might give rise to the TRS-breaking orbital-polarization, analogous to the spin magnetism.
We study a novel type of coupling between spin and orbital degrees of freedom which appears at triplet superconductor-ferromagnet interfaces. Using a self-consistent spatially-dependent mean-field theory, we show that increasing the angle between the ferromagnetic moment and the triplet vector order parameter enhances or suppresses the p-wave gap close to the interface, according as the gap antinodes are parallel or perpendicular to the boundary, respectively. The associated change in condensation energy establishes an orbitally-dependent preferred orientation for the magnetization. When both gap components are present, as in a chiral superconductor, we observe a first-order transition between different moment orientations as a function of the exchange field strength.
Superconductivity is a quantum phenomenon caused by bound pairs of electrons. In diverse families of strongly correlated electron systems, the electron pairs are not bound together by phonon exchange but instead by some other kind of bosonic fluctuations. In these systems, superconductivity is often found near a magnetic quantum critical point (QCP) where a magnetic phase vanishes in the zero-temperature limit. Moreover, the maximum of superconducting transition temperature Tc frequently locates near the magnetic QCP, suggesting that the proliferation of critical spin fluctuations emanating from the QCP plays an important role in Cooper pairing. In cuprate superconductors, however, the superconducting dome is usually separated from the antiferromagnetic phase and Tc attains its maximum value near the verge of enigmatic pseudogap state that appears below doping-dependent temperature T*. Thus a clue to the pairing mechanism resides in the pseudogap and associated anomalous transport properties. Recent experiments suggested a phase transition at T*, yet, most importantly, relevant fluctuations associated with the pseudogap have not been identified. Here we report on direct observations of enhanced nematic fluctuations in (Bi,Pb)2Sr2CaCu2O8+d by elastoresistance measurements, which couple to twofold in-plane electronic anisotropy, i.e. electronic nematicity. The nematic susceptibility shows Curie-Weiss-like temperature dependence above T*, and an anomaly at T* evidences a second-order transition with broken rotational symmetry. Near the pseudogap end point, where Tc is not far from its peak in the superconducting dome, nematic susceptibility becomes singular and divergent, indicating the presence of a nematic QCP. This signifies quantum critical fluctuations of a nematic order, which has emerging links to the high-Tc superconductivity and strange metallic behaviours in cuprates.
Superconductivity in FeSe has recently attracted a great deal of attention because it emerges out of an electronic nematic state of elusive character. Here we study both the electronic normal state and the superconducting gap structure using heat-capacity measurements on high-quality single crystals. The specific-heat curve, from 0.4 K to Tc = 9.1 K, is found to be consistent with a recent gap determination using Bogoliubov quasiparticle interference [P. O. Sprau et al., Science 357, 75 (2017)], however only if nodes are introduced on either the electron or the hole Fermi-surface sheets. Our analysis, which is consistent with quantum-oscillation measurements, relies on the presence of only two bands, and thus the fate of the theoretically predicted second electron pocket remains mysterious.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
