arXiv subjects

Dirk. K. Morr

Publications and source records attributed to Dirk. K. Morr.

4 recordsLinked to original sources

arXiv2024

The Non-collinear Path to Topological Superconductivity

Combining spin textures in ultra-thin films with conventional superconductors has emerged as a powerful and versatile platform for designing topologically non-trivial superconducting phases as well as spin-triplet Cooper pairs. As a consequence, two-dimensional magnet-superconductor hybrids (2D MSHs) are promising candidate systems to realize devices for topology-based quantum technologies and superconducting spintronics. So far, studies have focused mostly on systems hosting collinear ferromagnets or antiferromagnets. However, topologically non-trivial phases have been predicted to emerge in MSH systems with non-collinear spin textures as well. In this article, we present the experimental discovery of topological superconductivity in the MSH system Fe/Ta(110) where a magnetic spiral is realized in the Fe monolayer on the surface of the s-wave superconductor Ta. By combining low-temperature spin-polarized scanning tunneling microscopy measurements with theoretical modeling, we are able to conclude that the system is in a topological nodal-point superconducting phase with low-energy edge modes. Due to the non-collinear spin texture in our MSH system, these edge modes exhibit a magnetization direction-dependent dispersion. Furthermore, we identify direct signatures of Rashba spin-orbit coupling in the experimentally measured differential tunneling conductance. The present work realizes a non-collinear spin texture-based path to topological superconductivity.

cond-mat.supr-con↗

arXiv1999

Electronic Raman Scattering in Superconducting Cuprates

We show that the novel features observed in Raman experiments on optimally doped and underdoped Bi-2212 compounds in $B_{1g}$ geometry can be explained by a strong fermionic self-energy due to the interaction with spin fluctuations. We compute the Raman intensity $R(ω)$ both above and below $T_c$, and show that in both cases $R(ω)$ progressively deviates, with decreasing doping, from that in a Fermi-gas due to increasing contribution from the fermionic self-energy. We also show that the final state interaction increases with decreasing doping and gradually transforms the $2Δ$ peak in the superconducting state into a pseudo resonance mode below $2Δ$. We argue that these results agree well with the experimental data for Bi-2212.

cond-mat↗

arXiv1998

Effect of next-nearest neighbor hopping on the spin dynamics in antiferromagnets

Recently, inelastic neutron scattering (INS) experiments on the insulating parent compounds of high-T_c materials were analyzed to extract the value of the superexchange constant $J$. Starting point of the analysis was the nearest-neighbor Heisenberg model. Motivated by recent ARPES experiments, we consider the effects of a next-nearest neighbor hopping, $t'$ in the strong coupling limit of the spin-density wave formalism, where it leads to an antiferromagnetic exchange $J'>0$ between next-nearest neighbor spins. We show that a finite $J'$ (a) changes the spin-wave velocity and thus the value of $J$ extracted from the INS data, yielding almost identical values for $J$ in La_2CuO_4 and YBa_2Cu_3O_{6.15}, and (b) leads to a considerable change in the high-frequency spin-dynamics. Finally, we calculate the 1/S quantum corrections in the presence of $J'$ and discuss their relevance for the INS data.

cond-mat.str-el↗

arXiv1997

Comment on: ``Using Ni Substitution and $^{17}$O NMR to Probe the Susceptibility $χ'(q)$ in Cuprates''

In a recent letter (PRL 79, 2117 (1997)), Bobroff et al. presented novel $^{17}$O NMR measurements for YBa_2(Cu_{1-x}Ni_x)_3O_{6+y} which offer a new probe of the momentum dependence of the static spin susceptibility $χ'(q)$. They analyzed the $^{17}$O line width by assuming a Gaussian form for $χ'$, and came to the conclusion that the correlation length $ξ$ is independent of temperature $T$. Furthermore, they claim that a Lorentzian form of $χ'$ yields the same result. We will demonstrate that the Lorentzian and Gaussian form of $χ'$ actually yield qualitatively different results for the $^{17}$O line width and its dependence on $ξ$. We show that their data when combined with $T_{2G}$ data from Takigawa require that $ξ$ be T-dependent. Furthermore, assuming a Gaussian form of $χ'$ leads to the unphysical result that $ξ$ increases with $T$. In contrast, the Lorentzian form of $χ'$ yields that $ξ$ decreases with increasing $T$ and is thus fully compatible with the experimental results.

cond-mat.str-el↗