Research Highlights

Topological nodal-line semimetals host nearly flat “drumhead” surface bands, which create a sharp enhancement of the surface density of states and can strongly amplify interaction-driven instabilities. In our recent work, we investigate how such drumhead states bias the pairing symmetry of surface superconductivity in nodal-loop materials. Using a minimal tight-binding model that realizes a bulk nodal loop and drumhead surface states in a slab geometry, we perform a layer-resolved, self-consistent Bogoliubov–de Gennes analysis for competing chiral p-wave and  -wave channels. We find that the chiral p-wave order parameter is dramatically enhanced at the outermost layers and decays within only a few layers into the interior, whereas the d-wave solution remains more than an order of magnitude smaller across the entire slab. In the chiral p-wave state, the drumhead band is efficiently gapped out and the normal-state zero-energy surface peak splits into coherence peaks in the surface local density of states, directly reflecting the induced superconducting gap. These results suggest that drumhead-driven superconductivity is naturally predisposed toward surface-localized chiral p-wave pairing, providing qualitative guidance for surface-sensitive experiments on Pd-doped CaAgP.

Takeru Matsushima and Hiroki Tsuchiura, arXiv: 2602.22837

We demonstrate a Josephson diode effect mediated by Majorana zero modes at a junction between two Kitaev ladders. Each ladder consists of two spinless p-wave chains coupled by inter-leg hopping t⊥. A leg-to-leg phase φ within each ladder breaks time-reversal symmetry for φ ≠ 0, π (mod 2π), while a weak link between the ladders sets the across-junction phase θ. Interference between a phase-shifted intra-band channel, an unshifted inter-band channel, and the 4π Majorana channel near the topological transition yields a pronounced nonreciprocal current–phase relation. To our knowledge, this is the first explicit microscopic mechanism that links MZMs to the Josephson diode effect in a ladder–ladder junction. 

Read the preprint on arXiv, and see also coverage by Quantum Zeitgeist.

DyCo5 is a rare-earth cobalt ferromagnet that exhibits a temperature-driven spin reorientation transition (SRT), where the equilibrium magnetization rotates from in-plane to the c axis across a narrow temperature window. We propose a sensor-free, self-regulating thermal switch that exploits this intrinsic SRT as an internal trigger for the anomalous Ettingshausen effect (AEE). Using density-functional calculations combined with the Kubo linear-response formalism, we compute the energy-resolved anomalous Hall conductivity sigma_xy(epsilon) and the finite-temperature anomalous Nernst conductivity alpha_xy(T) for two magnetization orientations (M || c and M ⟂ c). While the intrinsic sigma_xy at the Fermi level remains sizable for both orientations, alpha_xy shows an about two-orders-of-magnitude contrast around the SRT, consistent with the low-temperature Mott relation through the slope d sigma_xy(epsilon)/d epsilon at the Fermi level. We trace this strong anisotropy to sharply peaked Berry-curvature hot spots generated by spin-orbit-coupling-induced avoided crossings of Co 3d bands, whose energies and intensities shift upon rotating M. Combining alpha_xy with longitudinal transport coefficients, we estimate device-level metrics (anomalous Nernst thermopower S_ANE and Ettingshausen coefficient Pi_AEE = T S_ANE) and demonstrate robust, orientation-controlled switching of transverse heat flow under a fixed in-plane bias current, enabling compact on-chip thermal control without external sensors or feedback electronics.

Shibo Wang, Hiroki Tsuchiura, and Nobuaki Terakado, “Sensor-free, self-regulating thermal switching via anomalous Ettingshausen effect and spin reorientation in DyCo5”, Appl. Phys. Lett. 128, 102405 (2026). Preprint: arXiv: 2512.14335.

DyCo5 is a ferrimagnetic rare-earth cobalt compound that exhibits both a magnetization compensation point and a spin reorientation transition, reflecting the strong competition between the Dy and Co sublattices. We performed the first high-field magnetization measurements on DyCo5 single crystals up to 14 T and found several unusual features, including a pronounced magnetization anisotropy and a clear minimum in the spontaneous magnetization near the compensation point without complete cancellation. To explain these behaviors, we combined precise experiments with two complementary theoretical approaches: an effective spin model based on crystal-field theory for Dy3+ ions and a multiscale framework combining DFT, DMFT, and atomistic spin dynamics. The calculations reproduce the temperature evolution of magnetization, the compensation behavior, and the spin reorientation, while also revealing that the low-temperature in-plane anisotropy is dominated by Dy and is gradually overtaken by the uniaxial Co contribution at higher temperatures. Near the compensation point, the theory further shows that thermal disorder and a slight non-collinearity between the Dy and Co sublattices prevent perfect magnetic compensation, providing a microscopic explanation for the complex magnetism of DyCo5.

Alena Vishina, Konstantin Skokov, Hiroki Tsuchiura, Patrik Thunström, Alex Aubert, Oliver Gutfleisch, Olle Eriksson, and Heike C. Herper, "New insights into the magnetism of DyCo5." arXiv:2511.17087.

Figure for highlight: Fig. 1 (temperature- and direction-dependent magnetization curves of DyCo5 single crystal) or Fig. 5 (temperature dependence of magnetization and compensation behavior).