E L E C T R O N I C S T R U C T U R E , M A G N E T I S M A N D D Y N A M I C S

S C I E N T I F I C H I G H L I G H T S

1 1 2 H I G H L I G H T S 2 0 2 2 I

the spin polarisation, most pronounced at the central circular state around the G-point. Furthermore, the TSS of the substrate exhibits an antiparallel chirality relative to that of the H-TaSe2 FS states.

In conclusion, this work demonstrated the preparation of a single TaSe2 monosheet by exploiting a simple interface

reaction that might also be applicable for many different systems. Symmetry reduction in the monosheet, combined with the proximity of the Dirac-type states of the Bi2Se3 substrate, induces a spin-momentum locking in the (non-magnetic) film, which points to a new approach to prepare chiral two-dimensional electron systems.

PRINCIPAL PUBLICATION AND AUTHORS

Fermi surface chirality induced in a TaSe2 monosheet formed by a Ta/Bi2Se3 interface reaction, A. Polyakov (a), K. Mohseni (a), R. Felici (b), C. Tusche (c,d), Y.-J. Chen (c,d), V. Feyer (c,d), J. Geck (e,f), T. Ritschel (e), A. Ernst (g), J. Rubio-Zuazo (h), G.R. Castro (h), H.L. Meyerheim (a), S.S.P. Parkin (a), Nat. Commun. 13, 2472 (2022); https:/doi.org/10.1038/s41467-022-30093-1 (a) Max Planck Institute of Microstructure Physics, Halle (Germany) (b) Consiglio Nationale delle Recherche SPIN, Rome (Italy) (c) FZ Jülich, Peter Grünberg Institut (PGI-6), Jülich (Germany) (d) Fakultät f. Physik, Univ. Duisburg-Essen, Duisburg (Germany) (e) Institut f. Festkörper und Materialphysik, TU Dresden, Dresden (Germany) (f) Würzburg-Dresden Cluster of Excellence ct. mat., TU Dresden, Dresden (Germany) (g) Institut f. Theoretische Physik, Johannes-Kepler Universität, Linz (Austria) (h) ESRF

REFERENCES

[1] D. MacNeill et al., Nat. Phys. 13, 300 (2017). [2] H. Xu et al., Adv. Mater. 32, 2000513 (2020). [3] J.M. Lu et al., Science 350, 1353 (2015).

The observation of Kondo charge accumulation

The Kondo effect refers to a minimum in the electrical resistance as a function of temperature observed in metals containing isolated magnetic (or spin) impurity atoms. Experiments on BM28 (XMaS) have observed for the first time a charge accumulation predicted to accompany the Kondo effect, albeit for a system comprising a dense lattice of magnetic ions.

The third law of thermodynamics requires that entropy must vanish for any system in equilibrium approaching absolute zero temperature. Local moments that are free to rotate in any direction cannot therefore survive. One solution is that interactions between the moments bring about magnetic order. Kondo physics provides another escape route, in which the moments are instead screened by conduction electrons, effectively setting the moments to zero. It can be visualised that local moments pair with a conduction electron of opposite spin to give a total spin of zero (a singlet) resulting in the accumulation of a (negative) charge around the moment site if there is a coupling between the electronic spin and charge.

Despite the confirmation of many predictions of the Kondo model, the observation of charge accumulation has eluded observation to date. The spin pairing with the conduction electron in Kondo screening has a characteristic binding energy kBTK, where TK is the Kondo temperature.

Fig. 106: The magnetic structure of UAu2. The uranium sites are shown with arrows that depict the ordered moments. The uranium lattice comprises triangular planes of atoms, such as ABC. If the moment on A is down, then an antiferromagnetic interaction between adjacent vertices would align B and C up. But B and C would then be parallel to each other, which is unfavourable, a phenomenon known as geometric frustration. The actual magnetic structure is shown by the arrows. The moments, rather than having fixed magnitude, have amplitudes that are sinusoidally modulated. The reduction of the moment amplitude can be achieved by Kondo screening.