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

Fig. 101: Reciprocal space mapping in the vicinity of the (420) (a) and (620) (b) main reflections of (TaSe4)2I

at 88 K, showing the main (m,n,o)=(000) and satellite reflections. The observed CDW wave vectors are given by

q=[m h(2p/a), n h(2p/a), o δ(2p/c)] with m+n+o ∈ 2 Z and h = 0.027 ± 0.001, δ = 0.012 ± 0.001.

PRINCIPAL PUBLICATION AND AUTHORS

Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7 δ, E. Wahlberg (a), R. Arpaia (a,b), G. Seibold (c), M. Rossi (b), R. Fumagalli (b), E. Trabaldo (a), N.B. Brookes (d), L. Braicovich (b,d), S. Caprara (e,f), U. Gran (a), G. Ghiringhelli (b,g), T. Bauch (a), F. Lombardi (a), Science 373, 1506 (2021); https:/doi.org/10.1126/science.abc8372 (a) Chalmers University, Göteborg (Sweden) (b) Politecnico di Milano (Italy) (c) BTU Cottbus-Senftenberg (Germany) (d) ESRF (e) Università La Sapienza (Italy) (f) CNR-ISC, Roma (Italy) (g) CNR-SPIN, Milano (Italy)

REFERENCES

[1] B. Keimer et al., Nature 518, 179 (2015). [2] G. Ghiringhelli et al., Science 337, 821 (2012). [3] E. Fradkin et al., Rev. Mod. Phys. 87, 457 (2015).

The charge-density wave topological semimetal (TaSe4)2I

(TaSe4)2I hosts a charge-density-wave (CDW) instability below 248 K, related to its quasi-one- dimensional structure. X-ray diffraction combined with theory indicates that in the CDW regime, the nesting vectors coupling Weyl points of opposite chirality are integer multiples of the CDW modulation vectors, demonstrating that the CDW couples the bulk Weyl points and opens a band gap.

(TaSe4)2I has long been known to host a charge-density- wave (CDW) instability below 248 K [1], and only recently has been shown in the high-temperature regime to represent a new class of structurally chiral topological semimetals [2,3].

Conventional 3D semimetals are materials whose bulk Fermi pockets derive from linearly dispersing, point- like nodal degeneracies. The Fermi pockets of 3D Weyl

The strain-induced disappearance of the CDW restores the strange metal state, which can therefore expand in a much larger temperature range.

This observation points towards an intimate connection between the onset of CDW and the departure from

the T-linear resistivity in underdoped cuprates (Figure 100) a link that was missing until now and that also challenges the relation between charge order and pseudogap. This experiment also illustrates the potentiality of strain control to manipulate the ground state of these quantum materials.