The Growing Charge-Density-Wave Order in CuTe Lightens and Speeds up Electrons 

(by I-Ta Wang from Prof. Ming-Wen Chu’s and Prof. Chun-Wei Chen’s group)

Charge density waves (CDWs) are pervasive orders in solids that usually enhance the effective mass (m*) and reduce the Fermi velocity ( v_F ) of carriers. Here, we report on the inverse — a reduced m* and an enhanced v_F correlated with the growth of the CDW order in CuTe with gapped, practically linearly dispersing bands — reminiscent of emergent CDW-gapped topological semimetals. Using momentum-dependent electron energy-loss spectroscopy (q-EELS), we simultaneously capture m* and v_F of the CDW-related, practically linearly dispersing electrons by plasmon dispersions across the transition (335 K, TCDW), with m* of 0.28 m₀ (m₀, the electron rest mass) and v_F  of ~0.005c (c, the speed of light) at 300K.With the growth of the CDW order parameter strength toward 100 K, the electrons become lighter and move faster by ~ 20%. Thorough inspection below TCDW unveils the essential role of the increasing opening of the CDW gap. CuTe is a rich platform for the exploration of CDW/correlation physics with q-EELS established as a useful probe for this type of physics.

(This work has been published in Nature Communications,15,9345,(2024) by NTU-MST PhD student Mr. I-Ta Wang and his research team.)