No abstract

We discovered the chirality of charge density waves (CDW) in 1T-TiSe 2 by using scanning tunnelling microscopy (STM) and optical ellipsometry. We found that the CDW intensity becomes Ia 1 : Ia 2 : Ia 3 = 1 : 0.7 ± 0.1 : 0.5 ± 0.1, where Ia i (i =1, 2, 3) is the amplitude of the tunnelling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise when we index each nesting vector in order of intensity in the Fourier transformation of the STM images. The chirality in CDW results in the three-fold symmetry breaking. Macroscopically, two-fold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H CDW ≡ q 1 · (q 2 × q 3 ), where q i are the nesting vectors, which is independent of the symmetry of components. The nonzero H CDW -the triple-q vectors do not exist in an identical plane in the reciprocal space -should induce a real-space chirality in CDW system.

We report the ultrafast optical response of quasiparticles (QPs) in both the pseudogap (PG) and superconducting (SC) states of an underdoped Bi2Sr2CaCu2O8 + y (Bi2212) single crystal measured with the time-resolved pump-probe technique. At a probe energy variant planck's over omegapr = 1.55 eV, it is found that the reflectivity change DeltaR/R changes its sign at exactly Tc, which allows the direct separation of the charge dynamics of PG and SC QPs. Further systematic investigations indicate that the transient signals associated with PG and SC QPs depend on the probe beam energy and polarization. By tuning them below Tc, two distinct components can be detected simultaneously, providing evidence for the coexistence of PG and SC QPs.