R. Y. Chen — Page 2

arXiv2014

Revealing a new charge density wave order in TbTe$_3$ by optical conductivity and ultrafast pump-probe experiments

Rare-earth tri-tellurium RTe$_3$ is a typical quasi-two dimensional system which exhibits obvious charge density wave (CDW) orders. So far, RTe$_3$ with heavier R ions (Dy, Ho, Er and Tm) are believed to experience two CDW phase transitions, while the lighter ones only hold one. TbTe$_3$ is claimed to belong to the latter. However in this work we present evidences that TbTe$_3$ also possesses more than one CDW order. Aside from the one at 336 K, which was extensively studied and reported to be driven by imperfect Fermi surface nesting with a wave vector $q=(2/7 c^*)$, a new CDW energy gap (260 meV) develops at around 165 K, revealed by both infrared reflectivity spectroscopy and ultrafast pump-probe spectroscopy. More intriguingly, the origin of this energy gap is different from the second CDW order in the heavier R ions-based compounds RTe$_3$ (R=Dy, Ho, Er and Tm).

cond-mat.str-el↗

arXiv2012

Electronic properties of 3d transitional metal pnictides : A comparative study by optical spectroscopy

Single-crystalline KFe2As2 and CaT2As2 (T = Fe, Co, Ni, Cu) are synthesized and investigated by resistivity, susceptibility and optical spectroscopy. It is found that CaCu2As2 exhibits a similar transition to the lattice abrupt collapse transitions discovered in CaFe2(As1-xPx)2 and Ca1-xRexFe2As2 (Re-rare earth element). The resistivity of KFe2As2 and CaT2As2 (T = Fe, Co, Ni, Cu) approximately follows the similar T^2 dependence at low temperature, but the magnetic behaviors vary with different samples. Optical measurement reveals the optical response of CaCu2As2 is not sensitive to the transition at 50 K, with no indication of development of a new energy gap below the transition temperature. Using Drude-Lorentz model, We find that two Drude terms, a coherent one and an incoherent one, can fit the low-energy optical conductivity of KFe2As2 and CaT2As2 (T = Fe, Co, Ni) very well. However, in CaCu2As2, which is a sp-band metal, the low-energy optical conductivity can be well described by a coherent Drude term. Lack of the incoherent Drude term in CaCu2As2 may be attributed to the weaker electronic correlation than KFe2As2 and CaT2As2 (T = Fe, Co, Ni). Spectral weight analysis of these samples indicates that the unconventional spectral weight transfer, which is related to Hund's coupling energy J_H, is only observed in iron pnictides, supporting the viewpoint that J_H may be a key clue to seek the mechanism of magnetism and superconductivity in pnictides.

cond-mat.supr-con↗