Browsing by Author "Li, L. J."

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Dirac fermion relaxation and energy loss rate near the Fermi surface in monolayer and multilayer graphene
(2014-08-07)
Luo, C. W.
;
Tseng, P. S.
;
Chen, H. -J.
;
Wu, K. H.
;
Li, L. J.
Ultrafast dynamics of Dirac fermions near the Fermi surface in monolayer and multilayer graphene are revealed using optical pump mid-infrared probe spectroscopy. The energy loss rate of Dirac fermions is also determined via energy-resolved transient transmissivity spectra, which is significantly suppressed as the number of layers in graphene increases.
Possibility of vortex lattice structural phase transition in the superconducting pnictide Ba(Fe(0.925)Co(0.075))(2)As(2)
(2010-03-01)
Kopeliansky, R.
;
Shaulov, A.
;
Shapiro, B. Ya.
;
Yeshurun, Y.
;
Rosenstein, B.
We present magnetic measurements in a single crystal of the newly discovered superconducting ironpnictide Ba(Fe(0.925)Co(0.075))(2)As(2). The magnetization loops exhibit a second magnetization peak (SMP) similar to that observed in most high-temperature superconductors (HTSs). Magnetic relaxation measurements reveal a minimum in the normalized relaxation rate, S = d ln M/d ln t, located in between the SMP onset and the peak fields. The SMP in HTSs is commonly associated with the vortex order-disorder phase transition. However, in Ba(Fe(0.925)Co(0.075))(2)As(2) the onset and peak fields, as well as the minimum point in S, exhibit strong temperature dependence down to low temperatures, excluding the possibility for such a transition. We suggest that the SMP in Ba(Fe(0.925)Co(0.075))(2)As(2) is associated with a vortex structural phase transition from rhombic to square lattice taking place at field and temperatures corresponding to the minimum point of S. A theoretical fit to the transition line, based on a recent theoretical model for vortex structural phase transition, shows good agreement with the experimental results.
Possibility of vortex lattice structural phase transition in the superconducting pnictide Ba(Fe0.925Co0.075)(2)As-2
(2010-03-01)
Kopeliansky, R.
;
Shaulov, A.
;
Shapiro, B. Ya.
;
Yeshurun, Y.
;
Rosenstein, B.
We present magnetic measurements in a single crystal of the newly discovered superconducting ironpnictide Ba(Fe0.925Co0.075)(2)As-2. The magnetization loops exhibit a second magnetization peak (SMP) similar to that observed in most high-temperature superconductors (HTSs). Magnetic relaxation measurements reveal a minimum in the normalized relaxation rate, S = d ln M/d ln t, located in between the SMP onset and the peak fields. The SMP in HTSs is commonly associated with the vortex order-disorder phase transition. However, in Ba(Fe0.925Co0.075)(2)As-2 the onset and peak fields, as well as the minimum point in S, exhibit strong temperature dependence down to low temperatures, excluding the possibility for such a transition. We suggest that the SMP in Ba(Fe0.925Co0.075)(2)As-2 is associated with a vortex structural phase transition from rhombic to square lattice taking place at field and temperatures corresponding to the minimum point of S. A theoretical fit to the transition line, based on a recent theoretical model for vortex structural phase transition, shows good agreement with the experimental results.