Wu Chang-Qin
Email Address
phywcq@nus.edu.sg
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Publication Reversal of thermal rectification in quantum systems(2009-11-12) Zhang, L.; Yan, Y.; Wu, C.-Q.; Wang, J.-S.; Li, B.; PHYSICSWe study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy, and size of the spin chains. © 2009 The American Physical Society.Publication Control of heat transport in quantum spin systems(2009-01-05) Yan, Y.; Wu, C.-Q.; Li, B.; PHYSICSWe study heat transport in quantum spin systems analytically and numerically. First, we demonstrate that heat current through a two-level quantum spin system can be modulated from zero to a finite value by tuning a magnetic field. Second, we show that a spin system, consisting of two dissimilar parts-one is gapped and the other is gapless-exhibits current rectification and negative differential thermal resistance. Possible experimental realizations by using molecular junctions or magnetic materials are discussed. © 2009 The American Physical Society.Publication Nonballistic heat conduction in an integrable random-exchange Ising chain studied with quantum master equations(2008-05-23) Yan, Y.; Wu, C.-Q.; Casati, G.; Prosen, T.; Li, B.; PHYSICSWe numerically investigate the heat conduction in a random-exchange Ising spin chain by using the quantum master equation. The chain is subject to a uniform transverse field h, while the exchange couplings { Qn } between the nearest neighbor spins are random; the largest size we simulate is up to 10. This model is integrable; i.e., the nearest neighbor level spacing distribution is Poissonian. However, we find clear evidence of nonballistic transport. In the small coupling regime (Qn h), an energy and/or temperature gradient in the bulk of the system is observed and the energy current appears to be proportional to the inverse of the system size. Moreover, we find that in the low and high temperature regimes, the thermal conductivity κ and the specific heat Cv have the same dependence on temperature. The large coupling case (Qn ∼h) is also discussed. © 2008 The American Physical Society.