arXiv subjects

C. -H. Dong

Publications and source records attributed to C. -H. Dong.

5 recordsLinked to original sources

arXiv2016

Experimental realization of optomechanically induced non-reciprocity

Non-reciprocal devices, such as circulators and isolators, are indispensable components in classical and quantum information processing in an integrated photonic circuit. Aside from those applications, the non-reciprocal phase shift is of fundamental interest for exploring exotic topological photonics, such as the realization of chiral edge states and topological protection. However, incorporating low optical-loss magnetic materials into a photonic chip is technically challenging. In this study, we experimentally demonstrate non-magnetic non-reciprocity using optomechanical interactions in a whispering-gallery microresonator, as proposed by Hafezi and Rabl. Optomechanically induced non-reciprocal transparency and amplification are observed, and a non-reciprocal phase shift of up to 40 degrees is demonstrated in this study. The results of this study represent an important step towards integrated all-optical controllable isolators and circulators, as well as non-reciprocal phase shifters.

physics.optics↗

arXiv2012

Observation of an isotropic superconducting gap at the Brillouin zone center of Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$

We performed a high-resolution angle-resolved photoemission spectroscopy study on superconducting (SC) Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$ ($T_c=29$ K) in the whole Brillouin zone (BZ). In addition to a nearly isotropic $\sim$ 8.2 meV 2-dimensional (2D) SC gap ($2Δ/k_BT_c\sim7$) on quasi-2D electron Fermi surfaces (FSs) located around M$(π,0,0)$-A$(π,0,π)$, we observe a $\sim 6.2$ meV isotropic SC gap ($2Δ/k_BT_c\sim5$) on the Z-centered electron FS that rules out any d-wave pairing symmetry and rather favors an s-wave symmetry. All isotropic SC gap amplitudes can be fit by a single gap function derived from a local strong coupling approach suggesting an enhancement of the next-next neighbor exchange interaction in the ferrochalcogenide superconductors.

cond-mat.supr-con↗

arXiv2011

Strong nodeless pairing on separate electron Fermi surface sheets in (Tl, K)Fe$_{1.78}$Se$_2$ probed by ARPES

We performed a high-resolution angle-resolved photoemission spectroscopy study of the Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$ superconductor ($T_c=29$ K). We show the existence of two electronlike bands at the M$(π, 0)$ point which cross the Fermi level at similar Fermi wave vectors to form nearly circular electronlike Fermi surface pockets. We observe a nearly isotropic $\sim$ 8.5 meV superconducting gap ($Δ/k_BT_c\sim 7$) on these Fermi surfaces. Our analysis of the band structure around the Brillouin zone centre reveals two additional electronlike Fermi surfaces: a very small one and a larger one with $k_F$ comparable to the FS pockets at M. Interestingly, a SC gap with a magnitude of $\sim$ 8 meV also develops along the latter FS. Our observations are consistent with the s-wave strong coupling scenario.

cond-mat.supr-con↗

arXiv2010

Plasmon modes of silver nanowire on a silica substrate

Plasmon mode in a silver nanowire is theoretically studied when the nanowire is placed on or near a silica substrate. It is found that the substrate has much influence on the plasmon mode. For the nanowire on the substrate, the plasmon (hybrid) mode possesses not only a long propagation length but also an ultrasmall mode area. From the experimental point of view, this cavity-free structure holds a great potential to study a strong coherent interaction between the plasmon mode and single quantum system (for example, quantum dots) embedded in the substrate.

physics.optics↗

arXiv2009

Mechanism of unidirectional emission of ultrahigh Q Whispering Gallery mode in microcavities

The mechanism of unidirectional emission of high Q Whispering Gallery mode in deformed circular micro- cavities is studied and firstly presented in this paper. In phase space, light in the chaotic sea leaks out the cavity through the refraction regions, whose positions are controlled by stable islands. Moreover, the positions of fixed points according to the critical line in unstable manifolds mainly determines the light leak out from which refraction region and the direction of the emission. By controlling the cavity shape, we can tune the leaky regions, as well as the positions of fixed points, to achieve unidirectional emission high Q cavities with narrow angular divergence both in high and low refractive index mater

physics.optics↗