Observability of Higgs Mode in a system without Lorentz invariance

We study the observability of the Higgs mode in BEC-BCS crossover. The observability of Higgs mode is investigated by calculating the spectral weight functions of the amplitude fluctuation below the critical transition temperature. At zero temperature, we find that there are two sharp peaks on the spectral function of the amplitude fluctuation attributed to Goldstone and Higgs modes respectively. As the system goes from BCS to BEC side, there is strong enhancement of spectral weight transfer from the Higgs to Goldstone mode. However, even at the unitary regime where the Lorentz invariance is lost, the sharp feature of Higgs mode still exists. We specifically calculate the finite temperature spectral function of amplitude fluctuation at the unitary regime and show that the Higgs mode is observable at the temperature that present experiments can reach.Comment: 5 pages, 2 figure

LED receiver impedance and its effects on LED-LED visible light communications

This paper experimentally demonstrates that the AC impedance spectrum of the LED as a photodetector heavily depends on the received optical power, which may cause the impedance mismatch between the LED and the post trans-impedance amplifier. The optical power dependent impedance of the LED is well fitted by a modified dispersive carrier transport model for inorganic semiconductors. The bandwidth of the LED-LED visible light communication link is further shown to decrease with the optical power received by the LED. This leads to a trade-off between link bandwidth and SNR, and consequently affects the choice of the proper dada modulation scheme.Comment: 9 pages, 9 figures, submitted to Optics Expres

Wideband Optical Filters with Small Gap Coupled Subwavelength Metal Structures

In this letter, we show that the bandwidth of optical band-stop filters made of subwavelength metal structures can be significantly increased by the strong plasmonic near-field coupling through the corners of the periodic metal squares. The effect of small gap coupling on the spectral bandwidth is investigated by varying the gap size between the metal squares. An equivalent transmission line model is used to fit the transmission and reflection spectra of the metal filters. The transmission line model can characterize well the metal structures with the gap size larger than the near-field decay length. However, it fails to model the transmission and reflection spectra when the gap size reaches the decay range of the near-field in the small gaps

Chinese Narratives of "National Humiliation" and Japan's Role in the Construction of China's National Identity, 1915 to the early 2000s

The sense of national humiliation in China derives from a huge psychological gap between a glorious Empire and a peripheral nation-state which invaded by foreign imperialists in the 19th century and the early 20th century. This gap let Chinese people tend to define the period from 1840s to 1940s as the “Century of National Humiliation”. Although, Chinese people suffer a lot during this “Century”, direct experience and the meaning attached it are not the same. Apart from history itself, this thesis argues that narratives of national humiliation are significant in constructing China’s national identity. In this sense, it will focus on China’s humiliation narratives in different periods, and try to find out what kind of role Japan plays in the construction of China’s national identity. In the first place, this thesis will focus on the narratives of humiliation/victim in different periods of China since its popularization in 1915, and try to give a comprehensive picture of the origin and evolution of this narrative. More specifically, it will examine Chinese humiliation narratives in the following three main periods chronologically: the origins and evolution of “national humiliation” in the pre-1949 era, the absence of “national humiliation” from the 1950s to the 1980s, and the reinvention of “national humiliation” in the post-1989 era. It argues that the narratives of the national past help construct China’s identities in different periods with different meanings. In the second place, this thesis examines not only the discourse of humiliation per se, but also the role that Japan assumes in both victim narratives and the none-victim narratives, and will utilize a social “self/other” approach to analyze Japan’s role in the construction of Chinese national identity. Overall, looking back on Chinese humiliation narratives in three main periods, this thesis concludes that China's national humiliation discourse is an integral part of the shaping of national identity and Japan plays an important role in this process. It also finds out that there is no certain consistency in the interpretations of the national humiliation throughout the last 100 years in China. The national humiliation discourse had once disappeared in China during Mao’s era from 1950s to 1980s. However, whether humiliation discourse dominants Chinese civil society or not, the ruling governments always play an essential role in shaping the nation’s identity. Besides, Japan has been an indispensable “other” in China’s construction of national identity. The popularization and intensification of humiliation discourse in China have always associated with anti-Japanese sentiments. Therefore, in Chinese context, Japan always assumes the role as an “enemy” when the humiliation/victim narrative dominates the civil society

Evolution of Higgs mode in a Fermion Superfluid with Tunable Interactions

In this letter we present a coherent picture for the evolution of Higgs mode in both neutral and charged $s$-wave fermion superfluids, as the strength of attractive interaction between fermions increases from the BCS to the BEC regime. In the case of neutral fermionic superfluid, such as ultracold fermions, the Higgs mode is pushed to higher energy while at the same time, gradually loses its spectral weight as interaction strength increases toward the BEC regime, because the system is further tuned away from Lorentz invariance. On the other hand, when damping is taken into account, Higgs mode is significantly broadened due to coupling to phase mode in the whole BEC-BCS crossover. In the charged case of electron superconductor, the Anderson-Higgs mechanism gaps out the phase mode and suppresses the coupling between the Higgs and the phase modes, and consequently, stabilizes the Higgs mode.Comment: 5 figures, 9 pages, including supplementary materia