Hidden Quantum Mirage by Negative Refraction in Semiconductor P-N Junctions
Update: 2017-03-02 15:24:17      Author: yangjuan@csrc.ac.cn

Half a century ago, Veselago [1] proposed the concept of negative refraction for electromagnetic waves: a sharp interface between a medium with positive refractive index and a negative index medium could refocus a diverging pencil of rays to form an image or “quantum mirage”, similar to the bending of light to create mirages in the atmosphere. In 2007, Cheianov et al. [2] shows that a sharp and specular graphene P-N interface can exhibit anomalous focusing and produce a quantum mirage. This effect has been widely used in theoretical proposals to control charge and/or spin transport for massless Dirac fermions in semiconductors. However, over many years anomalous focusing has not been clearly confirmed in experiments until very recently [3], because of its fragility to the finite width and disorder of the P-N interface [see Fig. 1(c) and (d)].

1.png

Fig.  1. Graphene P-N junction in real space (a) and gate-induced shift of the Dirac cones in momentum space (b). The quantum mirage is visible in a sharp P-N junction (c), but is gradually smeared out in a smooth junction (d).

Fig. 2. (a) and (b) Response amplitude (Green’s function) vs. pump-probe distance R2 R1 in (a) sharp or (b) smooth graphene P-N junctions. One slice (blue dashed line) of the contour is shown as the black solid lines in the lower panel. The dashed lines in the lower panel of (b) include on-site disorder of different strengths ξ inside the junction.


Recently, Wen Yang and Haiqing Lin’s group in CSRC in collaboration with Kai Chang’s group in the Institute of Semiconductors, CAS proposed a new interference phenomenon observable in a wide range of semiconductor P-N junctions [4]. Compared with the interface-induced anomalous focusing, this phenomenon enjoys two distinguishing features [see Fig. 2(a) and (b)]. First, it originates from the symmetry of the Fermi surfaces of the constituent materials, so it is insensitive to the details of the interface, such as the width, potential profile, and even disorder. Second, it does not produce a visible quantum mirage, but instead can be detected as a distance-independent response across the P-N interface, in sharp contrast to the nearly universal 1/R(d−1)/2 decay with distance R of the response in d-dimensional uniform systems. The predicted phenomenon could dramatically enhance many response properties in various semiconductors. The recently fabricated P-N junctions in 2D semiconductors provide ideal platforms to explore this phenomenon and its applications to dramatically enhance charge and spin transport as well as carrier-mediated long-range correlation between localized magnetic moments.

 

References:

[1]     V. G. Veselago, Sov. Phys. Usp. 10, 509 (1968).

[2]     V. V. Cheianov, V. Fal’ko, and B. L. Altshuler, Science 315, 1252 (2007).

[3]     [G.-H. Lee, G.-H. Park, and H.-J. Lee, Nat. Phys. 11, 925 (2015); Shaowen Chen et al., Science 353, 1522 (2016).

[4]     Shu-Hui Zhang, Jia-Ji Zhu, Wen Yang, Hai-Qing Lin, and Kai Chang, Phys. Rev. B 94, 085408 (2016).


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