Particle Interference: How QP Wavepacket Creates Standing Waves

[Niles]

Hi guys

Today my lecturer talked a little about quasiparticle interference (QPI). He said that if we place a QP on a metal containing a single impurity, then the QP wavepacket will travel outwards, and when it hits the impurity, it will get reflected back and create standing waves.

I don't understand why there are being created standing waves? I mean, we have a wavepacket expanding out from a point, and then it hits the impurity. Then some of the wave is reflected back: Then what is left for the back-reflected wave to interfere with?

 

[eljose79]

Hello,

Thank you for bringing up this interesting topic. Quasiparticle interference (QPI) is a phenomenon that occurs in condensed matter systems, where the collective behavior of particles can be described as quasiparticles. These quasiparticles can interact with the crystal lattice and create interference patterns, which can be observed using scanning tunneling microscopy (STM) or other techniques.

In the case of a single impurity in a metal, the QP wavepacket is initially traveling outwards from the point of origin. When it encounters the impurity, the wavepacket gets reflected back. This reflected wavepacket then interferes with the original wavepacket, creating standing waves. These standing waves are a result of the interference between the two wavepackets, and they can provide valuable information about the electronic structure of the material and the nature of the impurity.

To better understand this, imagine throwing a ball against a wall. When the ball hits the wall, it bounces back and interferes with the incoming ball, creating a standing wave. In the case of QPI, the impurity acts as the wall, and the reflected wavepacket interferes with the incoming one to create standing waves.

I hope this helps clarify why standing waves are created in QPI experiments. If you have any further questions, please don't hesitate to ask. QPI is a complex and fascinating phenomenon, and there is still much to be learned about it. Thank you for your interest in this topic.