My teacher recently told that there is a rumour that some element has been found by scientists which can travel faster than light. Is it true or just a rumour?
It would be untrue to say that an "element" has been found that can travel faster than the speed of light. However, recent results of high energy physics collisions have lead particle physicists to postulate that there may be a sub atomic particle called a neutrino which may be able to travel faster than the speed of light.
At this point it is an unconfirmed hypothesis based on observation is high energy physics. To date, no particle of any type has been found and verified to travel faster than the speed of light in a vacuum. If this hypothesis is verified, it will be the first. However, there are many questions concerning this theoretical particle including whether it has mass or not.
We should keep in mind that the "speed limit" of light is only truly valid for traveling through vacuums. As we know, light slows down as it travels into a medium. It is possible that some particles can travel faster than light inside a medium other than a vacuum. This is known as the Cherenkov Affect or Cherenkov Radiation.