When partner jumps in a suit and you bid a new suit at the 4 level or above, that is assumed to be a cue bid, showing control and exploring for slam. For example, 1♥ by partner; 1♠ by opponent; negative double by you; 3♥ by partner; 4♦ by you. That is assumed to be a control bid in diamonds, supporting hearts. If you had long, good diamonds, you should have been bidding them in the first place over the 1♠ overcall.
Ditto, when partner bids over a preempt (showing a good hand and usually a 6-card or longer suit), a new suit by you is assumed to be a control bid, looking for slam. For example, 3♥ by opponent, 3♠ by partner, 4♣ or 4♦ by you. You are not fighting it out this high on a misfit hand. You are showing a control in a minor suit, having agreed to support partner's spades.