The artificial sweetner used only for cold food is

Aspartame

Sugar substitutes are substances that are used in place of sweeteners with sugar (sucrose) or sugar alcohols. It may also be called artificial sweeteners. It is a methyl ester of the aspartic acid/phenylalanine dipeptide with the trade names NutraSweet, Equal, and Canderel.

Aspartame is the most successful and widely used artificial sweetener.  Also, it is the most commonly used sugar substitute in foods and beverages. It is roughly 100 times as sweet as cane sugar. It is a methyl ester of dipeptide formed from aspartic acid and phenylalanine. The use of aspartame is limited to cold foods and soft drinks because it is unstable at cooking temperatures.  Aspartame is unsuitable for baking and cooking at high temperatures as compared to the other sweeteners as it breaks down on heating and loses the sweetness. The melting point of aspartame is very low, thus it is suitable mainly for foods and beverages at low temperatures.

Since aspartame decomposes at cooking temperature, therefore, its use is widely limited to just cold food or we can say that it is used just as a sweetening agent in cold foods and soft drinks.