Let me first assume the strictest case, ie that you mean 0% literally, not 0% real rate (adjusted for inflation).
Imagine you are a big institution that holds $10 Billion in "cash", for instance a European bank. The interest offered to them by the ECB at the moment is -0.50%. Most banks prefer to pay that premium for storing "cash" in the ECB account over extracting physical notes. (The notes may not even be available.)
Whether or not private citizens are willing to lend at negative nominal interest rate, doesn't matter so much, as long as companies and institutions are willing.
But in the real world, there is usually some inflation. If the inflation is 5%, cash will lose 5% if its value per year if you store it as paper. Most people will store it in a bank deposit. In today's market, far below 5%, probably closer to 0 than 5. In other words, private persons often lend money to the bank at a negative real interest rate.
Whether your mean nominal or real rates, there are people or organizations out there that are willing to lend below a rate of 0% at this very moment.
Imagine you are a big institution that holds $10 Billion in "cash", for instance a European bank. The interest offered to them by the ECB at the moment is -0.50%. Most banks prefer to pay that premium for storing "cash" in the ECB account over extracting physical notes. (The notes may not even be available.)
Whether or not private citizens are willing to lend at negative nominal interest rate, doesn't matter so much, as long as companies and institutions are willing.
But in the real world, there is usually some inflation. If the inflation is 5%, cash will lose 5% if its value per year if you store it as paper. Most people will store it in a bank deposit. In today's market, far below 5%, probably closer to 0 than 5. In other words, private persons often lend money to the bank at a negative real interest rate.
Whether your mean nominal or real rates, there are people or organizations out there that are willing to lend below a rate of 0% at this very moment.