Tenant and landlord have signed a lease for a residential home in California. No money has yet to be exchanged. Tenant has not moved in to the home. Is the lease still binding?

As long as it's signed and it's intent is clear, then it's legally binding.

Well maybe, a true contract by contract law (first year law school) is not binding until there is some payment, and/or at least some action on one of the parties, to act upon the contract in a manner as if the contract is valid.

So if the landlord allowed the tenant to move in, then it can be assumeed that the lease is valid, since both parties acted on it, one by letting them movein ( give them key) and the other by moving in.

Also if there was a promise of the money to be paid, i.e." I will pay you friday" then they signed the contract and there was a agreement to be paid.

California is fairly tenant bias, so if this goes to court, I would guess the tenant could perhaps get out of it, or force the landlord to honor it.
But that is again my guess.

In the end, I may end up to the opinon of the judge if it goes that far.