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Title: Maximum $T_c$ from purely repulsive electron interactions
Plain: If electron repulsion alone can make electrons pair, there should be a largest possible transition temperature, measured in units of the energy for an electron to hop between neighboring atoms; in cuprates the transition temperature is only about 3 percent of that hopping energy.
Precise: For lattice models with purely repulsive interactions (Hubbard-type, bandwidth $W=8t$ on the square lattice), determine the maximum $T_c/t$ over interaction strength, filling and lattice geometry, and whether it exceeds the cuprate value $T_c/t\sim 0.03$. An answer is controlled numerical $T_c$ values with error bars, or a bound.
Settled by: Unbiased finite-temperature calculations (DQMC, diagrammatic Monte Carlo, cluster methods with size extrapolation) of $T_c$ across parameter space.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)