Spin Flop, Supersolids, and Bicritical and Tetracritical Points

Abstract

A scaling theory is introduced for bicritical points, such as antiferromagnetic spinflop points (with analogies to the upper $\lambda$ point in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$), where two distinct critical lines meet. Experimentally testable predictions follow from renormalization-group calculations which indicate that the bicritical exponents should be Heisenberg like for systems with $n\le 3$ components; the crossover exponent $\phi (\simeq 1.25 \mathrm{for} n=3)$ is directly observable. For $n>\mathrm{}3\mathrm{}$ an intermediate ("supersolid") low-temperature phase may appear, the bicritical point then becoming tetracritical.