Quantum Induced Asymmetric Phase Diagrams of Spin-Glass Systems

The spin-1/2 quantum Heisenberg spin-glass system is studied in all spatial dimensions $d$ by renormalization-group theory.[1] Strongly asymmetric phase diagrams in temperature and antiferromagnetic bond probability $p$ are obtained in dimensions $d\geq3$. The asymmetry at high temperatures approaching the pure ferromagnetic and antiferromagnetic systems disappears as $d$ is increased. However, the asymmetry at low but finite temperatures remains in all dimensions, with the antiferromagnetic phase receding to the ferromagnetic phase. A finite-temperature second-order phase boundary directly between the ferromagnetic and antiferromagnetic phases occurs in $d\geq6$, resulting in a new multicritical point at its meeting with the boundaries to the paramagnetic phase. In $d=3,4,5$, a paramagnetic phase reaching zero temperature intervenes asymmetrically between the ferromagnetic and reentrant antiferromagnetic phases. There is no spin-glass phase in any dimension. \newline \noindent [1] C.N. Kaplan and A.N. Berker, arXiv:0709.3589v1 [cond-mat.dis-nn], Phys. Rev. Lett., in press.