Field-induced quantum critical point in planar Heisenberg ferromagnets with long-range interactions: Two-time Green’s function framework

AAg2M[VO4]2Möller1, Amuneke2, Daniel3 et al. 2012Phys. Rev. B381480View full textAdd to dashboardCite

“…An interesting aspect is that for a 2D-FM spin system the ground state remains degenerate by symmetry whereas frustration phenomena will arise, e.g., from one of the three equal and effectively FM exchange coupling constants tuned into the AFM regime. Recently, frustrated FM lattices have emerged as an intriguing topic in condensed matter theory, [22][23][24][25][26][27] and we believe that our series of compounds may prove suitable for further development of new insights into the competition of various degrees of freedom.…”

Thermodynamics of the Classical Planar Ferromagnet Close to the Zero-Temperature Critical Point: A Many-Body Approach

“…As well known, it is perfectly legal in the classical context to put S = 1. However, for a more transparent and direct comparison with the quantum version [28], through this paper we will consider arbitrary S.…”

“…In particular, the spin-1/2 PFM has attracted great attention since, in the pioneering papers by Matsubara and Matsuda [23,24] on superfluidity in 4 He, a quantum lattice gas of hard-core bosons with long-range attractive interactions has been proven to be just equivalent to the spin-1/2 PFM in a longitudinal field (see also [25]). Remarkably, the Wilson RG [26,27], applied to a suitable functional representation of the spin-1/2 PFM, capturing the essential low-temperature physics, and the two-time Green's function technique [28], utilized to investigate the microscopic spin-S model, have provided a reliable scenario of the global phase diagram and crossovers in the vicinity of the QCP.…”

“…We will use the two-time Green's function method in classical statistical mechanics [29], developed and tested in [30][31][32][33], on microscopic classical spin model. This allows us to perform in parallel the quantum [28] and the classical analysis for any d, giving a transparent relation between the CPFM and the spin-S QPFM, both exhibiting a zerotemperature critical point. Hence, new insights on quantum criticality, at least for a class of anisotropic magnetic systems, will be provided.…”

Magnon–magnon interactions in O(3) ferromagnets and equations of motion for spin operators

“…We stress that the reduction of magnon-magnon interactions is is crucial for thermodynamics of O(3) ferromagnets, for spurious terms in low-temperature series for free energy are present whether or not the constrain v 0 p n p 0 p 2 = 0 is implemented [66]. As noted in the Introduction, RPA is widely used tool for studying magnetic systems [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][31][32][33][34][35][36][37][38][39][40][41][42]. Thus, to be able to correctly interpret results obtained from RPA, it is of interest to fully grasp the approximation in itself.…”