Quantum Transition Between Magnetically Ordered and Mott Glass Phases

• Published in: Annalen der Physik 2017-10, Vol.529 (10), p.n/a
• Main Author: Syromyatnikov, A. V.
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Bose‐systems; Couplings; Critical temperature; Free energy; Heisenberg antiferromagnets; Magnetic properties; Magnons; Mott glass; Order parameters; Phase transitions; Quantum phase transitions; Quantum physics; Quenched disorder; Superfluidity
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201700055

We discuss a quantum transition from a superfluid to a Mott glass phases in disordered Bose‐systems by the example of an isotropic spin‐12 antiferromagnet with spatial dimension d≥2 and with disorder in tunable exchange couplings. Our analytical consideration is based on general properties of a system in critical regime, on the assumption that the magnetically order part of the system shows fractal properties near the transition, and on a hydrodynamic description of long‐wavelength magnons in the magnetically ordered (“superfluide”) phase. Our results are fully consistent with a scaling theory based on an ansatz for the free energy proposed by M. P. Fisher et al. (Phys. Rev. B 40, 546 (1989)). We obtain z=d−β/ν for the dynamical critical exponent and φ=zν, where ϕ, β, and ν are critical exponents of the critical temperature, the order parameter, and the correlation length, respectively. The density of states of localized excitations (fractons) is found to show a superuniversal (i.e., independent of d) behavior. The interplay of quantum fluctuations and quenched disorder leads to a variety of unconventional phenomena and special quantum phases. The author discusses a quantum transition from a magnetically ordered to a Mott glass phase in an isotropic spin‐1/2 antiferromagnet with disorder in tunable exchange couplings. Results obtained should be relevant to various Bose‐systems from the same universality class. A new method is used for consideration of this transition.