Bose-Glass Phases in Disordered Quantum Magnets

Abstract

In disordered spin systems with antiferromagnetic Heisenberg exchange, transitions into and out of a magnetic-field-induced ordered phase pass through a unique regime. Using quantum Monte Carlo simulations to study the zero-temperature behavior, these intermediate regions are determined to be a Bose-Glass phase. The localization of field-induced triplons causes a finite compressibility and hence glassiness in the disordered phase.PACS numbers: 73.43. Nq, 75.10.Nr, 75.50.Lk, 75.50.Ee Bose-Glass phenomena have recently been reported in a variety of disordered quantum many-body systems, including trapped atoms, vortex lattices, and Heisenberg antiferromagnets. These experiments have in common signatures of finite compressibility in proximity to a BoseEinstein condensate. In atomic waveguides, the fragmentation of such a condensate is caused by a random modulation of the local atomic density.[1] It was shown that a quantum phase transition between the superfluid and the insulating Bose-Glass phase can be achieved under realistic experimental conditions.[2] Furthermore, recent transport measurements of vortex dynamics in hightemperature superconducting cuprates have shown evidence of a Bose-Glass transition. [3] In the context of quantum antiferromagnetism, recent measurements of the magnetization and the specific heat have suggested a glassy regime in proximity to a magnetic-field-induced triplon condensate. [4,5] However, a theoretical understanding of the Bose-Glass phenomena in quantum spin systems based on a microscopic Hamiltonian is still lacking.In this letter, we study how disorder affects the quantum phase transition between a valence bond solid and a magnetic-field-induced Néel-ordered phase in an antiferromagnetic Heisenberg spin system. Using largescale quantum Monte Carlo simulations down to ultralow temperatures, we observe that in cubic dimer systems with bond randomness, there is an intermediate Bose-Glass regime, separating an antiferromagnetically ordered phase of condensed triplons from a spin liquid phase of localized triplons at low magnetic fields. For weak inter-dimer couplings, this model can be mapped onto a lattice boson model with random potential.[6] The Néel-ordered phase of delocalized triplons corresponds to the superfluid regime in the bosonic language. It is characterized by a finite staggered magnetization perpendicular to the applied magnetic field m ⊥ s , analogous to the superfluid order parameter in a bosonic system. The Bose-Glass phase is distinguished by a finite slope of the uniform magnetization m u as a function of the applied magnetic field, i.e., compressible bosons, whereas the order parameter m ⊥ s vanishes.In order to probe these observables and thus study emerging quantum phase transitions in such disordered quantum magnets, we apply the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method. [7] In particular, the directed-loop algorithm is used to minimize bounce probabilities in the loop construction when magnetic fields are applied to the system.[8...

Disorder-Induced Revival of the Bose-Einstein Condensation inNi(Cl1−xBrxDupont1, Capponi2, Laflorencie3 2017Phys. Rev. Lett.145280View full textAdd to dashboardCite

“…For other experimental systems with a magnetic Bose glass regime (for a recent review, see Ref. 67) one could expect a similar disorder-induced BEC revival [23] provided the separa-tion of energy scale between clean and doped sites is large enough, as for instance in the metal-organic spin ladder (Hpip) 2 CuBr 4(1−x) Cl 4x [68].…”

“…Such an impurity-induced ordering mechanism of the type "order from disorder" [14,15] [21]. Nevertheless, only a few studies have focused on the effect of an external field [22][23][24][25][26][27].In this Letter, building on recent nuclear magnetic resonance (NMR) experiments [28], we achieve a realistic theoretical study of the high magnetic field regime of Ni(Cl 1−x Br x ) 2 -4SC(NH 2 ) 2 (DTNX): a threedimensional antiferromagnetic (AF) system made of weakly coupled chains of S = 1 spins subject to singleion anisotropy [panels (b-c) of Fig. 1].…”

“…Such an impurity-induced ordering mechanism of the type "order from disorder" [14,15] [21]. Nevertheless, only a few studies have focused on the effect of an external field [22][23][24][25][26][27].…”

“…Such an impurity-induced ordering mechanism of the type "order from disorder" [14,15] has been experimentally observed for a large number of spin-gapped compounds [16]: weakly coupled d = 1 systems such as spin-Peierls chains CuGeO 3 [17,18], spin ladders SrCu 2 O 3 [19] and BiCu 2 PO 6 [16], Haldane chains PbNi 2 V 2 O 8 [20], as well as weakly coupled dimers in TlCuCl 3 [21]. Nevertheless, only a few studies have focused on the effect of an external field [22][23][24][25][26][27].…”

Crystal growth and characterization of the dilutable frustrated spin-ladder compound Bi(Cu1−xZnx)2PO6

“…For example, in SrCu 2 O 3 (2-leg) and Sr 3 Cu 2 O 5 (3-leg) systems [8], doping non-magnetic Zn 2 + (S¼0) cations on Cu 2 + (S¼1/2) sites have been found to induce disordered magnetism or even antiferromagnetic long range order (LRO) at Neé l temperatures T N ranging from 3 to 8 K for 0:01 o x o 0:08. Recent suggestions that dilution or bond-disorder could lead to new phenomena such as a Bose-glass phase [9], have renewed interest in spin ladders in general, and dilutable systems in particular.…”