Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X35: New Kitaev MagnetsInvited Live
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Sponsoring Units: GMAG Chair: Faranak Bahrami, Boston College |
Friday, March 19, 2021 8:00AM - 8:36AM Live |
X35.00001: Molecular Orbitals from Chemical Pressure in Ag3LiIr2O6 Invited Speaker: Kemp Plumb The honeycomb iridates, α-Li2IrO3 and Na2PrO3 are among the closest material realizations of the Kitaev model. Although dominant Heisenberg exchange interactions in both of these compounds result in low temperature magnetic order, Kitaev interactions are known to be strong. The relevance of the Kitaev model stems from a balance of electronic correlations and spin orbit coupling that result in a localized spin-orbit entangled jeff=1/2 magnetic degree of freedom. Recently, a new honeycomb iridate, Ag3LiIr2O6 was shown to exhibit thermodynamic signatures of close proximity to the spin liquid limit [1]. In this talk, I will discuss a series of x-ray spectroscopy measurements on Ag3LiIr2O6 that reveal a strong modification of the Ir electronic structure from the parent α-Li2IrO6 such that a delocalized, molecular orbital picture is more appropriate for Ag3LiIr2O6. These measurements show how chemical pressure can influence the single ion state in transition metal magnets and provide further evidence for the fragility of the local jeff=1/2 picture. I will discuss these results in the context of the Kitaev model and possible magnetic ground states in Ag3LiIr2O6. |
Friday, March 19, 2021 8:36AM - 9:12AM Live |
X35.00002: Novel probe of the spatial distribution of the low-energy spin excitations in spin liquid candidate materials with disorder: inverse Laplace transform (ILT) T1 analysis of the NMR spin-lattice relaxation rate 1/T1 Invited Speaker: Takashi Imai Spin liquid candidate materials often suffer from disorder, if they are free from undesirable magnetic long range order. Since NMR is a site-specific probe, one can in principle use the NMR spin-lattice relaxation rate 1/T1 ~ ∑ Im χ(q,ωn)/ωn as the local probe of the disorder-induced spatial distribution of low-energy spin excitations, where Im χ(q,ωn) is the imaginary part of the dynamical electron spin susceptibility at the resonant frequency ωn. Nonetheless, NMR experts often deduce only the spatially averaged value of the distributed 1/T1 by fitting the time evolution of the nuclear magnetization with an empirical stretched exponential form, M(t) = A - B * exp[-(t/T1)β]. But the stretched fit value of 1/T1 does not necessarily reflect the intrinsic spin liquid behavior one is looking for, because 1/T1 in the vicinity of defects may be dominated by the properties of defects, and the distribution of 1/T1 often reaches as large as several orders of magnitude. In this talk, we will introduce the novel approach based on the inverse Laplace transform (ILT) T1 analysis techniques [1,2]. By numerically inverting M(t) based on ILT, one can deduce the histogram of the spatially distributed values of 1/T1 in the form of the density distribution function P(1/T1), i.e. the histogram of 1/T1. We demonstrate that the stretched fit 1/T1 is merely a crude approximation of the center of gravity of P(1/T1). From the multiple peaks observed in P(1/T1), we discuss the nature of the spatial distribution of the low energy spin excitations in spin liquid candidate materials, such as Cu2IrO3 [3], Ag3LiIr2O6 [4] and beyond [5]. |
Friday, March 19, 2021 9:12AM - 9:48AM Live |
X35.00003: Intercalated Kitaev magnets in the clean and disordered limits Invited Speaker: Fazel Tafti In recent years, a new class of intercalated Kitaev materials has emerged from the substitution of interlayer Li and Na atoms in Li2IrO3 and Na2IrO3 with Cu, Ag, and H. Examples of such materials include Cu2IrO3, Cu3LiIr2O6, Ag3LiIr2O6, and H3LiIr2O6. Some of the early studies on these materials have shown promising evidence of proximity to a Kitaev spin liquid grounds state with anyonic excitations. For example, the lack of magnetic ordering, a scaling behavior of the specific heat, and a two-step release of magnetic entropy are all consistent with the theoretical prediction of a spin liquid ground state with fractionalized excitations. Here we present a careful overview of the properties of these materials and compare their magnetic behaviors in the clean and disordered limits. Specifically, we scrutinize the role of interlayer coupling in the physics of Kitaev magnets and demonstrate how the stacking faults and bond randomness can impair our understanding of the magnetism in the clean limit. We also show that unlike some of the early reports, magnetic ordering is not always suppressed after Cu or Ag exchange. In fact, the magnetism can be fortified by intercalation in the limit of weak spin-orbit coupling. This presentation will give an honest overview of the recent candidate materials for the Kitaev spin liquid phase and clarifies some of the controversial findings in the field. |
Friday, March 19, 2021 9:48AM - 10:24AM Live |
X35.00004: Disorder effects in the Kitaev spin liquid Invited Speaker: Natalia Perkins Recently, the 5d-electron compound H3LiIr2O6 [1] has shown to be a strong candidate for Kitaev spin liquid [2] considering the absence of any signs of a long-range ordered magnetic state. In my talk I will discuss the role of disorder in the Kitaev spin liquid and its relevance to the experimental observations in H3LiIr2O6 [3,4]. Our findings suggest that a finite density of random vacancies in the Kitaev model give rise to a striking pileup of low-energy Majorana eigenmodes and reproduces the apparent power-law upturn in the specific heat measurements of H3LiIr2O6 [1]. Physically, the vacancies can originate from various sources such as missing magnetic moments or the presence of non-magnetic impurities (true vacancies), or from local weak couplings of magnetic moments due to strong but rare bond randomness (quasivacancies). We show numerically that the vacancy effect is readily detectable even at low vacancy concentrations and that it is not very sensitive neither to the nature of vacancies nor to different flux backgrounds. |
Friday, March 19, 2021 10:24AM - 11:00AM Live |
X35.00005: First principles calculations on chemically intercalated honeycomb Kitaev materials Invited Speaker: Ying Li Layered honeycomb-lattice with 4d and 5d trainsition metals are being intensively discussed as possible realizations of the Kitaev model where magnetism is dominated by a strong spin-orbit coupling resulting in highly nontrivial physical properties. In this talk, we will discuss the role of inter- and intra-layer chemical intercalation on the electronic and magnetic properties of some representative families from first principles calculations, model considerations and comparison with experiment. |
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