Paramagnetic Resonance and Optical Spectra of Divalent Iron in Cubic Fields. I. Theory

Löw, W.; Weger, M.

doi:10.1103/physrev.118.1119

Cited by 235 publications

(68 citation statements)

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“…In the single ion case, SOC splits the upper orbital triplet into three levels with energies ∆ CF − 3λ 0 , ∆ CF − arXiv:1410.6777v2 [cond-mat.str-el] 6 Sep 2016 λ 0 , and ∆ CF + 2λ 0 , where ∆ CF is the 5 E -5 T 2 splitting and λ 0 is the SOC constant [10,11]. The potentially huge tenfold ground state degeneracy coming from S = 2 and the orbital doublet is split at second order in the spin-orbit interaction into 5 levels equally separated by λ = 6λ 2 0 /∆ CF (Fig.…”

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confidence: 99%

Singlet-Triplet Excitations and Long-Range Entanglement in the Spin-Orbital Liquid CandidateFeSc2S4

et al. 2015

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Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through timedomain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate that the characteristic length of the singlet correlations to be ξ/(a/2) ≈ 8.2 (where a/2 is the nearest neighbor lattice constant) which establishes FeSc2S4 as a SOL with long-range entanglement.The search for ground states without classical analogs, e.g. quantum ground states, is a central focus of modern condensed matter physics. A zero temperature spin liquid would be a prime realization of such a state [1]. Such systems possess local moments, but, due to quantum fluctuations, typically enhanced due to geometric frustration, do not order even at zero temperature. They are proposed to have quantum mechanically entangled wavefunctions, with exotic fractionalized excitations. Orbital degrees of freedom can also be disordered by quantum fluctuations [2]. Systems with both spin and orbital fluctuations as well as spin-orbit coupling (SOC) have been proposed to form a "spin-orbital liquid" (SOL) ground state, characterized by entangled spin and orbital degrees of freedom but no long range order [3][4][5][6][7].Recent experiments have shown a SOL phase may exist in the geometrically frustrated A site cubic spinel compound FeSc 2 S 4 . A tetrahedral S 4 crystal field splits a 3d shell into an upper t 2 orbital triplet and a lower e orbital doublet. With Hund's coupling, an Fe 2+ ion in a tetrahedral environment assumes a high spin S = 2 configuration with a lower 5 E orbital doublet ground state and an upper 5 T 2 orbital triplet excited state (Fig. 1). The ground state's two-fold orbital degeneracy is associated with the freedom to place a hole in either e orbital. Although orbital degeneracy is often relieved by Jahn-Teller distortions, heat capacity experiments show no sign of orbital ordering down to 50 mK and the magnetic susceptibility displays essentially perfect Curie-Weiss behavior with θ CW = -45.1 K in the range from 15 -400K [3]. The possible removal of the ground state orbital degeneracy FIG. 1: (a) Energy levels of Fe 2+ ion in an S=2 configuration after tetrahedral crystal field splitting and first and second order SOC, without including lattice effects. Numbers in parenthesis represen...

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confidence: 99%

Singlet-Triplet Excitations and Long-Range Entanglement in the Spin-Orbital Liquid CandidateFeSc2S4

et al. 2015

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“…In that respect, substitutional Mn2+ with its degenerate 6 A 1 spin-only ground state represents a rather simple, though theoretically attractive case, since all the phenomena which involve orbital momenturn are absent.…”

Section: Magnetic Behavior Of 11-vi Group Diluted Magnetic Semiconducmentioning

confidence: 99%

“…Larson et al t6 (6) I DNN !Ju I being roughly between w-a and w-1 depending on the specific system. Though relatively small compared with the isotropie part of the interaction, this anisotropy can become of vital significanee for the magnetic properties at low temperatures where effects due to J 11 can be safely ignored.…”

Section: A Mn-containing Dmsmentioning

confidence: 99%

“…6 for some values of J. For the crystal-field splitting and spin-orbit parameter, we adopted the values reported 6 for ZnSe:Fe (Dq = 293 cm-1 ,…”

Section: Mtheorymentioning

confidence: 99%

“…In a way the substitutional Mn2+ with its degenera te 6 A 1 spin-only ground state, represents a rather simple, although theoretically attractive case, since all the phenomena which involve the orbital momenturn are absent. In contrast, substitutional iron Fe 2 + (d6) can serve as a much more general case, since it possesses both spin and orbital momenta (S = 2 and L = 2).…”

Section: Introductionmentioning

confidence: 99%

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