Frustrated magnetism in a Mott insulator based on a transition metal chalcogenide

Kawamoto, Shinya; Higo, Tomoya; Tomita, Takahiro; Suzuki, Shintaro; Tian, Zhaoming; Mochitzuki, K; Matsuo, Akira; Kindo, Koichi; Nakatsuji, Satoru

doi:10.1088/1742-6596/683/1/012025

Cited by 13 publications

(13 citation statements)

References 17 publications

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“…In this regard, our current study may indicate that the molecular J eff moments are frustrated in this material. This is compatible with recent experimental observations of the specific heat and magnetic susceptibility, interpreted as a formation of dimerization and a spin singlet state 36 , 39 .…”

Section: Discussionsupporting

confidence: 92%

“…Experimental identification of the relativistic Jeff state is necessary to understand the underlying mechanisms of quantum phenomena that have been reported and speculated for this material and others 3,[18][19][20][21][22][23]30,32,[36][37][38][39][40][41][42] . At low temperature, for example, GaTa4Se8 exhibits an intriguing transition [38][39][40] towards a non-magnetic and possibly spin singlet state, which are presumably related to a peculiar bump observed in the susceptibility and specific heat 39,40 .…”

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confidence: 99%

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Direct experimental observation of the molecular J eff = 3/2 ground state in the lacunar spinel GaTa4Se8

et al. 2017

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Strong spin–orbit coupling lifts the degeneracy of t 2g orbitals in 5d transition-metal systems, leaving a Kramers doublet and quartet with effective angular momentum of J eff = 1/2 and 3/2, respectively. These spin–orbit entangled states can host exotic quantum phases such as topological Mott state, unconventional superconductivity, and quantum spin liquid. The lacunar spinel GaTa4Se8 was theoretically predicted to form the molecular J eff = 3/2 ground state. Experimental verification of its existence is an important first step to exploring the consequences of the J eff = 3/2 state. Here, we report direct experimental evidence of the J eff = 3/2 state in GaTa4Se8 by means of excitation spectra of resonant inelastic X-ray scattering at the Ta L3 and L2 edges. We find that the excitations involving the J eff = 1/2 molecular orbital are absent only at the Ta L2 edge, manifesting the realization of the molecular J eff = 3/2 ground state in GaTa4Se8.

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Section: Discussionsupporting

confidence: 92%

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confidence: 99%

Direct experimental observation of the molecular J eff = 3/2 ground state in the lacunar spinel GaTa4Se8

et al. 2017

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“…In fact, GaNb 4 S 8 takes a structural phase transition with an anomalous magnetic susceptibility behavior [9] when the temperature decreases. The very similar anomalous magnetic susceptibility behavior has also been observed in GaTa 4 Se 8 , which strongly indicates there may be a similar phase transition in GaTa 4 Se 8 [10,11]. Recently, experimental measurements have shown that there is a structural phase transition to tetragonal phase at low temperature [11] and a change in Raman spectra at high pressure [12].…”

Section: Introductionsupporting

confidence: 58%

“…Also, the prevented long-range antiferromagnetic state may also come from the strong SOC. In spite of the absence of long-range antiferromagnetic order, we think the AFM interaction may be the reason for the dramatic drop of magnetic susceptibility at 53 K in experiment [10], because of the potential short-range of antiferromagnetic order. Since the metallic state conflicts with the experiment, we need to check whether the R3m structure GaTa 4 Se 8 is Mott insulator or not.…”

Section: B R3m Structurementioning

confidence: 71%

Crystal and Electronic Structure of GaTa$_4$Se$_8$ From First-Principle Calculations

Zhang,

Deng

et al. 2020

Preprint

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GaTa4Se8 belongs to the lacunar spinel family. Its crystal structures is still a puzzle though there have been intensive studies on its novel properties, such as the Mott insulator phase and superconductivity under pressure. In this work, we investigate its phonon spectra through firstprinciple calculations and proposed it most probably has crystal structure phase transition, which is consistent with several experimental observations. For the prototype lacunar spinel with cubic symmetry of space group F 43m, its phonon spectra have three soft modes in the whole Brillouin zone, indicating the strong dynamical instability of such crystal structure. In order to find the dynamically stable crystal structure, further calculations indicate two new structures of GaTa4Se8, corresponding to R3m and P 421m, verifying that at the ambient pressure, there does exist structure phase transition of GaTa4Se8 from F 43m to other structures when the temperature is lowered. We also performed electronic structure calculation for R3m and P 421m structure, showing that P 421m structure GaTa4Se8 is band insulator, and obtained Mott insulator state for R3m structure by DMFT calculation under single-band Hubbard model picture when interaction parameter U is larger than 0.40 eV vs. band width of 0.25 eV. It is reasonable to assume that while lowering the temperature, F 43m structure GaTa4Se8 becomes R3m structure GaTa4Se8 first, then P 421m structure GaTa4Se8, because of the symmetry of P 421m is lower than R3m after Jahn-Teller distortion. The structure transition may explain the magnetic susceptibility anomalous at low temperature.

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“…Second, there is no experimental signature for structural transition as a function of pressure and no drastic phonon mode change. Third, nevertheless, the anomalies in specific heat as well as magnetic susceptibility are repeatedly identified at around 50 K, which is an order of magnitude higher than superconducting T c 22,[33][34][35][36] . Most importantly, it is also noted that superconductivity is only observed in the case of M = Nb and Ta; namely, only when the low energy band structure is of j eff = 3/2 character 28 .…”

Section: Introductionmentioning

confidence: 90%

Pressure-induced topological superconductivity in the spin–orbit Mott insulator GaTa4Se8

et al. 2020

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Lacunar spinel GaTa4Se8 is a unique example of spin–orbit coupled Mott insulator described by molecular jeff = 3/2 states. It becomes superconducting at Tc = 5.8 K under pressure without doping. In this work, we show, this pressure-induced superconductivity is a realization of a new type topological phase characterized by spin-2 Cooper pairs. Starting from first-principles density functional calculations and random phase approximation, we construct the microscopic model and perform the detailed analysis. Applying pressure is found to trigger the virtual interband tunneling processes assisted by strong Hund coupling, thereby stabilizing a particular d-wave quintet channel. Furthermore, we show that its Bogoliubov quasiparticles and their surface states exhibit novel topological nature. To verify our theory, we propose unique experimental signatures that can be measured by Josephson junction transport and scanning tunneling microscope. Our findings open up new directions searching for exotic superconductivity in spin–orbit coupled materials.

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Frustrated magnetism in a Mott insulator based on a transition metal chalcogenide

Cited by 13 publications

References 17 publications

Direct experimental observation of the molecular J eff = 3/2 ground state in the lacunar spinel GaTa4Se8

Direct experimental observation of the molecular J eff = 3/2 ground state in the lacunar spinel GaTa4Se8

Crystal and Electronic Structure of GaTa$_4$Se$_8$ From First-Principle Calculations

Pressure-induced topological superconductivity in the spin–orbit Mott insulator GaTa4Se8

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