Superconductivity in layered nitride with small carrier density

Taguchi, Y.; Kasahara, Yuichi; Kishiume, Tsukasa; Takano, T.; Kobayashi, K.; Matsuoka, Eiichi; Onodera, Hidetoshi; Kuroki, Kazuhiko; Iwasa, Yoshihiro

doi:10.1016/j.physc.2009.10.071

Cited by 3 publications

(4 citation statements)

References 34 publications

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“…Our calculations show that χ 0s is not enhanced at the low-doping limit. Experimental measurements 23,24 carried out on Li x ZrNCl show that (i) the system is not magnetic and (ii) the spin susceptibility in Li x ZrNCl is strongly doping dependent with a marked enhancement in the low-doping limit 23,24 , which is different than the expected χ 0s behavior. It is then natural to look for exchange and correlation effects in the susceptibility.…”

Section: Spin Susceptibilitymentioning

confidence: 82%

“…Despite Li x ZrNCl being nonmagnetic, in the low-doping limit, the magnetic susceptibility is enhanced in a way very similar way to that in the superconducting T c . The interacting magnetic susceptibility χ s is not constant, and strongly deviates from the constant free-electron-like behavior in 2D 23,24 ; in particular, the susceptibility χ s is enhanced at the low-doping regime.…”

Section: Introductionmentioning

confidence: 85%

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Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study ofLixZrNCl

et al. 2016

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We investigate the capability of density functional theory (DFT) to appropriately describe the spin susceptibility, χs, and the intervalley electron-phonon coupling in LixZrNCl. At low doping, LixZrNCl behaves as a two-dimensional two-valley electron gas, with parabolic bands. In such a system, χs increases with decreasing doping because of the electron-electron interaction. We show that DFT with local functionals (LDA/GGA) is not capable of reproducing this behavior. The use of exact exchange in Hartree-Fock (HF) or in DFT hybrid functionals enhances χs. HF, B3LYP, and PBE0 approaches overestimate χs, whereas the range-separated HSE06 functional leads to results similar to those obtained in the random phase approximation (RPA) applied to a two-valley two-spin electron gas. Within HF, LixZrNCl is even unstable towards a ferromagnetic state for x < 0.16. The intervalley phonons induce an imbalance in the valley occupation that can be viewed as the effect of a pseudomagnetic field. Thus, similarly to what happens for χs, the electron-phonon coupling of intervalley phonons is enhanced by the electron-electron interaction. Only hybrid DFT functionals capture such an enhancement and the HSE06 functional reproduces the RPA results presented in M. Calandra et al. [Phys. Rev. Lett. 114, 077001 (2015)]. These results imply that the description of the susceptibility and electron-phonon coupling with a range-separated hybrid functional would be important also in other two-dimensional weakly doped semiconductors, such as transition-metal dichalcogenides and graphene.

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Section: Spin Susceptibilitymentioning

confidence: 82%

Section: Introductionmentioning

confidence: 85%

Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study ofLixZrNCl

et al. 2016

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“…Similar to T c , the magnetic spin susceptibility is enhanced in Li x ZrNCl at low doping 37,38 , whereas there are no experiments of spin susceptibility as a function of doping for Li x HfNCl. Spin susceptibility is the response of the spin magnetization to an applied magnetic field,…”

Section: B Spin Susceptibilitymentioning

confidence: 95%

High- Tc superconductivity in weakly electron-doped HfNCl

2017

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We investigate the magnetic and superconducting properties in electron-doped LixHfNCl. HfNCl is a band insulator that undergoes an insulator to superconductor transition upon doping at x ≈ 0.13. The persistence of the insulating state for x < 0.13 is due to an Anderson transition probably related to Li disorder. In the metallic and superconducting phase, LixHfNCl is a prototype two-dimensional two-valley electron gas with parabolic bands. By performing a model random phase approximation approach as well as first-principles range-separated Heyd-Scuseria-Ernzerhof (HSE06) calculations, we find that the spin susceptibility χs is strongly enhanced in the low-doping regime by the electronelectron interaction. Furthermore, in the low-doping limit, the exchange interaction renormalizes the intervalley electron-phonon coupling and results in a strong increase of the superconducting critical temperature for x < 0.15. On the contrary, for x > 0.15, Tc is approximately constant, in agreement with experiments. At x = 0.055 we found that Tc can be as large as 40 K, suggesting that the synthesis of cleaner samples of LixHfNCl could remove the Anderson insulating state competing with superconductivity and generate a high-Tc superconductor.

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“…It was suggested that this result can not be explained within the conventional BCS theory. Additionally, muon spin relaxation [175], 15 N-NMR [176], specific heat and magnetic susceptibility studies [177] of Li x ZrNCl suggest d þ id pairing with a spin-singlet state symmetry unlike the pairing mechanism within the BCStheory. This finding supports the assumption that the dynamical aspect of Coulomb interactions has to be taken into account.…”

Section: Electronic Structures and Superconducting Propertiesmentioning

confidence: 98%

Superconducting nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

Schurz

Shlyk

Schleid

et al. 2011

Zeitschrift Für Kristallographie

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Abstract. Two different polymorphs of the metal nitride halides MNX (M ¼ Ti, Zr, Hf; X ¼ Cl, Br, I) are known to crystallize in layered structures. The two crystal structures differ in the way 2 1 {X[M 2 N 2 ]X} slabs are stacked along the c-axes. Metal atoms and/or organic molecules can be intercalated into the van-der-Waals gap between these layers. After such an electron-doping via intercalation the prototypic band insulators change into superconductors with moderate high critical temperatures T c up to 25.5 K. This review gathers information on synthesis routes, structural characteristics and properties of the prototypic nitride halides and the derivatives after electron-doping with a focus on superconductivity.

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Superconductivity in layered nitride with small carrier density

Cited by 3 publications

References 34 publications

Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study ofLixZrNCl

Spin susceptibility and electron-phonon coupling of two-dimensional materials by range-separated hybrid density functionals: Case study ofLixZrNCl

High- Tc superconductivity in weakly electron-doped HfNCl

Superconducting nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I)

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