Tunneling spectroscopy of MgB2 and Li0.5(THF) HfNCl

Ekino, Toshikazu; Takasaki, Tomoaki; Muranaka, Toshiya; Fujii, Hiroki; Akimitsu, Jun; Yamanaka, Shōji

doi:10.1016/s0921-4526(02)01801-x

Cited by 39 publications

(27 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The cointercalation of organic molecules enhances T c [14], and this also seems to be understandable within this kind of spin fluctuation mediated pairing, where the quasi two dimensionality is favored [22,23]. As for the pairing symmetry, a fully open gap is observed in the experiments [15,16], and this is consistent with the present scenario provided that the d + id state is realized. It is hence interesting to investigate experimentally the possibility of time reversal symmetry breaking in the superconducting state of this material.…”

Section: Application To β-Mnclsupporting

confidence: 86%

See 1 more Smart Citation

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr)

Kuroki¹

2008

Science and Technology of Advanced Materials

View full text Add to dashboard Cite

We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride β-MNCl (M = Hf, Zr). Finally, we compare two groups of superconductors with disconnected Fermi surface, β-MNCl and the iron pnictides, which have high critical temperature T c , despite some faults against superconductivity are present.

show abstract

Section: Application To β-Mnclsupporting

confidence: 86%

“…These experiments suggest some kind of unconventional pairing. On the contrary, scanning tunneling spectroscopy experiments find an s-wave like, fully open gap [15,16]. Specific heat measurements also suggest an s-wave like gap, but again, the doping dependence of the gap value is unusual.…”

Section: Introductionmentioning

confidence: 93%

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr)

Kuroki¹

2008

Science and Technology of Advanced Materials

View full text Add to dashboard Cite

show abstract

“…Superconducting gap: A very large superconducting gap of 2D/k B T c (4.6-5.2; 5.0-5.6) was found for slightly doped b-ZrNCl, while the gap value expected within the BCS theory is 3.56 [172,173]. For compounds with a higher level of doping a smaller gap value of 3.2 was observed [172].…”

Section: Electronic Structures and Superconducting Propertiesmentioning

confidence: 92%

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

Schurz

Shlyk

Schleid

et al. 2011

Zeitschrift Für Kristallographie

View full text Add to dashboard Cite

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.

show abstract

“…The MN bilayer honeycomb structure is thought to play a major role in superconductivity. 8 The NMR Knight shift suggested a spin-singlet pairing, 23 and tunneling spectroscopy 24,25 as well as specific heat 26 revealed a fully open s-wave-like gap. The tunneling-current measurements 27,28 and specific heat 31 revealed quite a large superconducting gap with the ratio 2 /k B T ≈ 4.6-5.6 or even larger, suggesting strong-coupling superconductivity.…”

mentioning

confidence: 98%

Superconductivity in YbxMyHfNCl (M=NH3and

Ying

Yan

et al. 2012

Phys. Rev. B

View full text Add to dashboard Cite

We report the observation of superconductivity in rare-earth metal cointercalated compounds Yb x (M) y HfNCl with M = NH 3 and tetrahydrofuran (THF). The superconducting transition temperature is about 23 and 24.6 K for Yb 0.2 (NH 3 ) y HfNCl and Yb 0.3 (NH 3 ) y HfNCl, respectively. Replacing the NH 3 with a larger molecule THF, the superconducting transition temperature increases to 25.2 K in Yb 0.2 (THF) y HfNCl, which is almost the same as the highest T c reported in the alkali-metal intercalated HfNCl superconductors. The T c of Yb 0.2 (THF) y HfNCl is apparently suppressed by pressure up to 0.5 GPa, while the pressure effect on T c becomes very small above 0.5 GPa. Our results suggest that for the most part, the superconductivity in these layered intercalated superconductors does not rely on intercalated metal ions, even magnetic ions. PACS number(s): 74.62.Fj High-T c superconductivity has been observed in layered cuprates and recently discovered iron-based superconductors. 1-3 The proximity to magnetically ordered states for these systems suggests that the magnetic interactions are the crucial force for Cooper pairing in such high-T c superconductivity, which gives rise to the unconventional nature of the superconductivity in these systems. Superconductivity in various other exotic materials, such as Na x CoO 2 , Sr 2 RuO 4 , and heavy-fermion systems, was also found to be closely connected to magnetism. 4-6 However, for another type of superconducting material of the layered metallonitride halides (MNX, M = Ti, Zr, Hf; X = Cl, Br, I) with the maximum T c as high as 25.5 K, 7 their parent compounds are band insulators, and superconductivity seems to have no correlation with magnetism. 8 There exist two types of layered nitride compounds: one is the (FeOCl)-type structure (so-called α structure) with a two-dimensional (2D) metal-nitrogen (MN) layer of a rectangular lattice; the other is the (SmSI)-type structure (so-called β structure) with a 2D MN layer of a honeycomb lattice. 9 For the former, K x TiNCl was reported to display superconductivity with T c = 16 K. 10 For the latter, usually with M = Hf,Zr and X = Cl, a maximum of T c = 25.5 K has been achieved in Li x (THF) y HfNCl. 7 The parent compounds of the latter, so-called β-MNCl, consist of an alternative stacking of honeycomb MN bilayers sandwiched by Cl bilayers. 11 Superconductivity is usually induced through doping charge carriers by means of alkali-metal intercalation or producing the Cl deficiency. 12,13 Unlike the large pressure effect on T c observed in cuprates or iron-based superconductors, the T c in this type of superconductors decreases slightly as the pressure increases. 14,15 However, for cointercalated β-ZrNCl and β-HfNCl, the interlayer spacing would strongly affect the superconducting transition temperature. An increase of the basal spacing would lead to a reduction of the negligible warping along the K z direction, and thus to an increase in the nesting of the Fermi surface. 16 It is assumed that a modification of the Fermi su...

show abstract

Tunneling spectroscopy of MgB2 and Li0.5(THF) HfNCl

Cited by 39 publications

References 12 publications

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr)

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr)

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

Superconductivity in YbxMyHfNCl (M=NH3and

Contact Info

Product

Resources

About