Superconducting β-ZrNClx probed by scanning-tunnelling and break-junction spectroscopy

Ekino, Toshikazu; Sugimoto, Akihiro; Gabovich, A. M.; Zheng, Zhanfeng; Yamanaka, Shōji

doi:10.1016/j.physc.2013.05.009

Cited by 7 publications

(9 citation statements)

References 15 publications

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“…More recently, the same composition was measured (T. Ekino et al [641]) by the same group, but using a single crystal facet on a polycrystalline sample as the probing surface. In both works there were two gap features, one similar to the BCS value (2/kBTc ~ 3.52) plus a rather large gap feature (2/kBTc ~ 10), with both gaps disappearing as the sample is warmed to Tc ~ 13 K, leading the authors to conclude that this compound displays "unusual" superconducting properties.…”

Section: Superconducting Properties That Impinge On Possible Ucs -Formmentioning

confidence: 88%

Unconventional superconductivity

Stewart

2017

Advances in Physics

211

165

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Abstract:"Conventional" superconductivity, as used in this review, refers to electron-phonon coupled superconducting electron pairs described by BCS theory. Unconventional superconductivity refers to superconductors where the Cooper pairs are not bound together by phonon-exchange but instead by exchange of some other kind, e. g. spin fluctuations in a superconductor with magnetic order either coexistent or nearby in the phase diagram. Such unconventional superconductivity has been known experimentally since heavy fermion CeCu2Si2, with its strongly correlated 4f electrons, was discovered to superconduct below 0.6 K in 1979. Since the discovery of unconventional superconductivity in the layered cuprates in 1986, the study of these materials saw Tc jump to 164 K by 1994. Further progess in high temperature superconductivity would be aided by understanding the cause of such unconventional pairing. This review compares the fundamental properties of 9 unconventional superconducting classes of materialsfrom 4f-electron heavy fermions to organic superconductors to classes where only three known members exist to the cuprates with over 200 examples -with the hope that common features will emerge to help theory explain (and predict!) these phenomena. In addition, three new emerging classes of superconductors (topological, interfacial -e. g. FeSe on SrTiO3, and H2S under high pressure) are briefly covered, even though their "conventionality" is not yet fully determined.

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Section: Superconducting Properties That Impinge On Possible Ucs -Formmentioning

confidence: 88%

Unconventional superconductivity

Stewart

2017

Advances in Physics

211

165

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“…Direct observation of the superconducting gap has been reported using break junction technique and scanning tunneling spectroscopy [48,49]. The superconducting gap ratio 2∆ 0 /k B T c reaches 10 for ZrNCl 0.7 , indicating strong coupling superconductivity.…”

Section: Dmentioning

confidence: 99%

Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M= Ti, Zr, Hf; X= Cl, Br, I)

Kasahara

Kuroki

Yamanaka

et al. 2015

Physica C: Superconductivity and its Applications

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Unconventional superconductivity in electron-doped layered metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) AbstractIn this review, we present a comprehensive overview of superconductivity in electron-doped metal nitride halides MNX (M = Ti, Zr, Hf; X = Cl, Br, I) with layered crystal structure and two-dimensional electronic states. The parent compounds are band insulators with no discernible long-range ordered state. Upon doping tiny amount of electrons, superconductivity emerges with several anomalous features beyond the conventional electron-phonon mechanism, which stimulate theoretical investigations. We will discuss experimental and theoretical results reported thus far and compare the electron-doped layered nitride superconductors with other superconductors.

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“…Figure 1 shows STM images of the cleaved ab-plane at 4.9 K for (a) β-HfNCl 0.7 , (b) β-ZrNCl 0.7 , and (c) α-K 0.5 TiNCl. In the figure, the triangular lattices of bright spots are easily visible against the weakly inhomogeneous background with the vertical deviation of ~ 0.2 nm (a) and ~ 0.07 nm (b) [6,7]. On the other hand, the rectangular lattice spots are seen in Fig.…”

Section: Introductionmentioning

confidence: 89%

“…Among experimental methods of investigating such mechanisms, electron-tunneling spectroscopy is an essential technique since it directly probes the energy gap 2Δ. It seems that the huge gap previously found by us to be far above the weak-coupling BCS cannot be explained by the conventional approach [5][6][7]. In particular, the strong-coupling Migdal-Eliashberg theory fails to explain superconductivity of MNCl [4].…”

Section: Introductionmentioning

confidence: 95%

“…In particular, the strong-coupling Migdal-Eliashberg theory fails to explain superconductivity of MNCl [4]. In this paper, the superconducting gaps of α-and β-types of MNCl having different crystal structures are examined at the nanometer length scale by scanning-tunneling spectroscopy (STS) and are compared with their counterparts found from the break-junction tunneling spectroscopy (BJTS) measurements [5][6][7]. Polycrystals of MNCl were synthesized by a method reported elsewhere [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

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