N-type superconductors

Until 1988, all the high temperature superconductors that had been found were p-type, and it was assumed by many that this would be a feature of high temperature superconductors. However, some n-type superconductors have also been discovered, where the charge carriers are electrons the first to be found was based on the compound Nd2Cu04 with small amounts of the three-valent neodymium substituted by four-valent cerium—Nd2-/le/lu04-j where v 0.17 (samarium, europium, or praeseodymium can... 

In terms of formal charges on the ions, p-type (or hole-doped) YBCO may be written as Y +(Ba +)2(Cu +)2Cu (0 )7 5. YBCO becomes superconductive at < 0.4, with its most pronounced superconductivity at 8 = 0.05. It should be noted that there are other examples of p-type superconductors that involve metal doping rather than varying oxygen content, such as La2 xStxCu04 (Tc = 34 K at X = 0.15). Similarly, electron-doped (n-type) superconductors may be synthesized such as Nd2 xCcxCu04 (Tc = 20 K), written formally as Nd2 x -"Ce, (e )xCu2+04. 

High temperature superconductors (HTS), 23 814, 826, 829. See also Anisotropic HTS HTS entries applications of, 23 852-872 layered, 23 827, 840 magnetic phase diagram of, 23 838-842 p- and n-type, 23 838 structural anisotropy and fluxon line fragmentation in, 23 841 thallium- and mercury-based, 23 848-850... 

There is still no consensus for a mechanism for the high Tc in the cuprate superconductors. Nonetheless, we have learned much about the electronic structure of such materials. Some proposed theories may now be discarded. The discovery of the n-type cuprate superconductors was the clinching evidence needed to discard theories based on some unique feature of an oxygen 2p band, a x band, or overlapping bands. The central question now for the cuprate... 

Many people in the field believe that some high-temperature superconductors, most notably of the Nd jCe CuCU class, are n-type. But since most high-temperature superconductors rely on oxygen to superconduct, and since at least some oxygen in these materials is already in the O 2 state, to dope them n-type requires forming O 3, which does not form. 

This behavior is easy to understand, because O 4 can be doped p-type to, say O 1 but it cannot be doped n-type to, say O ", because the maximum negative charge on oxygen is approximately —2. Hence the claimed n-type simple doping cannot occur the doping must be more complex and also must be p-type. There are no n-type high-temperature superconductors. 

In Fig. 1 we show typical R T) behavior in parallel orientation of the magnetic field of 0.5 T for two samples, MLS with N w=5 (S type) and ML6 with Nbii=6 (N type). The resistive characteristics are quite different and depend on the type of the samples symmetry. For the N-type sample (ML6) the usual sharp curve reveals the resistive fall down to zero. For the S-type sample (MLS) the superconductor transition is broadened. At large magnetic fields R T) curves become sharp for both the samples. The behavior shown in Fig. 1 has been found for all our samples with... 

The studied SMN s are hard type II superconductors. So, the vortex lattice is formed while Hq becomes slightly less than H 2 iX). We will focus on the dependence of the vortex lattice nascent process on the R T) curves. At low temperatures, when the degeneracy of Hq is Ayi, a rather stable vortex lattice is formed. The perturbation of the lattice due to feeble bias current is smaller with respect to the interface pinning force. The R T) curve is sharp both for S- and N-type samples. This scenario is relatively trivial. 

The optical absorption spectra of intercalated 2H-M0S2 did not show appreciable changes on alkah metal intercalation up to concentrations of 30%, where a transition into a metallic phase at room temperature and a further transition into a superconductor at about 3-7 K was reported [139, 140]. Because the concentration of the intercalating metal atoms in the IF nanoparticles did not exceed 10%, no changes in the optical transmission spectra were anticipated nor were they found to occur. Also, the intercalation of alkah atoms in the IF particles induces n-type conductivity of the host. 

One different way of considering superconductors is related to their compliance with the classic BCS theory. Hence conventional (i.e., BCS-compatible) and unconventional (i.e., BCS-incompatible) materials exist. The common scientific language therefore distinguishes also between ITS (low-temperature superconductors) and HTS (high-temperature superconductors). In general, ITS are electron-doped (n-type), while HTS are hole-doped (p-type) phases. 

YBa2Cu307 x, which is one of the familiar high-temperature oxide superconductors with rare earths, reacts with NO and then decomposes (Huang et al. 1992). When n-type Ndi 85Ceo.i5Cu04-x oxide superconductor is used, no sensor response is observed in NO, or COi existing atmospheres. 

The finding of the first ic-type superconductor, >c-(BEDT-TTF)2l3, and the crystal and band structure examinations provided strong evidence of the existence of ideally two-dimensional n metals A. Kobayashi, R. Kato, H. Kobayashi, S. Moriyama, Y. Nishio, K. Kajita and W. Sasaki, Chem. Lett. 459 (1987) R. Kato, H. Kobayashi, A. Kobayashi, S. Moriyama, Y. Nishio, K. Kajita and W. Sasaki, Chem. Lett. 507 (1987). The main /c-type organic superconductors are listed in the review article J.M. Williams et al.. Organic Superconductors (Including Fullerenes) Synthesis, Structure, Properties, and Theory, Prentice-Hall, Englewood Cliffs, NJ, 1992. 

In Fig. 25-4, electron conduction mechanisms are displayed for p and n type semiconductors, which involve silicon doped with gallium and arsenic, respectively. Figure 25-5 gives the following speculative mechanism for electron conduction in the high temperature superconductor YBa2Cu307. It makes use of the instability of Pauling 3-electron bonds under compression (cf. Section 3-10). 

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