Hole doping

The concept of hole doping into charge reservoir layers can be explained with a number of examples. The materials are treated as if they are ionic. The simplest example is provided by the series of phases with a charge reservoir (AO AO), typified by La2Cu04, already described. 

The charge on each charge reservoir = 2(+3 — 2) = + 2 Superconducting layer (Cu2+02) 

Charge Reservoir Charge Reservoir Formula Superconducting Slab Formula Ideabzed Series Formula Examples  

These charges exactly balance, and the material would be an insulator, a normal ionic compound. Hole doping can be achieved by adding lower valence cation such as Sr2+ or oxygen interstitials to the charge reservoir. For Sr2+ aceptor dopants  

The charge difference between the charge reservoir and the superconducting layers must be achieved by the addition of balancing charges, xh in this case. For oxygen interstitials  

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Muller KA (2005) Essential Heterogeneities in Hole-Doped Cuprate Superconductors 114 1-11... 

In contrast, within (p-EPYNN)[Ni(dmit)2], first synthesized in 1996 [79], it has been proven that spin-ladder chains of the Ni(dmit)2 moiety coexist with the ferromagnetic one-dimensional chain of the p-EPYNN radical cation. Spin-ladders are of interest because of their potential applications in the area of quantum magnets and because it has been predicted that holes doped into even-leg ladders may pair and possibly superconduct [90-92]. 

Essential Heterogeneities in Hole-Doped Cuprate Superconductors... 

Hiroi Takano, 1995). Hole-doped derivatives of this cuprate of the type Laj- Sr CujOj do not, however, show superconductivity, but undergo an insulator-metal transition. 

Fig. 2. Resistivity-vs.-temperature transition curves for some C j based superconductors. (A) Variation of the hole doping from 1.3 to 3.2 holes per C o molecule. Inset the field-effect transistor geometry used in the experiment. (B) Comparison of optimum hole-doped C ). as grown and intercalated with CHCI3 and CHBrj)...

Angular variations of the dHvA frequencies of a hole-doped WC crystal (a floating zone-grown crystal) in the (0001), (1120) and (1010) planes are shown in Figure 6.6. The observed frequencies correspond to the a, fi, y, 6 and [x branches in Figure 6.5, but the signals corresponding to e, X and v branches can not be detected. 

A detailed comparison of dHvA frequencies of the hole-doped crystal with those of the flux-grown crystal gives some important information on the Fermi surface properties. The a and fi frequencies of the hole-doped crystal are about 2% larger than those of the flux-grown crystal. That is, the a frequency of the hole-doped crystal for the [0001] direction is 4.89 X 102 T, while those of the flux-grown crystal is 4.78 X 102 T. The fi frequency of the hole-doped crystal for the [0001] direction is 8.79 X 102 T, while that of the flux-grown crystal is 8.66 X 102 T. A comparison of dHvA frequencies of the hole-doped crystal with those of the flux-grown crystal is shown in Table 6.1. This comparison has been made carefully under the same experimental condition to confirm the frequency differences. 

The oscillation amplitudes of the a and fi branches of the hole-doped crystal become too small for detection within about 40° while the signals can be detected up to 12° in the case of the flux-grown crystal. This is due to the smaller mobility in the hole-doped crystal, because the RRR value is 20 in the hole-doped crystal while the RRR value is 70 in the flux-grown... 

Frequency differences between the flux-grown crystal and the floating zone-grown crystal are due to hole doping in the latter sample.5 That the dHvA frequencies change with addition of boron indicates that boron substitutes for carbon. Therefore, the dHvA data of the flux-grown crystal was analyzed to construct the Fermi surfaces. 

First, the carrier assignment is discussed using data of the hole-doped crystal. The dHvA frequencies corresponding to the a, Ji, y and 8 branches increase while those of the p branch decrease. This is due to the decrease in the Fermi energy by the hole-doping. In the dHvA specimen of the hole-doped crystal, chemical analysis indicates that the boron content is about 0.2% of the carbon sites, that is, 0.964 X 1020/cm3. Therefore it can be concluded that the a, Ji, y and 8 carriers are holes and the p carriers are electrons. 

Cross sections of the a and fi Fermi surfaces and the y and 6 Fermi surfaces in the plane which includes the axis of rotation are shown in Figure 6.8. Each of the experimental Fermi surfaces has the axis of rotation about the [0001] axis. The dFIvA frequency values used to construct the Fermi surfaces are shown in Table 6.2. The values in parentheses in Table 6.2 are estimated frequencies that take into account the angular dependencies and the frequency ratios between the flux-grown crystal and the hole-doped crystal. The obtained Fermi surface dimensions are summarized in Table 6.3. 

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