Cyclotron mass

Other techniques for mass measurement are available, but they are not as popular as those outlined above. These other methods include mass measurements on a standard substance to calibrate the instrument. The standard is then withdrawn, and the unknown is let into the instrument to obtain a new spectrum that is compared with that of the standard. It is assumed that there are no instrumental variations during this changeover. Generally, this technique is less reliable than when the standard and unknown are in the instrument together. Fourier-transform techniques are used with ion cyclotron mass spectrometers and give excellent mass accuracy at lower mass but not at higher. 

Dodecahedrene (40) is a highly strained hydrocarbon, for which calculations predict 42.5° (MM2) and 41.7° (MNDO)17. It has not yet been isolated, but there is strong evidence for its formation in a gas-phase ion-molecule reaction in a FT ion cyclotron mass spectrometer144. A tetrasubstituted derivative has been studied in condensed phase145. 

According to Falicov and Stahowiak [12] the contribution of every segment of the cyclotron orbit to the cyclotron mass parameter is proportional to the subtended angle of this segment, and the total cyclotron mass parameter equals the sum of the partial cyclotron mass parameters. We have estimated the effective mass parameters from the temperature dependence of the SdH oscillation amplitude using the standard formula... 

It is interesting to compare the temperature dependence of the amplitude for all frequencies (see Fig. 6 for T = 1.5 K and Fig. 7 T = 4.2 K). At 1.5 K the a and (P-a) oscillation amplitudes dominate whereas the (P-2a) amplitude oscillation is very small. However, the (P-2a) amplitude oscillation dominates and the P one disappears completely at 4.2 K. These results are in agreement with the effective mass values corresponding to these oscillation frequencies and satisfy the necessary relations between effective masses for the QI effect. Noting that below 4.2 K the oscillation amplitude connected with the (P-2a) frequency is constant within the experimental error (i.e., a zero cyclotron mass), we may assume that this oscillation can survive to considerably higher temperatures. An analogous situation has been previously found for the (k-BEDT-TTF)2Cu(NCS)2 salt [13],... 

Wang F, Weidt S, Xu J, Mackay CL, Langridge-Smith PRR, Sadler PJ (2008) Identification of clusters from reactions of ruthenium arene anticancer complex with glutathione using nanoscale liquid chromatography fourier transform ion cyclotron mass spectrometry combined with 180-labeling. J Am Soc Mass Spectrom 19 544-549... 

Fig. 13.6 Nudicaulin pigments isolated from Papaver nudicaule and analyzed using high-resolution ESI-Fourier transform ion cyclotron mass spectrometry.

Prom the temperature dependence of the dHvA (or SdH) oscillations it is possible to extract the effective cyclotron mass (see Sect. 3.1). Comparisons of the mass obtained by these measurements with values from band-structure calculations, cyclotron resonance and specific-heat measurements are sometimes inconsistent. Whether strong electron-electron or electron-phonon interactions play the dominant role for this discrepancy is still under considerable debate and further studies have to deal with this question. Chapter 4 will review the present-day knowledge of the highly active field of the fermiology of organic superconductors . 

Prom these two equations it can easily be seen that the electrons are moving on an orbit in k space which is given by a constant energy surface perpendicular to B. The angular frequency with which the so-called cyclotron orbit is traced is given by the cyclotron frequency Wc = eB/rric, where the cyclotron mass is defined by... 

Fig. 4.6. Angular dependence of the effective cyclotron mass of four organic superconductors. The solid lines are of the form trie = mco/cos ...

Recently another member of the a-phase family has successfully been synthesized [144]. a-(ET)2KHg(SeCN)4 behaves in many respects similar to a-(ET)2TlHg(SeCN)4. It neither becomes superconducting nor does it show a ground state instability, i. e., no resistivity hump around 10 K is observed. The band-structure parameters obtained from SdH measurements are almost the same for both materials. The SdH frequency follows the l/cos0 dependence with Fq S3 670 T. The effective cyclotron mass is Hc 2.0. No mass increase up to 23 T was observed [144]. 

Fig. 4.19. Angular dependence of the average dHvA frequency and of the effective cyclotron mass (inset) of /5h-(ET)2I3...

A large discrepancy is reported for the values of the effective cyclotron masses of the different orbits. Due to the non Lifshitz-Kosevich behavior of the temperature-dependent dHvA amplitude in [336] only data above 1K were analyzed resulting in effective masses between 2me and 3.5 me- In [334] in the low-field region all data down to the lowest temperature followed the usual behavior and yielded values of 0.66rUe, 0.92 me, and 1.2 me for the a,... 

In conclusion, the reconstructed FS shown in Fig. 4.27b seems to represent the measured data best. Similar to a-phase salts already discussed a SDW transition might change the high-temperature FS drastically. Some experimental discrepancies of the FS extremal areas and the effective cyclotron mass still exist which remain to be resolved. 

Some discrepancies concerning the effective cyclotron mass were found. In contrast to the first published result, all later experiments consistently report a value of rric = (3.9 0.1) me for the large orbit at 0 = 0° and fields below 13T (see also Fig. 4.6) [192, 362, 363]. The effective mass for... 

Fig. 4.35. Field dependence of the effective cyclotron mass of K-(ET)2l3- The closed circles are obtained from SdH data for B perpendicular to the ET layers. The open symbols are from dHvA data, the closed rectangle from SdH data with a slightly canted field. The solid line shows the field independent mass. The dotted line is a guide to the eye. Prom [363]...

The origin for this apparent field dependence of rric is not fully understood. However, the nearly perfect two-dimensionality of -(ET)2l3 discussed in Sect. 2.3.3 seems to be the principal reason for the observed strange temperature and field dependence of the magnetic quantum oscillations. It was suggested that in this extremely 2D system quasiparticles with fractional statistics [365] may occur if the cyclotron orbits lie within an individual 2D conducting plane [363]. Since these quasiparticles do not obey Fermi statistics they should not contribute to the quantum oscillations observed. Hence, the effective cyclotron mass determined by the 3D Lifshitz-Kosevich formula could be underestimated. Further experimental verification for this suggestion is lacking. 

---