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Submitted on 1 Jan 1978
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RF SURFACE IMPEDANCE OF TUNGSTEN AT
DIFFERENT SAMPLE SURFACE STATES
L. Tsymbal, A. Cherkasov
To cite this version:
JOURNAL D E PHYSIQUE Colloque
C6,
supplkment au no 8, Tome 39, aoiit 1978, page C6-1140RF SURFACE IMPEDANCE OF TUNGSTEN AT DIFFERENT SAMPLE SURFACE STATES
L.T. Tsymbal, A.N. Cherkasov
Physico-TechnicaZ Institute of the Ukrainian Academy of Sciences, Donetsk, 340048, U.S,S.R.
Rlsum6.- On a dtudil explrimentalement les oscillations d1impLdance de surface dans des lchantillons
de tungstene ayant des qualitls diffsrentes de leur surface. On a constate un doublement de psriode des oscillations des dopplerons et des oscillations de Gantmakher-Kaner quand l'excitation radio- frlquence n'est appliqude que d'un cStl de 1'Bchantillon. La prlsence des oscillations qu'on ne peut pas identifier dans le cadre des thlories exrstantes est discutle.
Abstract.- Oscillations of
W
surface resistance have been investigated experimentally at differentsample surface states. Doubling of doppleron and Gantmakher-Kaner oscillation periods have been found at one-sided excitation; Availability of unidentifiable oscillations within the scope of exis- ting theory is discussed.
This paper reports an experimental study of surface resistance oscillations due to the doppleron and Gantmakher-kaner (GK) wave excitations earlier
investigated / l / . The measurements were performed
using NMR-spectrometer type technique at frequencies
2 5 6 MtIz, at 4.2 K, and in magnetic fields up to 55
kG. Effect of atomic surface structure state on sur- face impedance oscillations was investigated under two-sided circularly polarized excitation.
Figure 1 shows the second derivative d2Re2
+
/dB2 from the real part of the surface impedance with the respect to the magnetic field at different cir-
cular polarization signs of the exciting rf field
.
Fig. l : The curves d 2 ~ e 2
+
/dB2 vs B and correspondingwave vector dispersions at two-sided excitation for W
sample with surfaces lapped by abrasive. Circular po- larization signs are shown in circles.
The
"-"
sign corresponds to the coincidence of the rotation direction of rf field and that of electronin the magnetic field. These curves were obtained on a sample with the surfaces lapped by a corrundum abrasive to disarrange their atomic structure. The
oscillations in
"-"
polarization have a stationaryperiod and are in phase with .the oscillations in "+"
polarization in the fields from 2 q kG up to the
highest possible ones. Most likely they are the GK-
oscillations. The oscillations in "+" polarization
are a superposition of doppleron -and GK-oscilla- tions. The oscillations in "-l' polarization have the dispersion of a period reciprocal to that of the dopplerons. This can be explained by different GK- oscillation phase shifts in high and low magnetic fields, dependent on the certain Fermi surface shape 121. Figure 2 shows curves obtained on samples with
Fig. 2 : The curves d2Rezf / d ~ ~ vs B at two-sided ex-
citation for W sample with chemically poli-
shed surfaces. Circular polarization signs are shown in circles.
chemically polished surfaces to remove the damaged layers. The pulsations indicating the existence of at least two periods are observed in each polariza-
tion. In the fields over = 35 kG, where the period
of oscillations becomes steady, the value of the
period in
"-"
polarization is = 1.6 % higher thanin the "+" one. After the abrasive lapping of the
sample surfaces the character and form of the oscil-
lations become similar to those shown in figure 1.
It can be supposed that the oscillations shown in
figure 2 are a superposition of doppleron-and GK-
oscillations, like those given in figure 1, with a new kind of oscillations. The characteristic fea- tures of these oscillations are the monotonous de- pendence of their amplitude on the magnetic field and discrepancy of their periods at different pola- rization signs. The above characteristics do not allow these oscillations to be identified within the available theoretical views /2,3/.
Fig. 3 : The curves ~ ' R ~ z - c / ~ B ~ vs B at one-sided
excitation for W sample with chemically polished
surfaces. Circular polarization signs are shown in circles.
Figure 3 shows curves obtained at one-sided excitation. It shows that, on one hand, the oscil- lations with the period twice as small as that of the oscillations at two-sided excitation and, on the other hand, the oscillations with the same pe- riod are observed in both polarizations. The oscil- lations with double frequency seem to have the sa-
me nature as that of the oscillations shown in fi-
gure 2. The double decrease of their periods com- pared to the two-sided excitation corresponds to
fictitious doubling of sample thickness. The detec- tion of the oscillations with the same period as that at two-sided excitation is unexpected. These
oscillations have a monotonous character of the ma-
gnetic field dependence of the amplitude and in "-lf
polarization oscillation period is 1.5
-
2 % higherthan that in the "+" one. Tnese features of the con-
sidered oscillations are quite similar to those of the non-identified oscillations found at two-sided excitation. Consequently, they are most likely of the same nature.
References
/l/ Vitebski,I.M., Vitchinkin,V.T., Galkin,A.A.,
OS troukhov,Yu. S., Panchenko ,O .A., Tsymbal ,L .T
.
and Cherkasov,A.N., Fiz. Niz. Temp.
1
(1975)4 0 0
/2/ Voloshin,I.F., Skobov,V.G., Fisher,L.M. and
Chernov,A.S., Zh. Exper. Teor. Fiz.
72
(1977)735
131 Falk,D.S., Gerson,B. and Carolan,J.F., Phys.
