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Collective electromagnetic wave excitation in Bi2Sr2CaCu2O8+δ in magnetic field nearly parallel to the CuO2-planes
__ iii3
Au
PHYSICA E
_-
ELSEVlER
Physica C 282-287
(1997) 2429-2430
Collective electromagnetic wave excitation in BizSrzCaCuz08+sin magnetic field nearly parallel to the CuOz-planes Marat B.Gaifullin”‘b, Yuji Matsudal, Kazuo Kadowakiqd, Takashi Mochikud , Ken-ichi Kumagai” ‘Department of Physics, Hokkaido University, Sapporo 060, Japan bDepartment of Physics, Far-Eastern State Technical University, Vladivostok 690600, Russia ‘Institute of Materials Science. The University of Tsukuba, l-l-l, Ten-nodai, Tsukuba, Ibaraki 305, Japan dNational Research Institute for Metals, 1-2-1 Sengen, Tsukuba, Ibaraki 305, Japan The angular dependence of the microwave resonant absorption of Bi2Sr2CaCu208+6in magnetic field was measured by angular alignment with -0.02’ precision. When the angle B between the field and the CuOz-plane is tilted from the c-axis, the resonance field scales as B sine in the range 0 > 4’. A disappearance of the resonance is unexpectedly observed for angles within B -0.13”. Possible origin of the phenomena is discussed.
1. INTRODUCTION The strongly anisotropic high-T= superconductors behave as vertically stacked intrinsic Josephson junctions. Recently the Josephson plasma excitation mode in which the supercurrents oscillate normal to the CuOZ planes is generated was discovered as a microwave resonant absorption in BizSrzCaCua08+s [l]. More recently Josephson plasma resonance was measured in an oblique field and found that as the field is tilted away from the c-axis, the resonance field moves rapidly to a higher fields and displays an unusual reentrant cusp when magnetic field is very close to the alignment with the layers [2]. This phenomenon has been discussed in light of the reduction of the plasma frequency due to the formation of Josephson vortices. In this paper we performed measurements of the precise angular dependence of the microwave resonant absorption in the vortex liquid state. It is revealed that phenomenon is more complicated than ref.[2].
Tl& mode (o =45GHz). The cavity is rotated from the top in the split pair magnet keeping E@]]c-axis. To measure microwave resonance absorption we used the bolometric technique [1,2].
3. RESULTS AND DISCUSSION Figure 1 shows the angular dependence of the resonance field B,, for samples with the different oxygen stoichiometry. The reentrant cusp is observed near 8-O. B. is well scaled as BI=BsinB at e>40. 0.14 ,““““““‘,“““““““‘,““““‘, 0.12 t_2
----I -20
/J
2. EXPERIMENTAL The Bi&&aCuzOa+s single crystals were grown the traveling solvent floating zone technique. The experiments were carried out on crystals with typical dimensions of 1.1x0.4x0.05mm3 which were annealed in order to change oxygen stoichiometry. The sample is located at the antinode of the ac electric field E,ll c-axis in rectangular cavity with by
0921-4534/97/%17.00 0 Elsevier Science B.V PI1 SO921 -4534(97)01279-3
All rights reserved.
-10
0
-5 8
5
10
(deg)
Figure 1. Busin versus angle B between the field and ah-plane. The lines are fits to the data with eq.(l). yis the anisotropy factor.
2430
b4.R.Gaijiillin et al. /Physica C 282-287
The features of resonance are consistent with the theory of the Josephson plasma resonance in the vortex liquid state in layered superconductors [3]. According to this theory the plasma frequency is given by
(1997) 2429-2430
considering the excitation modes of the Josephson vortex lattice.
(1) where Q0 is flux quantum; Bl and BI are the field component parallel and perpendicular to the layers, respectively. We assumed the dielectric constant &=2.5 and the interlayer spacing s=15.6& The Josephson critical current density in zero field is j, =c@~S(~&,)%, where &, is the in-plane penetration depth; y is the anisotropy factor [4]. Since &IX sZ -lOOT, the exponential factor is not important at angles 0 >4” and resonance fields are well scaled by Bl=BsinB. Figure 2 shows the angular dependence of the resonance for underdoped sample with y =720 taken at T=36.1K. The resonance vanishes within the critical angle 8,- 0.13” for this sample. In the experiment magnetic field is swept from t6T to -6T through zero field. The resonances are not symmetric in positive and negative fields. At minus side the intensity and shape of resonance lines depend on field sweeping rate. This may be caused by metastable vortex state. On the other hand the resonance does not show appreciable change at plus side (in Fig.1 we plotted data of the plus side). We suppose that 0, corresponds to the lock-in angle below which vortices are locked in &plane. The disappearance of the resonance within the lockin angle implies that the plasma resonance mode jumps to different frequency [5]. In parallel field the collective vortex oscillation and the plasma oscillation modes appear by analogy with the two different branches of phase collective mode in the long single Josephson junction [6]. Both modes accompany the supercurrent oscillation normal to the insulating layers. The former mode corresponds to sound wave-like collective oscillation without gap. The latter mode is analogous to the optical branch of the’phonon spectra and has gap which is always larger than zero field plasma frequency. Consequently, if microwave frequency is less than the zero field plasma frequency, no resonance is observed. Thus the vanishing of the resonance below the lock-in angle can be accounted for by
c
c t
JJ
(_
-0.250 -0.12s"
t
0.00
3.29
-1.6 -1.2 -0.8 -0.4
0
0.4
0.8
1.2
1.6
/@VT) Figure 2. The angular dependence of the Josephson plasma resonance spectra.
REFERENCES 1. Y.Matsuda, M.B.Gaifullin, KKumagai, T.Mochiku, and K.Kadowaki, Phys. Rev. Lett. 75,4512 (1995). 2. O.K.C.Tsui, N.P.Ong, and J.B.Peterson, Phys. Rev. Lett. 29,819 (1996). 3. A.Koshelev, Phys. Rev. Lett. 77, 3901 (1996). 4. Y.Matsuda, M.B.Gaifullin, K.Kumagai, M.Kosugi, K.Hirata, to be published in Phys. Rev. Lett. (1997) 5. L.N.Bulaevskii, D.Dominguez, M.P.Maley and A.R.Bishop, to be published in Phys. Rev. B 6. A.L.Fetter and M.J.Stephen, Phys. Rev. B 168, 475 (1968)
Au
PHYSICA E
_-
ELSEVlER
Physica C 282-287
(1997) 2429-2430
Collective electromagnetic wave excitation in BizSrzCaCuz08+sin magnetic field nearly parallel to the CuOz-planes Marat B.Gaifullin”‘b, Yuji Matsudal, Kazuo Kadowakiqd, Takashi Mochikud , Ken-ichi Kumagai” ‘Department of Physics, Hokkaido University, Sapporo 060, Japan bDepartment of Physics, Far-Eastern State Technical University, Vladivostok 690600, Russia ‘Institute of Materials Science. The University of Tsukuba, l-l-l, Ten-nodai, Tsukuba, Ibaraki 305, Japan dNational Research Institute for Metals, 1-2-1 Sengen, Tsukuba, Ibaraki 305, Japan The angular dependence of the microwave resonant absorption of Bi2Sr2CaCu208+6in magnetic field was measured by angular alignment with -0.02’ precision. When the angle B between the field and the CuOz-plane is tilted from the c-axis, the resonance field scales as B sine in the range 0 > 4’. A disappearance of the resonance is unexpectedly observed for angles within B -0.13”. Possible origin of the phenomena is discussed.
1. INTRODUCTION The strongly anisotropic high-T= superconductors behave as vertically stacked intrinsic Josephson junctions. Recently the Josephson plasma excitation mode in which the supercurrents oscillate normal to the CuOZ planes is generated was discovered as a microwave resonant absorption in BizSrzCaCua08+s [l]. More recently Josephson plasma resonance was measured in an oblique field and found that as the field is tilted away from the c-axis, the resonance field moves rapidly to a higher fields and displays an unusual reentrant cusp when magnetic field is very close to the alignment with the layers [2]. This phenomenon has been discussed in light of the reduction of the plasma frequency due to the formation of Josephson vortices. In this paper we performed measurements of the precise angular dependence of the microwave resonant absorption in the vortex liquid state. It is revealed that phenomenon is more complicated than ref.[2].
Tl& mode (o =45GHz). The cavity is rotated from the top in the split pair magnet keeping E@]]c-axis. To measure microwave resonance absorption we used the bolometric technique [1,2].
3. RESULTS AND DISCUSSION Figure 1 shows the angular dependence of the resonance field B,, for samples with the different oxygen stoichiometry. The reentrant cusp is observed near 8-O. B. is well scaled as BI=BsinB at e>40. 0.14 ,““““““‘,“““““““‘,““““‘, 0.12 t_2
----I -20
/J
2. EXPERIMENTAL The Bi&&aCuzOa+s single crystals were grown the traveling solvent floating zone technique. The experiments were carried out on crystals with typical dimensions of 1.1x0.4x0.05mm3 which were annealed in order to change oxygen stoichiometry. The sample is located at the antinode of the ac electric field E,ll c-axis in rectangular cavity with by
0921-4534/97/%17.00 0 Elsevier Science B.V PI1 SO921 -4534(97)01279-3
All rights reserved.
-10
0
-5 8
5
10
(deg)
Figure 1. Busin versus angle B between the field and ah-plane. The lines are fits to the data with eq.(l). yis the anisotropy factor.
2430
b4.R.Gaijiillin et al. /Physica C 282-287
The features of resonance are consistent with the theory of the Josephson plasma resonance in the vortex liquid state in layered superconductors [3]. According to this theory the plasma frequency is given by
(1997) 2429-2430
considering the excitation modes of the Josephson vortex lattice.
(1) where Q0 is flux quantum; Bl and BI are the field component parallel and perpendicular to the layers, respectively. We assumed the dielectric constant &=2.5 and the interlayer spacing s=15.6& The Josephson critical current density in zero field is j, =c@~S(~&,)%, where &, is the in-plane penetration depth; y is the anisotropy factor [4]. Since &IX sZ -lOOT, the exponential factor is not important at angles 0 >4” and resonance fields are well scaled by Bl=BsinB. Figure 2 shows the angular dependence of the resonance for underdoped sample with y =720 taken at T=36.1K. The resonance vanishes within the critical angle 8,- 0.13” for this sample. In the experiment magnetic field is swept from t6T to -6T through zero field. The resonances are not symmetric in positive and negative fields. At minus side the intensity and shape of resonance lines depend on field sweeping rate. This may be caused by metastable vortex state. On the other hand the resonance does not show appreciable change at plus side (in Fig.1 we plotted data of the plus side). We suppose that 0, corresponds to the lock-in angle below which vortices are locked in &plane. The disappearance of the resonance within the lockin angle implies that the plasma resonance mode jumps to different frequency [5]. In parallel field the collective vortex oscillation and the plasma oscillation modes appear by analogy with the two different branches of phase collective mode in the long single Josephson junction [6]. Both modes accompany the supercurrent oscillation normal to the insulating layers. The former mode corresponds to sound wave-like collective oscillation without gap. The latter mode is analogous to the optical branch of the’phonon spectra and has gap which is always larger than zero field plasma frequency. Consequently, if microwave frequency is less than the zero field plasma frequency, no resonance is observed. Thus the vanishing of the resonance below the lock-in angle can be accounted for by
c
c t
JJ
(_
-0.250 -0.12s"
t
0.00
3.29
-1.6 -1.2 -0.8 -0.4
0
0.4
0.8
1.2
1.6
/@VT) Figure 2. The angular dependence of the Josephson plasma resonance spectra.
REFERENCES 1. Y.Matsuda, M.B.Gaifullin, KKumagai, T.Mochiku, and K.Kadowaki, Phys. Rev. Lett. 75,4512 (1995). 2. O.K.C.Tsui, N.P.Ong, and J.B.Peterson, Phys. Rev. Lett. 29,819 (1996). 3. A.Koshelev, Phys. Rev. Lett. 77, 3901 (1996). 4. Y.Matsuda, M.B.Gaifullin, K.Kumagai, M.Kosugi, K.Hirata, to be published in Phys. Rev. Lett. (1997) 5. L.N.Bulaevskii, D.Dominguez, M.P.Maley and A.R.Bishop, to be published in Phys. Rev. B 6. A.L.Fetter and M.J.Stephen, Phys. Rev. B 168, 475 (1968)