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Anomalous magnetoresistance and Shubnikov-de Haas effect observed for Bismuth in pulsed magnetic fields up to 50T at temperatures down to 0.3K
PHYSICA@
Physica B 194-196 (1994) 1191-1192 North-Holland
Anomalous magnetoresistance and Shubnikov-de Haas effect observed for Bismuth in pulsed magnetic fields up to 50T at temperatures down to 0.3K N. Miura a, R.G. Clark b, R. Newbury b, R.P. Starrettb, and A.V. Skougarevskyb a Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan b National Pulsed Magnet Laboratory, University of New South Wales, P.O.Box 1, Kensington, NSW 2033, Australia Transverse magnetoresistance was measured for Bi single crystals in pulsed magnetic fields up to 50T parallel to the binary axis at 0.3K. The spin-split Shubnikov-de Haas oscillation of holes was resolved up to the N = 1 Landau level. An anomalously large decrease of magnetoresistance was observed above 32T.
Bismuth is a semimetal which has a small energy overlap of 38.5meV between the conduction and the valence bands. It undergoes a semimetal to semiconductor (SM-SC) transition at high magnetic field. The SM-SC transition was first observed in far-infrared transmission at 88T with the field applied parallel to the binary axis[I]. Near the SMSC transition where the energy gap or the overlap becomes small, it is anticipated that novel phenomena such as an excitonic phase transition[2] or a gas-liquid type first order transition[3] may occur at high magnetic fields and low temperatures. In addition to the SM-SC transition, series of Shubnikov-de Haas oscillations were observed in previous magnetoresistance measurements at 1.7K[4] up to the N - - 2 hole Landau level. In order to investigate the high field properties and the possible electronic phase transitions, measurements of the transverse magnetoresistance in single crystal Bi have been made in pulsed magnetic fields applied parallel to the binary axis at liquid 3He temperatures. The experiments were carried out using the high field - low temperature facilities recently eslablished at the Australian National Pulsed Magnet Laboratory (NPML). The intense magnetic fields (20ms pulse duration) are generated by thyristor-switched discharge of a 0.8MJ, 7kV capacitor bank (1 - 32mF adjustable) into a liquid nitrogen-cooled 22ram bore
glass-fibre reinforced Cu coil. A top-loading 3He cryostat with narrow glass tails is combined with this arrangement and the samples are immersed in liquid 3He in a sample space with an'inner diameter of 5mm. A calibrated ruthenium oxide thermometer is mounted next to the sample and the magnetic field intensity is obtained from a calibrated pick-up coil. Transport data during the field pulse is captured by a 5 MHz transient recorder. The equipment is contained in a steel reinforced concrete enclosure and is computer controlled from a remote location by fibreoptic links. In this facility, a field of 69.6T has previously been achieved in a 12mm bore coil with an 8ms pulse duration. The rectangular samples of Bi single crystal were oriented by X-ray in such a way that the faces were normal to binary, bisectrix and trigonal axes. Their dimensions were as large as a few mm along each edge avoiding the diffusion size effect[5]. Measurements were made using a standard four contact method with a constant current of 1001.tA. Contacts on the samples were made using Wood's metal. Very clean magnetoresistance traces for the Bi samples were obtained up to 50T at T = 0.3K, following optimisation of the measurement technique. Figure 1 shows the magnetoresistance data for two samples. Series of sharp spin-split Shubnikov-de Haas peaks originating from holes and
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D I 0921-4526(93)El176-M
1192
resistance diminishes to approximately 1/5 of its maximum value at 31.6T. Moreover, two weak structures are resolved at 0.3K superposed on the steep negative slope of the magnetoresistance, at 41.1T and 45.7T, which are absent at elevated temperatures (4.2K). Although these peaks are obscured by the falling background structure, they are clearly seen in the second derivative curves, as shown in Fig. 1. Assigning the structures to the 1+ and 1" hole Landau levels respectively, the present results are consistent with previous measurements of far-infrared magneto-transmission in megagauss fields[l], as shown at the top of Fig. 1.
FIR i-
r-
t
~
Sample1
IX,"
t\
I'°''
t
~
' 0
~
:
10
20
o
~ 30 40 B (T)
°3K
0.3K . 4.2K 50
60
Fig. 1 Magnetoresistance p in two Bi single crystal samples. The scale of the resistivity is indicated in the figure. B//binary. The bottom two traces show the second derivative of the resistance. The top figure shows the far-infrared transmission at k =3371.tm reported in ref. 1 for comparison. The arrows indicate the Shubnikov-de Haas hole peaks. heavy electrons were observed in the field range up to 26.5T, where the 2" hole level was observed. The spin splitting of hole peaks showed a small sample dependence arising from a slight misorientation of the crystal axis relative to the field direction. The magnetoresistance had a maximum at 31.6T, and with further increasing field, it exhibited a sharp decrease. The precursor of the large resistance drop has been reported previously[4], but a surprising new finding is that the magnetoresistance decreases monotonically between 32T and 50T, where the
The reasons for the dramatic drop of the magnetoresistance above 32T and the weakness of the structures at 41.1T and 45.7T ascribed to the 1+ and 1- hole levels, compared to Shubnikov-de Haas peaks observed at lower fields, are not clear. The calculated carrier density does not increase with field above about 35T[4,6]. It is more likely that an increase of the carrier scattering may explain both phenomena. The camel's back structure in the kH dispersion of the lowest Landau level[7] may be a possible mechanism of such an enhancement of the scattering. From a technical viewpoint, the data provide a demonstration of the resolution that is possible for low temperature transport measurements in intense, pulsed magnetic fields.
REFERENCES
1. N. Miura, K. Hiruma, G. Kido and S. Chikazumi, Phys. Rev. Lett. 49 (1982) 1339. 2. N. B. Brandt and S. M. Chudinov, J. Low Temp. Phys. 8 (1972) 339. 3. S. Nakajima and D. Yoshioka, J. Phys. Soc. Jpn. 40 (1976) 328. 4. K. Hiruma and N. Miura, J. Phys. Soc. Jpn. 52 (1983) 2118. 5. K. Hiruma, G. Kido and N. Miura, J. Phys. Soc. Jpn. 51 (1982) 3278. 6. M. P. Vecchi, J. R. Pereira and M. S. Dresselhaus, Phys. Rev. B 14 (1976) 298. 7. M. P. Vecchi, J. R. Pereira and M. S. Dresselhaus, Proc. hzt. Cot~ Phys. Semiconductors, ed. M. H. Pilkuhn (Taubner, Stuttgart, 1974), p.l181.
Physica B 194-196 (1994) 1191-1192 North-Holland
Anomalous magnetoresistance and Shubnikov-de Haas effect observed for Bismuth in pulsed magnetic fields up to 50T at temperatures down to 0.3K N. Miura a, R.G. Clark b, R. Newbury b, R.P. Starrettb, and A.V. Skougarevskyb a Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan b National Pulsed Magnet Laboratory, University of New South Wales, P.O.Box 1, Kensington, NSW 2033, Australia Transverse magnetoresistance was measured for Bi single crystals in pulsed magnetic fields up to 50T parallel to the binary axis at 0.3K. The spin-split Shubnikov-de Haas oscillation of holes was resolved up to the N = 1 Landau level. An anomalously large decrease of magnetoresistance was observed above 32T.
Bismuth is a semimetal which has a small energy overlap of 38.5meV between the conduction and the valence bands. It undergoes a semimetal to semiconductor (SM-SC) transition at high magnetic field. The SM-SC transition was first observed in far-infrared transmission at 88T with the field applied parallel to the binary axis[I]. Near the SMSC transition where the energy gap or the overlap becomes small, it is anticipated that novel phenomena such as an excitonic phase transition[2] or a gas-liquid type first order transition[3] may occur at high magnetic fields and low temperatures. In addition to the SM-SC transition, series of Shubnikov-de Haas oscillations were observed in previous magnetoresistance measurements at 1.7K[4] up to the N - - 2 hole Landau level. In order to investigate the high field properties and the possible electronic phase transitions, measurements of the transverse magnetoresistance in single crystal Bi have been made in pulsed magnetic fields applied parallel to the binary axis at liquid 3He temperatures. The experiments were carried out using the high field - low temperature facilities recently eslablished at the Australian National Pulsed Magnet Laboratory (NPML). The intense magnetic fields (20ms pulse duration) are generated by thyristor-switched discharge of a 0.8MJ, 7kV capacitor bank (1 - 32mF adjustable) into a liquid nitrogen-cooled 22ram bore
glass-fibre reinforced Cu coil. A top-loading 3He cryostat with narrow glass tails is combined with this arrangement and the samples are immersed in liquid 3He in a sample space with an'inner diameter of 5mm. A calibrated ruthenium oxide thermometer is mounted next to the sample and the magnetic field intensity is obtained from a calibrated pick-up coil. Transport data during the field pulse is captured by a 5 MHz transient recorder. The equipment is contained in a steel reinforced concrete enclosure and is computer controlled from a remote location by fibreoptic links. In this facility, a field of 69.6T has previously been achieved in a 12mm bore coil with an 8ms pulse duration. The rectangular samples of Bi single crystal were oriented by X-ray in such a way that the faces were normal to binary, bisectrix and trigonal axes. Their dimensions were as large as a few mm along each edge avoiding the diffusion size effect[5]. Measurements were made using a standard four contact method with a constant current of 1001.tA. Contacts on the samples were made using Wood's metal. Very clean magnetoresistance traces for the Bi samples were obtained up to 50T at T = 0.3K, following optimisation of the measurement technique. Figure 1 shows the magnetoresistance data for two samples. Series of sharp spin-split Shubnikov-de Haas peaks originating from holes and
0921-4526/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved S S D I 0921-4526(93)El176-M
1192
resistance diminishes to approximately 1/5 of its maximum value at 31.6T. Moreover, two weak structures are resolved at 0.3K superposed on the steep negative slope of the magnetoresistance, at 41.1T and 45.7T, which are absent at elevated temperatures (4.2K). Although these peaks are obscured by the falling background structure, they are clearly seen in the second derivative curves, as shown in Fig. 1. Assigning the structures to the 1+ and 1" hole Landau levels respectively, the present results are consistent with previous measurements of far-infrared magneto-transmission in megagauss fields[l], as shown at the top of Fig. 1.
FIR i-
r-
t
~
Sample1
IX,"
t\
I'°''
t
~
' 0
~
:
10
20
o
~ 30 40 B (T)
°3K
0.3K . 4.2K 50
60
Fig. 1 Magnetoresistance p in two Bi single crystal samples. The scale of the resistivity is indicated in the figure. B//binary. The bottom two traces show the second derivative of the resistance. The top figure shows the far-infrared transmission at k =3371.tm reported in ref. 1 for comparison. The arrows indicate the Shubnikov-de Haas hole peaks. heavy electrons were observed in the field range up to 26.5T, where the 2" hole level was observed. The spin splitting of hole peaks showed a small sample dependence arising from a slight misorientation of the crystal axis relative to the field direction. The magnetoresistance had a maximum at 31.6T, and with further increasing field, it exhibited a sharp decrease. The precursor of the large resistance drop has been reported previously[4], but a surprising new finding is that the magnetoresistance decreases monotonically between 32T and 50T, where the
The reasons for the dramatic drop of the magnetoresistance above 32T and the weakness of the structures at 41.1T and 45.7T ascribed to the 1+ and 1- hole levels, compared to Shubnikov-de Haas peaks observed at lower fields, are not clear. The calculated carrier density does not increase with field above about 35T[4,6]. It is more likely that an increase of the carrier scattering may explain both phenomena. The camel's back structure in the kH dispersion of the lowest Landau level[7] may be a possible mechanism of such an enhancement of the scattering. From a technical viewpoint, the data provide a demonstration of the resolution that is possible for low temperature transport measurements in intense, pulsed magnetic fields.
REFERENCES
1. N. Miura, K. Hiruma, G. Kido and S. Chikazumi, Phys. Rev. Lett. 49 (1982) 1339. 2. N. B. Brandt and S. M. Chudinov, J. Low Temp. Phys. 8 (1972) 339. 3. S. Nakajima and D. Yoshioka, J. Phys. Soc. Jpn. 40 (1976) 328. 4. K. Hiruma and N. Miura, J. Phys. Soc. Jpn. 52 (1983) 2118. 5. K. Hiruma, G. Kido and N. Miura, J. Phys. Soc. Jpn. 51 (1982) 3278. 6. M. P. Vecchi, J. R. Pereira and M. S. Dresselhaus, Phys. Rev. B 14 (1976) 298. 7. M. P. Vecchi, J. R. Pereira and M. S. Dresselhaus, Proc. hzt. Cot~ Phys. Semiconductors, ed. M. H. Pilkuhn (Taubner, Stuttgart, 1974), p.l181.