@PhDThesis{Okazaki:2019:InPrMa,
author = "Okazaki, Anderson Kenji",
title = "Investiga{\c{c}}{\~a}o das propriedades de magnetotransporte no
isolante topol{\'o}gico cristalino telureto de chumbo e estanho",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2019",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2019-06-03",
keywords = "telureto de chumbo e estanho, epitaxia de feixe molecular,
isolante topol{\'o}gico cristalino, magnetorresist{\^e}ncia
longitudinal, oscila{\c{c}}{\~o}es de Shubnikov-de Haas, lead
tin telluride, molecular beam epitaxy, topological crystalline
insulator, longitudinal magnetoresistance, Shubnikov-de Haas
oscillations.",
abstract = "O composto semicondutor Pb1-xSnxTe foi recentemente revelado como
um isolante topol{\'o}gico cristalino que apresenta uma
transi{\c{c}}{\~a}o de isolante trivial para topol{\'o}gico
acima da composi{\c{c}}{\~a}o cr{\'{\i}}tica xc de Sn onde
ocorre a invers{\~a}o de bandas. Este trabalho visa investigar as
propriedades de magnetotransporte em toda a faixa de
composi{\c{c}}{\~a}o da liga em intensos campos magn{\'e}ticos
B de at{\'e} 30 T. Para tanto, filmes monocristalinos de
Pb1-xSnxTe (0 \≤ x \≤ 1) foram crescidos por
epitaxia de feixe molecular sobre substratos de BaF2 (111). A
caracteriza{\c{c}}{\~a}o el{\'e}trica a baixo campo (B = 0,7 T)
e a 12 K mostrou que a densidade de portadores do tipo-p e a
mobilidade Hall variam de 2,6 × 1017 a 1,9 × 1020 cm-3 e de 23 000
a 1 500 cm²/Vs, respectivamente, assim que a
composi{\c{c}}{\~a}o da liga muda do PbTe para o SnTe. As
medi{\c{c}}{\~o}es da resist{\^e}ncia longitudinal, Rxx,
at{\'e} B = 30 T revelam oscila{\c{c}}{\~o}es qu{\^a}nticas de
Shubnikov-de Haas (SdH) para filmes com x \≥ 0,70. As
oscila{\c{c}}{\~o}es SdH mais intensas ocorrem no SnTe e, por
isso, permitem uma an{\'a}lise detalhada nesse material. A
segunda derivada (-d²Rxx/dB²) versus 1/B apresenta um claro
padr{\~a}o de batimento a 4,2 K que persisti at{\'e} 80 K. A
an{\'a}lise da transformada r{\'a}pida de Fourier (FFT) revela
que as oscila{\c{c}}{\~o}es s{\~a}o compostas de duas
componentes com frequ{\^e}ncias pr{\'o}ximas. A massa
ciclotr{\^o}nica correspondente a cada frequ{\^e}ncia foi
determinada pelo amortecimento t{\'e}rmico da amplitude FFT e
concorda com os valores publicados na literatura para o SnTe. Como
o SnTe tem elipsoides de Fermi alongados, o comportamento
1/costheta, observado na depend{\^e}ncia angular de ambas as
frequ{\^e}ncias SdH, n{\~a}o {\'e} suficiente para garantir a
condu{\c{c}}{\~a}o pelos estados de superf{\'{\i}}cie. O
ajuste das componentes oscilat{\'o}rias de Rxx {\`a}
equa{\c{c}}{\~a}o de Lifshitz-Kosevich confirmam as duas
frequ{\^e}ncias, o que permiti extrair as fases de Berry dos
portadores de carga. As an{\'a}lises demonstram que as
componentes oscilat{\'o}rias surgem da divis{\~a}o do elipsoide
longitudinal do SnTe volum{\'e}trico devido ao efeito Rashba de
polariza{\c{c}}{\~a}o de spin que coexiste com a fase
topol{\'o}gica. Devido a uma grande magnetorresist{\^e}ncia de
fundo, as amostras com concentra{\c{c}}{\~a}o de Sn abaixo de
0,70 n{\~a}o s{\~a}o capazes de produzir oscila{\c{c}}{\~o}es
intensas o suficiente para possibilitar a an{\'a}lise do
transporte de cargas. Por{\'e}m, o amortecimento t{\'e}rmico das
oscila{\c{c}}{\~o}es nas amostras com x \≥ 0,70 permite
observar a diminui{\c{c}}{\~a}o da massa efetiva
ciclotr{\^o}nica com o aumento de x, que {\'e} uma
evid{\^e}ncia da mudan{\c{c}}a da superf{\'{\i}}cie de Fermi
em fun{\c{c}}{\~a}o da composi{\c{c}}{\~a}o de Sn na liga. A
aplica{\c{c}}{\~a}o do campo magn{\'e}tico simultaneamente
paralelo {\`a} superf{\'{\i}}cie da amostra e {\`a}
dire{\c{c}}{\~a}o da corrente, revelou que a
magnetorresist{\^e}ncia longitudinal negativa n{\~a}o {\'e} uma
caracter{\'{\i}}stica exclusiva dos isolantes topol{\'o}gicos,
mas que pode ser uma propriedade geral de metais e semicondutores
afetada pela distor{\c{c}}{\~a}o das linhas de campo
el{\'e}trico. No Pb1-xSnxTe, essa altera{\c{c}}{\~a}o das
linhas equipotenciais {\'e} blindada pela fase ferroel{\'e}trica
que tem a temperatura de transi{\c{c}}{\~a}o diminu{\'{\i}}da
com a redu{\c{c}}{\~a}o de Sn na liga. ABSTRACT: The
semiconductor compound Pb1-xSnxTe has recently been revealed as a
topological crystalline insulator, which presents a transition
from trivial to topological insulator above a critical Sn
composition, xc, where the band inversion occurs. This work aims
the investigation of the Pb1-xSnxTe magnetotransport properties
covering the entire composition range at intense magnetic field B
up to 30 T. For this purpose, monocrystalline Pb1-xSnxTe films (0
\≤ x \≤ 1) were grown by molecular beam epitaxy on
(111) BaF2 substrates. The electrical characterization at low
field (B = 0.7 T) and 12 K showed that the p-type carrier density
and Hall mobility varied from 2.6 × 1017 to 1.9 × 1020 cm-3 and
from 23,000 to 1,500 cm²/Vs, respectively, as the Sn content
increased from PbTe to SnTe. The longitudinal resistance, Rxx,
measurements up to B = 30 T revealed Shubnikov-de Haas (SdH)
quantum oscillations for films with x \≥ 0.70. The most
intense SdH oscillations occurred for SnTe that allowed a detailed
analysis for this material. Second derivative (-d²Rxx/dB²) versus
1/B exhibited a clear beating pattern at 4.2 K, which persisted
until 80 K. From fast Fourier transform (FFT) analysis was
demonstrated that the oscillations are composed by two components
with close frequencies. The cyclotron mass correspondent to each
frequency was determined by the thermal damping of FFT amplitude
and agree with the values published in literature for SnTe. As
SnTe has elongated Fermi ellipsoids, the 1/costheta dependence
obtained in the angular evolution of both SdH frequencies is not
enough to ensure conduction via surface states. The
Lifshitz-Kosevich fitting of the Rxx oscillatory components
confirmed the two frequencies and allowed to extract the Berrys
phases of the carriers. The analyses show that the oscillatory
components originate from SnTe bulk longitudinal ellipsoid spin
splitting due to Rashba effect, which coexists with the
topological phase. Due to a large background magnetoresistance,
the samples with Sn content lower than 0.70 were not able to
produce oscillations with enough intensity to allow the carriers
transport analyses. However, the thermal damping of the
oscillations in the samples with x \≥ 0.70 permitted to
observe the effective cyclotron mass reduction with increasing x,
which is an evidence of the Fermi surface alteration as the Sn
content changes. The negative longitudinal magnetoresistance
observed with the magnetic field applied simultaneously parallel
to the sample surface and to the current direction is not an
exclusive feature of topological insulators but can be a general
property of metals and semiconductors affected by the electric
field lines distortion. In Pb1-xSnxTe, this modification of the
equipotential lines is shielded by ferroelectric phase, whose
transition temperature diminishes with the Sn content reduction in
the alloy.",
committee = "Rappl, Paulo Henrique de Oliveira (presidente/orientador) and
Abramof, Eduardo (orientador) and Corat, Evaldo Jos{\'e} and
Barreto, Patr{\'{\i}}cia Regina Pereira and Peres, Marcelos Lima
and Teles, Lara K{\"u}hl",
englishtitle = "Magnetotransport properties investigation of the topological
crystalline insulator lead tin telluride",
language = "pt",
pages = "91",
ibi = "8JMKD3MGP3W34R/3TH8PAL",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/3TH8PAL",
targetfile = "publicacao.pdf",
urlaccessdate = "06 maio 2024"
}