Anomalous phonon softening in the topological insulator Sn-doped Bi1.1Sb0.9Te2S

Li, Bowen; Jiang, Wenbing; Chen, Guan-Yu; Xiang, Ying; Xie, Wei; Dai, Y. M.; Zhu, Xiyu; Yang, Huan; Wen, Hao

doi:10.1007/s11433-020-1563-1

Cited by 5 publications

(9 citation statements)

References 29 publications

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“…The strongest absorption peak for both MBT and MBST is located at ∼1.5 THz, and can be identified as the IR active phonon mode E u , which is in agreement with the theoretical estimation from first principle DFT calculations [25]. The E u phonon mode displays two significant temperature dependent features: (i) the phonon peak undergoes a blue-shift (∼ 0.1 THz for MBT and ∼ 0.2 THz for MBST ) upon increasing the sample temperature (from 7K to 250K), which is an anomalous behaviour [35][36][37] The black continuous line represents the corresponding fit using Eq. ( 1).…”

Section: Methodssupporting

confidence: 84%

“…Such softening of the phonon mode upon cooling, has been seen in other TIs like Sb 2 Te 3 and Bi 2 Se 3 (both pristine and doped) samples [36,38,43]. The softening of the IR phonon mode, E u , upon cooling is called anomalous as it is in contrast to the usual temperature dependence (hardening upon cooling) of phonons driven via the anharmonic phonon decay process and the thermal lattice expansion [36,44,45]. It is well known that some specific phonon vibrations are unstable across the phase transitions like ferroelectric [46], magnetic [47,48], structural [49], causing their anomalous behavior with temperature.…”

Section: (B) (Shown For Few Temperatures For Clarity) and The Corresp...supporting

confidence: 61%

“…For both MBT and MBST, f F ano shifts towards the lower frequency side with decreasing temperature. Such softening of the phonon mode upon cooling, has been seen in other TIs like Sb 2 Te 3 and Bi 2 Se 3 (both pristine and doped) samples [36,38,43]. The softening of the IR phonon mode, E u , upon cooling is called anomalous as it is in contrast to the usual temperature dependence (hardening upon cooling) of phonons driven via the anharmonic phonon decay process and the thermal lattice expansion [36,44,45].…”

Section: (B) (Shown For Few Temperatures For Clarity) and The Corresp...mentioning

confidence: 86%

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Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Mukherjee¹,

Chakraborti²,

Mukhopadhyay³

2022

The Indian Journal of Chest Diseases and Allied Sciences

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MnBi 2 Te 4 , the first topological insulator with inherent magnetic ordering, has attracted significant attention recently for providing a platform to realize several exotic quantum phenomena at relatively higher temperatures. In this work, we have carried out an exhaustive investigation of MnBi 2 Te 4 and Sb doped MnBi 2 Te 4 thin films using THz time-domain spectroscopy. The extracted real THz conductivity displays a strong IR active E u phonon absorption peak (at ∼1.5 THz) merged on top of the Drude-like contributions from bulk and surface electrons. The extracted parameters from the THz conductivity data fitted to the Drude-Fano-Lorentz model, show significant changes in their temperature dependence around the magnetic ordering Néel temperature of ∼ 25K, which is suggestive of the coupling between magnetic ordering and electronic band structure. The frequency of the E u phonon displays an anomalous blue-shift with increasing temperatures by ∼ 0.1 THz (∼7%) for MnBi 2 Te 4 and ∼0.2 THz (∼13%) for Sb doped MnBi 2 Te 4 between 7K and 250K. The line-shape of the E u phonon mode in Sb doped MnBi 2 Te 4 shows significant Fano asymmetry compared to that of MnBi 2 Te 4 , indicating that Sb doping plays an important role in the Fano interference between the phonons and the electrons, in this system. These results indicate that the anomalous phonon behaviour seen in MBT arise mainly from positive cubic anharmonicity induced self energy parameter, whereas both anharmonicity and the electron phonon coupling are at play in making the relatively higher anomalous blue shift of phonons in MBST. Our studies provide the first comprehensive understanding of the phonon and electron dynamics of MnBi 2 Te 4 and Sb doped MnBi 2 Te 4 in the THz range using time-domain THz spectroscopy.

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Section: Methodssupporting

confidence: 84%

Section: (B) (Shown For Few Temperatures For Clarity) and The Corresp...supporting

confidence: 61%

Section: (B) (Shown For Few Temperatures For Clarity) and The Corresp...mentioning

confidence: 86%

See 1 more Smart Citation

Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Mukherjee¹,

Chakraborti²,

Mukhopadhyay³

2022

The Indian Journal of Chest Diseases and Allied Sciences

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“…This observation suggests that the scattering of phonons is increased with the increase of temperature and as a result the phonon lifetime decreases. Previously, anomalous phonon softening behaviour has been observed in Sn doped BSTS by IR spectroscopy [60] …”

Section: Resultsmentioning

confidence: 96%

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S

et al. 2022

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Intrinsically low lattice thermal conductivity (k lat ) while maintaining the high carrier mobility (μ) is of the utmost importance for thermoelectrics. Topological insulators (TI) can possess high μ due to the metallic surface states. TIs with heavy constituents and layered structure can give rise to high anharmonicity and are expected to show low k lat .Here, we demonstrate that Bi 1.1 Sb 0.9 Te 2 S (BSTS), which is a 3D bulk TI, exhibits ultra-low k lat of 0.46 Wm À 1 K À 1 along with high μ of � 401 cm 2 V À 1 s À 1 . Sound velocity measurements and theoretical calculations suggest that chemical bonding hierarchy and high anharmonicity play a crucial role behind such ultra-low k lat . BSTS possesses low energy optical phonons which strongly couple with the heat carrying acoustic phonons leading to ultra-low k lat . Further, Cl has been doped at the S site of BSTS which increases the electron concentration and reduces the k lat resulting in a promising ntype thermoelectric figure of merit (zT) of � 0.6 at 573 K.

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“…Previously, anomalous phonon softening behaviour has been observed in Sn doped BSTS by IR spectroscopy. [60] Figure 4a shows the phonon dispersion of BSTS along with the atom projected density of states (PhDOS), where the first three low-frequency phonon modes are acoustic branches shown in magenta, blue, red, and lowest lying optical (LLO) phonon branch is shown by orange color curves. Remaining optical branches are shown in black.…”

Section: Resultsmentioning

confidence: 99%

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S

et al. 2022

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Anomalous phonon softening in the topological insulator Sn-doped Bi1.1Sb0.9Te2S

Cited by 5 publications

References 29 publications

Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S

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Anomalous phonon softening in the topological insulator Sn-doped Bi1.1Sb0.9Te2S

Cited by 5 publications

References 29 publications

Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Physical, Psycho-social and Economic Burden of Chronic Obstructive Pulmonary Disease: A Hospital-Based Study in Kolkata, West Bengal, India

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi1.1Sb0.9Te2S

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi1.1Sb0.9Te2S

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Product

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Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi_1.1Sb_0.9Te₂S