Hikami Larkin Nagaoka Research Articles

Large magnetoresistance and de Haas–van Alphen oscillations in NbNiTe5 originated from nontrivial band topology

Quasi-one-dimensional topological materials have emerged as a captivating area of research due to their interesting electronic properties and potential applications. NbNiTe5 is one such quasi-1D material. In this work, we report the synthesis, structural characterization, and comprehensive investigation of the electrical transport and magnetic properties of NbNiTe5. NbNiTe5 crystallizes in the orthorhombic crystal system with the Cmcm space group. Experimental studies have uncovered metallic nature with a remarkably high residual resistivity ratio of 103, along with intriguing spin–orbit interaction-driven nonsaturating magnetotransport properties at low temperatures. A meticulous analysis incorporating magnetoconductivity measurements unveils signatures of weak anti-localization analyzed by using the Hikami–Larkin–Nagaoka formula. Furthermore, the de Haas–van Alphen oscillations demonstrate the high mobility of charge carriers with a significantly low effective mass at five frequencies: Fα=84.82 T, Fβ=131.21 T, Fγ=242.36 T, Fδ=31.93 T, and Fδ′=162.33 T. In light of these collective findings, NbNiTe5 can be defined as a quasi-1D topological semimetal.

Structural and electronic transport properties of Zn- and Ga-doped Bi2− x Sb x Te3− y Se y topological insulator single crystals

A comprehensive study of structural and magnetotransport properties of pristine Bi2−x Sb x Te3−y Se y (BSTS) single crystals and doped with Zn (BSTS:Zn) and Ga (BSTS:Ga) are presented here. Magnetic field dependent Hall resistivities of the single crystals indicate that the holes are the majority carriers. The field dependent resistivity curves at different temperatures of the crystals display cusp-like characteristics at low magnetic fields, attributed to two-dimensional (2D) weak antilocalization (WAL) effect. We fit the observed low-field WAL effects at low temperatures using 2D and three-dimensional (3D) Hikami-Larkin-Nagaoka (HLN) equations. The 2D HLN equation fits the data more closely than the 3D HLN equation, indicating a 2D nature. The 2D HLN equation fit to the low field WAL effects at various temperatures reveal a phase coherence length (l φ) that decreases as temperature increases. The variation of l φ with temperature follows T −0.41 power law for BSTS:Zn, suggesting that the dominant dephasing mechanism is a 2D electron–electron (e−e) interactions. For pristine BSTS and BSTS:Ga, l φ(T) is described by considering a coexistence of 2D e−e and electron–phonon (e−p) interactions in the single crystals. The temperature variation of the longitudinal resistance in BSTS:Ga is described by 3D Mott variable range hoping model. In contrast, the transport mechanisms of both pristine BSTS and BSTS:Zn are described by a combination of 2D WAL/EEI models and 3D WAL.

Charge transport in n-type As- and Sb-hyperdoped Ge

This paper presents a systematic study of the charge transport behavior of heavily doped n-type Ge layers with As and Sb. A nonequilibrium method ion implantation followed by milliseconds flash lamp annealing is applied to synthesize the n++ Ge layers (Ge:As and Ge:Sb). The resulting materials contain free electrons with a density above 3 × 1019 cm−3 and mobility more than 220 cm2/(V s). Quantum corrections to the conductance in a magnetic field are observed at low temperatures. Weak localization persists up to 30 K in Ge:Sb, while only up to 10 K in Ge:As. Using the Hikami–Larkin–Nagaoka model to fit the magnetoconductance data, we obtain the phase coherence length lϕ of the hyperdoped Ge samples in the range of 70–163 nm. This study may pave a way to explore possible applications for quantum technologies utilizing As- and Sb-hyperdoped Ge.

Probing surface states: A study of UCF and WAL in Bi1.9Sb0.1Te2Se topological insulator

In the exploration of three-dimensional quaternary topological insulators, understanding surface states has become pivotal for unraveling the underlying physics and tapping into potential applications. Our study delves into the temperature and magnetic field-angle dependence of universal conductance fluctuations (UCF) and weak anti-localization (WAL) effects in a Bi1.9Sb0.1Te2Se topological insulator-based mesoscopic device. Conventionally, other low-temperature transport phenomena in probing surface states may inevitably face interference from three-dimensional bulk conductance. However, we experimentally demonstrate that, at low temperatures, UCF reflects the properties of two-dimensional topological surface states more accurately, thereby providing a more reliable and distinct way to confirm their existence. Moreover, we carefully analyze the temperature-dependent WAL using the Hikami–Larkin–Nagaoka model, proposing a crucial role for charge puddles associated with electrostatic fluctuations in the electron dephasing process. Our findings not only emphasize the key role of UCF in unveiling the underlying behavior of topological surface states but also offer a deeper understanding of phase-coherent transport in quaternary topological insulators.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

Intrinsic magnetic topological insulators (MTIs) host exotic topological phases such as quantized anomalous Hall insulating phase, arising due to the large magnetic exchange gap. However, the interplay of magnetism and topology in these systems in different temperature regimes remains elusive. In this work, we present the logarithmic temperature-dependence of conductivity for sub-100 nm thick exfoliated flakes of MTI MnBi2Te4 in the presence of out-of-plane magnetic fields and extracted the linear slope, κ. We observed a characteristic change, in the low-temperature regime, indicating the gapped Dirac surface state according to Lu–Shen theory. We also report the recovery of topological properties in the system via the weak-antilocalization effect in the vicinity of antiferromagnetic to paramagnetic transition and in the paramagnetic regime. Hikami–Larkin–Nagaoka analysis suggested the presence of topological surface states. Therefore, our study helps in understanding how intrinsic magnetism masks topological properties in an MTI as long as magnetic ordering persists.

Synthesis and characterization of half-Heusler ScPtBi films via three-source magnetron co-sputtering on Nb superconductor buffer layer

The half-Heusler compounds exhibit simultaneous electrical, optical, and magnetic properties hence extensive research efforts have recently been dedicated to their development in diverse applications. Herein, we detail the fabrication and magnetic characterization of thin film ScPtBi was grown at 300 °C on Nb-buffered Si (100) single crystals (Nb/Si (100)) by using magnetron co-sputtering. X-ray diffraction examinations have unveiled the polycrystalline growth nature of the films. It is seen that the obtained ScPtBi thin film is strained by 1.4% compared to the single crystal of ScPtBi. The morphological observations, conducted by scanning electron microscopy (SEM), revealed that the Nb buffer layer has a smooth and crack-free surface. Moreover, it has been observed that the Bi islands are formed on the surface of ScPtBi film, which is confirmed by the high-resolution scanning transmission electron microscopy (HR-STEM) analyses. The presence of the weak antilocalization (WAL) effect has been observed in the samples. The Hikami-Larkin-Nagaoka (HLN) equation was used to analyze experimental data, aiming to calculate the phase coherence length (lφ) and the coefficient α. As the temperature increased, the phase coherence length decreased from 39 nm to 24 nm. The coefficient α was determined to be in the range of 500 to 1100. As a result, it has been concluded that the presence of the WAL effect might be connected to the strong spin-orbit coupling (SOC) nature of the films instead of from topologically protected surface states.

Topological transport properties of highly oriented Bi2Te3 thin film deposited by sputtering

Topological insulators (TIs) are the promising materials for next-generation technology due to their exotic features such as spin momentum locking, conducting surface states, etc. However, the high-quality growth of TIs by sputtering technique, which is one of the foremost industrial requirements, is extremely challenging. Also, the demonstration of simple investigation protocols to characterize topological properties of TIs using electron-transport methods is highly desirable. Here, we report the quantitative investigation of non-trivial parameters employing magnetotransport measurements on a prototypical highly textured Bi2Te3 TI thin film prepared by sputtering. Through the systematic analyses of the temperature and magnetic field dependent resistivity, all topological parameters associated with TIs, such as coherency factor , Berry phase (), mass term (m), the dephasing parameter (p), slope of temperature dependent conductivity correction () and the surface state penetration depth (λ) are estimated by using the modified ‘Hikami–Larkin–Nagaoka’, ‘Lu–Shen’ and ‘Altshuler–Aronov’ models. The obtained values of topological parameters are well comparable to those reported on molecular beam epitaxy grown TIs. The epitaxial growth of Bi2Te3 film using sputtering, and investigation of the non-trivial topological states from its electron-transport behavior are important for their fundamental understanding and technological applications.

Enhanced quantum oscillations and scattering effect in quaternary InAlGaN/GaN two-dimensional electron gas

Quantum transport properties of a large bandgap In0.15Al0.79Ga0.06N/GaN quaternary GaN high electron mobility transistor (HEMT) heterostructure are studied at low temperatures up to 2 K. Herein, we report the first evidence of weak localization in a quaternary GaN two-dimensional electron gas (2DEG) system. We observe negative magnetoresistance behavior and extracted dephasing time (τΦ) using a Hikami–Larkin–Nagaoka model at 2.2 K. Linear dependency of dephasing rate with temperature (τΦ−1∝T) is established below 20 K. Furthermore, Shubnikov–de Haas quantum oscillation induced by 2DEG is observed using perpendicular magnetic (B⊥) field strengths up to 14 T. From the temperature-dependent oscillation amplitude, we extracted an effective mass m*≈0.237me. The dominance of small-angle scattering in the 2DEG channel is identified from less than unit ratio (τq/τt≪1) of quantum lifetime (τq) to the Hall transport lifetime (τt). In our study, we have demonstrated that the In0.15Al0.79Ga0.06N/GaN quaternary heterostructure possesses high dephasing time (τΦ=5.4 ps) and larger quantum lifetime (τq=0.102 ps) indicating better suitability and a way forward to high-power–high-frequency GaN HEMT development.

Weak antilocalization and topological edge states in PdSn4

Here, we report a successful synthesis of single crystals of a topological semimetal (TSM) candidate, PdSn4, using a self-flux route. The synthesized crystal is well characterized through x-ray diffraction (XRD), field emission scanning electron microscopy, and x-ray photoelectron spectroscopy. A detailed Rietveld analysis of the powder XRD pattern of PdSn4 confirmed the same to crystallize in an Aea2 space group instead of reported Ccce. A large magnetoresistance (MR) along with Shubnikov–de Haas (SdH) oscillations have been observed in magneto-transport measurements at 2 K. The presence of weak antilocalization (WAL) effect in the synthesized PdSn4 crystal is confirmed and analyzed using Hikami Larkin Nagaoka formalism, being applied on magnetoconductivity of the same at a low magnetic field. An extended Kohler's rule is implemented on MR data to determine the role of scattering processes and temperature-dependent carrier density on the transport phenomenon in PdSn4. Furthermore, the non-trivial band topology and the presence of edge states are shown through density functional theory-based theoretical calculations. All calculations are performed considering the Aea2 space group symmetry. The calculated Z2 invariants (0; 0 1 0) suggest the presence of weak topological insulating properties in PdSn4. A clear evidence of topological edge states at Γ point is visible in calculated edge states spectra. This is the first report on PdSn4, showing the presence of SdH oscillation in magneto-transport measurements. Also, the presence of a weak insulating phase in PdSn4 is described for the first time on the basis of calculated Z2 invariants.

Concurrent weak localization and double Schottky barrier across a grain boundary in bicrystal SrTiO3

Stoichiometric ${\mathrm{SrTiO}}_{3}$ (STO) is a wide band-gap insulator in which oxygen deficiency generates a low-temperature metallic ferromagnetic state. Here, we report weak ferromagnetic-like and metallic transport in oxygen-deficient bicrystal of $\mathrm{STO}$ with a low-temperature electron mobility and surface carrier density of $2800\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and $3.500\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$, respectively. Moreover, we show that magnetotransport behavior in the bulk and across the grain boundary (GB) in $\mathrm{STO}$ single crystals are significantly different. In the bulk, our magnetotransport results agree with those reported in the literature. Importantly, low-temperature magnetotransport across the GB shows a disorder-induced metal-insulator transition, and it is modeled as a quasi--two-dimensional system below 10 K that accounts for weak localization (WL), supported by electron-electron, electron-phonon, and Hikami-Larkin-Nagaoka (HLN) quantum interference models. The HLN model accounts for realistic length scales: the dephasing length ${L}_{\ensuremath{\phi}}$, and the spin-orbit (SO) scattering length ${L}_{\mathrm{SO}}$, which are comparable to the electron mean-free path, resembling the surface-conducting nature across the GB. Our experimental work shows the importance of structural defects in the interpretation of magnetotransport in ${\mathrm{SrTiO}}_{3}$ and shows that WL is concurrent with a double Schottky barrier at the GB interface.

Density-Dependence of Surface Transport in Tellurium-Enriched Nanograined Bulk Bi2 Te3.

Three-dimensional topological insulators (3D TI) exhibit conventional parabolic bulk bands and protected Dirac surface states. A thorough investigation of the different transport channels provided by the bulk and surface carriers using macroscopic samples may provide a path toward accessing superior surface transport properties. Bi2 Te3 materials make promising 3D TI models; however, due to their complicated defect chemistry, these materials have a high number of charge carriers in the bulk that dominate the transport, even as nanograined structures. To partially control the bulk charge carrier density, herein the synthesis of Te-enriched Bi2 Te3 nanoparticles is reported. The resulting nanoparticles are compacted into nanograined pellets of varying porosity to tailor the surface-to-volume ratio, thereby emphasizing the surface transport channels. The nanograined pellets are characterized by a combination of resistivity, Hall- and magneto-conductance measurements together with (THz) time-domain reflectivity measurements. Using the Hikami-Larkin-Nagaoka (HLN) model, a characteristic coherence length of ≈200 nm is reported that is considerably larger than the diameter of the nanograins. The different contributions from the bulk and surface carriers are disentangled by THz spectroscopy, thus emphasizing the dominant role of the surface carriers. The results strongly suggest that the surface transport carriers have overcome the hindrance imposed by nanoparticle boundaries.

Weak antilocalization and ferromagnetism in magnetic Weyl semimetal Co3Sn2S2

Here, we report the synthesis of single crystalline magnetic Weyl semimetal Co3Sn2S2. The synthesized crystal is characterized through various tools, viz. x-ray diffraction, field emission electron microscopy, and x-ray photoelectron spectroscopy. A clear ferromagnetic transition is observed in magnetization and heat capacity at around 175 K, which is further verified through electrical transport measurements. Hysteresis is observed in ρ–T measurements in a cooling and a warming cycle, showing the presence of the first order phase transition and charge ordering in the synthesized sample. Synthesized Co3Sn2S2 exhibits a high magnetoresistance of around 230% at 2 K. The transport phenomenon in synthesized Co3Sn2S2 appears to have contributions from topological surface states at low temperature below, say, 70 K, and above that, the same is found to be strongly dependent on its bulk magnetic state. Magnetoconductivity data at low fields of up to ±1 T (Tesla) are fitted with the Hikami Larkin Nagaoka model, which shows the presence of a weak antilocalization (WAL) effect in the synthesized Co3Sn2S2 crystal at low temperatures below 30 K. Angle dependent magnetotransport measurements confirm that the observed WAL is the topological surface state dominated phenomenon.

Detailed structural and topological analysis of SnBi2Te4 single crystal

We report herein the successful synthesis of the topological material SnBi2Te4 in single-crystal form. Phase purity and unidirectional growth are evident from X-ray diffraction (XRD) patterns acquired from a powdered sample and a crystal flake. The crystalline morphology has also been visualized by acquiring a field-emission scanning electron microscope (FESEM) image. The crystal has been thoroughly characterized by means of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. The topological properties of SnBi2Te4 have been probed through magneto-transport measurements. SnBi2Te4 has been found to exhibit a small but non-saturating magneto-resistance (MR) up to ±12 T. The low-field magnetoconductivity (MC) of SnBi2Te4 at 2 K can be well explained through the Hikami–Larkin–Nagaoka (HLN) formalism, which confirms the presence of a weak anti-localization (WAL) effect in its crystal. Moreover, the non-trivial topological character has been evidenced through first-principles calculations using density functional theory (DFT), with and without spin-orbit coupling (SOC) protocols. A significant change in the bulk electronic band structure is observed upon the inclusion of SOC parameters, signifying topological properties of SnBi2Te4. Its topological non-trivial character has also been verified through calculation of Z2 invariants and the surface states spectrum in the (111) plane.

Investigation of structural and magneto-transport properties of PdTe2 single crystals

The growth and structural analysis of topological semimetal (TSM) PdTe2 were carried out in this study. The self-flux method was employed to grow the single crystals which were structurally characterized by XRD, SEM and EDAX, while the vibrational modes were observed by Raman spectroscopy. Further, the transport properties of the grown crystal are also investigated, which show the presence of the weak anti-localization effect. The low-field (≈1 Tesla) magnetoconductivity is studied by Hikami–Larkin–Nagaoka (HLN) model, and the physical parameters are extracted. Further, a quadratic term and a linear term in applied field were added in HLN model, which are accounted for quantum and classical contributions in conduction mechanism. The modified HLN model was used to study magneto-conductivity in entire field range and at temperature from 2 to 100 K. This study not only confirmed the growth of single crystal PdTe2, but also verified the presence of topological surface states (TSS) through the HLN analysis of magneto-transport measurements.

Probing the topological surface states in superconducting Sn4Au single crystal: a magneto transport study

Materials exhibiting bulk superconductivity along with magnetoresistance (MR) in their normal state have emerged as suitable candidates for topological superconductivity. In this article, we report a flux free method to synthesize single crystal of topological superconductor candidate Sn4Au. The phase purity and single crystalline nature are confirmed through various characterizations viz. x-ray diffraction, field emission scanning electron microscopy, selected area electron diffraction, and transmission electron microscopy. Chemical states of the constituent element viz. Sn and Au are analysed through x-ray photoelectron spectroscopy. Superconductivity in synthesized Sn4Au single crystal is evident form ρ-T plot, for which the critical field (H c) is determined through ρ-H plot at 2 K i.e. just below critical temperature T c. A positive MR is observed in ρ-H measurements at different temperatures above T c, viz. at 3 K, 5 K, 10 K and 20 K. Further, the magnetoconductivity (MC) is analysed by using Hikami–Larkin–Nagaoka formalism, which signifies the presence of weak antilocalization (WAL) effect in Sn4Au. Angle dependent magneto-transport measurement has been performed to detect the origin of observed WAL effect in Sn4Au single crystal. Normalized MC vs Hcosθ plot shows presence of topological surface states in the studied system. It is evident that Sn4Au is a 2.6 K topological superconductor.

Thickness-dependent magneto-transport of Bi2Se3/SiO2 topological insulator thin films

Topological insulators are immensely investigated for their surface states related properties as these materials can be used for various spintronics, quantum computing, and optoelectronics applications. In this perspective, different thicknesses of bismuth selenide thin films are deposited on the 250 nm SiO2 substrate with the help of thermal deposition. The motive of this study is to investigate the surface and bulk-related behaviour with different thicknesses. The deposited films are characterized through GI-XRD (grazing incidence X-ray diffractometer) and Raman spectroscopy, which ensure the impurity-less deposition. Further, the transport properties are investigated, using Hikami–Larkin–Nagaoka (HLN) model in low field regime (up to 1 Tesla). Also, a quadratic term in field and a constant term added in HLN model to investigate the occurrence of quantum scattering and defects in thin films and this shows thickness dependence of weak anti-localization effect (WAL) in the present Bi2Se3/SiO2 thin films.

Sn2Pd: a possible superconducting material with topological surface states

In this article, we report the detailed magneto transport measurements of topological semimetal candidate, Sn2Pd. Single crystal of Sn2Pd is synthesized through self-flux method. Phase purity and crystalline morphology are confirmed through powder x-ray diffraction pattern and field emission scanning electron microscopy image. Signatures of superconducting transition are seen in both transport and magneto transport measurements, which are further supported by the AC magnetization studies. Sn2Pd is found to show superconductivity onset at below 2.8 K, but not the zero resistivity down to 2 K. Although, isothermal magneto resistivity measurements below superconducting onset (2.8 K) clearly exhibited superconductor like behavior, but is not observed in heat capacity measurements, indicating the same to be of weak nature. Magneto transport measurements performed in normal state of Sn2Pd show the presence of weak antilocalization effect, which is confirmed by modelling of low field magneto-conductivity through Hikami Larkin Nagaoka formalism. Here, it is worth mentioning that the present article is the first report on magneto transport measurements of Sn2Pd, which show the same to be a topological material with weak superconducting phase below around 2.8 K.

Electron transport properties of a narrow-bandgap semiconductor Bi2O2Te nanosheet

A thin, narrow-bandgap semiconductor Bi2O2Te nanosheet is obtained via mechanical exfoliation, and a Hall-bar device is fabricated from it on a heavily doped Si/SiO2 substrate and studied at low temperatures. Gate transfer characteristic measurements show that the transport carriers in the nanosheet are of n-type. The carrier density, mobility, and mean free path in the nanosheet are determined by measurements of the Hall resistance and the longitudinal resistance of the Hall-bar device, and it is found that the electron transport in the nanosheet is in a quasi-two-dimensional (2D), strongly disordered regime. Magnetotransport measurements for the device at magnetic fields applied perpendicular to the nanosheet plane show dominantly weak antilocalization (WAL) characteristics at low fields and a linear magnetoresistance (LMR) behavior at high fields. We attribute the WAL characteristics to strong spin–orbit interaction (SOI) and the LMR to the classical origin of strong disorder in the nanosheet. Low-field magnetoconductivity measurements are also performed and are analyzed based on the multi-channel Hikami–Larkin–Nagaoka theory with the LMR correction being taken into account. The phase coherence length, spin relaxation length, effective 2D conduction channel number, and coefficient in the linear term due to the LMR in the nanosheet are extracted. It is found that the spin relaxation length in the Bi2O2Te nanosheet is several times smaller than that in its counterpart Bi2O2Se nanosheet, and thus, an ultra-strong SOI is present in the Bi2O2Te nanosheet. Our results reported in this study would greatly encourage further studies and applications of this emerging narrow-bandgap semiconductor 2D material.

Weak Antilocalization in Polycrystalline SnTe Films Deposited by Magnetron Sputtering

Previous works on weak antilocalization (WAL) of SnTe were mostly carried out in MBE-grown films, where the signals of WAL usually coexist with a large parabolic background of classical magnetoresistance. In this article, we present our study on WAL in polycrystalline SnTe films deposited by magnetron sputtering. Due to the polycrystalline nature and the relatively low mobility of the films, the background of conventional magnetoresistance was greatly suppressed, and clean WAL signals, which are well described by the Hikami–Larkin–Nagaoka equation, were obtained at low temperatures. A close analysis of the WAL data shows that the number of transport channels contributing to WAL increases monotonously with decreasing temperatures, reaching N=2.8 at T=1.6 K in one of the devices, which indicates the decoupling of Dirac cones at low temperatures. Meanwhile, as the temperature decreases, the temperature dependence of phase coherence length gradually changes from lϕ∼T−1 to lϕ∼T−0.5, suggesting that the dominant mechanism of phase decoherence switches from electron–phonon scattering to electron–electron scattering. Our results are helpful for understanding the quantum transport properties of SnTe.

Weak antilocalization effect and multi-channel transport in SnTe quantum well

Magnetoresistance measurements were performed on a 30 nm-thick SnTe quantum well (QW) grown by molecular beam epitaxy on the BaF2 substrate in the temperature range of 1.9–50 K. The weak antilocalization (WAL) effect was observed at low temperatures and low magnetic fields as a result of the strong spin–orbit coupling present in the QW. Using the Hikami–Larkin–Nagaoka equation, we analyzed the experimental data and found that the WAL effect is not purely 2D but composed of 2D and 3D channels that exist within the QW structure. The spin–orbit and phase coherence mechanisms are also extracted, and a general view of the transport properties of the QW is also provided.