Localization and interaction effects of epitaxial Bi<sub>2</sub>Se<sub>3</sub> bulk states in two-dimensional limit

Dey, Rik; Roy, Anupam; Pramanik, Tanmoy; Guchhait, Samaresh; Sonde, Sushant; Rai, Amritesh; Register, Leonard F.; Banerjee, S.

doi:10.1063/1.4965861

Cited by 10 publications

(8 citation statements)

References 49 publications

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“…Furthermore, the growth occurs along the c-axis (along (001) direction), as expected for the growth of a hexagonal thin film on an hcp(0001) or fcc(111) substrate. Similar (001)-oriented hexagonal thin film growth on fcc(111) surfaces also has been reported for Cr2Te3(0001), Bi2Te3(0001) and Bi2Se3(0001) on Si(111) substrates [23,49,50]. XRD is used to evaluate the structure of the films and to confirm their epitaxial nature.…”

Section: A Growth and Characterizationssupporting

confidence: 57%

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Roy

Dey

Pramanik

et al. 2020

Phys. Rev. Materials

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Chromium selenide thin films were grown epitaxially on Al2O3(0001) and Si(111)-(7×7) substrates using molecular beam epitaxy (MBE). Sharp streaks in reflection high-energy electron diffraction and triangular structures in scanning tunneling microscopy indicate a flat smooth film growth along the c-axis, and is very similar to that from a hexagonal surface. X-ray diffraction pattern confirms the growth along the c-axis with c-axis lattice constant of 17.39 Å. The grown film is semiconducting, having a small band gap of about 0.034 eV, as calculated from the temperature dependent resistivity. Antiferromagnetic nature of the film with a Néel temperature of about 40 K is estimated from the magnetic exchange bias measurements. A larger out-of-plane exchange bias, along with a smaller in-plane exchange bias is observed below 40 K. Exchange bias training effects are analyzed based on different models and are observed to be following a modified power-law decay behavior. as observed from neutron diffraction studies [6][7][8][9]. Because of Cr vacancies in alternate layers, the moment associated with Cr atoms located on two different layers are different due to different neighboring environment and this leads to the complexity in the magnetic structure below TN.Previously, chromium selenide systems have been studied to investigate their suitability as thermoelectric material for intermediate-temperature applications [10][11][12][13][14], intermediate temperature power generation [13], electrochemical sensors [15], etc. Several groups have studied the structural, magnetic, electrical and thermoelectric properties of single crystal Cr2+xSe3-x compounds grown using solid state reaction method [10][11][12][13]16], soft chemical and hydrothermal synthesis [15,17,18] and chemical vapor transport method [4,14,[19][20][21]. However, the studies focus mostly on the improvement in thermoelectric properties of transition-metal-doped bulk samples of Cr2Se3. The epitaxial growth and different physical properties of Cr2Se3 thin films are yet to be explored in detail. Molecular beam epitaxy (MBE) is a highly specialized technique used to grow ultra-high purity large-area epitaxial thin films with abrupt interfaces and with precise control over their thicknesses. Compared to other growth techniques, MBE offers greater control to incorporate dopants in thin films. This makes it even more suitable growth method, as the electrical, magnetic and thermoelectric properties of this material system can be largely varied with addition of transition-metal/chalcogen dopants [1, 9-13, 21,22].In this work, we report the epitaxial growth of Cr2Se3 thin films under ultra-high vacuum (UHV) directly on Al2O3(0001) and Si(111)-(7×7) surfaces using MBE. Interestingly, we show that the growth occurs along (001) direction (c-axis). We present the details of growth, structural, electrical and magnetic properties characterized by several in situ and ex situ techniques, e.g., reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), scanning...

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Section: A Growth and Characterizationssupporting

confidence: 57%

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Roy

Dey

Pramanik

et al. 2020

Phys. Rev. Materials

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“…Red empty squares correspond to data obtained in our samples. The rest have been taken from literature: Red circles, [13]; blue square, [30]; light green upwards triangle, [31]; cyan left-pointing triangle, [42]; downwards magenta triangles, [54]; right pointing orange triangle, [56]; dark green hexagon, [64]; violet pentagon, [69]; maroon star, [70].…”

Section: Remarks and Conclusionmentioning

confidence: 99%

Omnipresence of Weak Antilocalization (WAL) in Bi2Se3 Thin Films: A Review on Its Origin

et al. 2021

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Topological insulators are materials with time-reversal symmetric states of matter in which an insulating bulk is surrounded by protected Dirac-like edge or surface states. Among topological insulators, Bi2Se3 has attracted special attention due to its simple surface band structure and its relatively large band gap that should enhance the contribution of its surface to transport, which is usually masked by the appearance of defects. In order to avoid this difficulty, several features characteristic of topological insulators in the quantum regime, such as the weak-antilocalization effect, can be explored through magnetotransport experiments carried out on thin films of this material. Here, we review the existing literature on the magnetotransport properties of Bi2Se3 thin films, paying thorough attention to the weak-antilocalization effect, which is omnipresent no matter the film quality. We carefully follow the different situations found in reported experiments, from the most ideal situations, with a strong surface contribution, towards more realistic cases where the bulk contribution dominates. We have compared the transport data found in literature to shed light on the intrinsic properties of Bi2Se3, finding a clear relationship between the mobility and the phase coherence length of the films that could trigger further experiments on transport in topological systems.

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“…The transverse Hall resistance and the longitudinal resistance are measured using Ti/Au contacts deposited on the patterned thin film. and the bulk states are occupied [32][33][34]. The conductivity σ(B) obtained from the longitudinal resistance shows the signature of weak antilocalization (WAL).…”

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confidence: 99%

“…The 2D carrier concentration obtained from the slope of the linear fit is n 2D = 1.4 × 10 14 cm −2 . Such a high electron concentration indicates that both the surface and the bulk states are occupied [32][33][34]. The conductivity σ(B) obtained from the longitudinal resistance shows the signature of weak antilocalization (WAL).…”

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Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

Dey

Roy

Pramanik

et al. 2017

Applied Physics Letters

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We electrically detect charge current induced spin polarization on the surface of molecular beam epitaxy grown Bi2Te3 thin film in a two-terminal device with a ferromagnetic MgO/Fe and a nonmagnetic Ti/Au contact. The two-point resistance, measured in an applied magnetic field, shows a hysteresis tracking the magnetization of the Fe. A theoretical estimate is obtained for the change in resistance on reversing the magnetization direction of Fe from coupled spin-charge transport equations based on quantum kinetic theory. The order of magnitude and the sign of the hysteresis is consistent with spin-polarized surface state of Bi2Te3.The three dimensional (3D) topological insulators (TIs) having insulating bulk and Dirac-type two dimensional (2D) surface states (SSs) with spin-momentum locking have potential for spintronics [1][2][3][4][5][6]. The dispersion relation of the SS guarantees that any charge current flow within these states will induce a non-zero spin accumulation on the 2D surface of a 3D TI. This current induced spin polarization of the SS, controllable by the magnitude and the direction of the current, can be used to torque a ferromagnet (FM) [4,5]. In recent experiments [7][8][9][10][11][12][13][14][15][16][17][18][19], the spin accumulation on the surface of 3D TIs Bi 2 Se 3 , (Bi x Sb 1−x ) 2 Te 3 , Bi 1.5 Sb 0.5 Te 1.7 Se 1.3 , BiSbTeSe 2 , Bi 2 Te 2 Se and Sb 2 Te 3 , mostly grown by molecular beam epitaxy (MBE) or exfoliated, were electrically measured by the voltage probed with FM contact, where the voltage depends on the projection of SS spin polarization onto the FM magnetization direction.In this work, we detect the current induced spin polarization on the surface of an MBE grown Bi 2 Te 3 thin film using Fe contact deposited on the surface and separated by a thin MgO barrier. We also provide a theoretical estimate of the detected spin signal, i.e., the voltage probed with the FM contact. Previously, the voltage drop measured between a FM and a nonmagnetic (NM) contact placed on the surface of a TI was theoretically calculated either using non-equilibrium Green's function [20] or by solving the transport equations derived from Kubo formalism [21]. Here, we provide a different approach for the derivation of the coupled spin-charge transport differential equation based on quantum kinetic theory [22,23] in the diffusive limit. The experimentally measured spin signal matches well with the theory providing evidence for the spin polarized SS in our TI Bi 2 Te 3 thin film.The SSs of TIs are characterized by spin-momentum helically locked constant energy Fermi contour [1][2][3]. However, due to band-bending near the surface, a 2D electron gas (2DEG) can be formed from the quantum confinement of the bulk states in the band-bending potential with Rashba spin splitting arising from the gradient of the confinement potential [19,[24][25][26], and cannot be neglected a priori. Therefore, we obtain coupled spin and charge transport equations for SSs of a TI as well as a Rashba 2DEG. For ease of analysis, we...

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Localization and interaction effects of epitaxial Bi₂Se₃ bulk states in two-dimensional limit

Cited by 10 publications

References 49 publications

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Omnipresence of Weak Antilocalization (WAL) in Bi2Se3 Thin Films: A Review on Its Origin

Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

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Localization and interaction effects of epitaxial Bi2Se3 bulk states in two-dimensional limit

Cited by 10 publications

References 49 publications

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Structural and magnetic properties of molecular beam epitaxy grown chromium selenide thin films

Omnipresence of Weak Antilocalization (WAL) in Bi2Se3 Thin Films: A Review on Its Origin

Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

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Localization and interaction effects of epitaxial Bi₂Se₃ bulk states in two-dimensional limit