Browse
Submit Data
Databases
API
Help

Dataset Information

32 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Systematic Study of Ferromagnetism in Cr_xSb_2-xTe₃ Topological Insulator Thin Films using Electrical and Optical Techniques.

ABSTRACT: Ferromagnetic ordering in a topological insulator can break time-reversal symmetry, realizing dissipationless electronic states in the absence of a magnetic field. The control of the magnetic state is of great importance for future device applications. We provide a detailed systematic study of the magnetic state in highly doped Cr_xSb_2-xTe₃ thin films using electrical transport, magneto-optic Kerr effect measurements and terahertz time domain spectroscopy, and also report an efficient electric gating of ferromagnetic order using the electrolyte ionic liquid [DEME][TFSI]. Upon increasing the Cr concentration from x = 0.15 to 0.76, the Curie temperature (T_c) was observed to increase by ~5 times to 176 K. In addition, it was possible to modify the magnetic moment by up to 50% with a gate bias variation of just ±3 V, which corresponds to an increase in carrier density by 50%. Further analysis on a sample with x = 0.76 exhibits a clear insulator-metal transition at T_c, indicating the consistency between the electrical and optical measurements. The direct correlation obtained between the carrier density and ferromagnetism - in both electrostatic and chemical doping - using optical and electrical means strongly suggests a carrier-mediated Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling scenario. Our low-voltage means of manipulating ferromagnetism, and consistency in optical and electrical measurements provides a way to realize exotic quantum states for spintronic and low energy magneto-electronic device applications.

SUBMITTER: Singh A

PROVIDER: S-EPMC6242999 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Similar Datasets

Topological delocalization and tuning of surface channel separation in Bi2Se2Te Topological Insulator Thin films.

Project description:The surface states of a 3D topological insulator (TI) exhibit topological protection against backscattering. However, the contribution of bulk electrons to the transport data is an impediment to the topological protection of surface states. We report the tuning of the chemical potential in the bulk in Bi2Se2Te TI thin films, pinning it near the center of the bulk band gap, thereby suppressing the bulk carriers. The temperature dependent resistance of these films show activated behavior down to 50?K, followed by a metallic transition at lower temperatures, a hallmark of robustness of TI surface states. Manifestation of topological protection and surface dominated transport is explained by 2D weak antilocalization phenomenon. We further explore the effect of surface to bulk coupling in TI in this work, which is captured by the number of effective conducting surface channels that participate in the transport. The presence of a single conducting channel indicates a strong surface to bulk coupling which is detrimental to purely topological transport. We demonstrate the decoupling of topological surface states on opposite surfaces of thin films, thereby suppressing the bulk transport. Our findings provide a deeper understanding of surface to bulk coupling along with topological transport behavior and their respective tunability.

| S-EPMC5501793 | biostudies-literature

Carrier-mediated ferromagnetism in the magnetic topological insulator Cr-doped (Sb,Bi)2Te3.

Project description:Magnetically doped topological insulators, possessing an energy gap created at the Dirac point through time-reversal-symmetry breaking, are predicted to exhibit exotic phenomena including the quantized anomalous Hall effect and a dissipationless transport, which facilitate the development of low-power-consumption devices using electron spins. Although several candidates of magnetically doped topological insulators were demonstrated to show long-range magnetic order, the realization of the quantized anomalous Hall effect is so far restricted to the Cr-doped (Sb,Bi)2Te3 system at extremely low temperature; however, the microscopic origin of its ferromagnetism is poorly understood. Here we present an element-resolved study for Cr-doped (Sb,Bi)2Te3 using X-ray magnetic circular dichroism to unambiguously show that the long-range magnetic order is mediated by the p-hole carriers of the host lattice, and the interaction between the Sb(Te) p and Cr d states is crucial. Our results are important for material engineering in realizing the quantized anomalous Hall effect at higher temperatures.

| S-EPMC4673827 | biostudies-other

Topological quantum phase transitions driven by external electric fields in Sb₂Te₃ thin films.

Project description:Using first-principles calculations, we show that topological quantum phase transitions are driven by external electric fields in thin films of Sb(2)Te(3). The film, as the applied electric field normal to its surface increases, is transformed from a normal insulator to a topological insulator or vice versa depending on the film thickness. We identify the band topology by directly calculating the Z(2) invariant from electronic wave functions. The dispersion of edge states is also found to be consistent with the bulk band topology in view of the bulk-boundary correspondence. We present possible applications of the topological phase transition as an on/off switch of the topologically protected edge states in nano-scale devices.

| S-EPMC3271865 | biostudies-literature

Intrinsic topological insulator Bi(1.5)Sb(0.5)Te(3-x)Se(x) thin crystals.

Project description:The quaternary topological insulator (Bi,Sb)2(Te,Se)3 has demonstrated topological surface states with an insulating bulk. Scientists have identified an optimized composition of Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) with the highest resistivity reported. But the physics that drive to this composition remains unclear. Here we report the crystal structure and the magneto-transport properties of Bi(1.5)Sb(0.5)Te(3-x)Se(x) (BSTS) series. A correlation between the structure and the physical properties has been revealed. We found out that within the rhombohedral structure, the composition with most Te substituting Se has the highest resistivity. On the other hand, segregation of other composition phases will introduce much higher bulk concentration.

| S-EPMC4300459 | biostudies-other

In-plane topological p-n junction in the three-dimensional topological insulator Bi2-xSbxTe3-ySey.

Project description:A topological p-n junction (TPNJ) is an important concept to control spin and charge transport on a surface of three-dimensional topological insulators (3D-TIs). Here we report successful fabrication of such TPNJ on a surface of 3D-TI Bi2-xSbxTe3-ySey thin films and experimental observation of the electrical transport. By tuning the chemical potential of n-type topological Dirac surface of Bi2-xSbxTe3-ySey on its top half by using tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an organic acceptor molecule, a half surface can be converted to p-type with leaving the other half side as the opposite n-type, and consequently TPNJ can be created. By sweeping the back-gate voltage in the field effect transistor structure, the TPNJ was controlled both on the bottom and the top surfaces. A dramatic change in electrical transport observed at the TPNJ on 3D-TI thin films promises novel spin and charge transport of 3D-TIs for future spintronics.

| S-EPMC5155151 | biostudies-literature

Bi1Te1 is a dual topological insulator.

Project description:New three-dimensional (3D) topological phases can emerge in superlattices containing constituents of known two-dimensional topologies. Here we demonstrate that stoichiometric Bi1Te1, which is a natural superlattice of alternating two Bi2Te3 quintuple layers and one Bi bilayer, is a dual 3D topological insulator where a weak topological insulator phase and topological crystalline insulator phase appear simultaneously. By density functional theory, we find indices (0;001) and a non-zero mirror Chern number. We have synthesized Bi1Te1 by molecular beam epitaxy and found evidence for its topological crystalline and weak topological character by spin- and angle-resolved photoemission spectroscopy. The dual topology opens the possibility to gap the differently protected metallic surface states on different surfaces independently by breaking the respective symmetries, for example, by magnetic field on one surface and by strain on another surface.

| S-EPMC5413958 | biostudies-literature

Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films.

Project description:The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi(3+) in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

| S-EPMC4783712 | biostudies-literature

Optical control of spin-polarized photocurrent in topological insulator thin films.

Project description:Dirac electrons in topological insulators (TIs) provide one possible avenue to achieve control of photocurrents and spin currents without the need to apply external fields by utilizing characteristic spin-momentum locking. However, for TI crystals with electrodes it is actually difficult to characterize the net flow of spin-polarized photocurrents because of the coexistence of surface carriers and bulk carriers generated by optical excitations. We demonstrate here that the net flow directions of spin-polarized photocurrents in TI polycrystalline thin films without electrodes can be precisely and intentionally controlled by the polarization of the excitation pulse alone, which is characterized by performing time-domain terahertz (THz) wave measurements and time-resolved magneto-optical Kerr rotation measurements that are non-contact methods. We show that the amplitudes of s-polarized THz waves radiated from photocurrents under right- and left-circularly polarized excitations are inverted relative to one another. Moreover, we observe the inversion of time-resolved magneto-optical Kerr rotation signals between the two excitations. Our results will open the way as innovative methods to control spin-polarized electrons in optoelectronic and spintronic TI devices without the need to apply external fields.

| S-EPMC6193961 | biostudies-literature

Massive Dirac Fermion Observed in Lanthanide-Doped Topological Insulator Thin Films.

Project description:The breaking of time reversal symmetry (TRS) in three-dimensional (3D) topological insulators (TIs), and thus the opening of a 'Dirac-mass gap' in the linearly dispersed Dirac surface state, is a prerequisite for unlocking exotic physical states. Introducing ferromagnetic long-range order by transition metal doping has been shown to break TRS. Here, we present the study of lanthanide (Ln) doped Bi2Te3, where the magnetic doping with high-moment lanthanides promises large energy gaps. Using molecular beam epitaxy, single-crystalline, rhombohedral thin films with Ln concentrations of up to ~35%, substituting on Bi sites, were achieved for Dy, Gd, and Ho doping. Angle-resolved photoemission spectroscopy shows the characteristic Dirac cone for Gd and Ho doping. In contrast, for Dy doping above a critical doping concentration, a gap opening is observed via the decreased spectral intensity at the Dirac point, indicating a topological quantum phase transition persisting up to room-temperature.

| S-EPMC4621505 | biostudies-literature

High performing flexible optoelectronic devices using thin films of topological insulator.

Project description:Topological insulators (TIs) possess exciting nonlinear optical properties due to presence of metallic surface states with the Dirac fermions and are predicted as a promising material for broadspectral phodotection ranging from UV (ultraviolet) to deep IR (infrared) or terahertz range. The recent experimental reports demonstrating nonlinear optical properties are mostly carried out on non-flexible substrates and there is a huge demand for the fabrication of high performing flexible optoelectronic devices using new exotic materials due to their potential applications in wearable devices, communications, sensors, imaging etc. Here first time we integrate the thin films of TIs (Bi2Te3) with the flexible PET (polyethylene terephthalate) substrate and report the strong light absorption properties in these devices. Owing to small band gap material, evolving bulk and gapless surface state conduction, we observe high responsivity and detectivity at NIR (near infrared) wavelengths (39 A/W, 6.1 × 108 Jones for 1064 nm and 58 A/W, 6.1 × 108 Jones for 1550 nm). TIs based flexible devices show that photocurrent is linearly dependent on the incident laser power and applied bias voltage. Devices also show very fast response and decay times. Thus we believe that the superior optoelectronic properties reported here pave the way for making TIs based flexible optoelectronic devices.

| S-EPMC7804467 | biostudies-literature