Papers by Candice Forrester
arXiv (Cornell University), Dec 12, 2021
Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physic... more Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physical phenomena such as quantum anomalous Hall effect and intrinsic axion insulator state, both potentially important for the implementation in topological spintronics and error-free quantum computing. In the bulk, the materials are antiferromagnetic but appropriate stacking with non-magnetic layers or excess Mn in the crystal lattice can induce a net ferromagnetic alignment. In this work we report the growth of (Sb2Te3)x(MnSb2Te4)y layers with varying Mn content by molecular beam epitaxy. The Mn flux fraction provided during growth controls the percent of MnSb2Te4 that is formed in the resulting layers by a self-assembly process. Highly crystalline layers with compositions varying between Sb2Te3 (y=0) and MnSb2Te4 (x=0) were obtained. The results show that Mn incorporates as a structural component to form MnSb2Te4, and as an impurity element both in Sb2Te3 and in MnSb2Te4. Two modifications of the growth conditions were implemented to enhance the incorporation of Mn as a structural element to form MnSb2Te4. Annealing of a thin portion of the layer at the beginning of growth (pre-anneal step), and increasing the growth temperature, both result in a larger percent of MnSb2Te4 for similar Mn flux fractions during growth. Samples having at least a few percent of MnSb2Te4 layers exhibit ferromagnetic behavior likely due to the excess Mn in the system which stabilizes on Sb sites as MnSb antisite defects. Introduction: Incorporation of magnetic elements into 3D topological insulators (TIs) such as Bi2Te3 and Sb2Te3 has garnered a great deal of interest in recent years due to the potential to achieve
Physica Status Solidi B-basic Solid State Physics, Aug 28, 2017
We report on the growth and characterization of optical quality multiple quantum well structures ... more We report on the growth and characterization of optical quality multiple quantum well structures of Zn x Cd 1-x Se/Zn x Cd y Mg 1-x-y Se on an ultra-thin Bi 2 Se 3 /CdTe virtual substrate on c-plane Al 2 O 3 (sapphire). Excellent quality highly oriented films grown along the (111) direction were achieved as evidenced by reflection high energy electron diffraction and X-ray diffraction studies. We also observed room temperature and 77 K photoluminescence emission with peak energies at 77 K of 2.407 eV and linewidths of 56 meV comparable to those achieved on structures grown on InP. Exfoliation of the structures is also possible due to the van der Waals bonding of Bi 2 Se 3. Exfoliated (substrate free) films exhibit photoluminescence emission nearly identical to that of the supported film. Additionally, contactless electroreflectance measurements show good agreement with simulations of the multiple quantum well structure as well as evidence of excited state levels.
Scientific Reports
Magnetic topological materials are promising for realizing novel quantum physical phenomena. Amon... more Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb2Te4 is ferromagnetic due to MnSb antisites and has relatively high Curie temperatures (TC), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb2Te3)1−x(MnSb2Te4)x, where x varies between 0 and 1. Here we report on their magnetic and transport properties. We show that the samples are divided into three groups based on the value of x (or the percent septuple layers within the crystals) and their corresponding TC values. Samples that contain x < 0.7 or x > 0.9 have a single TC value of 15–20 K and 20–30 K, respectively, while samples with 0.7 < x < 0.8 exhibit two TC values, one (TC1) at ~ 25 K and the second (TC2) reaching values above 80 K, almost twice as high as any reported value to date for these types of materials. Structural analysis shows that samples with 0.7 < x <...
arXiv (Cornell University), Feb 21, 2023
Three-dimensional topological insulators (3D-TIs) are a new generation of materials with insulati... more Three-dimensional topological insulators (3D-TIs) are a new generation of materials with insulating bulk and exotic metallic surface states that facilitate a wide variety of groundbreaking applications. However, utilization of the surface channels is often hampered by the presence of crystal defects, such as antisites, vacancies and twin domains. For terahertz device applications, twinning is shown to be highly deleterious. Previous attempts to reduce twins using technologically important InP(111) substrates have been promising, but have failed to completely suppress twin domains while preserving high structural quality. Here we report growth of twin-free molecular beam epitaxial Bi2Se3 and Sb2Te3 structures on ultrathin In2Se3 layers formed by a novel selenium passivation technique during the oxide desorption of smooth, non-vicinal InP(111)B substrates, without the use of an indium source. The formation of un-twinned In2Se3 provides a favorable template to fully suppress twin domains in 3D-TIs, greatly broadening novel device applications in the terahertz regime.
Research Square (Research Square), Jan 4, 2023
Magnetic topological materials are promising for realizing novel quantum physical phenomena. Amon... more Magnetic topological materials are promising for realizing novel quantum physical phenomena. Among these, bulk Mn-rich MnSb 2 Te 4 is ferromagnetic due to Mn Sb antisites and has relatively high Curie temperatures (T C), which is attractive for technological applications. We have previously reported the growth of materials with the formula (Sb 2 Te 3) 1−x (MnSb 2 Te 4) x. Here we report their magnetic and transport properties. We show that the samples are divided into three groups based on the percent septuple layers (SLs) within the crystals and their corresponding T C values. Samples that contain less than 70% or more than 90% SLs have a single T C value of 15-20K and 30-40K, respectively, while samples with between 70-80% SLs exhibit two T C values, one at ~ 30-40K and the second (T C2) reaching values above 80K, almost twice as high as any reported value to date for these type of materials. Structural analysis shows that samples with 70-80% SLs have large regions of only SLs, which should give rise to a T C of ~ 30-40K, while other regions have isolated QLs embedded within the SL lattice. We propose that the latter regions are responsible for the higher T C2 values. Our results have important implications for the design of magnetic topological materials having optimum properties.
Bulletin of the American Physical Society, Mar 18, 2021
physica status solidi (b), 2017
We report on the growth and characterization of optical quality multiple quantum well structures ... more We report on the growth and characterization of optical quality multiple quantum well structures of ZnxCd1−xSe/ZnxCdyMg1−x−ySe on an ultra‐thin Bi2Se3/CdTe virtual substrate on c‐plane Al2O3 (sapphire). Excellent quality highly oriented films grown along the (111) direction were achieved as evidenced by reflection high energy electron diffraction and X‐ray diffraction studies. We also observed room temperature and 77 K photoluminescence emission with peak energies at 77 K of 2.407 eV and linewidths of 56 meV comparable to those achieved on structures grown on InP. Exfoliation of the structures is also possible due to the van der Waals bonding of Bi2Se3. Exfoliated (substrate free) films exhibit photoluminescence emission nearly identical to that of the supported film. Additionally, contactless electroreflectance measurements show good agreement with simulations of the multiple quantum well structure as well as evidence of excited state levels. These results open new avenues of resea...
Crystal Growth & Design, 2022
Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physic... more Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physical phenomena such as quantum anomalous Hall effect and intrinsic axion insulator state, both potentially important for the implementation in topological spintronics and error-free quantum computing. In the bulk, the materials are antiferromagnetic but appropriate stacking with non-magnetic layers or excess Mn in the crystal lattice can induce a net ferromagnetic alignment. In this work we report the growth of (Sb2Te3)x(MnSb2Te4)y layers with varying Mn content by molecular beam epitaxy. The Mn flux fraction provided during growth controls the percent of MnSb2Te4 that is formed in the resulting layers by a self-assembly process. Highly crystalline layers with compositions varying between Sb2Te3 (y=0) and MnSb2Te4 (x=0) were obtained. The results show that Mn incorporates as a structural component to form MnSb2Te4, and as an impurity element both in Sb2Te3 and in MnSb2Te4. Two modifications of the growth conditions were implemented to enhance the incorporation of Mn as a structural element to form MnSb2Te4. Annealing of a thin portion of the layer at the beginning of growth (pre-anneal step), and increasing the growth temperature, both result in a larger percent of MnSb2Te4 for similar Mn flux fractions during growth. Samples having at least a few percent of MnSb2Te4 layers exhibit ferromagnetic behavior likely due to the excess Mn in the system which stabilizes on Sb sites as MnSb antisite defects. Introduction: Incorporation of magnetic elements into 3D topological insulators (TIs) such as Bi2Te3 and Sb2Te3 has garnered a great deal of interest in recent years due to the potential to achieve
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Papers by Candice Forrester