Pressure induced topological and topological crystalline insulators

[EN] Research on topological and topological crystalline insulators (TCIs) is one of the most intense and exciting topics due to its fascinating fundamental science and potential technological applications. Pressure (strain) is one potential pathway to induce the non-trivial topological phases in some topologically trivial (normal) insulating or semiconducting materials. In the last ten years, there have been substantial theoretical and experimental efforts from condensed-matter scientists to characterize and understand pressure-induced topological quantum phase transitions (TQPTs). In particular, a promising enhancement of the thermoelectric performance through pressure-induced TQPT has been recently realized; thus evidencing the importance of this subject in society. Since the pressure effect can be mimicked by chemical doping or substitution in many cases, these results have opened a new route to develop more efficient materials for harvesting green energy at ambient conditions. Therefore, a detailed understanding of the mechanism of pressure-induced TQPTs in various classes of materials with spin-orbit interaction is crucial to improve their properties for technological implementations. Hence, this review focuses on the emerging area of pressure-induced TQPTs to provide a comprehensive understanding of this subject from both theoretical and experimental points of view. In particular, it covers the Raman signatures of detecting the topological transitions (under pressure), some of the important pressure-induced topological and TCIs of the various classes of spin-orbit coupling materials, and provide future research directions in this interesting field.V R and C N would like to dedicate this review to Professor C N R Rao who has been a mentor and inspiration for us. V R and C N acknowledge the Department of Science and Technology (DST) and JNCASR, India, for financial support. FJM acknowledges project MALTA Consolider Team network (RED2018-102612-T), financed by MINECO/AEI/10.13039/501100003329, I+D+i project PID2019-106383GB-42 financed by MCIN/AEI/10.13039/501100011033, as well as projects PROMETEO/2018/123 (EFIMAT) and CIPROM/2021/075 (GREENMAT) financed by Generalitat Valenciana. We sincerely thank Professor Umesh V Waghmare, Theoretical Sciences Unit, JNCASR, Professor Kanishka Biswas, New Chemistry Unit, JNCASR, Professor Sebastian C Peter, New Chemistry Unit, JNCASR, and Dr Boby Joseph, Elettra Sincrotrone Trieste, Italy for the active collaboration and fruitful discussion on these topics of interest.Rajaji, V.; Manjón, F.; Narayana, C. (2022). Pressure induced topological and topological crystalline insulators. Journal of Physics Condensed Matter. 34(42):1-16. https://doi.org/10.1088/1361-648X/ac8906116344

Comparison Analysis of Model Predictive Controller with Classical PID Controller For pH Control Process

pH control plays a important role in any chemical plant and process industries. For the past four decades the classical PID controller has been occupied by the industries. Due to the faster computing   technology in the industry demands a tighter advanced control strategy. To fulfill the needs and requirements Model Predictive Control (MPC) is the best among all the advanced control algorithms available in the present scenario. The study and analysis has been done for First Order plus Delay Time (FOPDT) model controlled by Proportional Integral Derivative (PID) and MPC using the Matlab software. This paper explores the capability of the MPC strategy, analyze and compare the control effects with conventional control strategy in pH control. A comparison results between the PID and MPC is plotted using the software. The results clearly show that MPC provide better performance than the classical controller

Pressure induced electronic topological transition in Sb2S3

Pressure induced electronic topological transitions in the wide band gap semiconductor Sb2S3 (Eg = 1.7-1.8 eV) with similar crystal symmetry (SG: Pnma) to its illustrious analog, Sb2Se3, has been studied using Raman spectroscopy, resistivity and the available literature on the x-ray diffraction studies. In this report, the vibrational and the transport properties of Sb2S3 have been studied up to 22 GPa and 11 GPa, respectively. We observed the softening of phonon modes Ag(2), Ag(3) and B2g and a sharp anomaly in their line widths at 4 GPa. The resistivity studies also shows an anomaly around this pressure. The changes in resistivity as well as Raman line widths can be ascribed to the changes in the topology of the Fermi surface which induces the electron-phonon and the strong phonon-phonon coupling, indicating a clear evidence of the electronic topological transition (ETT) in Sb2S3. The pressure dependence of a/c ratio plot obtained from the literature showed a minimum at ~ 5 GPa, which is consistent with our high pressure Raman and resistivity results. Finally, we give the plausible reasons for the non-existence of a non-trivial topological state in Sb2S3 at high pressures.Comment: 24 pages, 6 Figures, 2 tables submitted for publicatio

Switching of the topologically trivial and non-trivial quantum phase transitions in compressed 1T-TiTe2: Experiments and Theory

We report the structural, vibrational and electrical transport properties up to 16 GPa of the 1T-TiTe2, a prominent layered 2D system, which is predicted to show a series of topologically trivial - nontrivial transitions under hydrostatic compression. We clearly show signatures of two iso-structural transition at 2 GPa and 4 GPa obtained from the minima in c/a ratio concomitant with the phonon linewidth anomalies of Eg and A1g modes at around the same pressures, providing strong indication of unusual electron-phonon coupling associated to these transitions. Resistivity presents nonlinear behavior over similar pressure ranges providing a strong indication of the electronic origin of these pressure driven isostructural transitions. Our data thus provide clear evidences of topological changes at A and L point of the Brillouin zone predicted to be present in the compressed 1T-TiTe2. Between 4 GPa and 8 GPa, the c/a ratio shows a plateau suggesting a transformation from an anisotropic 2D layer to a quasi 3D crystal network. First principles calculations suggest that the 2D to quasi 3D evolution without any structural phase transitions is mainly due to the increased interlayer Te-Te interactions (bridging) via the charge density overlap. In addition to the pressure dependent isostructural phase transitions, our data also evidences the occurrence of a first order structural phase transition from the trigonal (P-3m1) phase at higher pressures. We estimate the start of this structural phase transition to be 8 GPa and the symmetric of the new high-pressure phase to be monoclinic (C2/m).Comment: 22 pages, 11 Figures, 2 Table

Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi

The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent powder x-ray diffraction measurements confirm martensitic transition from the high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature (LT) orthorhombic $Pmma$ structure similar to many previously reported shape memory alloys. The HT to LT phase transition is characterized by a sharp increase in resistivity associated with prominent thermal hysteresis. Further, we observe robust Bain distortion between cubic and orthorhombic lattice parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and $c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and elongation along $a$-axis respectively. The sample shows an unusual `non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field as high as 150 kOe. In addition, non-linear field dependence of Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm robust metallic states both in the LT and HT phases. It indicates complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electron and hole pockets.Comment: 13 pages, 12 figure

Structural, vibrational, and electrical properties of 1T-TiTe2 under hydrostatic pressure: Experiments and theory

We report the structural, vibrational, and electrical transport properties up to ∼16 GPa of 1T -TiTe2, a prominent layered 2D system. We clearly show signatures of two isostructural transitions at ∼2 GPa and ∼4 GPa obtained from the minima in c/a ratio concomitant with the phonon linewidth anomalies of Eg and A1g modes around the same pressures, providing a strong indication of unusual electron-phonon coupling associated with these transitions. Resistance measurements present nonlinear behavior over similar pressure ranges shedding light on the electronic origin of these pressure-driven isostructural transitions. These multiple indirect signatures of an electronic transition at ∼2 GPa and ∼4 GPa are discussed in connection with the recent theoretical proposal for 1T -TiTe2 and also the possibility of an electronic topological transition from our electronic Fermi surface calculations. Between 4 GPa and ∼8 GPa, the c/a ratio shows a plateau suggesting a transformation from an anisotropic 2D layer to a quasi-3D crystal network. First-principles calculations suggest that the 2D to quasi-3D evolution without any structural phase transitions is mainly due to the increased interlayer Te-Te interactions (bridging) via the charge density overlap. In addition, we observed a first-order structural phase transition from the trigonal (P3¯m1) to monoclinic (C2/m) phase at higher pressure regions. We estimate the start of this structural phase transition to be ∼8 GPa and also the coexistence of two phases [trigonal (P3¯m1) and monoclinic (C2/m)] was observed from ∼8 GPa to ∼16 GPa

Structural, magnetotransport and Hall coefficient studies in ternary Bi2Te2Se, Sb2Te2Se and Bi2Te2S tetradymite topological insulating compounds

International audienceTemperature and magnetic field dependent resistivity studies of topological insulating materials Bi2Te2Se, Sb2Te2Se and Bi2Te2S are examined using various transport characteristics with suitable XRD and Raman structural analyses. The longitudinal resistivity data with decreasing of temperature reveals the insulating phase in Bi2Te2Se and showed profound metallic nature in Sb2Te2Se and Bi2Te2S. We observed a bulk hole carrier concentration of 0.8 × 1019 cm−3 through Hall coefficient study for the compound Sb2Te2Se, whereas Bi2Te2S exhibit an electron carrier density of 0.3 × 1019 cm−3 at 2 K and 9 T. Magnetoresistance results suggest a residual carrier effect from these polycrystalline topological compounds would degrade the actual experimental observation of surface state, instead, bulk insulating behaviour has been realized. With controllable bulk carrier effect, a single crystal approach may unleash the definite Dirac surface state with absence of impurity scattering over topological characteristics

DNA binding, cleavage, catalytic, magnetic active; 2,2–bipyridyl based d-f hetero binuclear Gd(III), Cu(II) complexes and their Electrochemical, fluorescence studies

Several 2,2-bipyridyl-based d-f heterobinuclear [GdCuL1-5(bpy)2(NO3)2] complexes are present, where (Ligand 1) (9E)-N1-(2-Hydroxy-5-methylbenzylidene)–N2-((E)-2-(2-hydroxy-5-methyl benzylideneamino)ethyl)ethane-1,2-diamine. (Ligand 2) N1,N1-bis((E)-2-(2-hydroxy-5-methylbenzylideneamino)ethyl)ethane-1,2-diamine. (Ligand 3) (9E)-N1-(2-((E)-2-(2-hydroxy-5-methylbenzylideneamino)ethylamino)ethyl)–N2-(2-hydroxy-5-methylbenzylidene)ethane-1,2-diamine. (Ligand 4) (9E)-N1-(2-((E)-3-(2-hydroxy-5- methylbenzylideneamino) propylamino) ethyl)–N3-(2-hydroxy-5-methylbenzylidene)propane-1,3-diamine and (Ligand 5) (9E)-N-(2-hydroxy-5-methylbenzylidene)-3-(4-((E)-3-(2-hydroxy-5-methylbenzylideneamino)propyl)piperazin-1-yl)propan-1-amine. These compounds were described using spectroscopy and the elemental analysis method. Researches were conducted into the luminous, Genetic code, catalytic, magnetism, and breaking attributes of the [GdCuL1-5(bpy)2(NO3)2] complexes. In DMF with 0.1 M tetra-n-butylammonium perchlorate, the binuclear [GdCuL1-5(bpy)2(NO3)2] network complexes exhibit two one electron irreversible reduction events. VSM was used to calculate the complexes' magnetic susceptibility. There is ferromagnetic coupling in the [GdCuL1-5(bpy)2(NO3)2] complexes. The [GdCuL1-5(bpy)2(NO3)2] complexes' excited state lifetimes lengthen in the following order: [GdCuL5(bpy)2] [GdCuL1(bpy)2(NO3)2] [GdCuL3(bpy)2(NO3)2] [GdCuL4(bpy)2] and [GdCuL2(bpy)2(NO3)2]. The binuclear [GdCuL1-5(bpy)2(NO3)2] complexes' inceptive rate of progress for oxidizing 1,2-benzenediol to cyclohexa-3,5-diene-1,2-dione are longer chains with higher activity. Both the [GdCuL5(bpy)2(NO3)2] and [GdCuL4(bpy)2(NO3)2] complexes have strong DNA genetic code properties in the calf genus thymus. The complexes exhibit considerable singlet oxygen-mediated oxidative rift of circular recombinant plasmid pBR322 cloning vector in the existence of 2-sulfanylethanol