11 research outputs found
Centrosymmetric-noncentrosymmetric Structural Phase Transition in Quasi one-dimensional compound, (TaSe)I
(TaSe)I, a compound belonging to the family of quasi-one-dimensional
transition-metal tetrachalcogenides, has drawn significant attention due to a
recent report on possible coexistence of two antagonistic phenomena,
superconductivity and magnetism below 2.5~K (Bera et. al, arXiv:2111.14525).
Here, we report a structural phase transition of the trimerized phase at
temperature, ~145~K using Raman scattering, specific heat, and
electrical transport measurements. The temperature-dependent single-crystal
X-ray diffraction experiments establish the phase transition from a
high-temperature centrosymmetric to a low-temperature non-centrosymmetric
structure, belonging to the same tetragonal crystal family. The first-principle
calculation finds the aforementioned inversion symmetry-breaking structural
transition to be driven by the hybridization energy gain due to the off-centric
movement of the Ta atoms, which wins over the elastic energy loss.Comment: 11 pages, 5 figures, Under review as a regular articl
Enhanced coercivity and emergence of spin cluster glass state in 2D ferromagnetic material Fe3GeTe2
Two-dimensional (2D) van der Waals (vdW) magnetic materials with high
coercivity and high are desired for spintronics and memory storage
applications. FeGeTe (F3GT) is one such 2D vdW ferromagnet with a
reasonably high , but with a very low coercive field,
(100~Oe). Some of the common techniques of enhancing are
by introducing pinning centers, defects, stress, doping, etc. They involve the
risk of undesirable alteration of other important magnetic properties. Here we
propose a very easy, robust, and highly effective method of phase engineering
by altering the sample growth conditions to greatly enhance the intrinsic
coercivity (7-10 times) of the sample, without compromising its fundamental
magnetic properties (210K). The phase-engineered sample
(F3GT-2) comprises of parent F3GT phase with a small percentage of randomly
embedded clusters of a coplanar FeTe (FT) phase. The FT phase serves as both
mosaic pinning centers between grains of F3GT above its antiferromagnetic
transition temperature (70~K) and also as anti-phase domains
below . As a result, the grain boundary disorder and metastable
nature are greatly augmented, leading to highly enhanced coercivity, cluster
spin glass, and meta-magnetic behavior. The enhanced coercivity (1~kOe)
makes F3GT-2 much more useful for memory storage applications and is likely to
elucidate a new route to tune useful magnetic properties. Moreover, this method
is much more convenient than hetero-structure and other cumbersome techniques.Comment: 12 pages, 11 figure
Raman signatures of lattice dynamics across inversion symmetry breaking phase transition in quasi-1D compound, (TaSe)I
Structural phase transition can occur due to complex mechanisms other than
simple dynamical instability, especially when the parent and daughter structure
is of low dimension. This article reports such an inversion symmetry-breaking
structural phase transition in a quasi-1D compound (TaSe)I at T
141~K studied by Raman spectroscopy. Our investigation of collective lattice
dynamics reveals three additional Raman active modes in the low-temperature
non-centrosymmetric structure. Two vibrational modes become Raman active due to
the absence of an inversion center, while the third mode is a soft phonon mode
resulting from the vibration of Ta atoms along the \{-Ta-Ta-\} chains.
Furthermore, the most intense Raman mode display Fano-shaped asymmetry,
inferred as the signature of strong electron-phonon coupling. The group theory
and symmetry analysis of Raman spectra confirm the displacive-first-order
nature of the structural transition. Therefore, our results establish
(TaSeI as a model system with broken inversion symmetry and strong
electron-phonon coupling in the quasi-1D regime.Comment: Main text - 6 figures, 11 pages, supplementary - 10 figures, 13 page
High transport spin polarization in the van der Waals ferromagnet FeGeTe
The challenging task of scaling-down the size of the power saving electronic
devices can be accomplished by exploiting the spin degree of freedom of the
conduction electrons in van der Waals (vdW) spintronic architectures built with
2D materials. One of the key components of such a device is a near-room
temperature 2D ferromagnet with good metallicity that can generate a highly
spin-polarized electronic transport current. However, most of the known 2D
ferromagnets have either a very low temperature ordering, poor conductivity, or
low spin polarization. In this context, the FeGeTe (with )
family of ferromagnets stand out due to their near-room temperature
ferromagnetism and good metallicity. We have performed spin-resolved Andreev
reflection spectroscopy on FeGeTe ( 273 K) and
demonstrated that the ferromagnet is capable of generating a very high
transport spin polarization, exceeding 50. This makes FeGeTe a
strong candidate for application in all-vdW power-saving spintronic devices.Comment: Accepted for publication in Physical Review
Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet
Induced magnetic order in a topological insulator (TI) can be realized either
by depositing magnetic adatoms on the surface of a TI or engineering the
interface with epitaxial thin film or stacked assembly of two-dimensional (2D)
van der Waals (vdW) materials. Herein, we report the observation of spin-phonon
coupling in the otherwise non-magnetic TI BiTe, due
to the proximity of FePS (an antiferromagnet (AFM),
120 K), in a vdW heterostructure framework. Temperature-dependent Raman
spectroscopic studies reveal deviation from the usual phonon anharmonicity
at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of
the characteristic phonon modes of BiTe (106 cm and 138
cm) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism,
where the respective phonon frequencies of BiTe couple to phonons
of similar frequencies of FePS in the AFM phase, has been adopted to
understand the origin of the hybrid magneto-elastic modes. At the same time,
the reduction of characteristic of FePS from 120 K in
isolated flakes to 65 K in the heterostructure, possibly due to the interfacial
strain, which leads to smaller Fe-S-Fe bond angles as corroborated by
computational studies using density functional theory (DFT). Besides, our data
suggest a double softening of phonon modes of BiTe
(at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible
probe for delineating the magnetic ordering in bulk and surface of a hybrid
topological insulator
Review of recent progress on THz spectroscopy of quantum materials: superconductors, magnetic and topological materials
Recently, the THz spectroscopy has been efficiently used to investigate varieties of quantum materials, including superconductors, novel magnetic, and topological materials. These materials often exhibit strong correlation and competing interactions between various degrees of freedom, including charge, spins, orbital, and lattice dynamics, which lead to many exotic phenomena and novel phase transitions whose cause–effect correlations are challenging to determine. Whereas probing the ground state’s excitations can unravel the underlying mechanism of these complex phenomena. The characteristic energy scales of different elementary excitations and collective modes in many of these materials are in the THz frequency range. Therefore, THz spectroscopy has become a very effective probe and directly revealed many exciting physics. Many novel phenomena, including exotic quasiparticle excitations in magnetic systems, topological magneto-electric effect, and topological quantum phase transition in three-dimensional topological insulators, are studied with unprecedented success. Here, we review some recent research reports on many-body quantum materials, including superconductors, novel magnetic, and topological materials probed by few popular THz-spectroscopy techniques. We will also briefly discuss the prospects of using THz spectroscopy for observing some exotic quantum phenomena that are still elusive or under investigation
Aminoisophthalate Bridged Cd(II)-2D Coordination Polymer: Structure Description, Selective Detection of Pd<sup>2+</sup> in Aqueous Medium, and Fabrication of Schottky Diode
Photoluminescence activity of coordination polymers (CPs)
has evoked
intricate applications in the field of materials science, especially
sensing of ions/molecules. In the present study, 2,3,5,6-tetrakis(2-pyridyl)pyrazine
(tppz) and 5-aminoisophthalate (HAIPA–) coordinated
to Cd(II) to architect a coordination polymer, {[Cd(HAIPA)(tppz)(OH)]·3H2O}n (CP1) which unveils
blue emission in an aqueous acetonitrile (98% aqueous) suspension.
The emission is selectively quenched by Pd2+ only without
interference in the presence of as many as 16 other cations. The structure
of CP1 shows the presence of a free –COOH group,
and the interlayer (–CO)O(2)···O(7) (OC–)
distance, 4.242 Å, along with the π···π
interactions (3.990, 3.927 Ã…), may make a cavity which suitably
accommodates only Pd2+ (van der Waal’s radius, 1.7
Å) through the Pd(II)-carboxylato (–COO–Pd) coordination.
The stability of the composite, [CP1 + Pd2+] may be assessed from the fluorescence quenching experiment, and
the Stern–Volmer constant (KSV)
is 7.2 × 104 M–1. Therefore, the
compound, CP1, is a promising sensor for Pd(II) in a
selective manner with limit of detection (LOD), 0.08 μM. The
XPS spectra of CP1 and [CP1 + Pd2+] have proven the presence of Pd2+ in the host and the
existence of a coordinated –COO–Pd bond. Interestingly,
inclusion of Pd2+ in CP1 decreases the band
gap from 3.61 eV (CP1) to 3.05 eV ([CP1 +
Pd2+]) which lies in the semiconducting region and has
exhibited improved electrical conductivity from 7.42 × 10–5 (CP1) to 1.20 × 10–4 S m–1 ([CP1 + Pd2+]).
Upon light irradiation, the electrical conductivities are enhanced
to 1.45 × 10–4 S m–1 (CP1) and 3.81 × 10–4 S m–1 ([CP1 + Pd2+]); which validates the highly
desired photoresponsive device applications. Therefore, such type
of materials may serve as SDG-army (sustainable development goal)
to battle against the environmental issues and energy crisis
Anisotropic magnetodielectric coupling in layered antiferromagnetic FePS 3
We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic FePS3 (Néel temperature TN∼ 120 K) with perpendicular anisotropy. Above TN, while the dielectric response function along the c axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies