Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

&nbsp;

IIT Palakkad

We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ∼3.5 meV in MgB102 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown. © 2016 American Physical Society.

World University root node

Department of Physics

Fulltext

Physical Review B

Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

Verhandlungen der Deutschen Physikalischen Gesellschaft

" 7Li and" 2" 3Na NMR measurements on (Na_0_. _7_5Li_0_. _2_5) _2IrO_3

APS March Meeting Abstracts 2016, V27.

Systematic investigation of structural, transport, magnetic and thermodynamic properties of hexagonal R2Pt6Al15 (R = Y, La-Nd, Sm-Lu) series

The layered honeycomb magnet α-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled jeff=1/2 magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes β- and γ-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in α-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes. © 2016 American Physical Society.

Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb α-Li2IrO3

Na2IrO3 is an intriguing material for which spin-orbit coupling plays a key role. Theoretical predictions have been made that the surface of Na2IrO3 should exhibit a clear signature of the quantum spin Hall effect. We studied the surface of Na2IrO3 using scanning tunneling microscopy and density-functional theory calculations. We observed atomic level resolution of the surface and two types of terminations with different surface periodicity and Na content. By comparing bias-dependent experimental topographic images to simulated images, we determined the detailed atomistic structure of both observed surfaces. One of these reveals a strong relaxation to the surface of Na atoms from the subsurface region two atomic layers below. Such dramatic structural changes well below the surface are highly unusual and cast doubt on any prediction of surface properties based on bulk electronic structure. Indeed, using spatially resolved tunneling spectroscopy, we found no indication of the predicted quantum spin Hall behavior. © 2015 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Highly unconventional surface reconstruction of Na2IrO3 with persistent energy gap

Iridates have attracted considerable interest in the last few years due to their potential to host novel electronic and magnetic phases mediated by the combination of strong spin orbit coupling and electronic correlations. Layered honeycomb lattice iridates A_2IrO_3 (A =Na, Li) have been proposed as candidate materials for the realization of the highly frustrated Kitaev interaction as well as correlated topological insulator phases. &nbsp;In this thesis honeycomb iridates and rhodate (Li_2RhO_3) are experimentally investigated. Firstly, synthesis procedure, structural, magnetic, electrical and thermodynamic properties of the very well ordered honeycomb iridates and rhodate are reported including challenges faced due to disorder. Magnetic and electronic structures are also reported which were investigated using different scattering experiments and band structure calculations with the help of different international collaborators. Though both honeycomb iridates were proposed for Kitaev spin liquid state, bulk and microscopic investigation confirmed long range magnetic ordering below 15 K having zigzag and spiral magnetic structure for Na- and Li-system respectively. They also show novel spin-orbit Mott insulting state as proposed for iridates. Experimental investigations of honeycomb iridates raise many questions on the proposed spin Hamiltonians for these systems. &nbsp;To understand magnetic exchange in honeycomb iridates isoelectronic doping at A-site and nonmagnetic dilution at magnetic Ir-site were performed which clearly suggested very different magnetic exchanges in both the systems. Possible spin models for both of these systems are suggested from the comparison of the different proposed models with the experimental evidences. The Honeycomb rhodate Li_2RhO_3 which shows spin glass freezing at low temperature, hints degenerate magnetic ground state and possibility to find a spin liquid state. This thesis is one of the earliest investigations of the proposed Honeycomb lattice spin-orbit materials which can host Kitaev physics.&nbsp;

Synthesis and investigation of frustrated Honeycomb lattice iridates and rhodates

We have investigated, experimentally and theoretically, the series (Na1-xLix)2IrO3. Contrary to what has been believed so far, only for x≤0.25 does the system form uniform solid solutions where Li preferentially goes to the Ir2Na planes, as observed in our density functional theory calculations and consistent with x-ray diffraction analysis. For larger Li content, as evidenced by powder x-ray diffraction, scanning electron microscopy, and density functional theory calculations, the system shows a miscibility gap and a phase separation into an ordered Na3LiIr2O6 phase with alternating Na3 and LiIr2O6 planes, and a Li-rich phase close to pure Li2IrO3. For x≤0.25 we observe (1) an increase of c/a with Li doping up to x=0.25, despite the fact that c/a in pure Li2IrO3 is smaller than in Na2IrO3, and (2) a gradual reduction of the antiferromagnetic ordering temperature TN and ordered moment. In view of our results showing clear evidence for phase separation for 0.25≤x≤0.6, more detailed studies are needed to confirm the presence or absence of phase separation at the higher doping x∼0.7, where a continuum quantum phase transition has been proposed previously. © 2014 American Physical Society.

Effect of isoelectronic doping on the honeycomb-lattice iridate A2 IrO3

We have synthesized single crystals of Na2(Ir1-xTix)O3 and polycrystals of Li2(Ir1-xTix)O3 and studied the effect of magnetic depletion on the magnetic properties by measurements of the magnetic susceptibility, specific heat, and magnetocaloric effect at temperatures down to 0.1 K. In both systems, the nonmagnetic substitution rapidly changes the magnetically ordered ground state into a spin glass, indicating strong frustration. While for the Li system the Weiss temperature ΘW remains unchanged up to x=0.55, a strong decrease |ΘW| is found for the Na system. This suggests that only for the former system magnetic exchange beyond nearest neighbors is dominating. This is also corroborated by the observation of a smeared quantum phase transition in Li2(Ir1-xTix)O3 near x=0.5, i.e., much beyond the site percolation threshold of the honeycomb lattice. © 2014 American Physical Society.

Effect of nonmagnetic dilution in the honeycomb-lattice iridates Na2 IrO3 and Li2 IrO3

The recently synthesized iridate β-Li2IrO3 has been proposed as a candidate to display novel magnetic behavior stabilized by frustration effects from bond-dependent, anisotropic interactions (Kitaev model) on a three-dimensional "hyperhoneycomb" lattice. Here we report a combined study using neutron powder diffraction and magnetic resonant x-ray diffraction to solve the complete magnetic structure. We find a complex, incommensurate magnetic order with non-coplanar and counter-rotating Ir moments, which surprisingly shares many of its features with the related structural polytype "stripyhoneycomb" γ-Li2IrO3, where dominant Kitaev interactions have been invoked to explain the stability of the observed magnetic structure. The similarities of behavior between those two structural polytypes, which have different global lattice topologies but the same local connectivity, are strongly suggestive that the same magnetic interactions and the same underlying mechanism govern the stability of the magnetic order in both materials, indicating that both β- and γ-Li2IrO3 are strong candidates to realize dominant Kitaev interactions in a solid state material. © 2014 American Physical Society.

Unconventional magnetic order on the hyperhoneycomb Kitaev lattice in β-Li2IrO3: Full solution via magnetic resonant x-ray diffraction

APS March Meeting Abstracts 2014, A4.

Influence of non-magnetic dilution in honeycomb-lattice iridates A2IrO3 (A=Na,Li)

A burning question in the emerging field of spin-orbit driven insulating iridates, such as Na2IrO3 and Li2IrO 3, is whether the observed insulating state should be classified as a Mott-Hubbard insulator derived from a half-filled relativistic j eff=1/2 band or as a band insulator where the gap is assisted by spin-orbit interaction or Coulomb correlations or both. The difference between these two interpretations is that only for the former strong spin-orbit coupling (λâ‰W, where W is the bandwidth) is essential. We have synthesized the isostructural and isoelectronic Li2RhO3 and report its electrical resistivity and magnetic susceptibility. Remarkably, it shows insulating behavior together with fluctuating effective S=1/2 moments, similar to Na2IrO3 and Li2IrO3, although in Rh4+ (4d5) the spin-orbit coupling is greatly reduced. We show that this behavior has a nonrelativistic one-electron origin (although Coulomb correlations assist in opening the gap) and can be traced to the formation of quasimolecular orbitals, similar to those in Na2IrO 3. ©2013 American Physical Society.

Origin of the insulating state in honeycomb iridates and rhodates

The electronic structure of the honeycomb lattice iridates Na 2IrO3 and Li2IrO3 has been investigated using resonant inelastic x-ray scattering (RIXS). Crystal-field-split d-d excitations are resolved in the high-resolution RIXS spectra. In particular, the splitting due to noncubic crystal fields, derived from the splitting of jeff=3/2 states, is much smaller than the typical spin-orbit energy scale in iridates, validating the applicability of jeff physics in A2IrO3. We also find excitonic enhancement of the particle-hole excitation gap around 0.4 eV, indicating that the nearest-neighbor Coulomb interaction could be large. These findings suggest that both Na2IrO3 and Li2IrO3 can be described as spin-orbit Mott insulators, similar to the square lattice iridate Sr2IrO4. © 2013 American Physical Society.

Physical Review Letters

Crystal-field splitting and correlation effect on the electronic structure of A2IrO3

Combining thermodynamic measurements with theoretical calculations we demonstrate that the iridates A 2IrO 3 (A=Na, Li) are magnetically ordered Mott insulators where the magnetism of the effective spin-orbital S=1/2 moments can be captured by a Heisenberg-Kitaev (HK) model with interactions beyond nearest-neighbor exchange. Experimentally, we observe an increase of the Curie-Weiss temperature from θ-125K for Na 2IrO 3 to θ-33K for Li 2IrO 3, while the ordering temperature remains roughly the same T N 15K. Using functional renormalization group calculations we show that this evolution of θ and T N as well as the low temperature zigzag magnetic order can be captured within this extended HK model. We estimate that Na 2IrO 3 is deep in a magnetically ordered regime, while Li 2IrO 3 appears to be close to a spin-liquid regime. © 2012 American Physical Society.