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.

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IIT Palakkad

We study the spin-1/2 ferromagnetic Heisenberg-Kitaev-Γ model in the anisotropic (Toric code) limit to reveal the nature of the quantum phase transition between the gapped Z2 quantum spin liquid and a spin-ordered phase (driven by Heisenberg interactions) as well as a trivial paramagnet (driven by pseudodipolar interactions Γ). The transitions are obtained by a simultaneous condensation of the Ising electric and magnetic charges - the fractionalized excitations of the Z2 quantum spin liquid. Both these transitions can be continuous and are examples of deconfined quantum critical points. Crucial to our calculations are the symmetry implementations on the soft electric and magnetic modes that become critical. In particular, we find strong constraints on the structure of the critical theory arising from time reversal and lattice translation symmetries with the latter acting as an anyon permutation symmetry that endows the critical theory with a manifestly self-dual structure. We find that the transition between the quantum spin liquid and the spin-ordered phase belongs to a self-dual modified Abelian Higgs field theory while that between the spin liquid and the trivial paramagnet belongs to a self-dual Z2 gauge theory. We also study the effect of an external Zeeman field to show an interesting similarity between the polarized paramagnet obtained due to the Zeeman field and the trivial paramagnet driven pseudodipolar interactions. Interestingly, both the spin liquid and the spin-ordered phases have easily identifiable counterparts in the isotropic limit and the present calculations may shed insights into the corresponding transitions in the material relevant isotropic limit. © 2020 American Physical Society.

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Department of Physics

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Physical Review B

Phases and quantum phase transitions in an anisotropic ferromagnetic Kitaev-Heisenberg- Γ magnet

We study the uniform time-reversal-invariant U(1) quantum spin liquid (QSL) with low-energy fermionic quasiparticles for rare-earth pyrochlore magnets and explore its magnetic instability, employing an augmented fermionic parton mean field theory approach. Self-consistent calculations stabilize a uniform U(1) QSL with both gapped and gapless parton excitations as well as fractionalized magnetically ordered phases in an experimentally relevant part of the phase diagram near the classical phase boundaries of the magnetically ordered phases. The gapped QSL has a band structure with a nonzero Z2 topological invariant. The fractionalized magnetically ordered phases bear signatures of both QSL through fermionic excitations as well as magnetic order. Thus, this provides a possible way to understand the unconventional diffuse neutron scattering in rare-earth pyrochlores such as Yb2Ti2O7, Er2Sn2O7, and Er2Pt2O7 at low or zero external magnetic fields. We calculate the dynamic spin structure factor to understand the nature of the diffuse two-particle continuum. © 2019 American Physical Society.

Interplay of uniform U (1) quantum spin liquid and magnetic phases in rare-earth pyrochlore magnets: A fermionic parton approach

Proceedings of the national conference on quantum condensed matter

Magnetic instabilities of uniform U (1) spin liquids on pyrochlore lattice

The correspondence between the edge theory and the entanglement spectrum is firmly established for the chiral topological phases. We study a gapped, topologically ordered, nonchiral state with a conserved U(1) charge and show that the entanglement Hamiltonian contains not only the information about topologically distinct edges such a phase may admit, but also which of them will be realized in the presence of symmetry-breaking/-conserving perturbations. We introduce an exactly solvable, charge-conserving lattice model of a Z2 spin liquid and derive its edge theory and the entanglement Hamiltonian, also in the presence of perturbations. We construct a field theory of the edge and study its renormalization group flow. We show the precise extent of the correspondence between the information contained in the entanglement Hamiltonian and the edge theory. © 2017 American Physical Society.

Edge-entanglement correspondence for a gapped topological phase with symmetry

Paramagnetic impurities in a quantum spin liquid give rise to Kondo effects with highly unusual properties. We have studied the effect of locally coupling a paramagnetic impurity with the spin-12 honeycomb Kitaev model in its gapless spin-liquid phase. The (impurity) scaling equations are found to be insensitive to the sign of the coupling. The weak and strong coupling fixed points are stable, with the latter corresponding to a noninteracting vacancy and an interacting, spin-1 defect for the antiferromagnetic and ferromagnetic cases, respectively. The ground state in the strong coupling limit in both cases has a nontrivial topology associated with a finite Z2 flux at the impurity site. For the antiferromagnetic case, this result has been obtained straightforwardly owing to the integrability of the Kitaev model with a vacancy. The strong-coupling limit of the ferromagnetic case is, however, nonintegrable, and we address this problem through exact-diagonalization calculations with finite Kitaev fragments. Our exact diagonalization calculations indicate that the weak-to-strong coupling transition and the topological phase transition occur rather close to each other and are possibly coincident. We also find an intriguing similarity between the magnetic response of the defect and the impurity susceptibility in the two-channel Kondo problem. © 2016 American Physical Society.

Kondo route to spin inhomogeneities in the honeycomb Kitaev model

Bilayer graphene subjected to perpendicular magnetic and electric fields displays a subtle competition between different symmetry-broken phases, resulting from an interplay between the internal spin and valley degrees of freedom. The transition between different phases is often identified by an enhancement of the conductance. Here, we propose that the enhanced conductance at the transition is due to the appearance of robust conducting edge states at domain walls between the two phases. We formulate a criterion for the existence of such conducting edge states at the domain walls. For example, for a spontaneously layer polarized state at filling factor ν=2, domain walls between regions of opposite polarization carry conducting edge modes. A microscopic analysis shows that lattice-scale interactions can favor such a layer polarized state.

covering condensed matter and materials physics

Spontaneous layer polarization and conducting domain walls in bilayer graphene

Bilayer graphene subjected to perpendicular magnetic and electric fields displays a subtle competition between different symmetry-broken phases, resulting from an interplay between the internal spin and valley degrees of freedom. The transition between different phases is often identified by an enhancement of the conductance. Here, we propose that the enhanced conductance at the transition is due to the appearance of robust conducting edge states at domain walls between the two phases. We formulate a criterion for the existence of such conducting edge states at the domain walls. For example, for a spontaneously layer polarized state at filling factor ν=2, domain walls between regions of opposite polarization carry conducting edge modes. A microscopic analysis shows that lattice-scale interactions can favor such a layer polarized state. © 2015 American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Spontaneous layer polarization and conducting domain walls in the quantum Hall regime of bilayer graphene

Tata Institute of Fundamental Research Mumbai-400 005, India

Disorder and Magnetism in Two Dimensional Quantum Systems

We study theoretically and experimentally the frequency and temperature dependences of resistivity noise in semiconductor heterostructures δ-doped by Mn. The resistivity noise is observed to be nonmonotonous as a function of frequency. As a function of temperature, the noise increases by two orders of magnitude for a resistivity increase of about 50%. We study two possible sources of resistivity noise, dynamic spin fluctuations and charge fluctuations, and find that dynamic spin fluctuations are more relevant for the observed noise data. The frequency and temperature dependences of resistivity noise provide important information on the nature of the magnetic interactions. In particular, we show how noise measurements can help resolve a long-standing debate on whether the Mn-doped GaAs is a p-d Zener/Ruderman-Kittel-Kasuya-Yosida (RKKY) or double-exchange ferromagnet. Our analysis includes the effect of different kinds of disorder such as spin-glass type of interactions and a site-dilution type of disorder. We find that the resistivity noise in these structures is well described by a disordered RKKY ferromagnet model dynamics with a conserved order parameter. © 2012 American Physical Society.

Noise studies of magnetization dynamics in dilute magnetic semiconductor heterostructures

We study experimentally and theoretically the effects of disorder, nonlinear screening, and magnetism in semiconductor heterostructures containing a δ-layer of Mn, where the charge carriers are confined within a quantum well and hence both ferromagnetism and transport are two dimensional (2D) and differ qualitatively from their bulk counterparts. Anomalies in the electrical resistance observed in both metallic and insulating structures can be interpreted as a signature of significant ferromagnetic correlations. The insulating samples turn out to be the most interesting as they can give us valuable insights into the mechanisms of ferromagnetism in these heterostructures. At low charge carrier densities, we show how the interplay of disorder and nonlinear screening can result in the organization of the carriers in the 2D transport channel into charge droplets separated by insulating barriers. Based on such a droplet picture and including the effect of magnetic correlations, we analyze the transport properties of this set of droplets, compare them with experimental data for insulating samples, and find a good agreement between the model calculations and experiment. Our analysis shows that the peak or shoulder-like features observed in the temperature dependence of resistance of 2D heterostructures δ-doped by Mn can appear even in the absence of a phase transition at nonzero temperatures. Furthermore, the anomaly can lie significantly below the mean-field Curie temperature TC. This is unlike the three-dimensional case, where it lies close to the critical temperature T0, which is often not very far from TC. We also discuss the consequences of our description for understanding the mechanisms of ferromagnetism in the heterostructures under study. © 2011 American Physical Society.

Charge inhomogeneities and transport in semiconductor heterostructures with a Mn δ-layer

We study the effect of coupling magnetic impurities to the honeycomb lattice spin-1/2 Kitaev model in its spin-liquid phase. We show that a spin-S impurity coupled to the Kitaev model is associated with an unusual Kondo effect with an intermediate coupling unstable fixed point Kc∼J/S separating topologically distinct sectors of the Kitaev model. We also show that the massless spinons in the spin-liquid mediate an interaction of the form Siα2Sjβ2/Rij3 between distant impurities unlike the usual dipolar RKKY interaction SiαSjα/Rij3 noted in various 2D impurity problems with a pseudogapped density of states of the spin bath. Furthermore, this long-range interaction is possible only if the impurities (a) couple to more than one neighboring spin on the host lattice and (b) the impurity spin S≠ 1/2. © 2010 The American Physical Society.

Physical Review Letters

Magnetic impurities in the honeycomb Kitaev model

We study nuclear relaxation in the presence of localized electrons in a two-dimensional electron gas in a disordered delta-doped semiconductor heterostructure and show that this method can reliably probe their magnetic interactions and possible long-range order. In contrast, we argue that transport measurements, the commonly employed tool, may not sometimes distinguish between spatial disorder and long-range order. We illustrate the utility of using the nuclear relaxation method to detect long-range order by analyzing a recent proposal made on the basis of transport measurements, on the spontaneous formation of a two-dimensional Kondo lattice in a 2D electron gas in a heterostructure. © 2009 The American Physical Society.