Indra Dasgupta

Bio: Indra Dasgupta is an academic researcher from Indian Association for the Cultivation of Science. The author has contributed to research in topics: Ferromagnetism & Electronic structure. The author has an hindex of 27, co-authored 135 publications receiving 2701 citations. Previous affiliations of Indra Dasgupta include S.N. Bose National Centre for Basic Sciences & Indian National Association.

Band-Structure Trend in Hole-Doped Cuprates and Correlation with T c max

Abstract: By calculation and analysis of the bare conduction bands in a large number of hole-doped high-temperature superconductors, we have identified the range of the intralayer hopping as the essential, material-dependent parameter. It is controlled by the energy of the axial orbital, a hybrid between $\mathrm{Cu}4s$, apical-oxygen ${2p}_{z}$, and farther orbitals. Materials with higher ${T}_{c\mathrm{max}}$ have larger hopping ranges and axial orbitals more localized in the ${\mathrm{CuO}}_{2}$ layers.

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

Abstract: Debjani Karmakar,1 S. K. Mandal,2 R. M. Kadam,3 P. L. Paulose,4 A. K. Rajarajan,5 T. K. Nath,2 A. K. Das,2 I. Dasgupta,6 and G. P. Das7 1Technical Physics & Prototype Engineering Division, Bhabha Atomic Research Center, Mumbai 400085, India 2Department of Physics & Meteorology, Indian Institute of Technology, Kharagpur 721302, India 3Radiochemistry Division, Bhabha Atomic Research Center, Mumbai 400085, India 4Tata Institute of Fundamental Research, Mumbai 400005, India 5Solid State Physics Division, Bhabha Atomic Research Center, Mumbai 400085, India 6Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India 7Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata 700032, India Received 18 August 2006; revised manuscript received 7 December 2006; published 2 April 2007

Electronic structure and magnetism in half-Heusler compounds

Abstract: In this paper we have applied the full-potential linearized muffin tin orbital method and the tight-binding linearized muffin tin orbital method to investigate in detail the electronic structure and magnetism of a series of half-Heusler compounds XMZ with X = Fe,Co,Ni, M = Ti,V,Nb,Zr,Cr,Mo,Mn and Z = Sb,Sn. Our detailed analysis of the electronic structure using various indicators of chemical bonding suggests that covalent hybridization of the higher-valent transition element X with the lower-valent transition element M is the key interaction responsible for the formation of the d–d gap in these systems. However, the presence of the sp-valent element is crucial to provide stability to these systems. The influence of the relative ordering of the atoms in the unit cell on the d–d gap is also investigated. We have also studied in detail some of these systems with more than 18 valence electrons which exhibit novel magnetic properties, namely half-metallic ferro- and ferrimagnetism. We show that the d–d gap in the paramagnetic state, the relatively large X–Sb hybridization and the large exchange splitting of the M atoms are responsible for the half-metallic property of some of these systems.

Orbital-selective superconductivity in a two-band model of infinite-layer nickelates

Abstract: In the present Rapid Communication, we explore superconductivity in $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{2}$ and $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{2}$ employing a first-principles derived low-energy model Hamiltonian, consisting of two orbitals: Ni ${x}^{2}\ensuremath{-}{y}^{2}$, and an axial orbital. The axial orbital is constructed out of Nd/La $d$, Ni $3{z}^{2}\ensuremath{-}{r}^{2}$, and Ni $s$ characters. Calculation of the superconducting pairing symmetry and pairing eigenvalue of the spin-fluctuation mediated pairing interaction underlines the crucial role of the interorbital Hubbard interaction in superconductivity, which turns out to be orbital selective. The axial orbital brings in material dependence to the problem, making $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{2}$ different from $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{2}$, thereby controlling the interorbital Hubbard interaction-assisted superconductivity.

Magnetic properties and heat capacity of the three-dimensional frustrated S=1/2 antiferromagnet PbCuTe2O6

Abstract: We report magnetic susceptibility $(\ensuremath{\chi})$ and heat capacity $({C}_{p})$ measurements along with ab initio electronic structure calculations on ${\mathrm{PbCuTe}}_{2}{\mathrm{O}}_{6}$, a compound made up of a three-dimensional (3D) network of corner-shared triangular units. The presence of antiferromagnetic interactions is inferred from a Curie-Weiss temperature $({\ensuremath{\theta}}_{\mathrm{CW}})$ of about $\ensuremath{-}22$ K from the $\ensuremath{\chi}(T)$ data. The magnetic heat capacity ${C}_{m}$ data show a broad maximum at ${T}^{\mathrm{max}}\ensuremath{\simeq}1.15$ K (i.e., ${T}^{\mathrm{max}}/{\ensuremath{\theta}}_{\mathrm{CW}}\ensuremath{\simeq}0.05)$, which is analogous to the the observed broad maximum in the ${C}_{m}/T$ data of a hyper-kagome system, ${\mathrm{Na}}_{4}{\mathrm{Ir}}_{3}{\mathrm{O}}_{8}$. In addition, ${C}_{m}$ data exhibit a weak kink at ${T}^{*}\ensuremath{\simeq}0.87$ K. While the ${T}^{\mathrm{max}}$ is nearly unchanged, the ${T}^{*}$ is systematically suppressed in an increasing magnetic field $(H)$ up to 80 kOe. For $H\ensuremath{\ge}80$ kOe, the ${C}_{m}$ data at low temperatures exhibit a characteristic power-law $(T{}^{\ensuremath{\alpha}})$ behavior with an exponent $\ensuremath{\alpha}$ slightly less than 2. Hopping integrals obtained from the electronic structure calculations show the presence of strongly frustrated 3D spin interactions along with non-negligible unfrustrated couplings. Our results suggest that ${\mathrm{PbCuTe}}_{2}{\mathrm{O}}_{6}$ is a candidate material for realizing a 3D quantum spin liquid state at high magnetic fields.

Doping a Mott insulator: Physics of high-temperature superconductivity

Abstract: This article reviews the physics of high-temperature superconductors from the point of view of the doping of a Mott insulator. The basic electronic structure of cuprates is reviewed, emphasizing the physics of strong correlation and establishing the model of a doped Mott insulator as a starting point. A variety of experiments are discussed, focusing on the region of the phase diagram close to the Mott insulator (the underdoped region) where the behavior is most anomalous. The normal state in this region exhibits pseudogap phenomenon. In contrast, the quasiparticles in the superconducting state are well defined and behave according to theory. This review introduces Anderson's idea of the resonating valence bond and argues that it gives a qualitative account of the data. The importance of phase fluctuations is discussed, leading to a theory of the transition temperature, which is driven by phase fluctuations and the thermal excitation of quasiparticles. However, an argument is made that phase fluctuations can only explain pseudogap phenomenology over a limited temperature range, and some additional physics is needed to explain the onset of singlet formation at very high temperatures. A description of the numerical method of the projected wave function is presented, which turns out to be a very useful technique for implementing the strong correlation constraint and leads to a number of predictions which are in agreement with experiments. The remainder of the paper deals with an analytic treatment of the $t\text{\ensuremath{-}}J$ model, with the goal of putting the resonating valence bond idea on a more formal footing. The slave boson is introduced to enforce the constraint againt double occupation and it is shown that the implementation of this local constraint leads naturally to gauge theories. This review follows the historical order by first examining the U(1) formulation of the gauge theory. Some inadequacies of this formulation for underdoping are discussed, leading to the SU(2) formulation. Here follows a rather thorough discussion of the role of gauge theory in describing the spin-liquid phase of the undoped Mott insulator. The difference between the high-energy gauge group in the formulation of the problem versus the low-energy gauge group, which is an emergent phenomenon, is emphasized. Several possible routes to deconfinement based on different emergent gauge groups are discussed, which leads to the physics of fractionalization and spin-charge separation. Next the extension of the SU(2) formulation to nonzero doping is described with a focus on a part of the mean-field phase diagram called the staggered flux liquid phase. It will be shown that inclusion of the gauge fluctuation provides a reasonable description of the pseudogap phase. It is emphasized that $d$-wave superconductivity can be considered as evolving from a stable U(1) spin liquid. These ideas are applied to the high-${T}_{c}$ cuprates, and their implications for the vortex structure and the phase diagram are discussed. A possible test of the topological structure of the pseudogap phase is described.

Doping a Mott Insulator: Physics of High Temperature Superconductivity

Abstract: This article reviews the effort to understand the physics of high temperature superconductors from the point of view of doping a Mott insulator. The basic electronic structure of the cuprates is reviewed, emphasizing the physics of strong correlation and establishing the model of a doped Mott insulator as a starting point. A variety of experiments are discussed, focusing on the region of the phase diagram close to the Mott insulator (the underdoped region) where the behavior is most anomalous. We introduce Anderson's idea of the resonating valence bond (RVB) and argue that it gives a qualitative account of the data. The importance of phase fluctuation is discussed, leading to a theory of the transition temperature which is driven by phase fluctuation and thermal excitation of quasiparticles. We then describe the numerical method of projected wavefunction which turns out to be a very useful technique to implement the strong correlation constraint, and leads to a number of predictions which are in agreement with experiments. The remainder of the paper deals with an analytic treatment of the t-J model, with the goal of putting the RVB idea on a more formal footing. The slave-boson is introduced to enforce the constraint of no double occupation. The implementation of the local constraint leads naturally to gauge theories. We give a rather thorough discussion of the role of gauge theory in describing the spin liquid phase of the undoped Mott insulator. We next describe the extension of the SU(2) formulation to nonzero doping. We show that inclusion of gauge fluctuation provides a reasonable description of the pseudogap phase.

Electronic structure calculations with dynamical mean-field theory

Abstract: We present a review of the basic ideas and techniques of the spectral density functional theory which are currently used in electronic structure calculations of strongly{correlated materials where the one{electron description breaks down. We illustrate the method with several examples where interactions play a dominant role: systems near metal{insulator transition, systems near volume collapse transition, and systems with local moments.