arXiv subjects

Kalobaran Maiti

Publications and source records attributed to Kalobaran Maiti.

At least 55 records · Page 3Linked to original sources

arXiv2017

Dimensionality, nematicity and Superconductivity in Fe-based systems

Study of Fe based compounds have drawn much attention due to the discovery of superconductivity as well as many other exotic electronic properties. Here, we review some of our works in these materials carried out employing density functional theory and angle resolved photoemission spectroscopy. The results presented here indicate that the dimensionality of the underlying electronic structure plays important role in deriving their interesting electronic properties. The nematicity found in most of these materials appears to be related to the magnetic long range order. We argue that the exoticity in the electronic properties are related to the subtlety in competing structural and magnetic instabilities present in these materials.

cond-mat.supr-con↗

arXiv2017

Emergent electronic structure of CaFe2As2

CaFe2As2 exhibits collapsed tetragonal (cT) structure and varied exotic behavior under pressure at low temperatures that led to debate on linking the structural changes to its exceptional electronic properties like superconductivity, magnetism, etc. Here, we investigate the electronic structure of CaFe2As2 forming in different structures employing density functional theory. The results indicate better stability of the cT phase with enhancement in hybridization induced effects and shift of the energy bands towards lower energies. The Fermi surface centered around $Γ$ point gradually vanishes with the increase in pressure. Consequently, the nesting between the hole and electron Fermi surfaces associated to the spin density wave state disappears indicating a pathway to achieve the proximity to quantum fluctuations. The magnetic moment at the Fe sites diminishes in the cT phase consistent with the magnetic susceptibility results. Notably, the hybridization of Ca 4s states (Ca-layer may be treated as a charge reservoir layer akin to those in cuprate superconductors) is significantly enhanced in the cT phase revealing its relevance in its interesting electronic properties.

cond-mat.supr-con↗

arXiv2017

Observation of pseudogap in MgB2

Pseudogap phase in superconductors continues to be an outstanding puzzle that differentiates unconventional superconductors from the conventional ones (BCS-superconductors). Employing high resolution photoemission spectroscopy on a highly dense conventional superconductor, MgB2, we discover an interesting scenario. While the spectral evolution close to the Fermi energy is commensurate to BCS descriptions as expected, the spectra in the wider energy range reveal emergence of a pseudogap much above the superconducting transition temperature indicating apparent departure from the BCS scenario. The energy scale of the pseudogap is comparable to the energy of E2g phonon mode responsible for superconductivity in MgB2 and the pseudogap can be attributed to the effect of electron-phonon coupling on the electronic structure. These results reveal a scenario of the emergence of the superconducting gap within an electron-phonon coupling induced pseudogap.

cond-mat.supr-con↗

arXiv2015

Identification of the surface features in the electronic structure of Cr

We studied the electronic structure of high quality Cr(110) films grown on W(110) surface employing photoemission spectroscopy. Experiments on the differently aged samples revealed distinct signatures of the surface and bulk features in the electronic structure. It is observed that the adsorbed oxygens form covalent bonds with the surface Cr atoms at higher temperatures, while they remain almost unreacted at low temperatures. In addition to the spin density wave transition induced band folding across the bulk Neel temperature, we discover a weakly dispersing sharp feature emerging near the Fermi level at low temperatures presumably due to correlation induced effects.

cond-mat.mtrl-sci↗

arXiv2015

Anomalies in the electronic structure of Bi(2)Se(3)

We studied the electronic structure Bi(2)Se(3) employing density functional theory. The calculations show that the Dirac states primarily consists of the states at the interface of surface and sub-surface quintuple layers and the emergence of the Dirac states depends on the surface terminations in sharp contrast to their surface character expected for such systems. This manifests the complexity of real materials and the realization of topological order in real materials as an outstanding problem. We discover that the surface character of the Dirac states can be achieved by adsorption of oxygen on Bi-terminated surface due to the change in covalency by the relatively more electronegative oxygens.

cond-mat.mtrl-sci↗

arXiv2015

A review of the electronic structure of CaFe(2)As(2) and FeTe(0.6)Se(0.4)

Fe-based superconductors have drawn much attention during the last decade due to the finding of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity & magnetism. Extensive study of the electronic structure of these systems suggested dominant role of d states in their electronic properties, whereas the cuprate superconductors show major role of the ligand derived states. In this article, we review some of our results on the electronic structure of these fascinating systems employing high resolution photoemission spectroscopy. The combined effect of electron correlation and covalency reveal an interesting scenario in their electronic structure. The ligand p states contribution at the Fermi level is found to be much more significant than that indicated in earlier studies. Temperature evolution of the energy bands reveals signature of transition akin to Lifshitz transition in these systems.

cond-mat.supr-con↗

arXiv2014

Electronic structure of La(2)CoSi(3) - a non-Kondo analogue of a Kondo lattice, Ce(2)CoSi(3)

We study the electronic structure of a Pauli paramagnetic compound, La(2)CoSi(3) using photoemission spectroscopy and ab initio band structure calculations. Experimental valence band spectra exhibit signature of electron correlation induced feature around 2.5 eV - the correlation strength among Co 3d electrons is estimated to be close to 3 eV. The Co 2p core level spectra also exhibit correlation induced satellite features consistent with the scenario in the valence band spectra suggesting importance of conduction electron correlation in addition to the local moment in Kondo lattice systems. The La(2)CoSi(3) valence band spectra could be utilized to extract Ce 4f related spectral features and thus provide a good reference to study Kondo lattice systems in this class of materials. Temperature evolution of various core level spectra is found to be complex revealing deviations from a typical Fermi liquid behavior and emergence of distinct surface-bulk difference in the electronic structure at finite temperature.

cond-mat.str-el↗

arXiv2014

Aging of the surface of Bi(2)Se(3)

We study the electronic structure of Bi(2)Se(3) employing high resolution photoemission spectroscopy and discover the dependence of the behavior of Dirac particles on surface terminations. The Dirac cone apex appears at different energies and exhibits contrasting shift on Bi and Se terminated surface with complex time dependence emerging from subtle adsorbed oxygen-surface atom interactions. These results uncover the surface states behavior of real systems possessing topologically ordered surface.

cond-mat.mtrl-sci↗

arXiv2014

Complex electronic structure of Ca(1-x)Sr(x)RuO(3)

We investigate the core level spectra of Ca(1-x)Sr(x)RuO(3) employing high resolution photoemission spectroscopy. Sample surface appears to be dominated by the contributions from Ru-O layers. Sr 3p core level spectra are sharp and asymmetric in SrRuO(3) as expected in a metallic system, and exhibit multiple features for the intermediate compositions that can be attributed to the difference in Ca-O and Sr-O covalency. The Ru core level spectra exhibit distinct signature of satellite features due to the finite electron correlations strength among Ru 4d electrons. The intensity of the satellite feature is weaker in the surface spectra compared to the bulk. The low temperature spectra exhibit enhancement of satellite intensity in the spectra corresponding to ferromagnetic compositions due to the inter-site exchange coupling induced depletion of the intensity at the Fermi level. The increase in x leads to a decrease in satellite intensity that has been attributed to the increase in hopping interaction strength due to the enhancement of the Ru-O-Ru bond angle. Evidently, the complex electronic properties of these materials are derived from the interplay between the electron correlation and hopping interaction strengths.

cond-mat.str-el↗

arXiv2013

Interplay of electron correlation and covalency in FeTe(0.6)Se(0.4)

We investigate the electronic structure of FeTe(0.6)Se(0.4) employing high resolution photoemission spectroscopy and ab initio band structure calculations. Fe 2p core level and the valence band spectra exhibit signature of strong electron correlation in the electronic structure. The electronic states near the Fermi level reduces in intensity with the decrease in temperature in conformity with the insulating transport observed near 300 K. The observation of an insulator to metal transition around 150 K in the transport properties may be related to the spectral lineshape change in the vicinity of the Fermi level observed in this study. The spectral features near Fermi level exhibit significant p orbital character due to the correlation induced Fe d spectral weight transfer. The experimental spectra reveal dominant temperature dependence of the spectral functions possessing large p-character. These results demonstrate significant renormalization of the character of the conduction electrons due to electron correlation and emphasizes the importance of ligand states in the superconductivity of these materials.

cond-mat.str-el↗

arXiv2012

Electronic structure near quantum critical point

We studied the evolution of the electronic structure across the quantum critical point in V doped Cr employing high resolution photoemission spectroscopy. Experimental results exhibit signatures of pseudogap and orbital Kondo resonance peak at low temperatures for all the compositions studied suggesting a scenario of spin density wave quantum criticality corresponding to orbital Kondo effect. The pseudogap and the Kondo peak gradually reduces with V doping but remains finite at the quantum critical point indicating their relevance in widely discussed quantum phases in correlated electron systems. The spectral lineshape near the Fermi level exhibit (E_F - E)^{0.25} dependence evidencing deviation from Fermi liquid behavior.

cond-mat.str-el↗

arXiv2012

Evidence of the influence of magnetism on pseudogap states in the high resolution spectra of EuFe$_2$As$_2$

Employing {\it state of the art} high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe$_2$As$_2$, an unique pnictide, where antiferromagnetism of Eu layer survives within the superconducting phase due to `FeAs' layers achieved via substitution and/or pressure. High energy and angle resolution helped to reveal pseudogap-quasiparticle features having primarily As 4$p$ character and spin density wave transition induced band folding in the electronic structure. A weakly dispersing feature of dominant As 4$p$ character is discovered around 80 meV that becomes weaker in intensity below 20 K manifesting influence of antiferromagnetic order on conduction electrons. These results provide an evidence of a link between the pseudogap states and magnetism that could be revealed employing high resolutions.

cond-mat.supr-con↗

arXiv2011

Evolution of the Kondo resonance feature and its relationship to spin-orbit coupling across the quantum critical point in Ce2Rh{1-x}CoxSi3

We investigate the evolution of the electronic structure of Ce2Rh{1-x}CoxSi3 as a function of x employing high resolution photoemission spectroscopy. Co substitution at the Rh sites in antiferromagnetic Ce2RhSi3 leads to a transition from an antiferromagnetic system to a Kondo system, Ce2CoSi3 via the Quantum Critical Point (QCP). High resolution photoemission spectra reveal distinct signature of the Kondo resonance feature (KRF) and its spin orbit split component (SOC) in the whole composition range indicating finite Kondo temperature scale at the quantum critical point. We observe that the intensity ratio of the Kondo resonance feature and its spin orbit split component, KRF/SOC gradually increases with the decrease in temperature in the strong hybridization limit. The scenario gets reversed if the Kondo temperature becomes lower than the magnetic ordering temperature. While finite Kondo temperature within the magnetically ordered phase indicates applicability of the spin density wave picture at the approach to QCP, the dominant temperature dependence of the spin-orbit coupled feature suggests importance of spin-orbit interactions in this regime.

cond-mat.str-el↗

arXiv2009

Importance of conduction electron correlation in a Kondo lattice, Ce2CoSi3

Kondo systems are usually described by the interaction of strong correlation induced local moment with the highly itinerant conduction electrons. Here, we study the role of electron correlations among conduction electrons in the electronic structure of a Kondo lattice compound, Ce$_2$CoSi$_3$, using high resolution photoemission spectroscopy and {\it ab initio} band structure calculations, where Co 3$d$ electrons contribute in the conduction band. High energy resolution employed in the measurements helped to reveal signature of Ce 4$f$ states derived Kondo resonance feature at the Fermi level and dominance of Co 3$d$ contributions at higher binding energies in the conduction band. The line shape of the experimental Co 3$d$ band is found to be significantly different from that obtained from the band structure calculations within the local density approximations, LDA. Consideration of electron-electron Coulomb repulsion, $U$ among Co 3$d$ electrons within the LDA+$U$ method leads to a better representation of experimental results. Signature of electron correlation induced satellite feature is also observed in the Co 2$p$ core level spectrum. These results clearly demonstrate the importance of the electron correlation among conduction electrons in deriving the microscopic description of such Kondo systems.

cond-mat.str-el↗

arXiv2009

Spectral evolution in an insulator exhibiting linear specific heat

We investigate the spectral evolution of an antiferromagnetic insulator, La$_{0.2}$Sr$_{0.8}$MnO$_3$ exhibiting linear specific heat using state-of-the-art high resolution photoemission spectroscopy. Experimental spectral functions exhibit Fermi liquid like energy dependence at all the temperatures studied. Room temperature spectrum possess finite density of states at the Fermi level that vanishes generating a soft gap at about 260 K (the magnetic transition temperature). High resolution spectra reveal a hard gap in the magnetically ordered phase (C-type antiferromagnet). These results indicate signature of an amorphous phase coexisting with the long range ordered phase in these materials.

cond-mat.str-el↗

arXiv2009

Role of spin orbit coupling and electron correlation in the ground state properties of 5d electronic states

Electron correlation strength is predicted to be weak in 5d transition metal oxides and hence, various anomalous electronic properties observed in these systems are often attributed to the large spin-orbit interaction strength. Employing first principles approaches, we studied the electronic structure of Y2Ir2O7, which is insulating and exhibits ferromagnetic phase below 150 K. The results reveal breakdown of both the above paradigms. The role of spin-orbit interaction is found to be marginal in determining the ground state properties of Y2Ir2O7. A large electron correlation strength is required to derive the experimental bulk spectrum that is consistent with the bulk properties.

cond-mat.str-el↗

arXiv2009

Importance of Co 3d electron correlation in a Ce-based Kondo lattice, Ce(2)CoSi(3)

We study the role of electron correlations among Co 3d electrons contributing to the conduction band of a Kondo lattice compound, Ce2CoSi3, using high resolution photoemission spectroscopy and ab initio band structure calculations. Experimental results reveal signature of Ce 4$f$ states derived Kondo resonance feature at the Fermi level and dominance of Co 3d contributions at higher binding energies in the valence band. The line shape of the experimental Co 3$d$ band is found to be significantly different from that obtained from the band structure calculations within the local density approximations. Consideration of electron-electron Coulomb repulsion among Co 3d electrons leads to a better representation of experimental results. The correlation strength among Co 3$d$ electrons is found to be about 3 eV. Signature of electron correlation induced satellite feature is also observed in the Co 2p core level spectrum. Thus, these results demonstrate the importance of the electron correlation among conduction electrons to derive the microscopic description of such Kondo systems.

cond-mat.str-el↗

arXiv2009

Doping dependence of the chemical potential and surface electronic structure in YBa2Cu3O6+x and La2-xSrxCuO4 using hard x-ray photoemission spectroscopy

The electronic structure of YBa2Cu3O6+x and La2-xSrxCuO4 for various values of x has been investigated using hard x-ray photoemission spectroscopy. The experimental results establish that the cleaving of YBa2Cu3O6+x compounds occurs predominantly in the BaCuO3 complex leading to charged surfaces at higher x and to uncharged surfaces at lower x values. The bulk component of the core level spectra exhibits a shift in binding energy as a function of x, from which a shift of the chemical potential as a function of hole concentration in the CuO2 layers could be derived. The doping dependence of the chemical potential across the transition from a Mott-Hubbard insulator to a Fermi-liquid-like metal is very different in these two series of compounds. In agreement with previous studies in the literature the chemical potential shift in La2-xSrxCuO4 is close to zero for small hole concentrations. In YBa2Cu3O6+x, similar to all other doped cuprates studied so far, a strong shift of the chemical potential at low hole doping is detected. However, the results for the inverse charge susceptibility at small x shows a large variation between different doped cuprates. The results are discussed in view of various theoretical models. None of these models turns out to be satisfactory.

cond-mat.supr-con↗