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Research paper thumbnail of Interpretation of high pressure experimental data in mgb 2 : a challenge to current theories

High Pressure Research, 2004

ABSTRACT We review various anomalies seen in Raman spectroscopy, superconducting transition tempe... more ABSTRACT We review various anomalies seen in Raman spectroscopy, superconducting transition temperature T c and electrical resistance at room temperature and high pressure in the new high temperature superconductor MgB2. In order to explore the possibility of the anomalies being caused by an electronic topological transition (ETT), we have carried out detailed electronic structure studies of the band structure under pressure. Our calculations are done in the presence of a frozen-in phonon displacement that mimics the effects of thermal vibrations of the B-atoms at room temperature. Our results clearly establish the occurrence of a phonon-assisted ETT near 18 GPa. The dimensionless electron–phonon coupling λ is also found to be anomalous in its pressure variation at the same pressure. We also indicate why a detailed explanation of the phonon Raman anomaly needs the inclusion of effects arising from a non-linear electron–phonon coupling.

Research paper thumbnail of Electronic topological transition in AuX2 (X = In, Ga and Al) compounds at high pressures

Journal of Physics-condensed Matter, 2002

We present accurate x-ray diffraction data at high pressures for AuIn 2, AuGa 2 and AuAl 2, obtai... more We present accurate x-ray diffraction data at high pressures for AuIn 2, AuGa 2 and AuAl 2, obtained using a diamond anvil cell with the ELETTRA synchrotron source. The resulting P–V data obtained from the d-values were used to get the universal equation of state (UEOS) ...

Research paper thumbnail of Role of ab initio calculations in high pressure–high temperature studies and material properties

Journal of Physics and Chemistry of Solids, 2006

Research paper thumbnail of Electronic structure and superconductivity of MgB2

Bulletin of Materials Science, 2003

... Takahashi T et al 2001 Phys. Rev. Lett. 86 4915 Tinkham M 1996 in Introduction to superconduc... more ... Takahashi T et al 2001 Phys. Rev. Lett. 86 4915 Tinkham M 1996 in Introduction to superconductivity (New York: McGraw-Hill Inc.) p. 92 Vogt T et al 2001 preprint cond-mat/0102480 Yildirim T et al 2001 Phys. Rev. Lett. 87 037001

Research paper thumbnail of High-pressure resistance and equation-of-state anomalies in Zn: a possible Lifshitz transition

Journal of Physics-condensed Matter, 2002

Research paper thumbnail of Stability of the hcp phase and temperature variation of the axial ratio of iron near Earth-core conditions

Journal of Physics: Condensed Matter, 2007

Research paper thumbnail of On the electronic structure and equation of state in high pressure studies of solids

Bulletin of Materials Science, 2003

Research paper thumbnail of Possible high-temperature superconductivity in hole-doped MgB 2 C 2

Europhysics Letters (EPL), 2003

Research paper thumbnail of Iron at earth-core conditions

Journal of Materials Science, 2006

We have carried out electronic structure calculations for iron under high pressure using pseudopo... more We have carried out electronic structure calculations for iron under high pressure using pseudopotential plane wave methods. There is a controversy regarding the structure of iron at moderate pressures (30–100 GPa) and temperatures (1000–2400 K), with different experiments suggesting different structures, such as orthorhombic, double hexagonal close packed (dhcp), etc. Our earlier calculations using the linear muffin-tin orbital method within

Research paper thumbnail of High pressure phase transition in metallic LaB 6: Raman and X-ray diffraction studies

Solid State Communications, 2004

Research paper thumbnail of Interpretation of high pressure experimental data in mgb 2 : a challenge to current theories

High Pressure Research, 2004

ABSTRACT We review various anomalies seen in Raman spectroscopy, superconducting transition tempe... more ABSTRACT We review various anomalies seen in Raman spectroscopy, superconducting transition temperature T c and electrical resistance at room temperature and high pressure in the new high temperature superconductor MgB2. In order to explore the possibility of the anomalies being caused by an electronic topological transition (ETT), we have carried out detailed electronic structure studies of the band structure under pressure. Our calculations are done in the presence of a frozen-in phonon displacement that mimics the effects of thermal vibrations of the B-atoms at room temperature. Our results clearly establish the occurrence of a phonon-assisted ETT near 18 GPa. The dimensionless electron–phonon coupling λ is also found to be anomalous in its pressure variation at the same pressure. We also indicate why a detailed explanation of the phonon Raman anomaly needs the inclusion of effects arising from a non-linear electron–phonon coupling.

Research paper thumbnail of Electronic topological transition in AuX2 (X = In, Ga and Al) compounds at high pressures

Journal of Physics-condensed Matter, 2002

We present accurate x-ray diffraction data at high pressures for AuIn 2, AuGa 2 and AuAl 2, obtai... more We present accurate x-ray diffraction data at high pressures for AuIn 2, AuGa 2 and AuAl 2, obtained using a diamond anvil cell with the ELETTRA synchrotron source. The resulting P–V data obtained from the d-values were used to get the universal equation of state (UEOS) ...

Research paper thumbnail of Role of ab initio calculations in high pressure–high temperature studies and material properties

Journal of Physics and Chemistry of Solids, 2006

Research paper thumbnail of Electronic structure and superconductivity of MgB2

Bulletin of Materials Science, 2003

... Takahashi T et al 2001 Phys. Rev. Lett. 86 4915 Tinkham M 1996 in Introduction to superconduc... more ... Takahashi T et al 2001 Phys. Rev. Lett. 86 4915 Tinkham M 1996 in Introduction to superconductivity (New York: McGraw-Hill Inc.) p. 92 Vogt T et al 2001 preprint cond-mat/0102480 Yildirim T et al 2001 Phys. Rev. Lett. 87 037001

Research paper thumbnail of High-pressure resistance and equation-of-state anomalies in Zn: a possible Lifshitz transition

Journal of Physics-condensed Matter, 2002

Research paper thumbnail of Stability of the hcp phase and temperature variation of the axial ratio of iron near Earth-core conditions

Journal of Physics: Condensed Matter, 2007

Research paper thumbnail of On the electronic structure and equation of state in high pressure studies of solids

Bulletin of Materials Science, 2003

Research paper thumbnail of Possible high-temperature superconductivity in hole-doped MgB 2 C 2

Europhysics Letters (EPL), 2003

Research paper thumbnail of Iron at earth-core conditions

Journal of Materials Science, 2006

We have carried out electronic structure calculations for iron under high pressure using pseudopo... more We have carried out electronic structure calculations for iron under high pressure using pseudopotential plane wave methods. There is a controversy regarding the structure of iron at moderate pressures (30–100 GPa) and temperatures (1000–2400 K), with different experiments suggesting different structures, such as orthorhombic, double hexagonal close packed (dhcp), etc. Our earlier calculations using the linear muffin-tin orbital method within

Research paper thumbnail of High pressure phase transition in metallic LaB 6: Raman and X-ray diffraction studies

Solid State Communications, 2004

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