PhD University of California, San Diego (1973)
Condensed Matter Theory
Research interests include:specific properties of materials, such as magnetism and superconductivity. In magnetism, I have worked on the properties of magnetism arising from Nuclear moments. In a metal like Copper, as it is cooled, there are no phase transitions. Copper is nonmagnetic at ordinary temperatures; nor is it superconducting. When Copper is cooled to temperatures as low as 60 nK, that is a tenth of a millionth of a degree from absolute degree, the nuclei of Copper, which have a magnetic moment, undergo a magnetic ordering transition. The unusual feature of this transition, apart from the very low ordering temperature, is that the magnetic precession in this system is at the same energy scale as the energy scale for dissipation. While Copper is antiferromagnetic, Ag is expected to be ferromagnetic at 2 picoK, and Rh, also antiferromagnetic.
Certain compounds of Uranium and Cerium are extraordinary in that they have very large specific heat. For this, they are referred to as heavy fermion compounds. These materials are occasionally both magnetic and at lower temperatures they are also superconducting. Moreover, as superconductors, their transitions are in the range of 1-2K, hardly what might be called high. And yet their superconducting properties are similar to those of high Tc oxide superconductors. One can study the coexistence of magnetism and superconductivity in these materials as well as a glimpse of an insight into the workings of high Tc superconductors.
Recently, with some collaborators, we have proposed that the phase transition in Potassium doped Barium Bismuthate is novel and unique so far, in being of order four. This proposal is still being studied. There are occasional claims that it is controversial. I like to think that all ideas of some impact are that. It has certainly had impact.
Kumar P and Samalam VK. “Statistical Mechanics of an Easy-plane Ferromagnetic Chain”, Phys. Rev. Lett. 49, 1278 (1982).
Kumar P, Ruiz-Altaba M and Thomas BS. “Tunnelling, Supersymmetry and Riccati Equations”, Phys. Rev. Lett. 57, 2749 (1986).
Kumar P and Sullivan NS. “Magnetic Polarons in Low Density Solid 3He”, Phys. Rev. B 35, 3162 (1987).
“Exchange Interaction between Nuclear Spins”, a paper submitted to a festschrift volume in honor of Professor E. Raymond Andrew, Solid State Nuclear magnetic Resonance, 9, 55,(1997)
Kumar P, Hall D and Goodrich RG. “Thermodynamics of a Superconducting Phase Transition in Ba0.6 K0.4BiO3”, Phys. Rev. Lett. 82, 4532 (1999). cond-mat/9904288
Balatsky AV, Kumar P and Schrieffer JR. “Collective Mode in a dx2-y2+idxy Superconductor”,Â cond-mat/9910342